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

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ANALYSIS OF STRAIN IN A WELDED BLOCK AND ASH FLOW DEPOSIT, MOUNT MEAGER, SOUTHWESTERN BRITISH COLUMBIA by  KRISTA A. MICHOL B S c . (Honours), U n i v e r s i t y o f Ottawa, 2004  A THESIS S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE D E G R E E OF  M A S T E R OF SCIENCE .  in  THE F A C U L T Y OF G R A D U A T E STUDIES  (GEOLOGICAL SCIENCES)  THE UNIVERSITY OF BRITISH C O L U M B I A  December 2006  © K r i s t a A . M i c h o l , 2006  ABSTRACT The 2360 B P eruption o f M o u n t Meager, B r i t i s h C o l u m b i a has produced a rare welded b l o c k and ash f l o w deposit along w i t h non-welded equivalents. Here, I report on this sequence o f b l o c k and ash f l o w deposits (herein referred to as the K e y h o l e Falls M e m b e r ) w i t h the a i m o f documenting the effects o f w e l d i n g and the mechanisms o f strain attending the w e l d i n g process. M u l t i p l e 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 b l o c k and ash f l o w deposits to dense, vitroclastic breccias. Image analysis establishes a w e l d i n g trajectory, whereby average clast oblateness increases and average clast orientation (relative to the horizontal) decreases w i t h increasing w e l d i n g intensity. A f t e r accounting f o r an original oblateness o f approximately 3 0 % , estimates o f strain from image analysis o f f i e l d texture maps ( F T M s ) and slab texture maps ( S T M s ) y i e l d a v o l u m e strain o f - 1 2 % , or - 9 % i f treated as pure shear strain. A n empirical experiment u s i n g image analysis o f F T M s suggests that the most welded F T M s visually correspond to 30 - 4 0 % v o l u m e 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 i n indicating w e l d i n g intensity than do the average values. P h y s i c a l property measurements o f the non-welded and welded b l o c k and ash f l o w deposits correlate w e l l w i t h the empirical experiments. Unconsolidated deposits reveal an average total matrix porosity o f - 4 1 % , o f w h i c h less than 1 % is isolated porosity. A s s o c i a t e d clasts possess an average o f - 3 2 % total porosity, w i t h a m a x i m u m o f 1 1 % isolated porosity. A s w e l d i n g 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  ii  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 c k and A s h F l o w s and their Deposits  1  1.2.  W e l d i n g i n V o l c a n i c l a s t i c Deposits  2  CHAPTER TWO - GEOLGICAL SETTING.... 2.1. 2.2. 2.3. 2.4.  T h e 2360 B P E r u p t i o n o f M o u n t M e a g e r and the Pebble C r e e k F o r m a t i o n The K e y h o l e Falls M e m b e r Facies Variations Emplacement H i s t o r y  CHAPTER THREE - FABRIC ANALYSIS  5 5 6 9 13  16  3.1. TexturalData 3.1.1. F i e l d Texture M a p s ( F T M s ) 3.1.2. Slab Texture M a p s ( S T M s ) 3.2. Image A n a l y s i s 3.2.1. E m p i r i c a l Experiment w i t h Image A n a l y s i s 3.2.2. Distributions o f Oblateness and Orientation  CHAPTER FOUR - PETROGRAPHY & SEM ANALYSIS OF TEXTURES 4.1. Petrography 4.1.1. Non-welded Facies 4.1.2. Incipiently W e l d e d Facies 4.1.3. W e l d e d Facies 4.2. S E M Analysis 4.2.1 N o n - w e l d e d Facies 4.2.2. W e l d e d Facies 4.2.3. S E M A n a l y s i s o f Porosity  16 17 20 23 35 37  42 42 43 44 46 48 50 52 53  CHAPTER FIVE - PHYSICAL PROPERTIES 5.1. T h e ' Proto-deposit' 5.2. B u l k Density 5.2.1. N o n - w e l d e d vs. W e l d e d 5.2.2. Clasts vs. M a t r i x 5.3. Skeletal Density  56 62 63 65 65 66  iv  5.3.1 Non-welded vs. W e l d e d 5.3.2. Clasts vs. M a t r i x 5.4. R o c k Powder Density 5.4.1. Non-welded vs. W e l d e d 5.4.2. Clasts vs. M a t r i x  66 67 68 68 69  CHAPTER SIX - DISCUSSION 6.1 6.2 6.3 6.4  70  A n a l y s i s o f Porosity Welding Mechanisms O r i g i n a l Thickness and Average Strain Calculations C o m p a r i s o n to Other V o l c a n i c Deposits  70 74 78 81  CHAPTER SEVEN - CONCLUSIONS  86  REFERENCES  .  