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Analysis of strain in a welded block and ash flow deposit, Mount Meager, Southwestern British Columbia 2006

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ANALYSIS OF STRAIN IN A WELDED BLOCK AND ASH FLOW DEPOSIT, MOUNT MEAGER, SOUTHWESTERN BRITISH COLUMBIA by K R I S T A A . M I C H O L BSc . (Honours), Univers i ty o f Ottawa, 2004 A THES I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E . in T H E F A C U L T Y O F G R A D U A T E S T U D I E S ( G E O L O G I C A L S C I E N C E S ) T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A December 2006 © Kr is ta A . M i c h o l , 2006 ABSTRACT The 2360 B P eruption o f Mount Meager, Br i t ish Co lumbia has produced a rare welded block and ash f low deposit along with non-welded equivalents. Here, I report on this sequence o f b lock and ash f low deposits (herein referred to as the Keyhole Falls Member) with the a im o f documenting the effects o f welding and the mechanisms o f strain attending the weld ing process. Mu l t ip le texture maps are drawn at the decimeter scale (field texture maps), and at the centimeter scale (slab texture maps), and are used for image analysis purposes to quantify the transition from unconsolidated block and ash f low deposits to dense, vitroclastic breccias. Image analysis establishes a weld ing trajectory, whereby average clast oblateness increases and average clast orientation (relative to the horizontal) decreases with increasing welding intensity. Af ter accounting for an original oblateness o f approximately 3 0 % , estimates o f strain from image analysis o f f ie ld texture maps ( FTMs ) and slab texture maps (STMs) y ie ld a volume strain o f - 1 2 % , or - 9 % i f treated as pure shear strain. A n empir ical experiment using image analysis o f F T M s suggests that the most welded F T M s visual ly correspond to 30 - 4 0 % volume strain relative to the least welded portions o f the deposit. Distributions o f oblateness and orientation for each F T M also prove more accurate in indicating welding intensity than do the average values. Physical property measurements o f the non-welded and welded block and ash f low deposits correlate we l l with the empirical experiments. Unconsolidated deposits reveal an average total matrix porosity o f - 4 1 % , o f wh ich less than 1% is isolated porosity. Associated clasts possess an average o f - 3 2 % total porosity, wi th a max imum o f 1 1 % isolated porosity. A s weld ing intensity increases, these values o f average total porosity decrease to - 5 % for clasts and - 1 7 % for matrix. Isolated porosity is reduced to < 1% for both components. Thus, isolated i i porosity is present mostly in non-welded clasts, and is lost in conjunction with connected porosity as welding progresses. These results also reveal an approximately equal amount of strain in clasts and matrix. The variations in physical property measurements suggest that both components record a maximum volume strain of-38%, which is echoed in the results of the empirical experiment. There is also little manifestation of pure shear stress observed within the welded facies of the deposit (e.g. only occurs as rare pull-apart clasts and locally around accidental lithics), indicating that volume strain in the viscous regime is the main mechanism for welding of the Keyhole Falls Member. The deposit, as a whole, records an average of 31% strain, meaning that the lower block and ash flow deposits experienced 50 m of compaction during welding, form 162 to 112 m. In comparing the block and ash flow deposits to other volcanic deposits, it is evident that they were erupted in a more explosive manner than originally proposed. The most appropriate analogue is Soufriere Hills Volcano, Montserrat, where explosive dome collapse is triggered by a Vulcanian eruption. iii TABLE OF CONTENTS ABSTRACT ii LIST OF FIGURES vi LIST OF TABLES viii ACKNOWLEDGEMENTS ix CHAPTER ONE - INTRODUCTION 1 1.1. B l o ck and A s h F lows and their Deposits 1 1.2. We ld ing in Volcanic last ic Deposits 2 CHAPTER TWO - GEOLGICAL SETTING.... 5 2.1. The 2360 B P Eruption o f Moun t Meager and the Pebble Creek Format ion 5 2.2. The Keyhole Fal ls Member 6 2.3. Facies Variations 9 2.4. Emplacement History 13 CHAPTER THREE - FABRIC ANALYSIS 16 3.1. Textura lData 16 3.1.1. F i e ld Texture Maps ( FTMs ) 17 3.1.2. Slab Texture Maps ( STMs ) 20 3.2. Image Analys is 23 3.2.1. Empir i ca l Experiment with Image Analys is 35 3.2.2. Distributions o f Oblateness and Orientation 37 CHAPTER FOUR - PETROGRAPHY & SEM ANALYSIS OF TEXTURES 42 4.1. Petrography 42 4.1.1. Non-welded Facies 43 4.1.2. Incipiently We lded Facies 44 4.1.3. We lded Facies 46 4.2. S E M Ana lys is 48 4.2.1 Non-welded Facies 50 4.2.2. Welded Facies 52 4.2.3. S E M Analys is o f Porosity 53 CHAPTER FIVE - PHYSICAL PROPERTIES 56 5.1. The ' Proto-deposit' 62 5.2. B u l k Density 63 5.2.1. Non-welded vs. Welded 65 5.2.2. Clasts vs. Mat r ix 65 5.3. Skeletal Density 66 iv 5.3.1 Non-welded vs. Welded 66 5.3.2. Clasts vs. Ma t r i x 67 5.4. Rock Powder Density 68 5.4.1. Non-welded vs. We lded 68 5.4.2. Clasts vs. Mat r ix 69 CHAPTER SIX - DISCUSSION 70 6.1 Ana lys is o f Porosity 70 6.2 We ld ing Mechanisms 74 6.3 Or ig ina l Thickness and Average Strain Calculations 78 6.4 Compar ison to Other Vo l can i c Deposits 81 CHAPTER SEVEN - CONCLUSIONS 86 REFERENCES . 89 APPENDIX A - DETAILED DESCRIPTIONS OF FIELD TEXTURE MAPS 99 APPENDIX B - IMAGE ANALYSIS METHODS: FTMs 116 APPENDIX C - IMAGE ANALYSIS METHODS: STMs 131 APPENDIX D - PHYSICAL PROPERTY MEASUREMENTS & CALCULATIONS.... 149 APPENDIX E - COMPLETE TABLES OF PHYSICAL PROPERTY DATA 156 v LIST O F FIGURES Figure 1. Locat ion o f Mount Meager and distribution o f major Quaternary volcanoes in the Cascade volcanic belt 4 Figure 2. Stratigraphy and geology o f the Pebble Creek Formation 7 Figure 3. Photograph o f the b lock and ash f low deposits exposed at Keyhole Fal ls , L i l looet R iver Va l l e y 8 Figure 4. F i e ld photographs showing welding facies variations wi th in the b lock and ash f low deposits : 10 Figure 5. Summary o f procedures used for image analysis o f f ie ld texture maps, using F T M 01 as an example 18 Figure 6. Results o f image analysis o f F T M s 19 Figure 7. Graphical summary o f procedures used for image analysis o f slab texture maps, using S T M 01 as an example 21 Figure 8. Results o f image analysis o f S T M s 22 Figure 9. Proportions o f clasts and matrix based on cross-sectional area 26 Figure 10. F T M grain size distribution by clast area as calculated by image analysis 27 Figure 11. S T M grain size distribution by clast area as calculated by image analysis 28 Figure 12. Cumulat ive grain size distribution for F T M s and S T M s 29 Figure 13. Average clast orientation vs. average clast oblateness for F T M s and S T M s 32 Figure 14. Strain vs. expected oblateness for volume strain and pure shear strain 34 Figure 15. Results f rom an empirical experiment with image analysis o f F T M s 36 Figure 16. Dist ibut ion o f oblateness for F T M s 38 Figure 17. Distr ibut ion o f oblateness and orientation for a 5 0 % volume-reduced F T M 08 39 Figure 18. Distr ibution o f orientation for F T M s 41 v i Figure 19. Summary o f common features wi th in the non-welded to incipiently welded block and ash f low deposits 45 Figure 20. We ld ing textures observed in thin section 47 Figure 21. Shard types observed in the non-welded to incipiently welded b lock and ash f low deposits 51 Figure 22. Attributes o f the densely welded b lock and ash f low deposits 54 Figure 23. Ana lys is o f porosity using S E M and image analysis 55 Figure 24. Mass vs. volume plots for a l l samples o f b lock and ash f low deposits at Moun t Meager 64 Figure 25. Summary o f physical property data 73 Figure 26. Calculated total strain vs. total, connected, and isolated porosity 75 Figure 27. Uncommon textures indicating min imal effects o f pure shear strain 77 Figure 28. Strain profi le o f the lower Keyhole Fal ls Member 79 Figure 29. Total porosity vs. connected porosity o f volcanic deposits 82 v i i LIST O F T A B L E S Table 1. Locat ion and description o f field sites 12 Table 2. Summary o f properties o f the b lock and ash f low deposits derived f rom image analysis o f F T M s 24 Table 3. Summary o f properties o f the b lock and ash f low deposits derived from image analysis o f S T M s 25 Table 4. Sample suite chosed for S E M analysis o f block and ash f low deposits 49 Table 5. Summary o f physical property data for bulk samples o f unconsolidated b lock and ash f low deposits 58 Table 6. Summary o f measured density data listed by welding facies 59 Table 7. Summary o f calculated porosity values listed by welding facies 60 Table 8. Summary o f density and porosity values listed by component and weld ing intensity ..61 v i i i ACKNOWLEDGEMENTS Thank you first and foremost to my supervisor, K e l l y Russel l for his persistence and support throughout this project. I'd l ike to thank Greg Dipple and L o r i Kennedy for their insights and ideas during committee meetings. Thanks go to A l i s o n Rust and for her support over the past two years, and to Kirst ie Simpson at the Geologica l Survey o f Canada for valuable discussions and help with field preparations. I am also very grateful for the perspective and editing ski l ls o f Graham Andrews. M a n y thanks to Heather W i l son for f ie ld work assistance at Moun t Meager (and keeping me sane over the field season!). I am also indebted to my fe l low colleagues N i l s Peterson, Genevieve Robert, Stephen Moss , Curtis Brett, Rebecca-Ellen Farrel l , and Melan ie Ke lman for their insightful discussions, reviews, support and friendship. F ina l ly , I owe numerous thanks to the many friends I have made here at U B C , but most o f a l l to Danie l Ross, who kept me level-headed throughout this experience and occasionally provided me wi th some much-needed distractions. ix CHAPTER ONE INTRODUCTION 1.1. Block and Ash Flows and their Deposits B lock and ash f lows, also known as nuees ardentes, are small-volume pyroclastic f lows (generally less than 1 km 3 ) generated by the explosive or gravitational collapse o f lava f lows or domes (Cas and Wright, 1987). B l o ck and ash f low deposits are topographically control led, unsorted deposits with an ash-rich matrix and a near-monolithologic assemblage o f generally poor ly vesiculated clasts, commonly having radial cool ing joints (Cas and Wright, 1987). They are deposited as hot avalanche-type deposits, commonly with reversely graded f low units, and may contain carbonized wood. Classic examples include deposits from Merap i (Bardintzeff, 1984; Boudon et al . , 1993; Abdurachman et al . , 2000), Unzen (Sato et al . , 1992; U i et al . , 1999), and Montserrat (Calder et al . , 2002; Woods et al . , 2002). They differ from other pyroclastic f lows (i.e., ignimbrites) in that ignimbrites generally contain variable amounts o f ash, and the lap i l l i and block-sized clasts are pumiceous (e.g., porosity > 5 0 % ) (Cas and Wright, 1987). They are also distinguishable from debris f lows and rock avalanches in that debris f lows are much more diluted in terms o f pyroclastic material, and rock avalanches are deposited cold. S imi lar ly to rock avalanches, b lock and ash f lows represent a significant hazard to human l i fe and infrastructure, only more so due to their higher emplacement temperatures, increased f lu idizat ion from degassing, and the potential to decouple highly mobile elutriated ash clouds (Bourdier and Abdurachman, 2001; Stewart et al . , 2003). 1 1.2. Welding in Volcaniclastic Deposits Although most pyroclastic deposits are known to weld, welded block and ash flow deposits are apparently rare. Cas and Wright (1987, p.l 11) state that there are no previously documented occurrences. Welding is characterized by the coalescence of hot glassy pyroclasts (sintering) that typically involves concomitant flattening or stretching of pyroclasts due to a compactional load (Smith, 1960b; Guest and Rogers, 1967; Riehle et al., 1995). Generally, welding processes require temperatures above the melt's characteristic glass transition temperature (Tg: Giordano et al., 2000; Giordano et al., 2005; Russell and Quane, 2005). The best studied examples of welded pyroclastic deposits are silicic ignimbrites (Sheridan and Ragan, 1976; Streck and Grunder, 1995; Wilson and Hildreth, 2003; Quane and Russell, 2005a). However, welding processes operate on a variety of volcanic deposit types, including other pyroclastic flow deposits (Smith, 1960a,b; Boyd, 1961), pyroclastic fall deposits (Sparks and Wright, 1979), spatter-fed lavas (Wolff and Sumner, 2000; Gottsman and Dingwell, 2001), fire-fountain deposits (Sumner et al., 2005), the clastic bases and margins of lava flows (Naranjo et al., 1992; Sparks et al., 1993), and within infilled volcanic conduits (Kano et al., 1997; Tuffen et al., 2003). Welding is also common in subaqueous volcanic successions (e.g., Kokelaar & Busby, 1992; White & McPhie, 1997; Kokelaar & Koniger, 2000). Welded deposits encompass a variety of magma compositions, from basalts to rhyolites, and even carbonatites (Barker and Nixon, 1983). In extreme cases, intensely welded deposits also experience ductile flow (rheomorphism) both during and after emplacement (Schmincke and Swanson, 1967; Wolff and Wright, 1981; Branney and Kokelaar, 1992; Soriano et al., 2002). The extent or intensity of the welding process is commonly manifest by combinations of the following: (a) decreases in porosity, (b) increases in density (Ragan and Sheridan, 1972; Streck and Grunder, 1995; Rust and Russell, 2 2000), (c) development of a foliation (Smith 1960a,b; Ragan and Sheridan, 1972; Sheridan and Ragan, 1976; Peterson, 1979; Quane and Russell, 2005b), and (d) increasing rock strength (Quane & Russell, 2005a). Mechanisms for welding include one or a combination of: (a) viscous deformation controlled by bubble collapse (Sheridan and Ragan, 1976); (b) viscous deformation due to shear strain (Smith, 1960a; Guest and Rogers, 1967; Ragan and Sheridan, 1972); and/or (c) mechanical deformation, should the deposit be cooler than its glass transition temperature (Sheridan and Ragan, 1976). Factors that appear to govern welding intensity include: melt rheology, emplacement temperature, volatile content, mass flux during deposition, cooling history, deposit thickness, permeability, and particle size distribution (Sparks et al., 1999; Giordano et al., 2000; Quane and Russell, 2005b; Russell and Quane, 2005). Here I describe a unique welded block and ash flow deposit (the Keyhole Falls Member) at Mount Meager, southwestern British Columbia (Fig. 1). I define vertical welding facies variations within the deposit using a combination of field and laboratory techniques to quantify how strain is accommodated during welding. Texture mapping, image analysis, petrography, and physical property measurements allow me to document the welding trajectory of the Keyhole Falls member and recover the unique conditions and mechanism(s) under which this deposit has formed. These data sets also offer new insights into welding of non-coherent volcaniclastic deposits other than ignimbrites. My study demonstrates that components of welded block and ash flows behave differently than those found in ignimbrites, and that the amount of strain required to densely weld this particular block and ash flow deposit is significantly less than typical densely welded ignimbrites. Thus, my results will help to generalize our understanding of welding processes in volcanology. 3 F igure 1: Locat ion o f the Mount Meager (star) within the Canadian portion o f the Cascade volcanic belt (modif ied from Stewart et al . , 2003). Triangles represent major Quaternary volcanoes. Inset shows geographic location o f the Mount Meager Volcanic Complex ( M M V C ) . 4 CHAPTER TWO GEOLOGICAL SETTING 2.1. The 2360 BP Eruption of Mount Meager and the Pebble Creek Formation The Mount Meager Vo lcan ic Complex ( M M V C ) is a component o f the Gar iba ld i Vo lcan ic Belt , wh i ch is the northernmost segment o f the Cascade Vo lcan ic Be l t (F ig. 1; Mathews, 1958; Green et a l . , 1988; Read, 1990; Sherrod and Smith, 1990; Ke lman et al., 2002; Clague et al . , 2003; Green and Sinha, 2005). Mount Meager is a composite stratovolcano located approximately 50 k m northwest o f Pemberton in the Coast Mountains, and rises to an elevation o f 2645 m between the L i l looet R iver and Meager Creek (Stasiuk et al . , 1996). Vo l can i sm associated wi th the M M V C ranges from 2.2 M a (K-Ar) to its most recent eruption at 2360 B P (Nasmith et al . , 1967; Read, 1977; Read, 1978; Clague et al . , 1995). The edifice drapes over southern Coast Bel t rocks inc luding Mesozo ic metamorphic supracrustal rocks o f the Cadwallader Formation, and Tertiary monzonite intrusions o f the Coast Plutonic Complex (Read, 1978; Gabrielse et al . , 1992). The vent for the 2360 B P eruption cuts through deposits o f the preceding P l inth Assemblage (90 - 100 K a ; Read, 1978) and is situated at 1500 m elevation, roughly 1000 m above the present stream bed o f the L i l looet R iver (Stasiuk et al . , 1996). The 2360 B P eruption (Nasmith et al . , 1967; Clague et al . , 1995) produced the sequence o f volcaniclastic dacite-rhyodacite deposits o f the Pebble Creek Formation (Fig. 2a; Read, 1978; H i ckson et al . , 1999; Stewart, 2002; Stewart et al . , 2003). The Pebble Creek Formation records an init ial sub-Plinian eruption that produced a pumice fa l l deposit and an ignimbrite, fo l lowed by emplacement o f b lock and ash f low deposits, the Keyho le Fal ls Member (here defined). The eruption cycle ended wi th the extrusion o f a 5 rhyodacite lava (Stasiuk et al., 1996; H i ckson et al. , 1999; Stewart, 2002). There was no appreciable lapse in time during this sequence o f events. The M M V C region was original ly mapped by Anderson (1975), and Read (1977, 1978, 1990); however, a more detailed mapping o f the Pebble Creek Formation recognizing the presence and distributions o f pyroclastic f low and block and ash f low deposits was completed by Stasiuk et al . (1996), H i ckson et al . (1999), and Stewart (2002). Figure 2b is a s impl i f ied geological map f rom Stewart (2002) showing the distribution o f the Pebble Creek Formation volcanic deposits resulting from the 2360 B P eruption. 2.2. The Keyhole Falls Member The Keyho le Fal ls Member is chief ly confined to a steep-sided paleo-channel inferred to be a glacially-steepened, earlier incarnation o f the L i l looet R iver (Stasiuk et al. , 1996; H i ckson et al . , 1999). It is approximately 165 m thick immediately below the inferred vent at the type local ity o f Keyho le Fal ls (466400E 5614050N; F igs. 2a, 3). The Member is a wedge-shaped unit w i th an estimated volume o f 0.44 k m 3 (Stewart, 2002) that thins downstream to a total thickness o f 25 m after 2.5 km. 6 a) Stratigraphic column at Keyhole Falls (*): Figure 2: Stratigraphy and geology of the Pebble Creek Formation modified from Stewart (2002): (a) stratigraphic column for type locality Keyhole Falls (*), non-volcanic deposits labeled in grey; (b) simplified geological map showing the variably welded block and ash flow deposits (light - medium grey), the rhyodacite lava flow deposit (patterned), the outburst flood deposit (dark grey), and the pumiceous pyroclastic flow deposits (black). Field sites and corresponding Field Texture Maps (FTMs) are indicated with arrows. F igu re 3: Northwest-facing f ield photograph showing block and ash pyroclastic f low deposits exposed at Keyhole Falls in the L i l looet R iver Valley. The lower cl i ff-forming unit comprises the densely welded facies and is approximately 100 m thick at this location. The upper recessive units (here, approximately 60 m) are bedded and variably sorted, compris ing interbedded f luvia l gravels and non-welded to incipiently welded block and ash f low deposits. The section is capped by younger rock avalanche deposits. The present-day canyon was formed by an outburst f lood event shortly after deposition (Hickson et a l . , 1999; Stewart, 2002). The gorge i n the c l i f f wa l l results f rom 2360 years o f erosion by the L i l looet R iver through the residual welded block and ash f low deposit. 8 The Keyhole Fal ls Member is a dominantly monomict volcaniclastic breccia composed o f centimeter- to metre-sized crystal-rich, rhyodacite obsidian clasts supported by a pumiceous ash- sized matrix. Acc identa l , centimetre-sized angular l ifhic clasts o f monzonite, P l inth assemblage, and shale are uncommon. The Member is dominantly massive and very poorly sorted. Crypt ic reversely graded bedding is exhibited in the densely welded material by variations in the apparent max imum clast size. Detai led petrographic and geochemical studies o f the deposit can be found in Stasiuk et a l . (1996) and Stewart (2002). The Member is inferred to be a b lock and ash f low deposit because it exhibits: (1) very poor sorting; (2) mostly monol ithic clasts o f rhyodacite lava; (3) an ash-rich matrix; and (4) cool ing joints throughout the densely welded facies, indicating a hot emplacement (Stasiuk et al . , 1996; Stewart 2002). These characteristics parallel those o f b lock and ash f low deposits reported from other classic examples (e.g., Merap i , Unzen , Montserrat; Cas and Wright, 1987). 2.3. Facies Variations Variat ions in weld ing intensity are noted in several areas along the L i l looet R iver Va l l ey , f rom non-welded and incipiently welded (Streck and Grunder, 1995) deposits that form a significant slope, to a lower, densely welded deposit that forms a prominent steep-sided gorge (F ig. 3). O n the basis o f we ld ing intensity, I identify four separate weld ing facies i n the Keyho le Fal ls Member (F ig. 4): (1) a basal non-welded facies; (2) a densely welded facies at, and up to 3.15 k m downstream from Keyhole Fal ls ; (3) an oxidized and incipiently welded facies greater than 3.15 k m downstream from Keyhole Fa l ls ; and (4) an upper non-welded facies. 