APPENDIX A - DETAILED DESCRIPTIONS OF FIELD TEXTURE MAPS  89 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  v  156  LIST O F FIGURES  Figure 1. L o c a t i o n o f M o u n t M e a g e r and distribution o f major Quaternary volcanoes i n the Cascade v o l c a n i c belt  4  Figure 2. Stratigraphy and geology o f the Pebble Creek F o r m a t i o n  7  Figure 3. Photograph o f the b l o c k and ash f l o w deposits exposed at K e y h o l e F a l l s , L i l l o o e t River Valley  8  Figure 4. F i e l d photographs s h o w i n g w e l d i n g facies variations w i t h i n the b l o c k and ash f l o w deposits : 10 Figure 5. S u m m a r y o f procedures used for image analysis o f f i e l d texture maps, u s i n g F T M 01 as an example 18 Figure 6. Results o f image analysis o f F T M s  19  Figure 7. G r a p h i c a l summary o f procedures used for image analysis o f slab texture maps, u s i n g 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 o n cross-sectional area  26  Figure 10. F T M grain size distribution b y clast area as calculated b y image analysis  27  Figure 11. S T M grain size distribution b y clast area as calculated b y image analysis  28  Figure 12. C u m u l a t i v e grain size distribution for F T M s and S T M s  29  Figure 13. A v e r a g e clast orientation vs. average clast oblateness for F T M s and S T M s  32  Figure 14. Strain vs. expected oblateness for v o l u m e strain and pure shear strain  34  Figure 15. Results f r o m an empirical experiment w i t h image analysis o f F T M s  36  Figure 16. D i s t i b u t i o n o f oblateness for F T M s  38  Figure 17. D i s t r i b u t i o n o f oblateness and orientation for a 5 0 % volume-reduced F T M 08  39  Figure 18. D i s tri b u ti o n o f orientation for F T M s  41  vi  Figure 19. Summary o f c o m m o n features w i t h i n the non-welded to incipiently w e l d e d b l o c k and ash f l o w deposits 45 Figure 20. W e l d i n g textures observed i n thin section  47  Figure 21. Shard types observed i n the non-welded to incipiently w e l d e d b l o c k and ash f l o w deposits 51 Figure 22. Attributes o f the densely welded b l o c k and ash f l o w deposits  54  Figure 23. A n a l y s i s o f porosity using S E M and image analysis  55  Figure 24. M a s s vs. v o l u m e plots for a l l samples o f b l o c k and ash f l o w deposits at M o u n t Meager  64  Figure 25. S u m m a r y o f p h y s i c a l property data  73  Figure 26. Calculated total strain vs. total, connected, and isolated porosity  75  Figure 27. U n c o m m o n textures indicating m i n i m a l effects o f pure shear strain  77  Figure 28. Strain profile o f the lower K e y h o l e Falls M e m b e r  79  Figure 29. T o t a l porosity vs. connected porosity o f volcanic deposits  82  vii  LIST O F T A B L E S  Table 1 . L o c a t i o n and description o f field sites  12  Table 2. S u m m a r y o f properties o f the b l o c k and ash f l o w deposits derived f r o m image analysis of FTMs 24 Table 3. S u m m a r y o f properties o f the b l o c k and ash f l o w deposits derived f r o m image analysis ofSTMs 25 Table 4. Sample suite chosed for S E M analysis o f b l o c k and ash f l o w deposits  49  Table 5. Summary o f p h y s i c a l property data for b u l k samples o f unconsolidated b l o c k and ash f l o w deposits 58 Table 6. S u m m a r y o f measured density data listed by w e l d i n g facies  59  Table 7. S u m m a r y o f calculated porosity values listed by w e l d i n g facies  60  Table 8. S u m m a r y o f density and porosity values listed by component and w e l d i n g intensity ..61  viii  ACKNOWLEDGEMENTS Tha nk y o u first and foremost to m y supervisor, K e l l y R u s s e l l for his persistence and support throughout this project. I'd like to thank G r e g D i p p l e and L o r i K e n n e d y 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 K i r s t i e S i m p s o n at the G e o l o g i c a l Survey o f Canada for valuable discussions and help w i t h field preparations. I a m also very grateful for the perspective and editing skills o f G r a h a m A n d r e w s . M a n y thanks to Heather W i l s o n for f i e l d w o r k assistance at M o u n t M e a g e r (and keeping me sane over the field season!).  I a m also indebted to m y f e l l o w colleagues N i l s  Peterson, G e n e v i e v e Robert, Stephen M o s s , Curtis Brett, Rebecca-Ellen Farrell, and M e l a n i e K e l m a n for their insightful discussions, reviews, support and friendship. F i n a l l y , I owe numerous thanks to the many friends I have made here at U B C , but most o f a l l to D a n i e l R o s s , w h o kept me level-headed throughout this experience and occasionally p r o v i d e d me w i t h some much-needed distractions.  ix  CHAPTER ONE INTRODUCTION 1.1.  Block and Ash Flows and their Deposits  B l o c k and ash f l o w s , also k n o w n as nuees ardentes, are small-volume pyroclastic f l o w s (generally less than 1 k m ) generated b y the explosive o r gravitational collapse o f l a v a f l o w s o r 3  domes (Cas and W r i g h t , 1987). B l o c k and ash f l o w deposits are topographically controlled, unsorted deposits w i t h an ash-rich matrix and a near-monolithologic assemblage o f generally p o o r l y vesiculated clasts, c o m m o n l y having radial c o o l i n g joints (Cas and W r i g h t , 1987). T h e y are deposited as hot avalanche-type deposits, c o m m o n l y w i t h reversely graded f l o w units, and m a y contain carbonized w o o d . C l a s s i c examples include deposits from M e r a p i (Bardintzeff, 1984; B o u d o n et a l . , 1993; A b d u r a c h m a n et al., 2000), U n z e n (Sato et a l . , 1992; U i et al., 1999), and Montserrat (Calder et al., 2002; W o o d s et al., 2002). They differ from other pyroclastic f l o w s (i.e., ignimbrites) i n that ignimbrites generally contain variable amounts o f ash, and the l a p i l l i and block-sized clasts are pumiceous (e.g., porosity > 5 0 % ) (Cas and W r i g h t , 1987). T h e y are also distinguishable f r o m debris flows and rock avalanches i n that debris f l o w s are m u c h more diluted i n terms o f pyroclastic material, and rock avalanches are deposited c o l d . S i m i l a r l y to rock avalanches, b l o c k and ash f l o w s represent a significant hazard to human l i f e and infrastructure, only more so due to their higher emplacement temperatures, increased f l u i d i z a t i o n from degassing, and the potential to decouple h i g h l y m o b i l e elutriated ash clouds (Bourdier and A b d u r a c h m a n , 2 0 0 1 ; Stewart et a l . , 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 (T : Giordano et g  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 i g u r e 1: L o c a t i o n o f the M o u n t Meager (star) w i t h i n the Canadian portion o f the Cascade volcanic belt (modified 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 M o u n t M e a g e r V o l c a n i c C o m p l e x ( M M V C ) is a component o f the G a r i b a l d i V o l c a n i c Belt, w h i c h i s the northernmost segment o f the Cascade V o l c a n i c B e l t ( F i g . 1; M a t h e w s , 1958; G r e e n et a l . , 1988; Read, 1990; Sherrod and S m i t h , 1990; K e l m a n et al., 2002; C l a g u e et a l . , 2 0 0 3 ; G r e e n and Sinha, 2005). M o u n t M e a g e r is a composite stratovolcano located approximately 50 k m northwest o f Pemberton i n the Coast M o u n t a i n s , and rises to an elevation o f 2645 m between the L i l l o o e t R i v e r and M e a g e r Creek (Stasiuk et al., 1996). V o l c a n i s m associated w i t h the M M V C ranges f r o m 2.2 M a ( K - A r ) to its most recent eruption at 2360 B P (Nasmith et al., 1967; R e a d , 1977; R e a d , 1978; Clague et al., 1995). T h e edifice drapes over southern Coast B e l t rocks i n c l u d i n g M e s o z o i c metamorphic supracrustal rocks o f the Cadwallader F o r m a t i o n , and Tertiary monzonite intrusions o f the Coast Plutonic C o m p l e x (Read, 1978; Gabrielse et al., 1992).  