9 Figure 4: Field photographs showing the facies variations within the block and ash flow deposit: (a) basal, non-welded facies (Field Site 1, Fig. 2); (b) densely welded facies (Field Site 1, Fig. 2); (c) incipiently welded facies (oxidized) from the upper part of the succession (Field Site 2, Fig. 3); and, (d) non-welded facies (non-oxidized) from the upper part of the succession (Field Site 3, Fig. 2). 10 The basal non-welded facies (type locality F ie ld Site 1; Table 1) is an approximately 2 m thick, non-welded and poorly-sorted volcaniclastic breccia supported by a grey, ash-sized matrix (Fig. 4a). Juvenile clasts are dominantly pumice (45 - 5 5 % ) and moderately dense rhyodacite (40 - 5 0 % ) , wi th sporadic dense rhyodacite clasts (2 - 5%); rare accidental clasts o f P l inth assemblage and Tertiary monzonite country rock are present as we l l as f low banded pumice-like clasts. Clasts are mostly sub-angular to sub-rounded, typical ly 5 - 15 cm in diameter, and rarely up to 1 m. The base is not exposed, but this facies is inferred to sit conformably on a deposit o f pumiceous pyroclastic f low, and to grade upwards into the densely welded facies. The densely welded facies (type locality F ie ld Site 1, Table 1) is a 16 m thick, poorly-sorted volcaniclastic breccia supported by a grey, fine ash-sized matrix (F ig. 4b). Juvenile, angular to sub-rounded, vesicular and glassy rhyodacite clasts dominate (85 - 9 5 % ) , wi th lesser quantities o f accidental P l inth assemblage, granodiorite, monzonite and shale clasts present. Clasts are typical ly 5 - 1 5 cm in diameter, with local clasts up to 1 m across. Some clasts show vestiges o f f low banding textures. M a n y obsidian clasts are demonstrably pyroclastic in nature, and define a prominent sub-horizontal fabric similar to eutaxitic fabrics observed in welded ignimbrites (e.g., Smith, 1960b). Columnar joints are continuous throughout the thickness o f the densely welded facies, suggesting that it represents a single cool ing unit (sensu Smith, 1960b). 11 Table 1. Location and description of field sites, including associated field texture maps (FTMs) and slab texture maps (STMs). Field Site Description UTM Coordinates Easting Northing Block and Ash Flow Deposit Facies Field Texture Map Slab Texture Map Valley wall exposure in Lillooet River valley; cliff and fallen blocks 468404 5612192 Densely welded (middle of deposit) Unwelded (base of deposit) 01 02 03 04 05 06 07 08 13 16 11 12 13 14 15 01 02 07 08 09 10 03 04 05 06 2 Roadcut exposure ~300m NE of . , „„„ , , 468531 Field Site 1 5612414 Incipiently welded (upper oxidized section) 09 10 12 3 Roadcut exposure; on south side 466400 of bridge at Keyhole Falls 5614050 Unwelded (upper unoxidized section) 11 The incipiently welded facies (type locality Field Site 2; Table 1) is an approximately 5 m thick, poorly-sorted volcaniclastic breccia supported by an oxidized, orange-brown matrix of ash-sized particles and clast fragments (Fig. 4c). It contains sub-angular to sub-rounded juvenile clasts which vary in from pumice-like (70 - 95%) to dense and glassy (5 - 30%); observed lithics include rare Plinth assemblage and monzonite clasts. Some juvenile clasts display flow banded or bread-crust textures, and locally exhibit long-axis alignment. Clasts average 5 - 15 cm in diameter, with rare clasts up to 1.5 m. The upper non-welded facies (type locality Field Site 3; Table 1) is an approximately 5 m thick, poorly-sorted volcaniclastic breccia supported by a grey-brown matrix of ash-sized particles and clast fragments (Fig. 4d). Juvenile clasts (85 - 90%) are typically sub-angular to sub-rounded and variably dense (pumice to glassy); accidental lithic clasts of the Plinth assemblage are also present (5 - 10%), with minor amounts of intrusive igneous and metamorphic clasts (1 - 2%). Clasts average 5 - 15 cm in diameter, with local clasts up to 50 cm. Unlike the basal non-welded facies, no fabric or clast orientation is observed. 2.4. Emplacement History The distribution of welded facies within the block and ash flow deposit is an indication of their formation and depositional processes. The block and ash flow deposits resulted from continued effusion of block and ash flows from rhyodacite lava flows or domes (Stasiuk et al., 1996; Hickson et al., 1999; Stewart, 2002). Although the eruption was not observed, eruption analogues may include Monserrat, where block and ash flows are produced by Vulcanian 13 eruption-triggered explosive dome collapse (Cole et al., 2002; Woods et al., 2002; Formenti and Druitt, 2003); Merapi, where block and ash flows commonly result from the gravitational collapse of domes or lava flows (Bardintzeff, 1984; Boudon et al., 1993; Abdurachman et al., 2000.); or Unzen, where they can result from the exogenous or endogenous growth of domes (Sato et al., 1992; Ui et al., 1999; Miyabuchi, 1999). The flows then traveled down the steep slopes of the volcanic edifice and were captured and entrained by the paleo-Lillooet river valley. Continuously erupting over time, these flows accumulated in the valley, spreading downstream, increasing in thickness, and welding together. Regardless of how the block and ash flows were initiated (explosive vs. gravitational collapse), the welding was facilitated by the fact that the block and ash flows were contained within a steep, narrow, and mountainous drainage system. The pyroclastic flows must also have accumulated relatively rapidly to have retained heat and not entrained air as they traveled down the Lillooet River valley. The welding process was sufficiently intense that it transformed a significant portion of the originally unconsolidated material into a mass of dense, competent vitrophyre. Shortly after this phase of eruption began, the block and ash flow deposits proceeded to disrupt the Lillooet River drainage and cause the river to dam upstream of Keyhole Falls. The thickness and welded character of the pyroclastic deposits then caused the Lillooet River to back up and form a lake upstream of Keyhole Falls (Read, 1990; Stasiuk et al., 1996; Hickson, 1999; Stewart, 2002; Stewart et al., 2003). The block and ash flow deposit withheld its heat while a lake began to form behind it that was substantial enough to accumulate alluvial sediments (Cordy, 1999; Schipper, 2002; Stewart, 2002). The pyroclastic dam was maintained throughout the entire eruption until the lake built up to a level that overtopped the densely welded section. Once the 14 lake reached this critical level, the dam failed catastrophically (possibly in two stages) and the welded block and ash flow deposit was disrupted again by outburst flood events (Stewart, 2002). These deluge events excavated a large canyon (Fig. 3) exposing up to 100 m of densely welded vitrophyric breccia. Radial cooling joints are pervasive throughout the multitude of blocks found in the outburst flood deposit, indicating the block and ash flow was still hot when it fragmented for the second time (Hickson, 1999). In an effort to return to its original state, the Lillooet River has cut down through the block and ash flow deposit over the past 2400 years. In the following sections, I use a combination of detailed texture mapping, image analysis, and physical property measurements to quantify welding intensity within the various facies of the Keyhole Falls Member. These properties are used to document how welding of this deposit was accommodated. The variations in these properties provide estimates of volume strain and pure shear strain incurred by the welded block and ash flow deposits. 15 CHAPTER THREE FABRIC ANALYSIS Fabric analysis has previously been used to measure welding intensity in volcanic deposits (e.g. Ragan and Sheridan, 1972; Sheridan and Ragan, 1976; Ui et al, 1989; Boudon et al., 1993; Karatson et al., 2002; Quane and Russell, 2006), and thereby allow estimates of strain and rheology to be made. We employ two methods of fabric analysis to constrain the intensity of welding in the Keyhole Falls Member: (1) textural analysis undertaken on small-scale maps drawn in the field; and (2) textural analysis of fabrics observed in polished slabs of the densely welded facies. 3.1. Textural Data I have employed textural mapping to describe and quantify the change in fabric and flattening of particles within the Keyhole Falls Member. This was conducted at two scales: (1) on 1 m2 textural maps produced in the field; and (2) on polished slabs of the densely welded facies. By using these mapping methods in conjunction with image analysis software (Scion Image™, Image J™), the amount and type(s) of strain accumulated within the deposit can be constrained quantitatively, and the partitioning of strain between the clasts and matrix can be determined. 16 3.1.1. Field Texture Maps (FTMs) Field texture maps were created by placing aim 2 grid flush with the outcrop and then mapping the distribution, size, and shapes of all the clasts appearing in the designated area (Fig. 5a). 2 2 Mapping involved a hand-drawn reproduction of each clast within the lm area, using the 10 cm squares as a reference grid (Fig. 5b). All particles greater than 0.5 cm were identified as clasts, and the size fraction below this was treated as matrix. A total of thirteen FTMs were completed; twelve drawn perpendicular to bedding (non-welded facies) or foliation (welded facies), and one drawn on the foliation surface to gain a three-dimensional perspective. FTMs were drawn at a scale of 1:5 and a field photograph of the grid overlying the outcrop was taken for reference. The texture maps derive from individual outcrops at the three field sites (Fig. 2b; Table 1) and were selected to capture the full range of welding intensity within the Keyhole Falls Member. They were then retraced by hand, scanned (Fig. 5c) and imported into Scion Image™ and Image J™ for image analysis, where the specific dimensions, proportions and orientations of the clasts were determined (Fig. 5d). Output images from Scion Image™ are shown in Figure 6. For detailed descriptions and for a full suite of images depicting image analysis procedures for FTMs, refer to Appendices A and B, respectively. 17 Figure 5: Procedure used for image analysis o f f ie ld texture maps using F T M 01 as an example: (a) field photo o f l m x l m grid on an outcrop o f densely welded b lock and ash f low deposit (T denotes top o f grid); (b) hand-drawn field texture map based on a m in imum clast size o f 0.5 cm ; (c) digital scanned version F T M 01 used for image analysis (Scion Image™ or Image J™); (d) prel iminary results o f image analysis showing indiv idual numbered clasts. 18 Figure 6: Results of image analysis for the twelve other FTMs, selected to represent the full range of welding intensity. Numbers of FTMs indicate the chronological order in which the field mapping was completed (e.g., not welding intensity). 19 Figure 7: Graphical summary of procedures used for image analysis of slab texture maps, using STM 01 as an example: (a) hand sample photo of a slab (KM- 05-011, side 1/1) of densely welded block and ash flow deposit; (b) digital scanned version of hand-drawn STM 01 used for image analysis (Scion Image™ or Image J™), where the minimum clast size is 0.5 mm; (c) preliminary results of image analysis showing individual numbered clasts. 20 3.1.2. Slab Texture Maps ( STMs ) Sixteen slab texture maps were created from the densely welded block and ash f low deposits. This was accomplished by placing a sheet o f acetate over the slab (Fig. 7a), and tracing clasts 0.5 m m or greater by hand; particles less than 0.5 m m were treated as matrix. S T M s are drawn perpendicular to fol iation, at a scale o f 1:1 (Fig. 7b). These texture maps correspond to samples derived from five different F T M s (Table 1). The acetates were then retraced by hand, scanned into digital form (Fig. 7c), and imported into Sc ion Image™ and Image J™ for image analysis in the same manner as the F T M s (Fig. 7d). Result ing output images from Sc ion Image are displayed in Figure 8. For a fu l l suite o f images depicting image analysis procedures, refer to Append ix C. 21 Figure 8: Results o f image analysis for the fifteen other S T M s , representing the heterogeneity o f welding intensity in the block and ash f low deposit. Numbers indicate the chronological order in which the slab texture maps were completed (e.g., not welding intensity). 22 3.2. Image Ana l y s i s Image analysis software was used to quantify the F T M s and S T M s : Sc ion Image™ returned values o f clast area, perimeter, m in imum and max imum diameter, and orientation, whereas Image J™ calculated the proportions o f clasts and matrix for both the F T M s and S T M s (Tables 2 and 3, respectively). Clast-matrix ratios for the F T M s are almost constant, averaging 51 ± 5 % and ranging between 43 - 5 9 % (F ig. 9a). Clast-matrix proportions for the S T M s are more variable; clasts average 53 ± 9 % , and range from 39 - 6 9 % (Fig. 9b). Gra in size distributions were created using individual clast areas calculated wi th Sc ion Image™. F T M s show normal or near-normal distributions that are variably skewed towards smaller size fractions because the F T M data is truncated below 0.1 c m 2 , corresponding to a m in imum clast diameter o f ~0.5 cm (Fig. 10). Distributions o f the S T M s show a sharp decrease from the smallest clast size fraction to the largest because size fractions are s imilar ly truncated below 0.01 c m 2 due to a m in imum clast diameter o f 0.5 m m (Fig. 11). Neither the F T M s nor the S T M s demonstrate any appreciable shift in grain size distribution with welding intensity. Cumulat ive grain size distributions were also created for the F T M s (Fig. 12a) and S T M s (Fig. 12b); however, weld ing facies in the F T M s and blocks o f densely welded material in the S T M s are indistinguishable from one another based on their cumulative grain size distribution curves. 23 Table 2. Summary of properties of block and ash flow deposits derived from image analysis of FTMs, including: total map area (A T), clast area (A), clast perimeter (P), ratio of area to perimeter (A/P), minimum (c) and maximum (a) clast dimensions, ratio of maximum to minimum clast radius (a/c), clast orientation, volume strain (e v), pure shear strain (es), and % of clasts (C) and matrix (M) by area. F T M A T (m2) N 1 A (cm2) P(cm) A/P — a (cm) c (cm) a/c Orientation (°) Ev2 *s' C(%) M (%) avg. 5.68 7.56 0.41 1.37 0.72 1.91 23.6 0.42 0.31 1 1.00 563 max 440.5 94.0 4.69 16.2 8.68 6.52 89.8 0.85 0.71 47 53 min 0.14 1.44 0.06 0.28 0.15 1.03 0.2 0.02 0.02 avg. 12.1 9.04 0.49 1.62 0.88 1.84 26.2 0.40 0.30 2 0.98 386 max 2404.7 240.5 10.00 44.2 17.3 5.33 88.4 0.81 0.67 59 41 min 0.23 1.77 0.13 0.29 0.22 1.04 0.0 0.04 0.02 avg. 10.2 9.75 0.54 1.67 1.02 1.71 41.3 0.36 0.27 3 1.00 400 max 534.7 95.2 5.62 14.2 12.0 5.15 89.4 0.81 0.66 54 46 min 0.22 1.71 0.12 0.29 0.19 1.02 0.4 0.02 0.01 avg. 6.27 8.31 0.44 1.49 0.80 1.87 25.4 0.41 0.30 4 0.93 530 max 432.1 115.0 3.76 18.3 7.50 5.11 88.6 0.80 0.66 49 51 min 0.22 1.79 0.11 0.31 0.21 1.01 0.1 0.01 0.01 avg. 4.19 6.42 0.35 1.18 0.62 1.90 21.7 0.41 0.31 5 1.00 1064 max 592.7 94.1 6.30 14.6 13.0 5.91 90.0 0.83 0.69 47 53 min 0.17 1.58 0.10 0.25 0.18 1.03 0.0 0.03 0.02 avg. 3.57 6.51 0.35 1.19 0.62 1.98 25.0 0.43 0.32 6 1.00 883 max 190.0 60.9 3.15 11.4 6.05 13.2 89.9 0.92 0.82 52 48 min 0.17 1.52 0.11 0.25 0.16 1.03 0.0 0.03 0.02 avg. 5.95 7.60 0.45 1.31 0.84 1.57 34.1 0.32 0.23 7 0.88 487 max 166.9 64.3 2.84 10.9 5.84 4.96 89.8 0.80 0.66 46 54 min 0.13 1.33 0.10 0.23 0.19 1.02 0.1 0.02 0.01 avg. 6.24 7.85 0.48 1.36 0.89 1.55 31.3 0.32 0.23 8 0.93 571 max 194.9 55.4 3.58 10.3 6.55 4.95 89.8 0.80 0.66 45 55 min 0.19 1.53 0.12 0.27 0.22 1.01 0.0 0.01 0.01 avg. 4.22 6.61 0.37 1.19 0.66 1.74 26.7 0.38 0.28 9 0.79 613 max 149.0 57.2 2.72 10.5 4.58 4.82 90.0 0.79 0.65 56 44 min 0.15 1.59 0.06 0.27 0.16 1.01 0.0 0.01 0.01 avg. 5.52 7.90 0.45 1.40 0.81 1.74 29.3 0.37 0.27 10 0.60 340 max 337.1 84.5 3.99 14.9 7.19 4.70 89.0 0.79 0.64 59 41 min 0.23 1.80 0.13 0.28 0.26 1.02 0.1 0.02 0.01 avg. 10.3 10.1 0.58 1.74 1.09 1.62 35.9 0.33 0.24 11 1.00 370 max 332.9 81.1 4.10 14.5 7.31 4.84 88.1 0.79 0.65 51 49 min 0.23 1.77 0.13 0.29 0.22 1.02 0.5 0.02 0.01 avg. 7.28 8.22 0.45 1.46 0.82 1.79 28.3 0.39 0.29 12 0.91 505 max 396.4 81.2 4.88 13.9 9.09 7.80 89.9 0.87 0.75 52 48 min 0.14 1.35 0.10 0.24 0.19 1.03 0.0 0.03 0.02 avg. 6.83 7.78 0.45 1.37 0.82 1.66 31.6 0.35 0.26 13 0.76 436 max 212.2 64.1 3.31 12.3 6.34 3.49 90.0 0.71 0.57 43 57 min 0.17 1.47 0.05 0.26 0.21 1.01 0.1 0.01 0.01 ' N = number of particles; 2 E V = volume strain estimated from oblateness (1 -c/a); 3 E S = pure shear strain estimated from oblateness (1 -c/a M ) Table 3. Average properties of the block and ash flow deposits based on image analysis of STMs, including: total map area (A), clast area (A), clast perimeter (P), ratio of area to perimeter (A/P), minimum (c) and maximum (a) clast dimensions, ratio of maximum to minimum clast dimensions (a/c), clast orientation, volume strain (ev), pure shear strain (es), and % of clasts (C) and matrix (M) by area. Standard deviations (la) are shown where appropriate. STM Ax(cm2) N1 A (cm2) a (cm2) P(cm) A/P a (cm) a (cm) c (cm) o (cm) a/c Orientation (°) « ( ) 4 £ V es 5 C (%) M (%) 1 175.8 838 0.08 0.322 116.40 0.05 0.16 0.176 0.08 0.076 1.91 22.77 21.147 0.41 0.30 44 56 2 133.7 399 0.11 0.477 111.61 0.06 0.20 0.228 0.10 0.079 1.98 21.34 18.338 0.43 0.32 39 61 3 124.4 598 0.07 0.254 112.04 0.05 0.16 0.142 0.09 0.070 1.73 28.58 23.716 0.37 0.27 40 60 4 113.5 305 0.07 0.208 116.45 0.05 0.15 0.143 0.09 0.066 1.79 26.66 23.164 0.38 0.28 54 46 5 106.4 181 0.14 0.470 106.17 0.06 0.19 0.212 0.11 0.108 1.67 32.32 22.956 0.35 0.26 58 42 6 147.0 468 0.04 0.079 129.77 0.04 0.12 0.085 0.07 0.042 1.75 31.19 22.584 0.37 0.27 52 48 7 157.7 634 0.07 0.324 112.53 0.05 0.15 0.156 0.08 0.071 1.71 27.03 21.897 0.36 0.27 49 51 8 159.0 653 0.08 0.358 114.73 0.05 0.15 0.166 0.09 0.077 1.72 25.76 21.967 0.37 0.27 51 49 9 111.5 289 0.09 0.642 118.34 0.04 0.13 0.178 0.08 0.097- 1.73 35.98 25.315 0.37 0.27 68 32 10 113.3 340 0.11 0.699 114.28 0.05 0.15 0.238 0.08 0.096 1.77 31.23 23.746 0.37 0.27 56 44 11 108.1 304 0.07 0.152 105.23 0.05 0.16 0.119 0.09 0.067 1.90 25.60 22.463 0.41 0.31 45 55 12 113.9 234 0.06 0.213 107.23 0.05 0.14 0.124 0.09 0.072 1.70 30.38 24.104 0.36 0.26 61 39 13 122.7 284 0.09 0.564 114.52 0.05 0.15 0.177 0.08 0.103 1.85 28.33 23.633 0.39 0.29 69 31 14 88.7 226 0.08 0.196 108.67 0.05 0.16 0.143 0.10 0.074 1.71 32.75 26.046 0.36 0.27 62 38 15 78.3 288 0.07 0.279 120.79 0.05 0.15 0.140 0.08 0.071 1.81 34.37 25.325 0.38 0.28 55 45 16 124.5 590 0.06 0.254 119.79 0.04 0.14 0.149 0.07 0.070 1.94 32.83 22.535 0.41 0.31 44 56 ! N = number of particles; 2e v = volume strain estimated from oblateness (1-c/a); 3 £ s = pure shear strain estimated from oblateness (l-c/a2/3) 100 70 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 STM No. Figure 9: Proportions of clasts and matrix based on cross-sectional area, for: (a) FTMs, and (b) slab texture maps (STMs). The average proportion of clasts (>0.5 cm) in the FTMs is 51 ± 5%. Clasts never represent more than 60% of the total field texture map area. The average proportion of clasts (>0.5 mm) in the STMs is 53 ± 9%, but vary from 39-69%. 26 FTM 01 FTM 02 FTM 03 30 25 a 3 20 a is Limit of observation 121 IL8 Claat area (cm ) 30 25 £ S 20 3 15 o 10 113 "5 HP". Clast area (cm1) i SI A Clast area (cm ) FTM OS Clast area (cm1) Clast area (cm1) Clast area (cm1) 25 .2 20 u a 15 o 5 10 I 10 9 Clast area (cm2) Figure 10: FTM grain size distribution by clast area as calculated by image analysis. The distribution is truncated below 0.1 cm2 due to the scale limitations of the field texture map (i.e. minimum clast diameter = 0.5 cm). Note that there is no significant shift in dominant grain size with welding intensity. 27 STM 01 STM 02 STM 03 Clast araa (cm1) STM 16 Figure 11: STM grain size distribution by clast area as calculated by image analysis. The distribution is truncated below 0.01cm2 due to the scale limitations of the field texture map (i.e., minimum clast diameter = 0.5 mm). Note that there is no significant shift in dominant grain size with welding intensity. 28 - • - densely welded - * - indurated (upper, oxidized) • unwelded (basal) -e- unwelded (upper) CN> cv> <*N o > J> NFC & & Clast area (cm ) • Block#1 • Block#3 • Block#4 • Block#5 # ^ ^ Clast area (cm ) Figure 12: Cumulative grain size distribution for (a) FTMs, separated by facies, and (b) STMs, separated by block of densely welded block and ash flow deposit. It is important to note that the various facies/blocks of material cannot be distinguished by their grain size distribution at these scales. 