The vent for the 2360 B P eruption cuts through deposits o f the preceding P l i n t h A s s e m b l a g e (90 - 100 K a ; R e a d , 1978) and is situated at 1500 m elevation, roughly 1000 m above the present stream bed o f the L i l l o o e t R i v e r (Stasiuk et al., 1996). T h e 2360 B P eruption (Nasmith et a l . , 1967; C l a g u e et a l . , 1995) produced the sequence o f volcaniclastic dacite-rhyodacite deposits o f the Pebble C r e e k Formation (Fig. 2 a ; R e a d , 1978; H i c k s o n et al., 1999; Stewart, 2 0 0 2 ; Stewart et al., 2003). T h e Pebble C r e e k F o r m a t i o n records an initial sub-Plinian eruption that produced a p u m i c e f a l l deposit and an ignimbrite, f o l l o w e d b y emplacement o f b l o c k and ash f l o w deposits, the K e y h o l e F a l l s M e m b e r (here defined). T h e eruption cycle ended w i t h the extrusion o f a 5  rhyodacite lava (Stasiuk et al., 1996; H i c k s o n et al., 1999; Stewart, 2002). There was no appreciable lapse i n time during this sequence o f events.  The M M V C region was originally mapped b y A n d e r s o n (1975), and R e a d (1977, 1978, 1990); however, a more detailed mapping o f the Pebble Creek F o r m a t i o n recognizing the presence and distributions o f pyroclastic f l o w and b l o c k and ash f l o w deposits was completed b y Stasiuk et a l . (1996), H i c k s o n et a l . (1999), and Stewart (2002). Figure 2b is a s i m p l i f i e d geological map f r o m Stewart (2002) showing the distribution o f the Pebble Creek F o r m a t i o n v o l c a n i c deposits resulting f r o m the 2360 B P eruption.  2.2.  The Keyhole Falls Member  The K e y h o l e Falls M e m b e r is chiefly confined to a steep-sided paleo-channel inferred to be a glacially-steepened, earlier incarnation o f the L i l l o o e t R i v e r (Stasiuk et al., 1996; H i c k s o n et a l . , 1999). It is approximately 165 m thick immediately b e l o w the inferred vent at the type locality o f K e y h o l e F a l l s ( 4 6 6 4 0 0 E 5 6 1 4 0 5 0 N ; F i g s . 2 a , 3). The M e m b e r is a wedge-shaped unit w i t h a n estimated v o l u m e o f 0.44 k m (Stewart, 2002) that thins downstream to a total thickness o f 25 m 3  after 2.5 k m .  6  a) Stratigraphic column at Keyhole Falls (*):  (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. Figure 2: Stratigraphy and geology of the Pebble Creek Formation modified from Stewart  F i g u r e 3: Northwest-facing field photograph showing b l o c k and ash pyroclastic f l o w deposits exposed at K e y h o l e Falls i n the L i l l o o e t R i v e r Valley. The lower cliff-forming unit comprises the densely w e l d e d facies and is approximately 100 m thick at this location. The upper recessive units (here, approximately 60 m) are bedded and variably sorted, c o m p r i s i n g interbedded f l u v i a l gravels and non-welded to incipiently welded b l o c k and ash f l o w deposits. The section is capped by younger rock avalanche deposits. The present-day canyon was formed by an outburst f l o o d event shortly after deposition ( H i c k s o n et a l . , 1999; Stewart, 2002). The gorge i n the c l i f f w a l l results f r o m 2360 years o f erosion by the L i l l o o e t R i v e r through the residual welded b l o c k and ash f l o w deposit.  8  The K e y h o l e F a l l s M e m b e r is a dominantly monomict volcaniclastic breccia composed o f centimeter- to metre-sized crystal-rich, rhyodacite obsidian clasts supported b y a pumiceous ashsized matrix. A c c i d e n t a l , centimetre-sized angular lifhic clasts o f monzonite, P l i n t h assemblage, and shale are u n c o m m o n . The M e m b e r is dominantly massive and very p o o r l y sorted. C r y p t i c reversely graded bedding is exhibited i n the densely welded material b y variations i n the apparent m a x i m u m clast size. Detailed petrographic and geochemical studies o f the deposit can be found i n Stasiuk et a l . (1996) and Stewart (2002). The M e m b e r is inferred to be a b l o c k and ash f l o w deposit because it exhibits: (1) very poor sorting; (2) mostly monolithic clasts o f rhyodacite lava; (3) an ash-rich matrix; and (4) c o o l i n g joints throughout the densely w e l d e d facies, indicating a hot emplacement (Stasiuk et al., 1996; Stewart 2002). These characteristics parallel those o f b l o c k and ash f l o w deposits reported f r o m other classic examples (e.g., M e r a p i , U n z e n , Montserrat; Cas and Wright, 1987).  2.3.  Facies Variations  Variations i n w e l d i n g intensity are noted i n several areas along the L i l l o o e t R i v e r V a l l e y , f r o m non-welded and incipiently welded (Streck and Grunder, 1995) deposits that f o r m a significant slope, to a lower, densely welded deposit that forms a prominent steep-sided gorge ( F i g . 3). O n the basis o f w e l d i n g intensity, I identify four separate w e l d i n g facies i n the K e y h o l e F a l l s M e m b e r ( F i g . 4): (1) a basal non-welded facies; (2) a densely welded facies at, and up to 3.15 k m downstream f r o m K e y h o l e F a l l s ; (3) an o x i d i z e d and incipiently w e l d e d facies greater than 3.15 k m downstream f r o m K e y h o l e F a l l s ; 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 i e l d Site 1; Table 1) is an approximately 2 m thick, non-welded and poorly-sorted volcaniclastic breccia supported b y a grey, ash-sized matrix (Fig. 4a). Juvenile clasts are dominantly pumice (45 - 5 5 % ) and moderately dense rhyodacite (40 5 0 % ) , w i t h sporadic dense rhyodacite clasts (2 - 5%); rare accidental clasts o f P l i n t h assemblage and Tertiary monzonite country rock are present as w e l l as f l o w banded pumice-like clasts. Clasts are mostly sub-angular to sub-rounded, typically 5 - 15 c m i n diameter, and rarely up to 1 m. T h e base is not exposed, but this facies is inferred to sit conformably o n a deposit o f pumiceous pyroclastic f l o w , and to grade upwards into the densely welded facies.  The densely welded facies (type locality F i e l d Site 1, Table 1) is a 16 m thick, poorly-sorted volcaniclastic breccia supported by a grey, fine ash-sized matrix ( F i g . 4b). Juvenile, angular to sub-rounded, vesicular and glassy rhyodacite clasts dominate (85 - 9 5 % ) , w i t h lesser quantities o f accidental P l i n t h assemblage, granodiorite, monzonite and shale clasts present. Clasts are t y p i c a l l y 5 - 1 5 c m i n diameter, w i t h local clasts up to 1 m across. Some clasts show vestiges o f f l o w banding textures. M a n y obsidian clasts are demonstrably pyroclastic i n nature, and define a prominent sub-horizontal fabric similar to eutaxitic fabrics observed i n welded ignimbrites (e.g., S m i t h , 1960b). C o l u m n a r joints are continuous throughout the thickness o f the densely welded facies, suggesting that it represents a single c o o l i n g unit (sensu S m i t h , 1960b).  11  Table 1. Location and description of field sites, including associatedfieldtexture maps (FTMs) and slab texture maps (STMs). Field Site  Description  U T M Coordinates Easting  Northing  Block and Ash Flow Deposit Facies  Field Texture Map Slab Texture Map 01  02  16 11 12 13 14 15  03 Valley wall exposure in Lillooet River valley; cliff and fallen blocks  Densely welded (middle of deposit) 468404  5612192  04 05  06  Unwelded (base of deposit) 2  Roadcut exposure ~300m NE of , Field Site 1  .,„„„, 468531  3  Roadcut exposure; on south side of bridge at Keyhole Falls  466400  5612414  Incipiently welded (upper oxidized section)  5614050  Unwelded (upper unoxidized section)  07 08 13 09 10 12 11  01 02 07 08 09 10 03 04 05 06  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 resultedfromcontinued 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 m  2  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 a i m grid