29 Other properties o f the clast population were also examined through image analysis. Oblateness has been proposed as an indicator o f welding intensity (Quane and Russel l , 2005a) and it is calculated using the fo l lowing formula: Q Oblateness = 1 (1) a where c = min imum clast diameter, and a = max imum clast diameter. The more flattened and compacted a clast is, the more welded it is, and thus, the higher its oblateness w i l l be. Another indicator o f weld ing intensity may be clast orientation; Sheridan and Ragan (1976) reported that mechanical deformation (i.e., non-viscous, below T g ) was insufficient to change the orientation and alignment o f particles. They argued that a compactional load dr iv ing viscous deformation (i.e., above T g ) was responsible for producing elongated clasts that then rotate towards the horizontal (Ragan and Sheridan, 1972; Sheridan and Ragan, 1976). Alternatively, clasts in non- welded deposits are expected to have random orientations averaging 45° from the horizontal . Thus, a plot o f averages o f these two properties for each F T M (F ig. 13a) might serve to numerical ly distinguish between facies observed in the f ie ld. A s evident in Figure 13a, each facies o f this b lock and ash f low plots in order o f increasing welding intensity from the bottom right to the top left in terms o f orientation and oblateness. Upper non-welded deposits near Keyho le Fal ls have the highest (most random) average clast orientations (36°), and one o f the lowest (least deformed) values o f oblateness (0.33). The basal non-welded b lock and ash f low deposits, on average, have high clast orientations (32 - 34°), and low values o f clast oblateness (0.32 - 0.35). Incipiently welded deposits show a decrease in average clast orientation (27 - 29°), and as expected, an increase in average clast oblateness (0.37 - 0.39). F ina l ly , the densely welded block and ash f low deposits have the lowest average clast orientations (22 - 26°), and the 30 highest values o f average clast oblateness (0.40 - 0.43). The F T M drawn in the plane o f flattening has a near-random average clast orientation (41°), and an intermediate value o f average clast oblateness (0.36). The S T M s exhibit much greater ranges in these properties (Fig. 13b), suggesting that on the centimeter scale, weld ing intensity is h ighly heterogeneous. No t only are the blocks o f densely welded material indistinguishable from one another, but the ranges o f average oblateness and orientation for a l l S T M s nearly span the fu l l range o f oblateness (0.35 - 0.43) and orientation (21 - 36°) for the entire deposit. This is an indication that strain is much more local ized at this scale. 31 2 0 3 0 Orientation (°) 4 0 5 0 0 . 8 0 . 7 0 . 6 0 . 5 0 . 4 0 . 3 0 . 2 0 . 1 0 b) • B l o c k # 1 A B l o c k # 3 • B l o c k # 4 • B l o c k # 5 2 5 1 i 1 0 2 0 3 0 Orientation (°) 4 0 5 0 Figure 13: Average clast orientation is plotted against average clast oblateness for (a) F T M s , and (b) S T M s . F T M s are grouped by facies: (1) densely welded facies, (2) upper, incipiently welded facies, (3) non-welded basal facies, (4) upper, non- welded facies and, (5) densely welded facies mapped in the plane o f flattening. Welding is expected to promote high clast oblateness and low clast orientation due to compaction. Non-welded deposits would have a low clast oblateness (e.g. near- spherical), and a random clast orientation o f 45°. The deposit remains heterogeneous at the sub-metre scale as indicated by data from the S T M s . S T M samples originate from the densely welded section (group 1 o f the F T M s ) but show as large a range as the entire suite o f F T M s . 32 Oblateness is also a useful metric of strain. If all strain results in volume loss (e.g., volume strain, £v), then oblateness is mathematically equal to strain for spherical particles: (2) If the strain conserves volume (e.g., pure shear strain, Es), then: (3) Two end-member strain paths are therefore possible for the clasts in the block and ash flow deposit. Ideally, if the clasts start as spheres, oblateness and volume strain would have a linear 1:1 relationship. My values of oblateness define a curvilinear relationship against strain with a non-zero intercept (Fig. 14, inset). The non-zero intercept suggests that the clasts in the non- welded deposit had an original oblateness of approximately 0.30 (from Fig. 13a, 14). Taking into account original clast oblateness, the values of oblateness for the most welded deposits suggests a maximum of 12% volume strain, or approximately 9% pure shear strain. Strain values for densely welded ignimbrites are usually much higher. For example, Quane and Russell (2005a) define 'densely welded' ignimbrite deposits as those with oblateness values greater than 0.82. However, this deposit cannot be classified using Quane and Russell's (2005a) ranking because its original oblateness is greater than zero, and because the blocks are not pumiceous in nature. 33 0.1 0.2 0.3 0.4 Strain (volume or pure shear) 0.5 F igu re 14: Strain vs. expected oblateness (1-c/a) for volume strain (solid line), and pure shear strain (dashed line). Inset shows complete strain paths assuming that particles are init ial ly spherical. M a i n figure accounts for an original oblateness o f 0.3, wh ich is a conservative estimate based on non-welded deposits (Figure 13). I f this is the case, values o f strain incurred by the welded block and ash f low deposit are approximately 1 2 % for volume strain and 9 % for pure shear strain. 34 3.2.1. Empi r i ca l Experiment with Image Ana lys is The weld ing trajectory is defined by average values o f oblateness and orientation for F T M s , but they provide a substantially lower estimate o f strain (12%) than expected. A n empir ical experiment was devised to investigate the progression o f volume strain using the least welded F T M . F T M 08, a texture map deriving from a section o f the basal non-welded facies was digital ly reduced in its vertical dimension by 10, 20, 30, 40 and 5 0 % which is exactly equivalent to a volume strain o f 10, 20, 30, 40 and 5 0 % (Fig. 15). F T M s from the densely welded facies ( F T M 05, 06) were then compared to the digital ly 'strained' images o f F T M 08. The images o f F T M 05 and 06 most closely resembled F T M 08 after a 'strain' o f 30 - 4 0 % . This experiment and visual comparison o f images implies that the densely welded facies have undergone 30 - 4 0 % volume strain, relative to the non-welded facies. This is a value much higher than 1 2 % , as estimated using average oblateness o f F T M s . Subsequently, image analysis o f F T M 08 after a 'strain' o f 5 0 % was completed to obtain values o f oblateness and orientation. Sc ion Image™ revealed F T M 08 had an average oblateness o f only 0.54 after being digital ly 'strained' by 5 0 % . Thus, an accommodation o f 5 0 % volume strain only resulted i n a 0.22 increase in average oblateness. This is consistent with the lower-than-expected average oblateness values associated wi th the densely welded F T M s and S T M s . 35 F igu re 15: Dig i ta l images produced f rom computer- simulated shortening o f F T M 08, wh ich represents the unwelded block and ash f low deposit. Simulations show incremental shortenings (e.g., volume strains) o f 10, 20, 30, 40, and 5 0 % . F T M 05 and 06 are displayed to show their similarity to F T M 08 after undergoing 30-40% volume strain. O f note is that average oblateness should parallel values o f volume strain incurred, but e v = 5 0 % produces a lower than expected average oblateness o f 0.54. FTM 06 (oblateness = 0.43) FTM 08 basal unwelded £ v=0% oblateness = 0.32 £v= 10% (volume strain by collapsing pores) e = 20% £v= 50% oblateness = 0.54 36 3.2.2. Distributions o f Oblateness and Orientation Distributions o f clast oblateness and orientation were examined in the F T M s in an effort to further examine the nature o f strain. The distributions were created using plots o f normal ized frequency vs. oblateness (bin size = 0.1) or orientation (bin size = 10°). Oblateness shows near- normal distributions whereby the degree o f skewness to the right (towards larger values o f oblateness) defines the degree o f welding (Fig. 16). The densely welded facies ( F T M s 01 , 02, 04 - 06) show the most skewness towards the right, whereas non-welded facies ( F T M s 07, 08, 13) show more normal distributions or even a skewness towards the left. Incipiently welded facies ( F T M s 09, 10, 12) show intermediate trends. In most cases, a we l l defined peak also appears in those distributions representing densely welded sections. F T M s 04 - 06 show this feature, whereas some non-welded sections (i.e., F T M 11) show irregular distributions. Incipiently welded sections, once again, show intermediate results. The peak values o f oblateness are also signif icantly higher than the averages calculated for each F T M . O n average, the densely welded facies show a max imum frequency at 0.4 - 0.5, whereas the incipiently welded facies peak at 0.3 - 0.5, and the non-welded facies peak at 0.2 - 0.4. The distribution o f oblateness seen in the digital ly deformed F T M 08 ( 5 0 % volume strain) is a prime example o f these three features in a densely welded deposit (F ig. 17). F T M 03, drawn o f the densely welded facies i n the plane o f flattening; it shows a sharp peak but it is skewed to the left at a max imum frequency o f 0.3 - 0.4. 37 Oblateness (1-c/a) Oblateness (1-c/a) ^' S ^ ^ J f j Oblateness (1-c/a) F igu re 16: Distr ibut ion o f oblateness for each F T M . Most display a normal or near- normal distribution which becomes progressively more skewed to the right as weld ing intensity and the peak oblateness values increase. Numbers indicate the chronological order in which the f ie ld texture maps were completed (e.g., not weld ing intensity). 38 FTM 08 (-50%) N 0.2 Q- <a" cs- fc- fc- fcv fc- fc- fc- \- fc- fc- fc- fc- fc- fc- fc> fc- fc- Oblateness (1-c/a) 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 Orientation (°) F igu re 17: Distr ibution o f (a) oblateness and (b) orientation for a 5 0 % volume- reduced F T M 08. Oblatess shows a near-normal distribution skewed to the right, wi th a peak oblateness o f 0.6 - 0.7. Orientation shows a negative exponential distribution with less than 1% o f clasts at angles greater than 40° from the horizontal. 39 A s weld ing intensifies, orientation shows an increasingly negative exponential distribution from low to h igh clast orientations (Fig. 18). Densely welded F T M s show the most pronounced exponential distributions with a strong peak at 0 - 10°. Incipiently welded facies commonly show a more subtle or irregular curve with a max imum frequency at 0 - 10 °. Non-welded deposits show an irregular or nearly flat trend, although the max imum frequency st i l l occurs at 0 - 10°. The F T M drawn o f the densely welded facies in the plane o f flattening ( F T M 03) demonstrates a nearly flat trend, with a max imum frequency o f 30 - 40 °. The distribution o f orientation seen in the digital ly deformed F T M 08 shows an extremely steep negative exponential curve, with less than 1% o f clasts having an orientation greater than 40° (F ig. 17). 40 FTM 01 F T M 02 F T M 03 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 60-90 Orientation f ) 1 n n n . n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 Orientation O 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-60 80-90 Orientation f ) 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 Orientation (°) II n . n . n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 60-90 Orientation {") 1, II , n , n , n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-60 80-90 Orientation (°) n.n n . n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-60 80-90 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-60 80-90 Orientation f> Orientation (°) _ln n n n n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 Orientation (*) 1 n.n n.n n n n n n n l . n .n n n .n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 Orientation (°) 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 Orientation (°) 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-60 Orientation (°) "111 I M l fl P n n n n 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-60 80-90 Orientation (°) F igu re 18: Distr ibution o f orientation for each F T M . The distributions become progressively more exponential in shape as weld ing intensity increases. Numbers indicate the chronological order in which the f ie ld texture maps were completed (e.g., not welding intensity). 41 CHAPTER FOUR PETROGRAPHY & SEM ANALYSIS OF TEXTURES Petrography and analysis using the scanning electron microscope ( S EM ) are used to provide a description o f the Keyhole Fal ls Member at the micro-scale. These observations reinforce the fact that this deposit is a welded block and ash f low. The textural observations provide evidence o f weld ing processes that cause flattening o f particles, development o f fabric, and a loss o f porosity. This chapter also serves to contrast components, porosity, textures and relations from non-welded to densely welded deposits. Last ly, these observations constrain the mechanisms involved in weld ing the b lock and ash f low deposits. For a detailed description o f Pebble Creek Formation mineralogy, refer to Stasiuk et a l . (1996). 4 . 1 . Petrography Petrographic descriptions derive from 36 thin sections ranging from non-welded to densely welded facies o f the b lock and ash f low deposit. Th in section analysis records the development o f a fol iat ion, progressive deformation o f the clasts, and a reduction in total porosity in both clasts and matrix with increasing welding intensity. 42 4.1.1. Non-welded Facies Due to the unconsolidated nature of the non-welded matrix, only non-welded juvenile clasts were examined in thin section. Clasts possess a glassy, highly vesicular groundmass with phenocrysts of plagioclase, orthopyroxene, amphibole, and biotite, with rare phenocrysts of clinopyroxene, quartz and apatite. Subhedral, sieve-textured plagioclase crystals dominate the phenocryst population, ranging in length from 1.5-4.0 mm. They are commonly complexly zoned, sometimes bearing an outer euhedral rim of plagioclase growth. Plagioclase also occurs as smaller, 0.2 - 1.0 mm, euhedral, albite-twinned, lath-shaped crystals. Euhedral crystals of 0.2 - 0.4 mm-long orthopyroxene represent the most abundant ferro-magnesian phase. Amphibole occurs as individual subhedral, 0.2 - 0.5 mm-long crystals as well as reaction rims on biotite crystals. Biotite is clearly out of equilibrium, occurring as 0.5 - 1.0 mm, highly corroded crystals or coring a reaction rim of amphibole+oxides±pyroxene. Also present are crystal clots or glomerocrysts. These clusters of crystals vary from 2-7 mm in diameter, but are present in all samples of block and ash flow deposits. Glomerocrysts comprise crystals of plagioclase, biotite-cored amphiboles and oxides, orthopyroxene, and apatite. Vesicles represent approximately 30 - 40% of the clast volume and are frequently located adjacent to phenocrysts or glomerocrysts (Fig. 19a). They are sub-spherical to elongate in shape, and range in size from 0.1-1.0 mm. Clasts may also demonstrate flow banding or mingling textures, whereby darker- coloured, more phenocryst-rich material is mingled with the material described above. 43 4.1.2. Incipiently Welded Facies Juvenile clasts from the incipiently welded facies are mineralogically equivalent to those from the non-welded facies. Clast sizes range upwards from 0.5 mm in diameter and are sub-spherical to irregular in shape. Juvenile clasts are glassy to highly vesicular in nature, whereas clasts from the Plinth assemblage are plagioclase-porphyritic. Intrusive igneous clasts are noncrystalline and noticeably coarser grained, whereas other lithic clasts contain abundant acicular or lath- shaped plagioclase phenocrysts. Small, fine-grained lithic clasts of sedimentary rocks are also observed. Vesicles are variable in shape and size, but the largest ones are found in pumice-like clasts (Fig. 19b). Flow banding is visible in some juvenile clasts, similar to those found in juvenile clasts from the non-welded facies. The incipiently welded matrix of the block and ash flow deposits is vitroclastic; the matrix contains many broken crystals/clast fragments that are less than 0.25 mm in diameter. There is also, in general, a greater concentration of crystals in the matrix than in juvenile clasts. The porosity in the matrix is difficult to identify at this scale, but appears to consist of a network of small, connected vesicles. This material is sintered together, and there is little evidence of clast deformation. There may be slight differences in porosity between the non-welded and incipiently welded facies, but they are difficult to discern with the naked eye. 44 Figure 19: Summary of common features within the non-welded to incipiently welded block and ash flow deposits at Mount Meager: (a) vesicular, non-welded pumice-like clast (FOV = 3.9 mm);(b) vesicular pumice-like clast in incipiently welded deposits (FOV = 3.0 mm);(c) shard size range averaging 50 - 500 |Jm, (d) fragmented crystal and glass amalgamations; note the stretched vesicles in the larger shard all aligned in the same general manner, (e) moss-like adhesion of fine ash to larger particles, (f) spherical to discoid-shaped vesicles within a large blocky shard. 45 4.1.3. We lded Facies The componentry and mineralogy o f the welded facies parallels that described for the non- welded and incipiently welded facies. However, deformation due to compaction and volume strain is prominent. Clasts are noticeably more elongate in shape (F ig. 20a), in comparison to their less welded counterparts. In addition, elongate clasts show a particle alignment (perpendicular to flattening), resulting in a fol iation (F ig. 20b). Loss o f porosity due to volume strain is most evident in the clasts, where collapsed pores have left behind wispy structures (F ig. 20c). These wispy structures also have formed parallel to the length o f the flattened clast (F ig. 20a). Where these wispy structures are absent, the collapsed pores may have been completely obliterated by the welding process. Where these structures are not aligned parallel to fabric, the clasts' groundmass has collapsed around a crystal/crystal fragment (F ig. 20d). Opt ica l ly , there is very little discernable porosity remaining in the clasts (<5%) (Fig. 20e), and only sl ightly more remaining in the matrix (5-10%). Deformation in the matrix is less noticeable due to its glassy nature, but can be observed in areas between larger clasts. In these areas, the matrix has been reduced in volume to the extent that clasts in close proximity are interacting and deforming (F ig. 20f). 46 F igu re 20: Welding textures observed in thin section: (a) elongated clast formed due to loss o f porosity ( F O V = 3.9 mm). It is important to note that the collapsed vesicles are consistently parallel to the length o f the clast. (b) elongated clasts forming a parallel fabric ( F O V = 3.9 mm); (c) close-up o f collapsed vesicles around a small crystal fragment ( F O V =1.0 mm); and, (d) compacted vitrophyric rhyodacite clast showing collapsed vesicles (wispy structures) and local ized strain in proximity to crystals ( F O V = 3.9 mm) ; (e) dense vitrophyric glassy clast lacking porosity ( F O V = 7.8 mm) ; and, (f) deformation in matrix evident between two larger clasts ( F O V = 2.0 mm). 47 4.2. SEM Analysis The SEM facilitates the detailed study of the ash fraction, which includes particles smaller than 2 mm (2000 um). A detailed SEM examination of volcanic shards from samples of the Keyhole Falls Member is presented below, representing the following facies: (a) non-welded to incipiently welded, (b) moderately welded, and (c) densely welded block and ash flow deposits (Table 4). Samples from the non-welded to incipiently welded sections allow for primary textures and attributes of the pyroclastic material to be identified. SEM analysis of moderately to densely welded samples will reveal the changes in pyroclast texture due to welding and, thus, will constrain the mechanisms of the welding process. The material used for SEM analysis comprised loose grains (matrix from non-welded deposits), small (~1 cm) rock fragments (from densely welded and incipiently welded deposits), and polished thin sections (from densely welded and incipiently welded deposits). The variety of sampling allows for two-dimensional and three-dimensional visualizations of the glass shards and pore space. Back-scattered electron images were acquired with a Philips XL-30 Scanning Electron Microscope with Princeton Gamma-Tech energy-dispersion X-ray spectrometer and image analysis systems. Attributes such as shard type, shard shape, shard size, and texture were observed in each sample, and then compared to each other in an effort to identify distinguishing features associated with the welding process. Image analysis software (Image J™) was used in conjunction with the SEM images taken from polished thin sections to recover porosity. This method, however, is approximate (total porosity (Oy) ± 5%) due to the thresholding limitations of the software and the subjectivity involved in identifying void space. 48 Tab l e 4. Sample suite chosen for S E M study o f a variably welded block and ash flow deposit, and expectations according to parallel research i n ignimbrites. Sample Format We ld ing facies Expectation in ignimbrites KM-04-018 loose grains * non-welded no deformation KM-04-031 loose grains non-welded no deformation KM-04-015c thin section incipiently welded little to no deformation KM-04-017 rock fragment incipiently welded* little to no deformation KM-05-063 thin section moderately welded moderate deformation KM-05-017c rock fragment densely welded extensive deformation KM-05-012 thin section densely welded extensive deformation ox id ized sample 49 4.2.1 Non-welded Facies S E M analysis o f non-welded samples o f the b lock and ash f low deposit, al lows the study o f primary, non-welded pyroclasts. Samples are o f loose to barely consolidated ash o f the b lock and ash f low deposit, and they comprise four main types o f shards. Mos t (60% ) o f the particles are b locky in habit; others are bubble-wall (20%) , platy (10%) , and pumiceous (10%) shards (F ig. 21). The shards show little evidence o f mechanical abrasion during transport as their overal l shapes remain sharp, arcuate, curvil inear, or angular. Shard size varies f rom approximately 5 pm to several hundred um, with most shards in the 50 - 500 p m range (F ig. 19c). The non-welded to incipiently welded section o f the b lock and ash f low deposit comprise euhedral crystals o f plagioclase, pyroxene, and amphibole enclosed by glass selvages. Some crystal and glass selvage ensembles are fragmented (Fig. 19d). Finer particles (5 - 50 pm) tend to adhere in a moss-like manner to the larger glass shards (Fig. 19e). Larger ash particles (500 - 1500 pm) commonly contain multiple vesicles which are stretched in the same general orientation (F ig. 19d). Otherwise, b locky, platy and bubble wa l l shards show vesicles that are dominantly spherical to discoid in shape (F ig. 19f). The more pumiceous shards commonly host abundant tubular vesicles (Fig. 2Id) . 50 F igu re 2 1 : Shard types observed in the non-welded to incipiently welded block and ash f low deposits at Mount Meager: (a) blocky, (b) bubble-wall/cuspate, (c) platy, and (d) pumiceous. 51 4.2.2. We lded Facies The examination o f the densely welded block and ash f low deposits at Mount Meager under the S E M a l low for a contrast with the non-welded deposits. It also al lows for features that are only associated with the weld ing process to be isolated from those brought about by earlier processes such as fragmentation and transportation. In general, there are five main types o f glass shards identif ied in the ash o f the densely welded deposits: (a) larger (>50 um) b locky shards (50%) , (b) bubble-wall shards (10% ) and (c) platy (5%) shards (F ig. 22a-c), as we l l as smaller shards (<50 um) that are (d) dendritic to moss-like (75%) , or (e) acicular (25%) (Fig. 22d). The shards remain angular, curvil inear, and arcuate in shape, but tend to be more elongated than the non-welded samples (Fig. 22e). Shard size varies from less than 5 um to approximately 1500 um, where the bulk o f the glass shards are 50 - 500 um. The densely welded block and ash f low deposit samples comprise euhedral crystals o f plagioclase, pyroxene, and amphibole enclosed wi th in glass selvages. The amount o f glass encompassing the crystals does not appear to be any thicker or thinner than the selvages observed in the non-welded to incipiently welded samples. The crystal and glass selvage assemblages, however, are fragmented more frequently than those in the non-welded samples. Finer particles, especially those less than 50 um, tend to adhere in a moss-like fashion to the larger glass shards, and accumulate in the depressions o f the larger shards (F ig. 22d). Some pitting and irregular surfaces are evident in larger shards (Fig. 22a, d) and vesicles are less common. Some larger ash particles (500 - 1500 um) contain multiple vesicles that are stretched in the same direction. Otherwise, the b locky, platy and bubble wa l l shards show very few 52 vesicles. Approximate ly 1 0 % o f shards larger than 500 pm contain vapor-phase crystal l ization o f feldspars wi th in their isolated pores (Fig. 22f). 4.2.3. S E M Analys is o f Porosity A t the outcrop or hand sample scale, the b lock and ash f low deposit shows a v is ible densification o f the material w i th weld ing intensity. Analys is o f porosity at the micro-scale w i l l a id in determining whether this densification is due to a loss in porosity or whether shear stresses also contributed to the welding process. Twenty S E M images o f three thin sections analyzed wi th Image J revealed that the non-welded samples have an average o f 2 9 % total porosity (range = 26 - 3 2 % ) (F ig. 23a). Densely welded samples have an average o f 1 9 % total porosity (range = 13 - 2 3 % ) (F ig. 23c). One sample o f moderately welded block and ash f low deposit revealed a higher-than-expected average total porosity o f 2 8 % (range = 24 - 3 4 % ) (Fig. 23b). These values o f total porosity can be further subdivided into two types - isolated and connected porosity. Both types are observed in the welded and non-welded deposits, and both are destroyed as weld ing intensity increases. Isolated porosity is identified qualitatively as voids that are completely hosted by shards or clasts, and where there is a lack o f in f i l l ing material. In addit ion, vapour-phase crystall ization occurs within some pores, suggesting that these pores were also sealed o f f f rom the surrounding environement (e.g., isolated). Pores that are f i l led wi th smaller ash or shard particles are common, and these are assumed to represent connected pores. Us ing these parameters, isolated porosity is visible only in the larger glass shards (> 50 pm). Connected porosity appears in a l l ash size fractions as both intra- and inter-shard porosity. 53 F igu re 22: Attributes o f the densely welded block and ash f low deposit: (a) large, b locky shard showing pitting or irregular surface textures, (b) platy shard with bubble-wall remnants, (c) bubble-wall/cuspate shard, (d) dendritic/acicular/moss-like fine ash f i l l ing depressions in larger shards, (e) elongated shards, (f) vapour-phase crystall ization o f feldspars wi th in isolated pores o f large shards. 54 F igu re 23 : Output images from Image J™, where black = porosity and white = shards/crystals. There is a substantial decrease in average porosity f rom (a) the unwelded/incipiently welded sections (29%) to (c) the densely welded sections (19%) . O n average, however, the moderately welded section (b) conserves its high porosity (28%) . A l l scale bars represent 200 um. 55 CHAPTER FIVE PHYSICAL PROPERTIES Density and porosity are strongly coupled properties o f pyroclastic rocks, and vary strongly with weld ing and compaction (Ragan and Sheridan 1972; Streck and Grunder 1995; Rust and Russel l 2000; Quane and Russel l , 2005a). A suite o f more than 100 samples was collected from al l facies o f the b lock and ash f low deposits. Sample selection was done such that both matrix and clast components o f the deposits are we l l represented. Density and porosity were measured for a l l samples and are used below to investigate the welding process. Specif ic methods and procedures for measuring density are summarized in Appendix D. In this study, measurements o f density and porosity involve three separate experiments. B u l k density (p B ) is used here to denote the density o f the rock and al l o f its pores, inc luding both connected and isolated pore space. B u l k density o f consolidated samples derives f rom measurements o f sample mass and geometrical volume (e.g., wi th digital calipers) calculated for cy l indr ica l cores. For unconsolidated materials, a graduated cyl inder was packed wi th sample to a specified volume and the mass was recorded (Appendix D) . Skeletal density (ps) is the density o f the rock and its isolated (non-penetrated) porosity. Skeletal density o f both cy l indr ica l cores and unconsolidated materials was measured by he l ium pycnometry (K lug and Cashman, 1994; Russel l and Stasiuk, 1997). Last ly, an aliquot o f each sample was crushed into a powder and the rock powder density (p R ) was measured using He-pycnometry (Rust et a l . , 1999). The rock powder density represents the density o f the sol id material (powdered rock) only. These three 56 values o f density are useful metrics o f welding intensity but can also be used to calculate three forms o f porosity (O): total (T), connected (C), and isolated (I): O r = l - — (2) PR ®c=l-— (3) Ps 4 > 7 = 1 - ^ (4) PR These calculated values o f porosity can also be validated by equating total porosity to the sum o f connected and isolated porosity: ® T * ® C + ® , (5) The physical properties for a l l samples are summarized in Tables 5-8. Complete tables o f physical property data can be found in Appendix E. 57 Table 5. Summary of physical property measurements on bulk samples of unconsolidated block and ash flow deposits, including: bulk density (p B), skeletal density (ps), rock density (pR), total porosity (O t), connected porosity and isolated porosity (O,). Standard deviations are reportec as lo. Sample PB (g/cm 3) o Ps (g/cm 3) c PR (g/cm 3) a 0>T (%) a ® c ( % ) a 0>, (%) <T KM-04-0181 1.47 0.003 2.50 0.003 2.54 0.006 42.1 0.17 41.2 0.13 1.65 0.25 KM-04-019' 1.48 0.012 2.52 0.002 2.55 0.002 42.1 0.48 41.3 0.49 1.42 0.12 KM-04-0201 1.52 0.014 2.52 0.002 2.53 0.002 39.8 0.57 39.5 0.57 0.41 0.10 KM-04-0312 1.59 0.025 2.54 0.002 2.55 0.002 37.8 0.98 37.4 0.98 0.68 0.10 KM-05-0233 1.54 0.028 2.52 0.003 2.55 0.003 39.5 1.11 38.7 1.13 1.32 0.14 KM-05-0321 1.39 0.028 2.52 0.001 2.53 0.004 45.0 1.09 44.8 1.09 0.34 0.15 KM-05-0362 1.43 0.057 2.53 0.001 2.54 0.001 43.6 2.26 43.5 2.27 0.11 0.07 Upper, incipiently welded block and ash flow deposit Basal, non-welded block and ash flow deposit Upper, non-welded block and ash flow deposit Table 6. Summary of measured densities listed by welding facies of the block and ash flow deposit. Facies N Bulk Density (g/cm  3 ) Skeletal Density (g/cm 3) Rock Density (g/cm 3 ) Avg. a Max Min Avg. o Max Min Avg. a Max Min Non-welded (upper section) 16 1.70 0.122 1.89 1.43 2.46 0.061 2.54 2.37 2.52 0.032 2.59 2.47 Incipiently welded (upper section) 12 1.83 0.275 2.10 1.39 2.44 0.062 2.52 2.34 2.50 0.029 2.55 2.46 Densely welded (middle of section) 57 2.19 0.113 2.37 1.98 2.51 0.040 2.58 2.42 2.52 0.034 2.60 2.45 Moderately welded (middle of section) 6 2.08 0.041 2.13 2.02 2.52 0.030 2.57 2.48 2.53 0.012 2.55 2.51 Non-welded (base of section) 15 1.64 0.126 1.88 1.50 2.31 0.069 2.52 2.24 2.49 0.023 2.55 2.46 All samples 106 1.99 0.273 2.37 1.39 2.47 0.084 2.58 2.24 2.52 0.033 2.60 2.45 Table 7. Summary of calculated porosity values listed by welding facies of the block and ash flow deposit. Facies N Avg. Total Porosity (%) o Max Min Avg. Connected Porosity (%) a Max Min Avg. Isolated Porosity (%) a Max Min Non-welded (upper section) 16 32.7 4.88 43.6 24.3 31.0 4.76 43.5 25.0 2.38 1.953 5.7 -1.1 Incipiently welded (upper section) 12 27.4 11.96 45.0 16.1 25.4 13.07 44.8 14.5 2.54 1.821 5.5 0.3 Densely welded (middle of section) 57 13.5 5.41 22.6 3.6 13.1 5.51 21.5 3.8 0.53 1.231 3.9 -2.0 Moderately welded (middle of section) 6 17.5 1.59 20.1 15.8 17.2 2.16 21.4 15.4 0.37 1.268 1.9 -1.7 Non-welded (base of section) 15 33.9 5.64 40.4 23.9 28.9 5.30 38.7 20.0 7.02 2.610 10.8 1.3 All samples 106 21.2 10.88 45.0 3.6 19.8 10.05 44.8 3.8 1.92 2.729 10.8 -2.0 Table 8. Summary of density and calculated porosity values listed by component and welding intensity of the block and ash flow deposit. Component/Welding Intensity N Bulk Density (g/cm3) Avg. o Skeletal Density (g/cm 3) Avg. a Rock Density (g/cm3) Avg. o Total Porosity (%) Avg. o Connected Porosity (%) Avg. o Isolated Porosity (%) Avg. a Non-welded 28 1.68 0.120 2.37 0.091 2.50 0.029 32.39 4.754 28.95 3.831 4.90 3.133 Clasts Indurated 8 2.01 0.059 2.41 0.041 2.49 0.017 18.91 2.253 16.01 1.578 3.45 1.623 Welded 11 2.34 0.035 2.46 0.022 2.48 0.026 5.35 1.070 4.79 0.992 0.98 1.071 Non-welded 3 1.52 0.081 2.53 0.011 2.55 0.010 40.28 2.963 39.86 3.222 0.70 0.598 Matrix Indurated 4 1.46 0.054 2.51 0.012 2.54 0.011 42.24 2.159 41.69 2.249 0.94 0.662 Welded 46 2.13 0.082 2.52 0.029 2.54 0.025 16.63 2.954 16.29 3.031 0.39 1.261 Mixed Welded 6 2.26 0.078 2.49 0.046 2.50 0.028 9.63 3.329 9.10 3.519 0.60 1.196 AU samples 106 1.99 0.273 2.47 0.084 2.52 0.033 21.21 10.883 19.81 10.052 1.92 2.729 5.1. The 'Proto-deposit' In order to relate variations in density and porosity to strain accumulated during weld ing, an estimate o f the b lock and ash f low deposit properties when it was init ia l ly emplaced is required (e.g., prior to sintering and compaction). Our best estimate o f this state derives f rom measurements on samples o f the unconsolidated facies o f the b lock and ash f low deposits (Table 5). A total o f seven bulk samples from non-welded to incipiently welded facies were collected (F ig. 4d). Values o f bulk densities (graduated cyl inder technique) for the matrix vary by 1 5 % between 1.39 - 1.59 ± 0.057 g/cm 3. Skeletal density, based on hel ium pycnometry, show less variation (1 .5%) , and range from 2.50 - 2.54 ± 0.003 g/cm 3. Last ly, the densities o f powdered samples measured by hel ium pycnometry vary by less than 1% and return values between 2.53 - 2.55 ± 0.006 g/cm 3. F rom these three values o f density, porosity can be inferred. The resulting values o f total porosity for the non-welded/unconsolidated matrix range from 3 8 - 4 5 ± 2 .26% , where 37 - 45 ± 2 . 2 7 % is connected, and 0.3 - 1.7 ± 0 . 2 5 % is isolated. The average values o f O t = 4 1 . 4 % , O c = 4 0 . 9 % , and O i = 0. 8 5 % are used as a baseline for subsequent calculations and analysis on matrix samples o f block and ash f low deposit. Large clasts sampled from the unconsolidated and incipiently welded facies were also sampled to estimate original conditions o f the block and ash f low deposit. B u l k density values (geometric volume technique) for clasts vary 2 6 % , ranging from 1.50 - 1.89 ± 0.020 g/cm 3 . Skeletal density based on hel ium pycnometry shows less variation (13%) , and ranges f rom 2.24 - 2.52 ± 0.007 g/cm 3. Last ly , the densities o f powdered samples measured by hel ium pycnometry vary by 5 % and return values o f 2.46 - 2.59 ± 0.009 g/cm 3. F rom these three values o f density, porosity 62 can be inferred. The values o f total porosity for these non-welded/unconsolidated clasts range f rom 24 - 40 ± 4 . 7 5 % , where 1 9 - 3 4 ± 3 .83% is connected, and 0 - 12 ± 3 .48% is isolated. The average values o f O t = 3 2 . 4 % , O c = 2 8 . 9 % , and O i = 5 .26% are used as a baseline for subsequent calculations and analysis o f clasts belonging to the b lock and ash f low deposit at Mount Meager. 5.2. Bulk Dens i ty B u l k densities were calculated for al l 106 samples, representing the fu l l welding spectrum o f the deposit. They were calculated in order to determine the overall sample density ( including a l l its porosity), and how it varies throughout the weld ing facies (Table 6), as we l l as how it varies between components o f the b lock and ash f low deposit (F ig. 24a; Table 8). B u l k density values, in combination with other density measurements, are also used in obtaining total porosity values (Tables 7, 8). 63 Volume - skeletal (cm ) c) 120 100 8 0 TO I 60 S 40 20 range- p B - - - range - p s o matrix • clasts x mixed range- p R 10 20 30 40 50 Volume - rock (cm ) F igu re 24: Mass-volume plots for al l samples showing total ranges of: (a) bulk density (p B ) , (b) skeletal density (p s ) , and (c) rock density (p R) for clasts (solid circle), matrix (open circles), and mixed samples (x's). In each case, the m in imum and max imum densities are represented by sol id lines. Grey shaded regions in (b) and (c) represent the range in bulk density shown in (a). Dashed line in (c) represents the variation in skeletal density. In (a), clasts show a wide range o f bulk densities, but they are generally lower than the matrix. The matrix shows a tighter but higher overall range in bulk density. In (b), the same pattern is observed, except ranges o f skeletal density are much smaller than the ranges in bulk density. The range o f rock powder densities seen in (c) is extremely narrow, and is independent o f componentry. 64 5.2.1. Non-welded vs. Welded Dist inct variations in bulk density exist between non-welded and welded facies o f the block and ash f low deposit. A n average o f fifteen basal non-welded samples resulted in a bu lk density o f I. 64 ± 0.126 g/cm 3. Sixteen upper non-welded samples averaged a bulk density o f 1.70 ± 0.122 g/cm 3. The incipiently welded facies shows a slight increase in bulk density, but are more variable, averaging 1.83 ± 0.275 g/cm 3 for twelve samples. S ix samples o f a moderately welded b lock o f material revealed a signif icantly higher average bu lk density o f 2.08 ± 0.041 g/cm 3 , whereas the densely welded samples (N = 57) had the highest average wi th 2.19 ± 0.113 g/cm 3. Total porosity is inversely related to bulk density. The basal non-welded section contains an average total porosity o f 33.9 ± 5.64%, whereas the upper, non-welded section averages only sl ightly less at 32.7 ± 4 . 8 8 % . The incipiently welded facies maintains a total porosity o f 27.4 ± I I . 9 6 % . Moderately welded samples show a much lower total porosity o f 17.6 ± 1.59%, and the densely welded samples have the lowest porosity at 13.5 ± 5 .41% . 5.2.2. Clasts vs. Mat r ix A s wi th the trends seen in the different facies o f the b lock and ash f low deposit, the bulk density trends between clasts and matrix are the most distinctive. Bo th clasts and matrix show an increase in bulk density as welding intensifies. Average clast density progresses from 1.68 ± 0.120 g/cm 3 (non-welded) to 2.01 ± 0.059 g/cm 3 in the incipiently welded facies, and f inal ly to 2.34 ± 0.035 g/cm 3 for the welded facies. The matrix begins with a bulk density o f 1.52 ± 0.081 g/cm 3 , averages 1.46 ± 0.054 g/cm 3 where incipiently welded, and ends with a welded bulk 65 density o f 2.13 ± 0.082 g/cm 3. M i x e d samples reveal an intermediate welded density o f 2.26 ± 0.078 g/cm 3 . Total porosity again mirrors bulk density with an inverse relationship. Non- welded clasts start with an average total porosity o f 32.4 ± 4 . 7 5 % , decreasing to 18.9 ± 2 . 2 5 % where incipiently welded, and f inal ly decrease to 5.35 ± 1.070% where they have become densely welded. The matrix contains 40.3 ± 2 . 9 6 % total porosity when non-welded, and remains similar at 42.2 ± 2 . 1 6 % where incipiently welded, but decreasing to 16.6 ± 2 . 9 5 % in the densely welded facies. M i x e d samples show an intermediate average total porosity o f 9.63 ± 3 .329% where welded. 5.3. Skeletal Density Skeletal density has been measured by he l ium pycnometry on al l 106 samples in order to determine the amount o f connected porosity in the samples, and how it varies throughout the deposit and its components (Tables 5, 7). Overal l , values o f skeletal density are much higher than the values obtained for bulk density (Fig. 24b). 5.3.1 Non-welded vs. Welded M u c h less variation in skeletal density is observed when comparing non-welded and welded facies o f the b lock and ash f low deposit. Basal non-welded samples resulted in a skeletal density o f 2.31 ± 0.069 g/cm 3, and averaged 28.9 ± 5 .30% connected porosity. The upper non-welded samples had an average skeletal density o f 2.46 ± 0.061 g/cm 3 wi th a connected porosity o f 31.0 ± 4 . 7 6 % . The incipiently welded facies shows a similar average skeletal density o f 2.44 ± 0.062 66 g/cm 3 , but has a corresponding connected porosity o f 25.4 ± 13 .07% . The large variation in this section is largely due to the presence o f dense clasts, which represent only a small proportion o f this facies. The basal section is therefore distinct f rom the upper non-welded to incipiently welded sections in terms o f skeletal density, but not in terms o f connected porosity. The moderately welded and densely welded samples show near identical values o f 2.52 ± 0.030 g/cm 3 and 2.51 ± 0.040 g/cm 3, respectively. Connected porosity values are similar, wi th an average o f 17.2 ± 2 . 1 6 % for the moderately welded samples, and 13.1 ± 5 . 5 1 % for the densely welded samples. Therefore, the upper non-welded facies o f b lock and ash f low deposit has the most connected porosity, and, as expected, the densely welded intermediate facies retains the least amount o f connected porosity. In addition, there is a general increase in skeletal density and decrease in connected porosity as weld ing progresses. 5.3.2..Clasts vs. Mat r ix Both the clast and matrix components show very little variation in skeletal density despite their transition f rom the non-welded to the densely welded state. Clasts show a small increase in skeletal density as welding intensifies, but this increase is small relative to analytical uncertainty. Clasts, on average, have a starting skeletal density o f 2.37 ± 0.091 g/cm 3 in the non-welded facies, wh ich increases slightly to 2.41 ± 0.041 g/cm 3 in the incipiently welded section, and f inal ly to a skeletal density o f 2.46 ± 0.022 g/cm 3 where welded. Mat r ix samples show minute variations that are also wi th in measurement error. The non-welded matrix has an average skeletal density o f 2.53 ± 0.011 g/cm 3 , averages 2.51 ± 0.012 g/cm 3 when incipiently welded, and ends wi th a welded skeletal density o f 2.52 ± 0.082 g/cm 3. M i x e d samples reveal an 67 intermediate skeletal density o f 2.49 ± 0.046 g/cm 3 when welded. Connected porosity shows a more significant change as the components become welded. Non-welded clasts start wi th an average connected porosity o f 29.0 ± 3 .83% , decreasing to 16.0 ± 1.58% when incipiently welded, and are reduced to 4.79 ± 0 . 9 9 2 % once the clasts have undergone welding. The matrix contains 39.9 ± 3 .22% connected porosity when non-welded, stays fairly constant at 41.7 ± 2 . 2 5 % when incipiently welded, and finishes o f f at 16.3 ± 3 .03% when welded. M i x e d samples show an intermediate average connected porosity o f 9.10 ± 3 .519% when welded. Note that values o f total porosity and connected porosity for the matrix samples are very similar. 5.4. R o c k P o w d e r Dens i ty Rock powder density is the f inal step in characterizing the physical properties o f the Mount Meager b lock and ash f low deposit, and is important in conf irming the presence o f isolated porosity. Overa l l observations reveal there is a further reduction in range for rock powder density, as we are measuring the rock only (i.e., accounting for a l l pore space) (F ig. 24c). This should remain constant throughout a deposit unless there is a geochemical or crystal content change during its eruption from the source. 5.4.1. Non-welded vs. We lded Values o f rock powder density for a l l facies show very little variation, and on average, range f rom 2.49 ± 0.040 g/cm 3 to 2.53 ± 0.040 g/cm 3 in the basal non-welded and moderately welded facies, respectively. The powder pycnometry does, however, conf i rm the presence o f isolated 68 porosity. The basal non-welded facies contains the highest average isolated porosity, wi th 7.02 ± 2 .610% . The upper non-welded facies possesses 2.38 ± 1.953% isolated porosity, whereas the incipiently welded facies possess 2.54 ± 1.821%. The welded facies contain little to no isolated porosity, w i th values o f 0.53 ± 1.231% and 0.37 ± 1.268% for the moderately and densely samples, respectively. Therefore, there is a general decrease in isolated porosity wi th increasing weld ing intensity. 5.4.2. Clasts vs. Mat r ix Clasts and matrix are nearly indistinguishable from each other on the basis o f the results o f powder pycnometry. Clasts, on average, range from 2.48 ± 0.026 g/cm 3 to 2.50 ± 0.029 g/cm 3 regardless o f their weld ing intensity. Mat r ix samples show minute variations wi th in analytical uncertainty, but are sl ightly denser than the clasts. The matrix has an overall average rock powder density o f 2.54 ± 0.025 g/cm 3 to 2.55 ± 0.010 g/cm 3. M i x e d samples contain a similar rock powder density o f 2.50 ± 0.028 g/cm 3. Isolated porosity shows a slightly more evident trend. Non-welded clasts start with an average isolated porosity o f 4.90 ± 3 .133% , decreasing sl ightly to 3.45 ± 1.623% when incipiently welded, and end up wi th 0.98 ± 1 .071% isolated porosity (essentially none) once the clasts have been densely welded. The matrix and m ixed samples a l l demonstrate average isolated porosities o f less than 1%. 69 CHAPTER SIX DISCUSSION The a im o f this study is to document the welding trajectory o f the Keyhole Fal ls Member and recover the conditions and mechanism(s) under which this unique deposit formed. In previous chapters, I have described a welded block and ash f low deposit and presented data collected from f ie ld mapping, petrography, image analysis, S E M analysis and physical property measurements. In this chapter, those data sets and observations are used to: (a) document the weld ing process at Moun t Meager, (b) discern the mechanism(s) involved, and (c) calculate the amount o f strain accommodated by the deposit. This chapter w i l l also compare the welding process as evidenced in the Keyhole Fal ls Member against weld ing features commonly found in ignimbrites. 6.1 Analysis of Porosity Weld ing intensity is evaluated relative to the original properties in the non-welded b lock and ash f low deposit. These properties are represented by physical property measurements on the unconsolidated facies o f the Keyhole Fal ls Member. Non-welded clasts reveal an init ia l bulk density o f 1.50 - 1.89 ± 0.020 g/cm 3 ; given a rock powder density o f 2.50 ± 0.029 g/cm 3 , this corresponds to a total porosity o f 24 - 40 ± 4 . 7 5 % . Non-welded matrix shows an init ial bulk density o f 1.39 - 1.59 ± 0.057 g/cm 3 ; g iven a rock powder density o f 2.55 ± 0.010 g/cm 3 , this corresponds to a porosity range o f 38 - 45 ± 2 .26%. 70 Porosity can be further broken down into two categories: isolated and connected. The presence o f isolated porosity is first demonstrated in Figure 25a, in which connected porosity is plotted against bulk density. The y-intercepts in this plot represent the range in skeletal density (2.24 - 2.57 g/cm 3) i f there is no isolated porosity. The max imum y-intercept corresponds to a reasonable value; however, the m in imum y-intercept is much lower than the density o f the rock (2.49 - 2.53 g/cm 3). It can therefore be inferred that isolated porosity is the cause o f the lower density samples. Rock powder pycnometry confirms this hypothesis, as illustrated in Figure 25b, in wh ich rock powder density is plotted against skeletal density for a l l samples. Samples plotting be low the 1:1 l ine, and outside the 9 5 % confidence l imits represent samples wi th apparent isolated porosity. It is further reinforced by a plot o f total porosity vs. connected porosity (F ig . 25c), whereby several samples demonstrate total porosities greater than their connected porosities. In terms o f b lock and ash f low componentry, min imal isolated porosity exists in the matrix (<1.65%), regardless o f welding intensity; most is connected (Fig. 25d). Overa l l , the matrix experiences a - 2 4 % reduction in porosity, f rom the non-welded to the densely welded facies o f the b lock and ash f low deposit. The impl icat ion is that as the deposit undergoes compaction during welding, the original interstitial gas contained with in matrix porosity was a l lowed to escape out o f the deposit and, thus, the matrix o f the deposit maintained connected pathways (e.g., permeability) unti l the very end o f welding. Clasts contain mostly connected porosity (up to 4 0 % ) ; however, up to 1 2 % isolated porosity exists in the more porous non-welded clasts (Fig. 25d). On average, both types o f porosity are drastically reduced during the weld ing process: connected porosity is reduced to 5 % and isolated 71 porosity is reduced to 1% in the dense, vitrophyric clasts. This is unforeseen, as it was expected that compaction and weld ing wou ld cut o f f existing connected porosity pathways and create isolated porosity, and the same effect wou ld be observed in the matrix. Thus, there must be additional processes acting upon these deposits causing isolated pores to collapse. For isolated porosity to collapse, however, is sl ightly more complicated because there are no existing gas escape pathways. A s compaction and welding proceed, isolated pores could become connected by cracks forming with in the deposit that are created mechanical ly during compaction. Alternat ively, they could be infinitely flattened, due to pure shear strain. Another possibi l i ty is that the volatiles may be resorbed back into the glass rather than escaping from the compacting b lock and ash f low deposit (Sparks et al . , 1999). This occurs when the isolated pore pressures remain high despite the deposit as a whole having degassed subsequent to eruption. This wou ld create a pressure gradient, possibly a l lowing the gas to dissolve back into the v iscously deforming deposit, and the empty pores to collapse. 72 F igu re 25 : Plots o f physical properties inc luding: (a) connected porosity (<J>C) vs. bulk density (p B ) ; y-intercepts define min imum and max imum values o f density where there is no isolated porosity (O,); (b) Rock powder density (p R ) plotted vs. skeletal density (p s). Samples with no isolated porosity plot on the 1:1 line (solid line); samples with isolated porosity plot below the line ( p R > p s). 9 5 % confidence l imits on 1:1 line are also shown as dashed lines; (c) Total porosity (O T ) vs. connected porosity (O C ) . Samples ly ing below the 1:1 line (solid line) have isolated porosity represented by the vertical or horizontal distance to the 1:1 l ine; (d) Isolated porosity (O,) vs. total porosity (0 T ) , showing that the isolated porosity content is posit ively correlated to total porosity. 6.2 W e l d i n g Mechan i sms Physica l property measurements demonstrate that porosity decreases wi th increasing weld ing intensity. This decrease in porosity can be used to compute strain. The strain estimate is the total strain i f a l l strain is volume strain (e.g., no shear strain) or is a m in imum estimate o f total strain i f there is appreciable shear strain (e.g., constant volume strain). Quane and Russel l (2006) use the original and f inal values o f porosity to define total strain as: <D o-<D, — (6) where it is assumed that (a) al l strain is accommodated by porosity reduction, and (b) clasts and matrix each have a single starting porosity ( 4 0 % and 4 5 % , respectively). A plot o f total strain vs. total porosity can be used to examine how porosity is affected by an increasing weld ing intensity, and can reveal how indiv idual components accommodate strain. The resulting graph reveals two key aspects o f the weld ing process occurring at Mount Meager (F ig. 26). First, clasts and matrix show parallel pathways with increasing strain (e.g., welding intensity). It therefore appears as though both components are simultaneously losing porosity at the same rate. This is contrary to observations o f Sheridan and Ragan (1972) who state that pumiceous clasts in ignimbrites deform more rapidly than the surrounding matrix due their low relative viscosities and high init ia l porosities. Ross and Smith (1961) also observed that glass viscosity is very sensitive to volati le content and that pumice clasts in ignimbrite appear to retain a higher proportion o f volati les than the particulate ash. 74 0.5 0.4 0.3 0>T O Matrix • Clasts 0.5 0.4 0.1 H 0, 0.5 0.4 0.3 H 0.2 H 0.1 -T -0.1 0.1 0.2 0.3 0.1 0.2 0.3 0.4 a) 0.5 ' o b) • •• So ] 0.1 0.2 0.3 0.4 0 c) A t . < 0.4 0.5 F igu re 26 : Values o f calculated total strain (£T= 0 0 - 0 / l - O f ) are plotted vs. (a) observed total porosity (0T), (b) observed connected porosity (0C), and (c) observed isolated porosity (O,) for clasts (closed circles) and matrix (open circles). Values o f £ T are calculated assuming: (i) a l l strain is due to volume loss, and (ii) clasts and matrix each had a single starting porosity ( 4 0 % and 4 5 % , respectively). 75 Second, both clasts and matrix record the same amount of maximum total strain, approximately 38%. This value correlates well with the empirical experiments presented in chapter 3.2.1, where the most welded FTM appears to have accumulated 30 - 40% volume strain. Also, the change in particle shape is fully consistent with volume strain. In other words, values of oblateness are low enough that they can be fully accounted for by volume strain, and a pure shear strain component need not be invoked. Thus it appears that the maximum amount of strain accommodated by the welded block and ash flow deposit at Mount Meager can be expressed as ~38% volume strain. This was expected because there is little evidence supporting other welding mechanisms. Mechanical deformation is not observed nor expected because the subsequent outburst flood event produced hot blocks of densely welded block and ash flow deposit. Pure shear strain in the viscous regime would produce a change in the radial dimensions of clasts; however, this is not evident when examining outcrop in the plane of flattening, where pure shear strain would produce a higher oblateness. Little other evidence is seen except rare pull-apart clasts or local deformation around lithics (e.g., clasts of Plinth assemblage) (Fig. 27). This localization likely results from small areas losing all or most of their porosity before the rest of the deposit, thus having to resort to a form of constant volume strain to deform further. Because values of strain correlate well between empirical experiments and physical property measurements, and manifestations of shear strain are localized, it can be deduced that viscous volume strain is the dominant mechanism in welding the block and ash flow at Mount Meager. 76 Figure 27: Uncommon textures indicating min imal effects o f shear strain: (a) glassy pull-apart clast; (b) extreme flattening o f glassy clasts near a l ithic Pl inth clast (P). 7 7 6.3 Original Thickness and Average Strain Calculations The strain calculations depicted in Figure 26 can also be used to determine the deposit thickness prior to welding, as we l l as the average strain over the entire deposit. Accord ing to Stewart (2002), there is roughly 20 m o f a l luvia l deposits, and 20 m o f rock avalanche deposits over ly ing the welded block and ash f low deposits (Fig. 2a). Over ly ing these non-volcanic deposits is a further 60 m o f non-welded to incipiently welded block and ash f low deposits. Because the deposits are not stratigraphically comformable, only the lower section w i l l be used in this calculation. The lower section is currently a total o f 112 m at Keyhole Fal ls , wh ich can be broken down into thicknesses o f the three indiv idual welding facies distinguished in section 2.3: (1) 10 m o f basal non-welded facies, (2) 90 m o f densely welded facies, and (3) 12 m o f incipiently welded facies. Values o f strain calculated using equation 6 are then averaged over the three weld ing facies to produce a strain profi le (F ig 28). The facies thicknesses and average strain values are then combined to give an estimate o f the original deposit thickness using the formulae be low (Quane and Russel l , 2005a). 78 840 avalanche deposits non-welded & incipiently welded block and ash avalanche deposits avalanche deposits alluvial deposits - 8 2 0 6:0 variably welded block and ash avalanche deposits 700 4 600 CP : 112 m 600 A incipiently welded block and ash flow deposits densely welded block and ash flow deposits non-welded block and ash flow deposits h =12 m £,=18.5 h =90 m £,=34.7 h3=10 m £ =9.8% average total strain = 30.8% F i g u r e 28: Strain profile of the lower welded block and ash f low deposits at Mount Meager, southwestern Br i t ish Columbia , based on the stratigraphy o f Stewart (2002). On ly the lower section was used for the calculations due to the avalanche and al luvial deposits separating the upper and lower b lock and ash f low deposits. A total o f 112 m of block and ash f low deposits exists in the lower section, consisting of: i) 12 m o f incipiently welded deposits with an average strain o f 1 9 % ; ii) 90 m of densely welded deposits with an average total strain o f 3 5 % ; and, iii) 10 m o f basal, non-welded block and ash f low deposits bearing an average total strain o f 1 0 % . Us ing the procedure fo l lowed in Quane and Russel l (2005a), these values correspond to an overall average total strain of 3 1 % . First, the component of strain contributed by each welding facies (EO must be calculated: E.. = 5>, xe, (7) The sum of these four strain components yields the average total strain (E T ) accommodated by the deposit as a whole: £r=E£, (8) This equation returns an average total strain of - 3 1 % for the Keyhole Falls Member. In comparison, the Bishop Tuff in California yields an average total strain of 43%, the Bachelor Mountain Tuff yields 46%, and the Therasia welded tuff yields an average of 45% total strain (Quane and Russell, 2005a). Thus, the average strain value obtained for the Keyhole Falls Member is much lower than values obtained for welded ignimbrites. Assuming that strain is represented by the ratio of change in thickness to the original thickness of the deposit, the original thickness of the Keyhole Falls Member can be determined: T ^observed {Q\ °~\-ET ( 9 ) It is estimated that the original thickness at Keyhole Falls was -162 m, meaning that welding and compaction reduced the block and ash flow deposit by 50 m. 80 6.4 Comparison to Other Volcanic Deposits Physical properties of the Keyhole Falls Member sample suite provide a basis for comparing this welded block and ash flow deposit to other volcanic deposits. Below, porosity data for samples of the block and ash flow deposit at Mount Meager are compared to porosity data of: (a) pumices from the Pebble Creek Formation of Mount Meager, Lascar Volcano, Chile, and Soufriere Hills, Montserrat (Rust et al., 1999; Formenti and Druitt, 2003); (b) breadcrust bombs from Guagua Pichincha, Ecuador (Wright et al., 2007); (c) rhyodacite, andesite, and basalt lava flow deposits (Rust et al., 1999); (d) lava blocks from dome-collapse pyroclastic flow deposits at Soufriere Hills, Merapi, Cayambe, and Mount St. Helens (Formenti and Druitt, 2003); and (e) basalt scoria from Mauna Ulu (Rust et al., 1999). My comparison is based on total porosity (<DT), connected porosity (Oc), and isolated porosity (Fig. 29). Figure 29 shows plots of total porosity vs. connected porosity; the presence of isolated porosity is identified by points that plot below the 1:1 line. These data indicate that the values of total porosity cannot be fully explained by connected porosity. 81 • Clasts o Matrix o Mixed 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 4>r 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.8 0.7 b) • Pumice • Jr V , , , , r- x Breadcrust bombs 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 cp C 0.4 0.3 0.2 0.1 c) + V* A Lava + Lava blocks from pyroclastic flows - Scoria 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Figure 29: Plots of total porosity (0T) vs. connected porosity (<3>c) for: (a) Mount Meager block and ash flow deposits (clasts, matrix and mixed samples), (b) pumices (squares) from Mount Meager, Lascar Volcano, and Soufriere Hills (Rust et al., 1999; Formenti and Druitt, 2003), as well as breadcrust bombs (x's) from Guagua Pichincha (Wright et al., 2007), with block and ash deposits in grey, and (c) lava flow deposits (triangles) from Mount Meager, Ring Creek, and Cheakamus (Rust et al., 1999); lava blocks (pluses) from Soufriere Hills, Merapi, Cayambe, Mount St. Helens (Formenti and Druitt, 2003); and, scoria deposits (dashes) from Mauna Ulu (Rust et al., 1999), with Mount Meager block and ash flow deposits, pumices, and breadcrust bombs in grey. 82 Samples from the matrix f rom the Mount Meager b lock and ash f low deposits contain negligible isolated porosity (Fig. 29a). In contrast, the blocks within the deposit contain up to 1 2 % isolated porosity. The max imum value o f isolated porosity is found in the non-welded to incipiently welded facies, in which clasts contain 20 - 4 0 % total porosity. However, as weld ing proceeds, that isolated porosity is destroyed along wi th most o f the connected porosity. Pumice f rom Mount Meager, Lascar Vo lcano, and Soufriere H i l l s develop a max imum o f 1 1 % isolated porosity, but possess 52 - 7 5 % total porosity (Fig. 29b). Breadcrust bombs from Guagua P ichincha have total porosities o f 32 - 7 1 % , and develop up to 1 2 % isolated porosity when total porosity values are a m in imum o f 4 0 % (Fig. 29b). Thus, the b lock and ash f low deposits at Mount Meager develop an isolated porosity at lower total porosities than typical pumices or breadcrust bombs. W i th the exception o f one location (Mount St. Helens), lava f low deposits, lava blocks f rom dome-collapse pyroclastic f low deposits and scoria deposits show no development o f isolated porosity. Despite their broad range in total porosities (2 - 5 9 % ) , only deposits f rom a disrupted cryptodome blast deposit at Mount St. Helens show any departure from the 1:1 l ine (up to 5 % isolated porosity, wi th total porosities - 5 0 % ) (Fig. 29c). Thus, b lock and ash f low deposits at Mount Meager develop isolated porosities when lava f low deposits and dome-collapse pyroclastic f low deposits o f similar densities fai l to do so. These trends in porosity can be explained by bubble nucleation events occurring prior to eruption. A l l pumice samples from fountain-collapse pyroclastic f lows possess an isolated porosity, as do the non-welded to incipiently welded clasts f rom the b lock and ash f low deposits at Moun t Meager. B locks from dome-collapse pyroclastic f lows only contain connected 83 porosity, and cryptodome blast samples from Mount St. Helens show a small amount of isolated porosity. Upon examination of samples under the SEM, Formenti and Druitt (2003) observe two populations of bubbles in the pumice samples: i) populations of large, connected vesicles, and ii) populations of small, isolated vesicles. There is no such distinction in porosity in the dome- collapse samples. As a result, it appears that fountain-collapse deposits undergo two nucleation events prior to eruption. The first population nucleates, grows and coalesces as the magma ascends in the conduit. The second population forms during a depressurization event just before erupting, when the magma is still above its glass transition temperature, producing smaller, isolated vesicles. Rapid quenching of the pumice as it is ejected from the volcanic edifice prevents the small isolated vesicles from coalescing. Dome-collapse deposits result from the gradual growth of a dome fueled by ascending magma, which possesses a population of bubbles that have nucleated, grown and coalesced as magma rises in the conduit. Given that domes are exposed to the external environment, they are commonly chilled below their glass transition temperatures. Thus, they may undergo depressurization prior to failure, but cannot produce a second population of vesicles. A cryptodome, however, forms below the surface, and can remain above its glass transition. A depressurizing event causing its exposure could cause a second nucleation event producing small isolated vesicles as measured by Formenti and Druitt (2003) at Mount St. Helens (Fig. 29). The non-welded to incipiently welded clasts in the block and ash flow deposits possess significant isolated porosity; hence, it can be deduced that a depressurizing event occurred just prior to eruption, causing a population of small isolated vesicles to form. This signifies that the eruption at Mount Meager is not likely a Merapi-type eruption as previously thought, because the deposits would not have erupted above their glass transition temperature. The most likely 8 4 analogue is that of Soufriere Hills, Montserrat, where hot, explosive dome-collapse is triggered by a Vulcanian eruption. The presence of breadcrust bombs in the incipiently welded facies also supports this hypothesis (Wright et al, 2007). Furthermore, this eruption produced a block and ash flow that was also above its glass transition temperature such that it could undergo dense welding in the viscous regime. 85 CHAPTER SEVEN CONCLUSIONS Excel lent outcrops and exposures at Mount Meager provide an opportunity to study a unique, welded b lock and ash pyroclastic f low deposit. Texture mapping and image analysis at two scales were completed as independent and objective means o f quantifying the change in fabric and flattening o f particles in the Keyhole Fal ls Member. Results indicate the fo l lowing : • Image analysis o f F T M s demonstrate a welding trajectory whereby average oblateness increases and average orientation decreases with increasing weld ing intensity. • This weld ing trajectory is more subtle than expected due to an original clast oblateness o f approximately 3 0 % ; this results in an estimated max imum volume strain o f 1 2 % in the deposit or a max imum o f 8 % pure shear strain. • Conversely, S T M s show heterogeneity or strain local ization in terms o f average orientation and oblateness. • A n empir ical experiment with image analysis reveals average oblateness does not reflect total volume strain for these deposits due to the original clast oblateness; however, the most welded F T M s visual ly correspond to experimental results having undergone a total volume strain o f 30 - 4 0 % . • Distributions o f oblateness and orientation for each F T M are more accurate in indicating weld ing intensity than average F T M values alone. 86 Petrography and S E M analysis were used to describe and identify micro-scale textures associated wi th the weld ing o f the b lock and ash deposit. In addition, deposit components and porosity were examined to document the changes from non-welded to welded facies. • We ld ing textures observed in thin section include: (a) v is ib ly flattened clasts, (b) col lapsed vesicles, (c) deformation around clasts/crystals, and (d) parallel alignment o f clasts, clast length, and collapsed vesicles. • Shards observed in the b lock and ash f low deposit are (in decreasing order f rom most abundant): (a) b locky, (b) bubble-wall, (c) platy, and (d) pumiceous. • Porosity evolution can be documented using image analysis o f S E M photos such that results correspond wel l to values obtained in physical property measurements. Phys ica l property measurements were used to elucidate the progression from non-welded to welded facies o f the block and ash f low deposit. Us ing values o f density and porosity, several inferences can be made regarding the welding process involv ing the 2360 B.P. eruption o f the Keyho le Fal ls Member : • Non-welded clasts reveal an original bulk density o f 1.50 - 1.89 ± 0.020 g/cm 3 , corresponding to a porosity o f 24 - 40 ± 4 . 7 5 % . Non-welded matrix shows an or iginal bu lk density o f 1.39 - 1.59 ± 0.057 g/cm 3 , wi th a corresponding porosity o f 38 - 45 ± 2 .26% . • Both clasts and matrix record strain equally, unl ike in ignimbrites whereby clasts accommodate more strain than the surrounding matrix. • The max imum total (volume) strain accommodated by the deposit is approximately 3 8 % . 87 Isolated porosity exists in highly-porous, non-welded clasts only, and is reduced along wi th connected porosity during the welding process; possible vehicles for this are volati le resorption or connection o f isolated porosity during compaction. Vo lume strain in the viscous regime is the dominant strain mechanism, reducing the or iginal thickness o f the Keyhole Fal ls Member by 50 m (from 162 - 112 m) ; this corresponds to an average o f 3 1 % volume strain over the entire deposit. Pure shear strain (constant volume) in the viscous regime is a min imal component, only occurring local ly as pull-apart clasts or shearing in proximity to l ithic clasts. Compar ison o f porosity data f rom other volcanic deposits demonstrates that the b lock and ash f low was most l ike ly generated by an explosive dome collapse triggered by a Vu lcan ian event, as evidenced by the presence o f isolated porosity in clasts, and the presence o f breadcrust bombs o f the b lock and ash f low deposit at Moun t Meager. 88 REFERENCES Abdurachman, E.K., Bourdier, J.-L., Voight , B., 2000. Nuees ardentes o f 22 November 1994 at Merap i Vo lcano , Java, Indonesia. Journal o f Vo lcanology and Geothermal Research 100, 345- 361. Anderson, R.G., 1975. The geology o f the volcanics i n the Meager Creek map-area, southwestern Br i t ish Columbia . B.Sc. thesis, Department o f Geologica l Sciences, The Univers i ty o f Br i t i sh Columbia . Bardintzeff, J . M . , 1984. Merap i Vo lcano (Java, Indonesia) and Merapi-Type Nuee Ardente. Bu l le t in o f Vo lcano logy 47, 433-446. Barker, D.S., N i x o n , P.H., 1983. Carbonatite lava and welded air fa l l tuff, Fort Portal f ie ld, Western Uganda. Eos, Transactions, Amer ican Geophysical Un ion 64, 896. Boudon, G. , Camus, G. , Gourgaud, A . , Lajoie, J . , 1993. The 1984 nuee-ardente deposits o f Merap i volcano, Central Java, Indonesia: stratigraphy, textural characteristics, and transport mechanisms. Bu l le t in o f Vo lcanology 55, 327-342. Bourdier, J.-L., Abdurachman, E.K., 2001. Decoupl ing o f small-volume pyroclastic f lows and related hazards at Merap i volcano, Indonesia. Bu l le t in o f Vo lcano logy 63, 309-325. B o y d , F.R., 1961. Welded tuffs and f lows in the rhyolite plateau o f Yel lowstone Park, Wyoming . Geo log ica l Society o f Amer i ca Bul le t in 72, 387- 426. 89 Branney, M.J., Kokelaar, B.P., 1992. A reappraisal of ignimbrite emplacement: Changes from particulate to non-particulate flow during progressive aggradation of high-grade ignimbrite. Bulletin of Volcanology 54, 504-520. Calder, E.S., Luckett, R., Sparks, R.S.J., Voight, B., 2002. Mechanisms of lava dome instability and generation of rockfalls and pyroclastic flows at Soufriere Hills Volcano, Montserrat. In: T.H. Druitt and B.P. Kokelaar (eds.), The Eruption of Soufriere Hills Volcano, Montserrat, from 1995-1999. Geological Society of London, Memoir 21, London, England. Cas, R.A.F., Wright, J.V., 1987. Volcanic Successions; modern and ancient. Chapman and Hall, London, 528 p. Clague, J.J., Evans, S.G., Rampton, V.N., Woodsworth, G.J., 1995. Improved age estimates for White River and Bridge River tephras, western Canada. Canadian Journal of Earth Sciences 32, 1172-1179. Clague, J.J., Friele, P.A., Hutchinson, I., 2003. Chronology and hazards of large debris flows in the Cheekye River basin, British Columbia, Canada. Environmental and Engineering Geoscience 9(2), 99-115. Cole, P.D., Calder, E.S., Sparks, R.S.J., Clarke, A.B., Druitt, T.H., Young, S.R., Herd, R.A., Harford, C.L., Norton, G.E. 2002. Deposits from dome-collapse and fountain-collapse pyroclastic flows at Soufriere Hills Volcano, Montserrat. In: T.H. Druitt and B.P. Kokelaar (eds.), The Eruption of Soufriere Hills Volcano, Montserrat, from 1995-1999. Geological Society of London, Memoir 21, London, England. 90 Cordy, P., 1999. Sedimentological evidence for the damming o f the L i l looet R iver by the 2350 B.P. eruption o f Mount Meager, Southern Coast Mountains, B C . B.Sc. Thesis, The Univers i ty o f Br i t i sh Co lumbia . Evans, S., 1992. Landsl ide and river damming events associated with the Pl inth Peak volcanic eruption, southwestern Br i t ish Co lumbia ; Geotechnical and Natural Hazards, B i Te ch Publ ishing, Vancouver, Br i t i sh Co lumbia , pp. 405-412. Formenti , Y . , and Druitt, T . H . 2003. Ves ic le connectivity in pyroclasts and implications for the f lu idizat ion o f fountain-collapse pyroclastic f lows, Montserrat (West Indies). Journal o f Vo lcano logy and Geothermal Research 214, 561-574. Gabrielse, H., Monger , J .W.H. , Wheeler, J .O., Yorath, C.J., 1992. Tectonic framework; Part A , Morphogeologica l belts, tectonic assemblages and terranes. In: H . Gabrielse and C.J. Yorath (eds.), Geo logy o f the Cordi l leran Orogen in Canada. Geologica l Survey o f Canada. Giordano, D., D ingwe l l , D.B., Romano, C , 2000. V iscos i ty o f a Teide phonolite in the weld ing interval. In: Mar t i J . , Wo l f f , J .A . (eds.), The geology and geophysics o f Tenerife. Elsevier. Giordano, D., N icho ls , A .R . L . , D ingwe l l , D.B., 2005. Glass transition temperatures o f natural hydrous melts: a relationship with shear viscosity and implications for the weld ing process. Journal o f Vo lcanology and Geothermal Research 142, 105-118. Gottsman, J . , D ingwe l l , D.B., 2001. Coo l ing dynamics o f spatter-fed phonolite obsidian f lows on Tenerife, Canary Islands. Journal o f Vo lcano logy and Geothermal Research 105, 323-342. 91 Green, N.L., Armstrong, R.L., Harakal , J.E., Souther, J .G. , Read, P.B., 1988. Eruptive history and K-Ar geochronology o f the late Cenozoic Garabaldi volcanic belt, southwestern Br i t ish Co lumbia . Geologica l Society o f Amer i ca Bul le t in 100, 563-579. Green, N.L., Sinha, A . K . , 2005. Consequences o f varied slab age and thermal structure on enrichment processes in the sub-arc mantle o f the northern Cascadia subduction system. Journal o f Vo lcano logy and Geothermal Research 140, 107-132. Guest, J.E., Rogers, P.S., 1967. The sintering o f glass and its relationship to weld ing in ignimbrites. Proceedings o f the Geologica l Society o f London 1641, 174-177. H i ckson , C.J., Russel l , J .K. , Stasiuk, M .V . , 1999. Vo lcanology o f the 2350 B.P. Erupt ion o f Moun t Meager Vo lcan ic Complex , Br i t ish Co lumbia , Canada: implications for Hazards from Eruptions in Topographical ly Complex Terrain. Bul let in o f Vo lcano logy 60, 489-507. Kano , K., Matsuura, H., Yamauch i , S., 1997. Miocene rhyolit ic welded tuff in f i l l ing a funnel- shaped eruption conduit Shiotani, southeast o f Matsue, S W Japan. Bu l le t in o f Vo lcano logy 59, 125-135 . Karatson, D., Sztano, O., Telbisz, T., 2002. Preferred clast orientation in volcaniclastic mass- f low deposits: application o f a new photo-statistical method. Journal o f Sedimentary Research 72(6), 823-835. Ke lman , M .C . , Russel l , J .K. , H i ckson , C.J., 2002. Effusive intermediate glac iovolcanism in the Gar ibaldi volcanic belt, southwestern Br i t ish Co lumbia , Canada. In: J .L . Smell ie and M . G . 92 Chapman (eds.), Volcano-ice interaction on Earth and Mars , Geologica l Society Special Publications 202, 195-211, Geologica l Society o f London. K l u g , C , Cashman, K.V. , 1994. Vesiculat ion o f M a y 18, 1980, Mount St. Helen 's magma. Geo logy 22: 468-472. Kobberger, G., Schmincke, H.U. , 1999. Deposit ion o f rheomorphic ignimbrite D (Mogan Formation) Gran Canaria, Canary Islands, Spain. Bu l le t in o f Vo lcano logy 60, 4 6 5 - 4 8 5 . Kokelaar , P., Busby, C , 1992. Subaqueous Explos ive Eruption and We ld ing o f Pyroclastic Deposits. Science 257, 196-201. Kokelaar , P., Koniger , S., 2000. Mar ine emplacement o f welded ignimbrite: the Ordov ic ian Pitts Head Tuff, Nor th Wales. Journal o f the Geologica l Society, London 157, 517-536. Mathews, W .H . , 1958. Geology o f the Mount Gar ibaldi map-area, southwestern Br i t i sh Co lumbia , Canada; Part 1, Igneous and metamorphic rocks; Part 2, Geomorphology and Quaternary volcanic rocks. Geologica l Society o f Amer i ca Bul le t in 69(2), 161-198. McPh i e , J . , Doy le , M . , A l l e n , R., 1993. Vo lcan ic Textures; a guide to the interpretation o f textures in volcanic rocks. Centre for Ore Deposit and Explorat ion Studies, Univers i ty o f Tasmania, Austra l ia , 196p. M i yabuch i , Y . , 1999. Deposits associated with the 1990 - 1995 eruption o f Unzen volcano, Japan. Journal o f Vo lcano logy and Geothermal Research 89, 139-158. 93 Naranjo, J .A. , Sparks, R.S.J., Stasiuk, M.V . , Moreno, H., Ab lay , G.J., 1992. Morpho log ica l , textural and structural variations in the 1988-1990 andesite lava o f Lonquimay Vo lcano , Ch i le . Geolog ica l Magazine 129, 657-678. Nasmith , H., Mathews, W .H . , Rouse, G.E., 1967. Br idge River ash and some other recent ash beds in Br i t ish Columbia . Canadian Journal o f Earth Sciences 4, 163-170. Peterson, D.W., 1979. Signif icance o f the flattening o f pumice fragments in ash f low tuffs. In: Chapin , C.E. , E lston, W.E . (eds), Ash-f low tuffs. Special Paper, Geologica l Society o f Amer i ca . Quane, S.L., Russel l , J .K. , 2005a. Ranking welding intensity in pyroclastic deposits. Bu l le t in o f Vo lcano logy 67, 129-143. Quane, S.L., Russel l , J .K. , 2005b. We ld ing : insights from high-temperature analogue experiments. Journal o f Vo lcanology and Geothermal Research 142, 67-87. Quane, S.L., Russel l , J .K. , 2006. B u l k and particle strain analysis in high-temperature deformation experiments. Journal o f Vo lcanology and Geothermal Research 154, 63-73. Ragan, D.H. , Sheridan, M.F. , 1972. Compact ion o f the B ishop Tuff, Cal i fornia . Geolog ica l Society o f Amer i ca Bul le t in 83, 95-106. Read, P.B., 1977. Meager Creek volcanic complex, southwestern Br i t ish Co lumbia . In: Report o f Act iv i t ies , Part A . Geologica l Survey o f Canada Paper 77-1 A . Read, P.B., 1978. Geology o f Meager Creek geothermal area, Br i t ish Co lumbia . Geolog ica l Survey o f Canada, Open F i le 603. 94 Read, P.B., 1990. Mount Meager Complex, Garibaldi Belt, Southwestern British Columbia. Geoscience Canada 17(3), 167-170. Riehle, J.R., Miller, T.F., Bailey, R.A., 1995. Cooling, degassing and compaction of rhyolitic ash-flow tuffs: a computational model. Bulletin of Volcanology 57, 319-336. Russell, J.K., Quane, S.L., 2005. Rheology of welding: inversion of field constraints. Journal of Volcanology and Geothermal Research 142, 173-191. Russell, J.K., Stasiuk, M.V. 1997. Characterization of volcanic deposits with ground penetrating radar. Bulletin of Volcanology 58: 515-527. Rust, A.R., Russell, J.K., Knight, R.J., 1999. Dielectric constant as a predictor of porosity in dry volcanic rocks. Journal of Volcanology and Geothermal Research 91, 79-96. Rust, A.R., Russell, J.K., 2000. Detection of welding in pyroclastic flows with ground penetrating radar: insights from field and forward modeling data. Journal of Volcanology and Geothermal Research 95, 23-34. Sato, H., Fujii, T., Nakada, S., 1992. Crumbling of dacite dome lava and generations of pyroclastic flows at Unzen volcano. Nature 360, 664-666. Schipper, C.I., 2002. The catastrophic failure of a volcanic dam at Mount Meager, Southwest British Columbia., 2360 BP: an engineering approach to volcanic hazards. B.A.Sc. Thesis, The University of British Columbia. 95 Schmincke, H.U. , Swanson, D.A., 1967. Laminar viscous flowage structures in ash-flow tuffs from Gran Canaria, Canary islands. Journal o f Geology 75, 6 4 1 - 664. Sherrod, D.R., Smith, J .G. , 1990. Quaternary extrusion rates o f the Cascade Range, northwestern Un i ted States and southern Br i t ish Columbia . Journal o f Geophysical Research 95, 19645-19474. Sheridan, M.F. , Ragan, D.H. , 1976. Compact ion o f ash-flow tuffs. In: G .V . Chi l ingar ian and K . H . Wol f , (eds.), Compact ion o f coarse-grained sediments, II. Elsevier. Smith, R.L., 1960a. A s h f lows. Geologica l Society o f Amer i ca Bul le t in 71(6), 795-841. Smith, R.L., 1960b. Zones and zonal variations in welded ash f lows. U.S. Geolog ica l Survey Professional Paper 354-F, 149-159. Soriano, C , Zafr i l la , S., Mar t i , J . , Bryan, S., Cas, R., Ab lay , G., 2002. We ld ing and rheomorphism o f phonolit ic fallout deposits f rom the Las Cafiadas caldera, Tenerife, Canary Islands. Geolog ica l Society o f Amer i ca Bul le t in 114(7), 883-895. Sparks, R.S.J., Wright, J .V. , 1979. Welded air-fall tuffs. In: Chapin , C.E. , E lston, W.E . (eds.), Ash-F low Tuffs. Special Paper, Geologica l Society o f Amer i ca 180, 155-166. Sparks, R.S.J., Stasiuk, M .V . , Gardeweg, M . , Swanson, D.A. , 1993. Welded breccias in andesite lavas. Journal o f the Geologica l Society (London) 150, 897- 902. Sparks, R.S.J., Tait, S.R., Yanev, Y . , 1999. Dense welding caused by volati le resorption. Journal o f the Geolog ica l Society o f London 156, 217-225. 96 Stasiuk, M .V . , Russel l , J .K. , H ickson, C.J., 1996. Distr ibution, nature, and origins o f the 2400 B P eruption products o f Moun t Meager, Br i t i sh Co lumbia : l inkages between magma chemistry and eruption behaviour. Geologica l Survey o f Canada Bul le t in 486. Stewart, M .L . 2002. Dacite block and ash avalanche hazards in mountainous terrain: 2360 yr. B P eruption o f Mount Meager, Br i t ish Co lumbia . M.Sc . Thesis, The Univers i ty o f B r i t i sh Co lumbia . Stewart, M.L . , Russel l , J .K. , H i ckson , C.J., 2003. Discr iminat ion o f hot versus co ld avalanches: Implications for hazard assessment at Mount Meager, B.C. Natural Hazards and Earth System Science 3, 712-724. Streck, M.J., Grander, A . L . , 1995. Crystal l izat ion and weld ing variations in a widespread ignimbrite sheet; the Rattlesnake Tuff, eastern Oregon, U S A . Bu l le t in o f Vo lcano logy 57(3), 151-169. Sumner, J . M , B lake, S., Mate la , R.J., Wol f f , J .A . , 2005. Spatter. Journal o f Vo lcano logy and Geothermal Research 142, 49-65. Tuffen, H., D ingwe l l , D.B., Pinkerton, H., 2003. Repeated fracture and healing o f s i l ic ic magma generate f low banding and earthquakes? Geology 31, 1089-1092. U i , T., Suzuki-Kamata, K., Matsusue, R., Fujita, K., Metsugi , H., A r a k i , M . , 1989. F l o w behavior o f large-scale pyroclastic f lows; evidence obtained from petrofabric analysis. Bu l le t in o f Vo lcano logy 51(2), 115-122. 97 U i , T., Matsuwo, N. , Sumita, M . , Fuj inawa, A . 1999. Generation o f b lock and ash f lows during the 1990-1995 eruption o f Unzen volcano, Japan. Journal o f Vo lcano logy and Geothermal Research 89, 123-137. White , M.J., McPh i e , J . , 1997. A submarine welded ignimbrite-crystal-rich sandstone facies association in the Cambrian Tyndal l Group, western Tasmania, Austral ia. Journal o f Vo lcano logy and Geothermal Reseach 76, 277-295. W i l son , C.J .N., Hi ldreth, W., 2003. Assembl ing an ignimbrite: mechanical and thermal bu i ld ing blocks in the B ishop Tuff, Cal i fornia . Journal o f Geology 111, 653-670. Wo l f f , J .A . , Sumner, J . M . , 2000. Lava fountains and their products. In: Sigurdson, H. (Ed.), Encyc lopedia o f Volcanoes. Academic Press, pp. 3 2 1 - 329. Wo l f f , J .A . , Wright, J .V. , 1981. Rheomorphism o f welded tuffs. Journal o f Vo lcano logy and Geothermal Research 10, 13-34. Woods, A .W . , Sparks, R.S.J., Ritchie, L.J., Batey, J . , Gladstone, C , Burs ik, M.I., 2002. The explosive decompression o f a pressurized volcanic dome: the 26 December 1997 collapse and explosion o f Soufriere H i l l s Vo lcano, Montserrat. In: T . H . Druitt and B.P. Kokelaar (eds.), The Erupt ion o f Soufriere H i l l s Vo lcano, Montserrat, from 1995-1999. Geologica l Society o f London, M e m o i r 21 , London, England. Wright, H., Cashman, K.V. , Ros i , M . , C i on i , R. 2007. Breadcrust bombs as indicators o f Vu lcan ian eruption dynamics at Guagua Pichincha volcano, Ecuador. Bu l le t in o f Vo lcano logy 69(3), 281-300. 98 APPENDIX A DETAILED DESCRIPTIONS OF FIELD TEXTURE MAPS 99 FIELD T E X T U R E M A P #1 (Densely Welded Block and Ash Flow Deposit, Block #1, Field Site 1) Clast types: o Black: • Glassy • Dense • Variably welded showing different shades of grey - black • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (20-40%) • 95-98% of clasts • Subangular-subrounded • Some flow banding • Up to 1 m in diameter o Light grey: • Partially welded pumiceous clasts (?) • Porphyritic, with (avg. 2 mm) phenos. of hbl/plag/pyx (<20%) • Subrounded • 1-3% of clasts • Up to 35 cm in diameter o Flow banded: • Partially welded pumiceous clasts (?) • White and grey coloured • Porphyritic, with (avg. 1 mm) phenos. of plag/hbl/pyx (10-15%) • Subrounded, with wavy/irregular margins • 1% of clasts • Banding is wavy in nature • Up to 7 cm in diameter o White/beige/light pink monzonite: • Medium-grained • Slightly weathered/altered • Subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (<5%) • 1% of clasts • Less than 5 cm in diameter Overall clast shape: subrounded - subangular Overall clast size: variable, from 1 mm to ~1 m Matrix: Grey, fine-grained, ashy, also with fragments of the clasts listed above; oxidized in some areas Matrix supported, but locally nearly clast supported Sections with larger clasts mingled with sections of smaller clasts (different flow units? explosivity?) Some clasts appear to fit together (pull-aparts) Some clasts have rounded embayments, or tails Poorly sorted, no structure Clasts are elongated, mostly in the same direction - deformation/flattening due to welding & compaction 100 F I E L D T E X T U R E M A P #2 (Densely welded block and ash flow deposit, B lock #3, F ield Site 1) Clast types: o Black: • Glassy • Dense • Variably welded showing different shades of grey - black • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (<20%) • 95% of clasts • Subangular - subrounded • Some flow banding, at a maximum of 60o to fabric, but no preference to orientation • Up to 1 m in diameter o Medium - light grey: • Partially welded pumiceous clasts (?) • Porphyritic, with (avg. 2 mm) phenos. of hbl/plag/pyx (<20%) • Subangular • Some flow banding at acute angles • 1% of clasts • Up to 15 cm in diameter o Plinth clasts: • Medium grey • Porphyritic, with plag/qtz/some biot (<2%) • Irregular margins • Subrounded - subangular • 1-2% of clasts • Up to 20 cm in diameter o White/beige/light pink monzonite: • Medium-grained • Slightly weathered/altered • Subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (<5% mafic phenocrysts) • 1-2% of clasts • Up to 6 cm in diameter Overall clast shape: subrounded - subangular Overall clast size: variable, from 1 mm to ~1 m Matrix: Grey, fine-grained, ashy, also with fragments of the clasts listed above; oxidized in some areas Matrix supported More random size distribution than Block #1 Some alignment of medium-sized clast sizes in the gridded area Preferred orientation/elongation of clasts Some very irregular shapes Poorly sorted, no structure 101 FIELD T E X T U R E M A P # 3 (Densely welded block and ash flow deposit (plane of flattening), Block #4, Field Site 1) Clast types: o Black: • Glassy • Dense • Variably welded showing different shades of grey - black • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (<20%) " 85-90% of clasts • Subangular - subrounded • Up to 40 cm in diameter, but variable o Dark grey #1: • Slate (?) • Microcrystalline • Subrounded • 1% of clasts • Up to 7 cm in diameter o Grey #2: • Weathered Plinth? Partially welded pumiceous clasts? • Porphyritic, with small phenos. of plag/mafic minerals (biot?) • Subangular • 1% of clasts • Up to 7 cm in diameter o Plinth clasts: • Light - dark grey • Porphyritic, with plag/qtz/some biot (<2%) • Irregular margins • Subangular • 5% of clasts • Up to 70 cm in diameter o Black & white: • Granodiorite (?) • Subrounded • 1% of clasts • Up to 10 cm in diameter o White/beige/light pink monzonite: • Medium-grained • Slightly weathered/altered • Subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (<5% mafic phenocrysts) • 1-2% of clasts • Up to 15 cm in diameter, but variable Overall clast shape: subrounded - subangular Overall clast size: variable, from 1 mm to ~1 m Matrix: Grey, fine-grained, ashy, also with fragments of the clasts listed above (sometimes lone phenocrysts) Clasts are noticeably more rounded, for the most part, in the plane of flattening; some exceptions include small clasts in proximity to the edges of larger clasts 102 Matrix supported Embayments in some clasts Several clasts are in contact with each other Slate clasts? They have a sheen indicative of fine-grained micas & contain a few phenos/porphyroblasts Flow banded clasts exist on the surface, but none present in mapped area; banding is inconsistent in orientation Some dense, glassy clasts appear very porphyritic like the Plinth clasts Inclusions in some dense clasts (?) 103 F I E L D T E X T U R E M A P #4 (Densely welded block and ash flow deposit, B lock #4, Field Site 1) Clast types: o Black: • Glassy • Dense • Variably welded showing different shades of grey - black • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (<20%) • 90-95% of clasts • Angular - rounded • Some flow banding, but difficult to see • Up to 40 cm in diameter, but mostly 5-15 cm o Grey: • Weathered Plinth? Partially welded pumiceous clasts? • Porphyritic, with small phenos. of plag/maflc minerals (biot?) • Subangular • Some flow banding • 3-5% of clasts • Up to 40 cm in diameter, but most 1-10 cm o White/beige/light pink monzonite: • Medium-grained • Slightly weathered/altered • Subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (<5% mafic phenocrysts) • 1-2% of clasts • Up to 5 cm in diameter Matrix: Grey, fine-grained, ashy, also with fragments of the clasts listed above (sometimes lone phenocrysts) Matrix supported Surface is very weathered, making it difficult to distinguish clast types Clasts much more angular - even polygonal at times, but some are still very rounded Clasts don't appear particularly aligned or deformed, like lower down on the block surface Pull-aparts observed 104 FIELD T E X T U R E M A P #5 (Densely welded block and ash flow deposit, Block #4, Field Site 1) Clast types: o Black: o Plinth: Grey: Glassy Dense Variably welded showing different shades of grey - black Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (<20%) 90-95% of clasts Subangular - subrounded Some flow banding Very elongated Up to 50 cm in diameter, but mostly 5-15 cm Very weathered (tan-coloured) Subrounded Can't see texture due to weathering 3 % of clasts Up to 25 cm in diameter Weathered Plinth? Partially welded pumiceous clasts? Porphyritic, with small phenos. of plag/mafic minerals (biot?) Subangular < 1 % of clasts Up to 40 a few em's in diameter o Other: • Sandstone & slate clasts? • Subrounded • < 1 % of clasts • Up to a few em's in diameter o White/beige/light pink monzonite: • Medium-grained • Very weathered/altered " Subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (<5% mafic phenocrysts) • < 1 % of clasts • Up to a few em's in diameter Matrix: Grey, fine-grained, ashy, also with fragments of the clasts listed above (sometimes lone phenocrysts) Matrix supported Surface is very weathered, making it difficult to distinguish clast types Deformation is especially evident around lithics (especially Plinth) and their boundaries Clasts are visibly deformed/elongated, displaying a fabric Pull-aparts observed 105 F I E L D T E X T U R E M A P #6 (Densely welded block and ash flow deposit, Block #5, F ie ld Site 1) Clast types: o Black: • Glassy • Dense • Variably welded showing different shades of grey - black • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (<20%) • 90-95% of clasts • Subangular - subrounded • Some flow banding (-2%) at 55-60° from fabric • Some very elongated, arcuate shapes • Up to 75 cm in diameter, but mostly <20 cm o Plinth: • Light grey • Porphyritic, with plag/qtz.. .biot seems to have weathered out • Subrounded • 3% of clasts • Up to 50 cm in diameter o Grey: • Weathered Plinth? Partially welded pumiceous clasts? • Porphyritic, with small phenos. of plag/mafic minerals (biot?) • Subrounded • Some flow banding • 1% of clasts • Up to 40 cm in diameter, but mostly just a few em's o Other: - Slate? • Subrounded - subangular • Microcrystalline • Dark grey « Platy habit • 1% of clasts • Up to 5 cm in diameter o Other: • Sandstone? • Grey • Fine-grained • Structureless • Subrounded • < 1 % of clasts • Up to a 6 cm in diameter o White/beige/light pink monzonite: • Medium-grained • Subangular - subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (<5% mafic phenocrysts) • 1% of clasts • Less than 10 cm in diameter Matrix: Grey, fine-grained, ashy, full of fragments (<1 cm in diameter) 106 Matrix supported Shearing and folding of densely welded clasts around Plinth clasts Possible areas at edges/corners of clasts which resemble pressure shadows Clasts are visibly deformed/elongated, displaying a fabric Pull-aparts observed 107 FIELD T E X T U R E M A P #7 (Basal non-welded block and ash flow deposit, Field Site 1) Clast types: o Black: o Plinth: Glassy Densely welded Variably welded showing different shades of grey - black Phenocryst-poor 3 % of clasts Subangular Some flow banding (-2%) at 55-60° from fabric Some very elongated, arcuate shapes Up to 5 cm in diameter • None seen in mapped area, but they do exist nearby in the outcrop • Light grey • Porphyritic, with plag/qtz/biot • Subrounded " Trace - 1% of clasts • Up to 15 cm in diameter o Dark grey: • Welded • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (10-20%) • Subangular • 4 6 % of clasts • Up to 1 m+ in diameter, but mostly 5-15 cm o Pumiceous clasts: • White - light grey • Subrounded • Porphyritic, with mafic phenos of hbl/pyx visible (10-20%) • 5 0 % of clasts • Up to 1 m in diameter, but mostly 5-15 cm o White/beige/light pink monzonite: • Medium-grained • Weathered orange • Subangular - subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (5-10% mafic phenocrysts) • 1% of clasts • Up to 4 cm in diameter Matrix: Light grey/brown, sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported Very pumice-rich compared to densely welded blocks Erosional surface/gradation up to densely welded block and ash flow deposit? Not much elongation/flattening or fabric, although some larger clasts seem to have their long axis parallel to the fabric observed above in the densely welded zone Possible imbrication Generally, clasts are more rounded, especially the pumice, although the welded clasts have more distinctive boundaries (maybe b/c they aren't as welded?) 108 Poorly sorted Slight fining-upward trend see at the outcrop scale 109 FIELD T E X T U R E M A P #8 (Basal non-welded block and ash flow deposit, Field Site 1 (1-1.5 m NE of TM#7)) Clast types: o Black: • Glassy • Densely welded • Variably welded showing different shades of grey - black • Phenocryst-poor • 2 % of clasts • Subangular • Some flow banding (-2%) at 55-60° from fabric • Some very elongated, arcuate shapes • Up to 6 cm in diameter o Dark grey: • Welded • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (10-20%) • Subangular • 4 2 % of clasts • Up to 30 cm in diameter, but mostly 5-15 cm o Pumiceous clasts: • White - light grey • Subrounded • Porphyritic, with mafic phenos of hbl/pyx visible (10-20%) • 5 5 % of clasts • Up to 1 m in diameter, but mostly 5-15 cm o White/beige/light pink monzonite: • Medium-grained • Weathered orange • Subangular - subrounded • Small phenos. of plag (less than 1 mm)/qtz (avg. 1 mm)/pyx (avg. 1 mm) (5-10% mafic phenocrysts) • 1% of clasts • Up to 3 cm in diameter Matrix: Light grey/brown, sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported Very pumice-rich compared to densely welded blocks Erosional surface/gradation up to densely welded block and ash flow deposit? Not much elongation/flattening or fabric, although some larger clasts seem to have their long axis parallel to the fabric observed above in the densely welded zone Possible imbrication Generally, clasts are more rounded, especially the pumice, although the welded clasts have more distinctive boundaries (maybe b/c they aren't as welded?) Poorly sorted Slight fining-upward trend see at the outcrop scale 1 1 0 FIELD T E X T U R E M A P #9 (Upper, incipiently welded block and ash flow deposit (oxidized), Field Site 2) Clast types: o Black: • Glassy • • Densely welded • Variably welded showing different shades of grey - black • Mafic phenocrysts of hbl/pyx visible (-10%) • 5% of clasts • Subangular • Up to 6 cm in diameter o Pumiceous clasts: • Various shades of grey, incipiently welded • Subangular - subrounded • Porphyritic, with felsic & mafic phenos of hbl/pyx visible (-20%) • 9 5 % of clasts • Up to 1.5 m in diameter, but mostly 5-15 cm Matrix: Orange/brown (oxidized), sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported, but with a lot of small <1 cm clasts/grains Pumice-rich, but some pumice seems more welded/dense than at the base of the Classic Section Not much elongation/flattening or fabric, although some larger clasts seem to have their long axis parallel to the fabric observed above in the densely welded zone Possible imbrication Pumice-like clasts are less rounded that at the base of the Classic Section Poorly sorted Weathered surface makes it difficult to note clast types and textures Pumice-like clasts sometimes have a -1 cm, orange alteration ring Flow banding only seen in very small clasts; no breadcrusting observed Apparent thickness of indurated section: 2-2.5 m Other types of clasts? Accidental sed/plutonic/meta. rocks? Il l FIELD T E X T U R E M A P #10 (Upper, incipiently welded block and ash flow deposit (oxidized), Field Site 2 (90 m SE of TM#9)) Clast types: o Black: • Glassy • Densely welded • Variably welded showing different shades of grey - black • Mafic phenocrysts of hbl/pyx visible (~5 -10%) • 25-30% of clasts • Subangular • Up to 10 cm in diameter o Pumiceous clasts: • • Various shades of grey, incipiently welded. . , • Subangular - subrounded • Porphyritic, with felsic & mafic phenos of hbl/pyx visible (-20%) • 7 0 % of clasts • Up to 1 m in diameter, but mostly 5-15 cm o White/beige/light pink monzonite: • Only 1 clast observed in mapped area • Medium-grained • Weathered orange/brown • Subrounded • Small mafic phenos. observed (-5%) • In general, 1% of clasts • Up to 5 cm in diameter Some Plinth Assemblage clasts observed outside of mapped area; - 1 % of clasts; some are red, grey in colour Matrix: Light pink/orange/brown (oxidized), sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported, but with a lot of small <1 cm clasts/grains Rich in pumice-like clasts Not much elongation/flattening or fabric, although some larger clasts seem to have their long axis parallel to the fabric observed above in the densely welded zone Pumice-like clasts are more rounded that at TM#9 Poorly sorted Weathered surface makes it difficult to note clast types and textures Pumice-like clasts sometimes have a -1 cm, orange alteration ring No breadcrusting observed Apparent thickness of indurated section: 2 m with a -10 m talus slope 112 FIELD T E X T U R E M A P #11 (Upper, non-welded block and ash flow deposit, Field Site 3) Clast types: o Black: • Glassy • Densely welded • Variably welded showing different shades of grey - black • Mafic phenocrysts of hbl/pyx visible (~5-10%) - 60-70% of clasts • Some red oxidation/alteration • Subangular • Up to 20 cm in diameter o Pumiceous clasts: • Whitish, altered orange/brown • Subangular - subrounded • Porphyritic, with mafic phenos of hbl/pyx visible (~5-15%) • 15-20% of clasts " • No flow banding observed • Up to 35 cm in diameter o Plinth: • Dark grey - black, with white/pink alteration • Porphyritic, with plag/qtz/biot • Subrounded • 5-10% of clasts • Up to 50 cm in diameter, but most 5-15 cm o White/beige/light pink monzonite: • None in mapped area.. .granite? • Medium-grained • Pink/red alteration • Subrounded • Rich in large, felsic phenocrysts • < 1% of clasts • 2-8 cm in diameter o Metamorphosed bedrock: • Only 2 clasts seen in mapped area • Blue-green with white (oxidized orange) stringers/veins • Porphyritic, with plag/qtz/biot • Subangular • In general, accounts for ~ 1 % of clasts • 5-10 cm in diameter Matrix: Grey/brown, sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported, but with a lot of small <1 cm clasts/grains Not much elongation/flattening or fabric, although some larger clasts seem to have their long parallel to the fabric observed above in the densely welded zone Poorly sorted Weathered surfaces makes it difficult to note clast types and textures 113 FIELD T E X T U R E M A P #12 (Upper, incipiently welded block and ash flow deposit (oxidized), Field Site 2) Clast types: o Black: • Glassy • Densely welded • Variably welded showing different shades of grey - black • Mafic phenocrysts of hbl/pyx visible (~5-10%) • 25-30% of clasts • No flow banding observed, but weathering/oxidation commonly masks texture • Subangular - subrounded • Up to 30 cm in diameter, but mostly 5-15 cm o Pumiceous clasts: • Various shades of grey, incipiently welded • Subrounded - subangular • Porphyritic, with mafic phenos of hbl/pyx visible (-10-20%) • 70% of clasts • No flow banding observed • Up to 1 m in diameter, but mostly 5-15 cm Plinth and monzonite clasts weren't observed in mapped area, but exist in outcrop & could also be masked by weathering/oxidation Matrix: Light pink/orange/brown (oxidized), sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported, but with a lot of small <1 cm clasts/grains Rich in pumice-like clasts Not much elongation/flattening or fabric, although some larger clasts seem to have their long axis parallel to the fabric observed above in the densely welded zone Poorly sorted Weathered surface makes it difficult to note clast types and textures Pumice-like clasts sometimes have a ~1 cm, orange alteration ring Apparent thickness of indurated section: 2 m with 5 m talus slope No breadcrusting observed 114 FIELD T E X T U R E M A P #13 (Basal, non-welded block and ash flow deposit, Field Site 1 (3 m NE of bulk sample area)) Clast types: o Black: " Glassy • Densely welded • Variably welded showing different shades of grey - black • Phenocryst-poor • 5 5 % of clasts • Subangular - subrounded • Some flow banding observed • Up to 30 cm in diameter, but mostly ~5 cm o Pumiceous clasts: • White - light grey • Subangular - subrounded • Porphyritic, with mafic phenos of hbl/pyx visible (10-20%) • 4 5 % of clasts • No flow banding observed • Up to 50 cm in diameter, but mostly 10-15 cm o No monzonite or Plinth observed in mapped area Matrix: Light grey/brown, sand-like, fine-grained, ashy, full of fragments of clast types mentioned above Matrix supported Very pumice-rich compared to densely welded blocks Erosional surface/gradation up to densely welded block and ash flow deposit? Not much elongation/flattening or fabric, although some larger clasts seem to have their long axis parallel to the fabric observed above in the densely welded zone Possible imbrication Generally, clasts are more rounded, especially the pumice, although the welded clasts have more distinctive boundaries (maybe b/c they aren't as welded?) Poorly sorted Slight fining-upward trend see at the outcrop scale 115 APPENDIX B IMAGE ANALYSIS METHODS: FTMs 116 The fo l lowing sequences o f photos document the process o f recovering data from the f ie ld to obtaining results f rom image analysis (e.g. from Scion Image™, Image J™). The F T M s represent the fu l l spectrum o f welding intensity observed in the Keyhole Fal ls Member . The process for each F T M is as fo l lows: (a) a field photo is taken o f the mapped area overlain by the 1 m 2 gr id, where " T " represents the top o f the f ie ld texture map; (b) clasts greater than 0.5 c m are hand- drawn wi th the aid o f the grid and graph paper; (c) the original F T M is retraced and scanned into a digital image; (d) the image in (c) is run through image analysis software and the output image is created based on clast recognition wi th in the 1 m 2 area. 117 Figure B l : F T M 0 1 - Densely welded facies 118 Figure B 2 : F T M 02 - Densely welded facies 119 Figure B3: F T M 03 - Densely welded facies, in the plane of flattening 120 Figure B4: F T M 04 - Densely welded facies 121 Figure B5: F T M 05 - Densely welded facies 122 F igu re B6: F T M 06 - Densely welded facies 123 F igu re B7: F T M 07 - Basal non-welded facies 124 125 126 1 . A- ' - - - J i - >—• • P , . • * * * f •« - * •- • b) c) d) Figure BIO: F T M 10 - Incipiently welded facies 127 Figure B l l : F T M 11 - Upper non-welded facies 128 129 F igu re B13: F T M 13 - Basal non-welded facies 130 A P P E N D I X C I M A G E A N A L Y S I S M E T H O D S : S T M s 131 The fo l lowing sequences o f photos document the process o f recovering data from the slabs/hand samples to obtaining results from image analysis (e.g. f rom Sc ion Image™, Image J™). A l l S T M s were created from slabs o f densely welded material due to its ' competence. The process for each S T M is as fo l lows: (a) a photo is taken o f the pol ished slab; (b) clasts greater than 0.5 m m are hand-drawn with the aid o f an acetate and permanent marker; (c) the original F T M is retraced and scanned into a digital image; (d) the image obtained in (c) is run through image analysis software where the output image is created based on clast recognition. 132 133 134 135 136 SSSEB& k t w - C T - B ' i i It-d-fl) t$IMM«o c) d) Figure C5: S T M 05 - Densely welded facies 137 138 139 140 Figure C 9 : STM 09 - Densely welded facies 141 Figure CIO: STM 10 - Densely welded facies 142 143 144 145 146 147 Figure C16: STM 16 - Densely welded facies 148 APPENDIX D PHYSICAL PROPERTY MEASUREMENTS & CALCULATIONS 149 Sample Preparation 1. ) A l l sol id rock samples are cut into cores using a dr i l l press and a 30 m m diameter cy l indr ica l dr i l l bit. 2. ) The ends o f the cored samples are cut with a rock saw and ground down using a lap and 240 AI2O3 grit to make a cylinder. 3. ) Individual cores are placed in a sonic bath for 5-10 minutes to remove any residual grit or rock fragments. 4. ) Cored samples (mass = 26-101 g) are dried in an oven at 120°C for a m in imum o f 12 hours and cooled to room temperature. 5. ) Residual materials (min imum 10 g) from each cored sample are powdered in a tungsten carbide r ing m i l l for 20-60 seconds. Bulk Density - Consolidated Samples ; . 1. ) D ig i ta l calipers are used to obtain average values o f core height and diameter based on at least six measurements o f each. 2. ) Us ing the cy l indr ical shape o f the core, the bulk density is calculated using the geometrical equation for the volume o f a cylinder: V b u i k = rcr2h. 3. ) This value o f volume is then used to calculate bulk density: p b u i k = m s a m p / Vbuik- Quality Control Issues Accuracy: D ig i ta l calipers were used, which are accurate to 0.01 m m ; ends were flattened to A h < 0.5 mm. The balance used is accurate to within 0.001 (<40 g) or 0.01 (>40g). Precision: Measurements used are averages o f at least six measurements o f height and diameter. Results are precise wi th in ± 4 % . Bulk Density - Unconsolidated Samples 1. ) The mass o f a 500 m L graduated cyl inder is determined. 2. ) The graduated is f i l led carefully with a precise volume o f the unconsolidated material (250-500 mL ) . 3. ) The sample and graduated cyl inder (tempered glass) are placed in an oven at 120°C for a m in imum o f 12 hours, and then cooled to room temperature. 4. ) The mass o f the graduated cyl inder and sample are determined (F ig. D l ) 5. ) The mass and volume are then used to calculate bulk density: pbuik = m s a m p/Vsamp Quality Control Issues Accuracy: The graduated cyl inder is accurate to ~5 m L ; the balance is accurate to 0.1 g. Precision: Measurements were done twice to obtain an average and standard deviation. Results are precise wi th in ± 4 % . 150 Skeletal Density 1. ) Skeletal density is determined using the cored sample and an automated he l ium pycnometer (Fig. D 2 i , D3) . The largest a luminum cel l insert is placed inside the sample and reference cells to maximize the sample to vo id ratio. Smaller cores require an additional f i l ler (F ig. D2 i i ) to achieve this result. 2. ) Each o f the four sample cells and the reference cel l o f the pycnometer are calibrated against steel spheres o f a known volume (Fig. D2 i i i ) . The sample cel l and reference ce l l volumes are thus determined by the fo l lowing equations: Vcell = ( F ^ v J C ^ l -jP2 ) w h e r e y q w =22.1880 c m 3 (with filler) or C E" ( P I -P2 )-(P2 /P2)(Pl-P2) • V =V ' ref ' cell 31.0082 c m 3 (without filler) (P\-P? The resulting values o f V c e i i and V r e f are calibration factors for each cel l . These values are unique to each cel l and depend on temperature. They represent an average o f five consecutive measurements. 3.) The core is placed in the pycnometer to acquire an averaged value o f volume (over five consecutive measurements): V V =V -• re/ skeletal cell (pyp2)-\ 4.) The volume acquired is used to calculate skeletal density (that is, the density o f rock ± isolated porosity): p s k e ie ta i = m s a m p / V s k e i e t a i . Quality Control Issues A c c u r a c y : Experiments were performed on various combinations o f steel spheres (of known volume) prior to running samples, in order to check the accuracy o f the pycnometer; results were wi th in 1% relative error. The temperature was controlled in such a way (dwell time = 1-2 hrs.) that it varied <1°C from time o f cal ibration to the f inal run o f the day. The smallest possible configuration o f inserts was used i n order to maximize the sample to vo id space ratio. P r e c i s i on : Cal ibrat ion values are averages o f five measurements (five wi th the cel l empty, f ive with the known volume in the cel l ) ; sample volumes are also averages o f f ive consecutive measurements. Results are precise wi th in ±0.3%. Rock Powder Density 1.) Rock powder density is determined using the powdered sample and an automated hel ium pycnometer (F ig. D 2 i , F i g D3) . The largest a luminum ce l l insert and the accompanying f i l ler (F ig. D2 i i ) are placed inside the sample and reference cells in order to a l low large amounts o f powder to be used (maximum powder mass = -45-60 g), thus m in im iz ing the vo id space to sample ratio. 151 2.) Each o f the four sample cells o f the pycnometer is calibrated against steel spheres o f a known volume (Fig. D2 i i i ) . The sample cel l and reference ce l l volumes are thus determined by the fo l lowing equations: Kell = 1 (VknoWn)(P\ ^ ) fa y = ^ l g g 3 (PI -P2)- (P2 /P2)(P\ - P2) (P\-P2^ V =V ref cell ^ p2 These calibration values are unique to each cel l and depend on temperature. They represent an average o f five consecutive measurements. 3.) The powder (-15-60 g) is placed in the pycnometer to acquire an averaged value o f volume (over five consecutive measurements): V y rock ' cell ( P l /P2 )-1 4.) The volume acquired is used to calculate matrix density (that is, the density o f the rock only) : p r o c k = m s a m p / V r o c k . Quality Control Issues A c c u r a c y : Experiments were performed on various combinations o f steel spheres (of known volume) prior to running samples, i n order to check the accuracy o f the pycnometer; results were wi th in 1 % relative error. The temperature was controlled in such a way (dwell time =1-2 hrs.) that it varied <1°C from time o f cal ibration to the f inal run o f the day. The max imum amount o f powder was used in order to ensure that the powder is representative o f the sample, and to maximize the sample to vo id space ratio. A l s o , a standard powder is measured with the other samples in order to monitor the variabi l i ty f rom day to day, run to run. P r e c i s i on : Cal ibrat ion values are averages o f five measurements (five wi th the cel l empty, five wi th the known volume in the cel l ) ; sample volumes are also averages o f five consecutive measurements. Results are precise wi th in ±0.6%. 152 Figure D l : Measurement of bulk density for unconsolidated samples. A 500 mL graduated cylinder is packed full with material and mass is acquired with a digital balance precise to 0.1 g. 153 Figure D 2 : He l i um pycnometry setup: (i) automatic hel ium pycnometer; (ii) a luminum cel l insert (left) and fi l ler (right) for use wi th smaller samples; (iii) steel balls o f known volume used for calibration. 154 reference cell cell #4 cell #3 cell #2 cell #1 low voltage switch vent rate vent regulator , y e circuit board connector valve valve overpressure valve © to He tank © to serial port on computer ® to parallel port on computer © to power source F i g u r e D 3 : Schematic diagram o f automated hel ium pycnometer, indicating major components and connections. 155 APPENDIX E COMPLETE TABLES OF PHYSICAL PROPERTY DATA 156 Tab le E l . Fu l l summary o f core pycnometry, including: component measured (C = clast, M = matrix), mass (m), volume by geometry ( V g e o ) , volume by core pycnometry (Vs), bulk density (p B ) , skeletal density (ps), and connected porosity (O c)- Standard deviations are reported as l a . FIELD SITE LITHOFACIES LOCATION SAMPLE # C/M m(g) o Veto(cm3) 0 Vs (cm3) a pB (g/cm3) o Ps (g/cm3) a 4>c (%) o KM-05-059a(2) M 52.15 0.010 23.705 0.4932 20.277 0.0243 2.20 0.046 2.572 0.0031 14.46 1.337 KM-05-060a(l) M 78.14 0.010 38.061 0.1532 30.350 0.0226 2.05 0.008 2.575 0.0019 20.38 1.241 KM-05-060a(2) M 84.22 0.010 40.126 0.3822 33.103 0.0254 2.10 0.020 2.544 0.0020 17.46 1.412 KM-05-060a(3) M 76.27 0.010 36.283 0.4518 30.191 0.0255 2.10 0.026 2.526 0.0021 16.87 1.427 KM-05-060a(4) M 44.62 0.010 20.905 0.1165 17.715 0.0200 2.13 0.012 2.519 0.0028 15.44 1.125 KM-05-012(l) M 46.68 0.010 22.566 0.1968 18.181 0.0320 2.08 0.018 2.568 0.0045 18.99 1.760 KM-05-012(2) M 44.93 0.010 20.109 0.2605 17.733 0.0355 2.23 0.029 2.534 0.0051 11.99 1.981 KM-05-012(3) M 42.23 0.010 20.013 0.8065 16.773 0.0096 2.11 0.085 2.518 0.0014 16.20 ' 0.541 KM-05-057a(l) M 49.01 0.010 24.371 0.2308 19.680 0.0263 2.01 0.019 2.490 0.0033 19.29 1.494 KM-05-057a(2) M 43.80 0.010 21.385 0.2537 17.381 0.0093 2.05 0.024 2.520 0,0014 18.65 0.524 K.M-05-057a(3) M 32.62 0.001 16.499 0.3296 12.939 0.0304 1.98 0.039 2.521 0.0059 21.46 1.707 K.M-05-057b(l) M 82.70 0.010 40.184 0.1800 32.987 0.0222 2.06 0.009 2.507 0.0017 17.83 1.250 KM-05-057b(2) M 54.14 0.010 26.904 0.2109 21.527 0.0212 2.01 0.016 2.515 0.0025 20.08 1.190 KM-05-057b(3) M 78.94 0.010 38.832 0.1954 31.449 0.0350 2.03 0.010 2.510 0.0028 19.13 1.970 KM-05-057b(4) M 62.35 0.010 30.520 0.2929 24.884 0.0300 2.04 0.020 2.506 0.0030 18.58 i.693 K.M-05-057b(5) M 77.99 0.010 38.840 0.1278 30.980 0.0133 2.01 0.007 2.517 0.0011 20.16 0.748 ICM-05-057b(6) M 31.25 0.001 15.549 0.2111 12.421 0.0141 2.01 0.027 2.516 0.0029 20.11 0.793 KM-05-057c(l) C 98.04 0.010 41.867 0.1665 39.876 0.0125 2.34 0.009 2.459 0.0008 4.82 0.721 KM-05-057c(2) C 88.54 0.010 37.959 0.1032 36.188 0.0140 2.33 0.006 2.447 0.0009 4.77 0.810 KM-05-057c(3) C/M 98.14 0.010 42.456 0.3043 39.722 0.0231 2.31 0.017 2.471 0.0014 6.50 1.325 KM-05-057c(4) C/M 101.02 0.010 44.993 0.2366 40.752 0.0140 2.25 0.012 2.479 0.0008 9.23 0.797 KM-05-057c(5) C/M 93.53 0.010 41.040 0.2231 37.935 0.0277 2.28 0.012 2.466 0.0018 7.53 1.588 KM-05-057c(6) C 98.44 0.010 41.718 0.2260 40.021 0.0146 2.36 0.013 2.460 0.0009 4.05 0.840 KM-05-057c(7) c 85.41 0.010 36.173 0.1431 34.778 0.0073 2.36 0.009 2.456 0.0005 3.90 ' 0.420 (CM-05-057c(8) C/M 66.47 0.010 31.433 0.4713 26.770 0.0247 2.11 0.032 2.483 0.0023 15.02 1.408 KM-05-058a(l) C 47.60 0.010 20.086 0.3470 19.324 0.0091 2.37 0.041 2.463 0.0012 3.78 0.524 KJvl-05-058a(2) M 51.33 0.010 22.944 0.1977 20.674 0.0189 2.24 0.019 2.483 0.0023 9.78 1.075 KM-05-058a(3) C/M 52.23 0.010 22.492 0.2241 21.308 0.0168 2.32 0.023 2.451 0.0019 5.35 0.972 KM-05-058b(l) M 51.77 0.010 23.909 0.1651 20.555 0.0188 2.17 0.015 2.519 0.0023 13.84 1.055 KM-05-058b(2) M 59.91 0.010 27.102 0.5498 23.800 0.0194 2.21 0.045 2.517 0.0021 12.21 1.092 1 Intermediate, densely welded block and ash flow deposit Block #3 Block #4 00 Basal, non- KM-05-058d(l) M 76.89 0.010 34.795 0.2888 30.478 0.0223 2.21 0.018 2.523 0.0018 12.40 1.249 K.M-05-058d(2a) M 59.87 0.010 27.927 0.2037 23.748 0.0191 2.14 0.016 2.521 0.0020 15.12 1.072 KM-05-058d(2b) M 64.82 0.010 28.607 0.1442 26.168 0.0156 2.27 0.011 2.477 0.0015 8.36 0.893 KM-05-058d(3) M 86.05 0.010 37.140 0.3433 34.242 0.0262 2.32 0.021 2.513 0.0019 7.68 1.476 K.M-05-058d(4a) M 62.96 0.010 27.745 0.1070 25.164 0.0115 2.27 0.009 2.502 0.0011 9.27 0.649 KM-05-058d(4b) M 64.29 0.010 29.745 0.1167 25.592 0.0167 2.16 0.008 2.512 0.0016 14.02 0.941 K.M-05-058d(5) M 54.43 0.010 24.244 0.2584 21.627 0.0178 2.25 0.024 2.517 0.0021 10.60 0.998 KM-05-058d(6) M 87.16 0.010 38.962 0.3220 34.913 0.0286 2.24 0.018 2.497 0.0020 10.27 1.618 KM-05-058d(7) M 101.08 0.010 45.068 0.1971 40.062 0.0090 2.24 0.010 2.523 0.0006 11.22 0.506 KM-05-058d(8a) M 57.84 0.010 26.683 0.1324 23.911 0.0117 2.17 0.011 2.419 0.0012 10.29 0.683 KM-05-058d(8b) M 60.54 0.010 28.311 0.1531 23.702 0.0081 2.14 0.012 2.554 0.0009 16.22 0.446 ICM-05-017b(la) M 65.05 0.010 30.111 0.3105 25.450 0.0285 2.16 0.022 2.556 0.0029 15.45 1.576 KM-05-017b(lb) M 67.89 0.010 31.800 0.2863 26.659 0.0095 2.13 0.019 2.547 0.0009 16.16 0.528 KM-05-017b(2) M 88.00 0.010 41.283 0.2432 34.574 0.0259 2.13 0.013 2.545 0.0019 16.24 1.439 KM-05-017b(3) M 63.61 0.010 29.915 0.1969 24.803 0.0232 ' 2.13 0.014 2.565 0.0024 17.10 1.282 KM-05-017b(4) M 79.62 0.010 37.538 0.1964 31.501 0.0222 2.12 0.011 2.528 0.0018 16.08 1.243 KM-05-017b(5a) M 61.02 0.010 28.827 0.3113 24.065 0.0238 2.12 0.023 2.536 0.0025 16.51 1.327 KM-05-017b(5b) M 67.11 0.010 31.709 0.2013 26.268 0.0125 2.12 0.013 2.555 0.0012 17.14 0.690 Block #5 ICM-05-017b(6) C 63.55 0.010 26.896 0.3551 25.861 0.0257 2.36 0.031 2.457 0.0024 3.84 1.478 KM-05-017b(7) C/M 48.54 0.010 21.147 0.1212 18.826 0.0389 2.30 0.013 2.578 0.0053 10.99 2.133 KM-05-017c(l) M 36.24 0.001 17.048 0.2582 14.130 0.0455 2.13 0.032 2.565 0.0083 17.11 2.510 KM-05-017c(2) c 50.82 0.010 22.134 0.2447 20.614 0.0233 ' 2.30 0.025 2.465 0.0028 6.87 1.334 KM-05-018d(l) M 41.51 0.010 19.921 0.1945 16.287 ' 0.0260 2.08 0.020 2.549 0.0041 18.23 1.444 KM-05-018d(2) C 62.03 0.010 27.023 0.1967 25.387 0.0162 2.30 0.017 2.443 0.0016 6.03 0.939 KM-05-018d(3) C 49.07 0.010 21.611 0.2641 20.265 0.0196 2.27 0.028 2.421 0.0023 6.21 1.144 K.M-05-019b(l) C 92.07 0.010 39.060 0.2635 36.665 0.0288 .2.36 0.016 2.511 0.0020 6.14 1.621 K.M-05-019b(2) C 81.18 0.010 34.236 0.2966 32.760 0.0108 2.37 0.021 2.478 0.0008 4.32 0.617 KM-05-O63(l) M 39.30 0.001 18.740 0.3022 15.675 0.0263 2.10 0.034 2.507 0.0042 16.24 1.484 KM-05-063(2) M 39.51 0.001 19.300 0.2449 15.951 0.0204 2.05 0.026 2.477 0.0032 17.24 1.165 Near Classic KM-05-063(3) M 94.25 0.010 44.745 0.3688 37.494 0.0165 2.11 0.017 2.514 0.0011 16.06 0.931 KM-05-063(4) M 52.49 0.010 26.025 0.1858 20.417 0.0196 2.02 0.014 2.571 0.0025 21.43 1.077 KM-05-063(5) M 49.00 0.010 23.053 0.3241 19.457 0.0295 2.13 0.030 2.518 0.0038 15.42 1.658 KM-05-063(6) M 51.15 0.010 24.483 0.3909 20.321 0.0295 2.09 0.033 2.517 0.0037 16.97 1.658 Base of KM-05-023 bulk 57.13 0.010 - - 22.713 0.0152 1.54 0.028 2.515 0.0017 38.73 0.867 welded block Classic and ash flow Section deposit KM-05-024(l) KM-05-024(2a) C c 68.39 46.30 0.010 0.010 44.833 29.589 0.1092 0.3119 30.032 20.028 0.0215 0.0471 1.53 1.56 0.004 0.016 2.277 2.312 0.0016 0.0054 32.81 32.52 1.335 2.882 KM-05-024(2b) c 47.46 0.010 31.559 0.2277 21.164 0.0122 1.50 0.011 2.243 0.0013 33.11 0.771 KM-05-024(3) c 70.94 0.010 45.541 0.3387 31.486 0.0306 1.56 0.012 2.253 0.0022 30.76 1.920 KM-05-024(4a) c 41.75 0.010 27.613 0.2063 18.501 0.0232 1.51 0.011 2.257 0.0028 33.09 1.457 KM-05-024(4b) c 49.16 0.010 31.335 0.2383 21.808 0.0334 1.57 0.012 2.254 0.0035 30.35 2.095 KM-05-026(l) c 49.46 0.010 30.197 0.1215 21.629 ' 0.0267 1.64 0.007 2.287 0.0028 28.28 1.651 KM-05-026(2) c 60.37 0.010 36.435 0.2000 26.006 6.0238 1.66 0.009 2.321 0.0021 28.49 1.450 KM-05-026(3) c 68.37 0.010 40.454 0.2160 29.183 0.0372 1.69 0.009 2.343 0.0030 27.90 2.245 KM-05-026(4) c 42.33 0.010 27.015 0.2276 18.692 0.0202 1.57 0.013 2.265 0.0025 30.67 1.264 KM-05-046(1) c 26.14 0.001 15.926 0.1661 11.401' 0.0349 1.64 0.017 2.293 0.0070 28.47 2.155 KM-05-046(2) c 60.37 0.010 28.130 0.2520 26.006 0.0238 1.80 0.016 2.335 0.0021 22.92 1.441 KM-05-046(3) c 89.09 0.010 47.503 • 0.4274 37.535 0.0662 1.88 0.017 2.374 0.0042 20.79 3.946 KM-05-046(4) c 36.81 0.001 19.549 0.1356 15.665 0.0269 1.88 0.013 2.350 0.0040 19.99 1.616 KM-04-018 bulk 56.14 0.010 - - 22.504' 0.0267 1.47 0.003 2.495 0.0030 41.15 1.516 Oxidized KM-04-019 bulk 52.16 0.010 - - 20.735. 0.0185 1.48 0.012 2.516 0.0022 41.25 1.042 Roadcut KM-04-020 bulk 61.94 0.010 - •- 24.633 • 0.0161 1.52 0.014 2.515 0.0016 39.51 0.905 KM-05-032 bulk 59.87 0.010 - - 23.723' . 0.0062 1.39 0.028 2.524 0.0007 44.84 0.349 2 Upper, incipiently welded NearTM#10 (oxidized) block and ash flow KM-05-033(l) KM-05-033(2) KM-05-033(3) C C C 100.18 60.29 60.07 0.010 0.010 0.010 47.711 29.393 28.759 0.2490 0.2772 0.1722 40.772 24.745 24.566 0.0215 0.0296 0.0168 2.10 2.05 2.09 0.011 0.019 0.013 2.457 2.437 2.445 0.0013 0.0029 0.0017 14.53 15.86 14.53 1.236 1.719 0.969 deposit KM-05-056(la) C 62.80 0.010 31.986 0:1776 25.955 0.0344 1.96 0.011 2.420 0.0032 18.99 2.012 KM-05-056(lb) C 67.55 0.010 33.751 0.2454 28.349 • . 0.0364 2.00 0.015 2.383 0.0031 16.06 2.161 NearTM#12 KM-05-056(2a) C 47.33 0.010 24.097 0.2446 19.779 0.0313 1.96 0.020 2.393 0.0038 18.09 1.851 KM-05-056(2b) C 53.05 0.010 27.107 0.2304 22.434 0.0207 1.96 0.017 2.365 0.0022 17.11 1.240 KM-05-056(3) C 67.08 0.010 33.950 0.2931 28.615 0.0253 1.98 0.017 2.344 0.0021 15.54 1.526 3 Upper, non- Keyhole welded, block Falls and ash flow KM-04-031 KM-05-036 bulk bulk 68.14 45.49 0.010 0.010 - - 26.868 17.964 ' 0.0212 0.0076 1.59 1.43 0.025 0.057 2.536 2.532 0.0020 0.0011 37.35 43.49 1.184 0.422 deposit KM-05-043(1) C 44.38 0.010 26.917 0.0744 18.301! 0.0205 1.65 0.005 2.425 0.0027 31.96 1.194 KM-05-043(2) C 60.31 0.010 34.257 0.1433 24.964 0.0250 1.76 0.007 2.416 0.0024 27.15 1.463 KM-05-043(3) C 49.20 0.010 30.336 0.1658 20.780 0.0228 1.62 0.009 2.368 0.0026 31.58 1.364 KM-05-043(4) C 54.20 0.010 30.108 0.1254 22.542 0.0250 1.80 0.008 2.404 0.0027 25.14 1.469 KM-05-044(l) C 74.62 0.010 43.432 0.2176 29.858 0.0100 1.72 0.009 2.499 0.0008 31.18 0.565 KM-05-044(2) C 72.17 0.010 41.652 0.1323 28.971 0.0222 1.73 0.006 2.491 0.0019 30.55 1.262 KM-05-044(3) C 82.89 0.010 47.322 0.1470 32.890 0.0197 1.75 0.005 2.520 0.0015 30.56 1.107 KM-05-044(4) C 82.27 0.010 45.654 0.4345 33.158 0.0138 1.82 0.017 2.511 0.0010 27.53 0.775 KM-05-045(l) C 55.27 0.010 29.191 0.1667 21.931 0.0113 1.89 0.011 2.520 0.0013 25.01 0.632 KM-05-045(2) C 58.16 0.010 30.927 0.2378 • 23.170 0.0209 1.88 0.014 2.510 0.0023 25.10 1.178 KM-05-054(l) C 73.31 0.010 45.054 0.0964 30.615 0.0238 1.63 0.003 2.395 0.0019 31.93 1.408 KM-05-054(2) C 71.23 0.010 43.144 0.1561 29.375 0.0224 1.65 0.006 2.425 0.0018 31.95 1.305 KM-05-054(3) C 33.44 0.001 20.665 0.2319 14.072 0.0190 1.62 0.018 2.376 0.0032 31.83 1.131 KM-05-054(4) C 50.71 0.010 31.805 0.1113 21.105 0.0157 1.59 0.006 2.403 0.0018 33.83 0.922 as o Tab le E2. Fu l l summary o f rock powder pycnometry, including: f ield site (FS), lithofacies (LF) , location ( LOC ) , component measured (C = clast, M = matrix), mass o f powder (m R ) , volume o f powder ( V R ) , rock powder density (p R ) , total porosity (OT), connected porosity (<l>c), and isolated porosity (Oi). Standard deviations are reported as l a . FS LF LOC SAMPLE # C/M mR(g) g VR(cm3) g pR (g/cm3) a «PT (%) +/- a»i (%) 1 Intermediate, densely welded block and ash flow deposit Block #1 KM-05-061(l) KM-05-062(3) M M 28.51 46.75 0.001 0.010 11.245 18.674 0.0302 0.0168 2.535 2.504 0.0068 0.0023 Block #3 KJVI-05-059a(l) KM-05-059a(2) KM-05-060a(l) KM-05-060a(2) KM-05-060a(3) KM-05-060a(4) M M M M M M 26.87 45.04 33.22 38.69 37.51 45.33 0.001 0.010 0.001 0.001 0.001 0.010 10.335 17.763 13.032 15.333 14.713 17.963 0.0117 0.0059 0.0092 0.0140 0.0130 0.0092 2.600 2.536 2.549 2.523 2.550 2.524 0.0029 0.0010 0.0018 0.0023 0.0023 0.0014 15.38 13.23 19.58 16.77 17.63 15.60 1.763 1.805 0.329 0.796 1.029 0.474 1.782 1.782 0.326 0.788 1.039 0.482 . 1.08 -1.43 -1.00 -0.83 0.91 0.19 Block #4 KM-05-012(l) KM-05-012(2) KM-05-012(3) KM-05-057a(l) KM-05-057a(2) KM-05-057a(3) KM-05-057b(l) KM-05-057b(2) KM-05-057b(3) KM-05-057b(4) KM-05-057b(5) KM-05-057b(6) KJVl-05-057c(l) KM-05-057c(2) KM-05-057c(3) KM-05-057c(4) KM-05-057c(5) M M M M M M M M M M M M C C C/M C/M C/M 28.60 24.03 25.10 24.43 21.00 32.23 35.04 38.09 27.26 28.76 28.08 46.38 26.61 37.87 28.75 40.08 37.21 0.001 0.001 0.001 0.001 0.001 ,0.001 0.001 0.001 0:001 0.001 0.001 0.010 0.001 0.001 0.001 0.010 0.001 11.252 9.396 9.773 9.429 8.350 12.599 14.039 15.187" 10.779 11.530 10.966 18,207 10.634 15.331 11.496 16.035 15.135 0.0132 0.0260 0.0158 0.0348 0.0280 0.0250 0.0197 0.0111 0.0061 0.0031 0.0206 0.0231 0.0048 0.0107 0.0211 0.0171 0.0021 2.542 2.557 2.568 2.591 2.515 2.558 2.496 2.508 2.529 2.494 2.561 2.547 2.502 2.470 2.501 2.500 2.459 0.0030 0.0071 0.0041 0.0096 0.0084 0.0051 0.0035 0.0018 0.0014 0.0007 0.0048 0.0033 0.0011 0.0017 0.0046 0.0027 0.0003 18.17 12.80 17.85 22.43 18.49 22.60 17.46 19.86 19.73 18.21 21.50 21.09 6.49 5.68 7.63 9.98 7.26 0.719 1.157 3.313 0.789 1.004 1.552 0.387 0.632 0.407 0.786 0.297 1.076 0.374 0.265 0.684 0.483 0.504 0.717 1.156 3.378 0.772 0.965 1.577 0.372 0.632 0.417 0.789 0.265 1.088 0.380 0.262 0.673 0.477 0.507 -1.01 0.93 1.97 3.89 -0.20 1.45 -0.45 -0.28 0.74 -0.45 1.69 1.24 1.75 0.95 1.20 0.82 -0.28 0.163 0.128 0.104 0.120 0.121 0.126 0.213 0.339 0.168 0.378 0.340 0.303 0.156 0.123 0.124 0.124 0.189 0.169 0.054 0.079 0.190 0.114 0.075 KM-05-057c(6) C 32.58 0.001 13.314 0.0144 2.447 0.0027 3.56 0.533 0.521 -0.51 0.115 KM-05-057c(7) C 19.07 0.001 7.647 0.0056 2.494 0.0018 5.37 0.381 0.381 1.53 0.075 KM-05-057c(8) C/M 31.07 0.001 12.374 0.0303 2.511 0.0061 15.97 1.279 0.078 1.12 0.258 KM-05-058a(l) C 31.36 0.001 12.530 0.0185 2.503 0.0037 5.30 1.642 0.045 1.58 0.153 KM-05-058a(2) M 28.43 0.001 11.112 0.0114 2.559 0.0026 12.45 0.759 0.082 2.96 0.133 KM-05-058a(3) C/M 25.13 0.001 10.043 0.0173 2.502 0.0043 7.29 0.938 0.947 2.04 0.185 KM-05-058b(l) M 37.07 0.001 14.596 0.0104 2.540 0.0018 14.56 0.592 0.599 0.83 0.115 KM-05-058b(2) M 39.16 0.001 15.438 0.0067 2.537 0.0011 12.88 1.768 1.783 0.76 0.092 KM-05-058d(l) M 45.69 0.010 18.153 0.0345 2.517 0.0048 12.20 0.748 0.730 -0.23 0.205 KM-05-058d(2) M 37.93 0.001 14.903 0.0216 2.545 0.0037 15.92 0.626 0.624 0.95 0.164 KM-05-058d(4) M 34.40 0.001 13.454 0.0176 2.557 0.0033 15.52 0.350 0.342 1.75 0.144 KM-057058d(5) M 48.95 0.010 19.442 0.0288 2.518 0.0038 10.63 0.960 0.954 0.04 0.171 KM-05-058d(6) M 40.83 0.010 16.250 0.0112 2.513 0.0018 10.85 0.739 0.744 0.64 0.109 KM-05-058d(7) M 48.78 0.010 18.998 0.0104 2.568 0.0015 12.76 0.385 0.389 1.73 0.062 KM-05-058d(8) M 44.97 0.010 17.814 0.0233 2.524 0.0033 15.23 0.472 0.454 -1.18 0.138 KM-05-017b(l) M 45.58 0.010 17.981 0.0318 2.535 0.0045 15.77 0.773 0.755 -0.46 0.182 KM-05-017b(2) M 45.01 0.010 17.713 0.0212 2.541 0.0031 16.10 0.505 0.497 -0.17 0.143 KM-05-017b(3) M 15.20 0.001 6.047 0.0180 2.514 0.0075 15.43 0.611 0.551 -2.02 0.318 KM-05-017b(4) M 46.03 0.010 18.183 0.0084 2.532 0.0013 16.26 0.440 0.443 0.16 0.087 KM-05-017b(5) M 43.08 0.010 17.003 0.0244 2.534 0.0037 16.45 0.910 0.905 -0.07 0.176 KM-05-017b(6) C 32.11 0.001 13.040 0.0204 2.462 0.0038 4.04 1.276 1.273 0.20 0.185 Block #5 KM-05-017b(7) C/M 47.69 0.010 18.737 0.0235 2.545 0.0032 9.64 0.530 0.542 -1.30 0.246 . KM-05-017c(l) M 22.84 0.001 8.807 0.0566 2.594 0.0167 18.37 1.347 1.283 1.11 0.711 KM-05-018d(l) M 16.78 0.001 6.684 0.0169 2.510 0.0063 16.99 0.837 0.809 -1.53 0.304 KM-05-018d(2) C 23.21 0.001 9.368 0.0418 2.478 0.0111 4.63 0.798 0.686 1.38 0.445 KM-05-018d(3) C 19.61 0.001 7.968 0.0210 2.461 0.0065 6.75 1.154 1.149 1.62 0.276 KM-05-019b(l) c 35.58 0.001 14.308 0.0378 2.487 0.0066 5.10 0.687 0.638 -0.98 0.279 KM-05-019b(2) c 34.75 0.001 13.697 0.0434 2.537 • 0.0080 6.55 0.862 0.829 2.33 0.311 Intermediate, KM-05-063(l) M 45.37 0.010 17.957 0.0079 2.527 0.0012 16.88 1.339 1.356 0.77 0.173 moderately KM-05-063(2) M 45.37 0.010 17.976 0.0164 2.524 0.0024 18.78 1.032 1.054 1.86 0.156 welded Near KM-05-063(3) M 41.15 0.010 16.164 0.0075 2.546 0.0013 17.12 0.683 0.692 1.26 0.068 block and Classic KM-05-063(4) M 45.47 0.010 17.985 0.0130 2.528 0.0019 20.10 0.573 0.565 -1.69 0.124 ash flow deposit KM-05-063(5) M 45.66 0.010 18.056 0.0136 2.529 0.0020 15.77 1.184 1.194 0.41 0.170 KM-05-063(6) M 45.39 0.010 18.108 0.0285 2.507 0.0040 16.62 1.337 1.331 -0.42 0.216 KM-05-023 bulk 47.15 0.010 18.501 0.0190 2.549 0.0026 39.53 1.112 0.041 1.30 0.145 KM-05-024(l) C 35.07 0.001 14.024 0.0404 2.501 0.0072 38.82 0.231 0.170 8.94 0.270 KM-05-024(2) C 33.13 0.001 13.175 0.0225 2.515 0.0043 40.35 0.443 0.485 10.82 0.161 KM-05-024(3) C 45.93 0.010 18.381 0.0135 2.499 0.0019 37.57 0.466 0.519 9.83 0.112 Basal, non- KM-05-024(4) C 31.50 0.001 12.643 0.0369 2.492 0.0073 39.40 0.487 0.508 9.43 0.288 welded Base of Classic KM-05-026(l) C 46.74 0.010 18.715 0.0225 2.498 0.0031 34.33 0.277 0.301 8.44 0.159 block and ash flow KM-05-026(2) KM-05-026(3) C C 35.91 35.22 0.001 0.001 14.476 14.212 0.0165 0.0238 2.481 2.478 0.0028 0.0041 33.08 31.80 0.374 0.382 0.397 0.396 6.42 5.45 0.137 0.199 deposit KM-05-026(4) C 40.60 0.010 16.509 0.0228 2.459 0.0035 36.16 0.544 0.588 7.92 0.163 KM-05-046(l) C 28.64 0.001 11.570 0.0110 2.475 0.0024 33.75 0.694 0.778 7.37 0.297 KM-05-046(2) C 45.61 0.010 18.387 0.0083 2.481 0.0012 27.44 0.650 0.833 5.86 0.098 KM-05-046(3) C 45.65 0.010 18.331 0.0226 2.490 0.0031 24.51 0.684 0.724 4.69 0.206 KM-05-046(4) C 45.72 0.010 18.513 0.0173 2.470 0.0024 23.87 0.534 0.573 4.85 0.187 Near TM#10 (oxidized KM-05-031 C 50.45 0.010 20.407 0.0101 2.472 0.0013 - - - - KM-05-032 bulk 41.22 0.010 16.277 0.0239 2.532 0.0038 45.03 1.092 0.014 0.34 0.151 KM-05-033(l) C 50.43 0.010 20.149 0.0193 2.503 0.0025 16.10 0.445 0.448 1.83 0.109 Upper, roadcut) KM-05-033(2) C 47.49 0.010 18.985 0.0041 2.501 0.0008 18.05 0.774 0.800 2.59 0.120 incipiently welded 2 (oxidized) block and KM-05-033(3) C 49.15 0.010 19.737 0.0078 2.490 0.0011 16.07 0.504 0.515 1.81 0.080 Near KM-05-056(l) C 42.44 0.010 17.096 0.0132 2.482 0.0020 21.05 0.444 0.463 2.53 0.151 TM#12 KM-05-056(2) C 21.73 0.001 8.680 0.0128 2.504 0.0037 21.71 0.674 0.708 5.55 0.164 ash flow (oxidized KM-05-056(3a) C 48.21 0.010 19.502 0.0056 2.472 0.0009 19.90 0.691 0.731 5.17 0.090 deposit roadcut) KM-05-056(3b) C 46.09 0.010 18.737 0.0175 2.460 0.0024 19.51 0.698 0.731 4.70 0.124 Oxidized Roadcut KM-04-018 KM-04-019 bulk bulk 50.06 50.28 0.010 0.010 19.741 19.709 0.0436 0.0162 2.536 2.551 0.0056 0.0022 42.11 42.07 0.170 0.479 0.070 0.053 1.62 1.40 0.248 0.121 KM-04-020 bulk 37.45 0.001 14.832 0.0112 2.525 0.0019 39.76 0.568 0.040 0.41 0.100 3 Upper, non- Keyhole KM-04-031 bulk 51.63 0.010 20.220 0.0119 2.553 0.0016 37.77 0.976 0.050 0.68 0.100 welded, block and ash flow Falls KM-05-036 bulk 50.55 0.010 19.941 0.0090 2.535 0.0013 43.55 2.265 0.024 0.11 0.065 KM-05-043(l) C 40.40 0.010 16.146 0.0210 2.502 0.0033 34.06 0.202 0.203 3.08 0.168 deposit KM-05-043(2) C 40.49 0.010 16.136 0.0273 2.509 0.0043 29.86 0.317 0.313 3.73 0.191 KM-05-043(3) C 30.80 0.001 12.264 0.0142 2.512 0.0029 35.50 0.361 0.382 5.73 0.150 KM-05-043(4) C 42.31 0.010 16.962 0.0225 2.494 0.0034 27.84 0.316 0.323 3.61 0.168 KM-05-044(l) C 18.28 0.001 7.047 0.0239 2.594 0.0088 33.69 0.401 0.345 3.65 0.329 KM-05-044(2) C 40.76 0.010 15.973 0.0126 2.552 0.0021 32.20 0.223 0.227 2.38 0.110 KM-05-044(3) C 28.68 0.001 11.393 0.0145 KM-05-044(4) C 38.11 0.001 15.023 0.0142 KJVl-05-045(l) c 43.41 0.010 17.114 0.0107 KM-05-045(2) c 19.58 0.001 7.885 0.0096 KM-05-054(l) c 36.63 0.001 14.832 0.0072 KM-05-054(2) c 36.45 0.001 14.622 0.0120 KM-05-054(3) c 46.46 0.010 18.619 0.0397 KM-05-054(4) c 46.25 0.010 18.449 0.0364 2.517 0.0032 30.48 0.234 0.220 -0.12 0.141 2.537 0.0024 28.26 0.688 0.692 1.01 0.102 2.537 0.0017 25.49 0.429 0.431 0.64 0.084 2.483 0.0030 24.29 0.590 0.580 -1.08 0.154 2.470 0.0012 34.00 0.145 0.155 3.04 0.089 2.493 0.0021 33.81 0.246 0.252 2.73 0.109 2.495 0.0053 35.08 0.741 0.770 4.77 0.241 2.507 0.0050 36.57 0.256 0.237 4.15 0.203

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