flush with the outcrop and then mapping 2  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 i e l d texture maps using F T M 01 as an example: (a) field photo o f l m x l m g r i d o n an outcrop o f densely w e l d e d b l o c k and ash f l o w deposit (T denotes top o f grid); (b) hand-drawn field texture map based o n a m i n i m u m clast size o f 0.5 c m ; (c) digital scanned version F T M 01 used for image analysis ( S c i o n Image™ or Image J™); (d) preliminary results o f image analysis s h o w i n g i n d i v i d u a l 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 (KM05-011, 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 M a p s ( S T M s )  Sixteen slab texture maps were created from the densely welded b l o c k and ash f l o w deposits. T h i s was accomplished b y p l a c i n g a sheet o f acetate over the slab (Fig. 7a), and tracing clasts 0.5 m m or greater b y hand; particles less than 0.5 m m were treated as matrix. S T M s are d r a w n perpendicular to foliation, at a scale o f 1:1 (Fig. 7b). These texture maps correspond to samples derived f r o m five different F T M s (Table 1). The acetates were then retraced b y hand, scanned into digital f o r m (Fig. 7c), and imported into S c i o n Image™ and Image J™ for image analysis i n the same manner as the F T M s (Fig. 7d). Resulting output images from S c i o n Image are displayed i n Figure 8. F o r a f u l l suite o f images depicting image analysis procedures, refer to Appendix C.  21  Figure 8: Results o f image analysis for the fifteen other S T M s , representing the heterogeneity o f w e l d i n g intensity i n the b l o c k and ash f l o w deposit. N u m b e r s indicate the chronological order i n w h i c h the slab texture maps were completed (e.g., not w e l d i n g intensity).  22  Image Analysis  3.2.  Image analysis software was used to quantify the F T M s and S T M s : S c i o n Image™ returned values o f clast area, perimeter, m i n i m u m and m a x i m u m 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 i g . 9a). Clast-matrix proportions for the S T M s are more variable; clasts average 53 ± 9 % , and range f r o m 39 - 6 9 % (Fig. 9b).  G r a i n size distributions were created using i n d i v i d u a l clast areas calculated w i t h S c i o n Image™. F T M s show n o r m a l or near-normal distributions that are variably skewed towards smaller size fractions because the F T M data is truncated b e l o w 0.1 c m , corresponding to a m i n i m u m clast 2  diameter o f ~0.5 c m (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 i m i l a r l y truncated b e l o w 0.01 c m due to a m i n i m u m clast diameter o f 0.5 m m (Fig. 11). Neither the F T M s nor the S T M s 2  demonstrate any appreciable shift i n grain size distribution w i t h w e l d i n g intensity. C u m u l a t i v e grain size distributions were also created for the F T M s (Fig. 12a) and S T M s (Fig. 12b); however, w e l d i n g facies i n the F T M s and b l o c k s o f densely w e l d e d material i n the S T M s are indistinguishable from one another based o n their cumulative grain size distribution curves.  23  2. Summary of properties of block and ash flow deposits derived from image analysis of FTMs, 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 radius (a/c), clast orientation, volume strain (e ), pure shear strain (e ), and % of clasts (C) and matrix (M) by area. — Table  T  v  FTM 1  2  3  4  5  6  7  8  9  10  11  12  13  A  T  (m ) 2  1.00  0.98  1.00  0.93  1.00  1.00  0.88  0.93  0.79  0.60  1.00  0.91  0.76  N  s  A (cm ) P(cm)  1  2  avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min avg. max min  563  386  400  530  1064  883  487  571  613  340  370  505  436  A/P  5.68  7.56  0.41  440.5  94.0  4.69  0.14  1.44  0.06  a (cm) c (cm)  a/c  Orientation (°)  Ev  0.72  1.91  23.6  0.42  0.31  16.2  8.68  6.52  89.8  0.85  0.71  0.28  0.15  1.03  0.2  0.02  0.02  1.37  2  *s'  12.1  9.04  0.49  1.62  0.88  1.84  26.2  0.40  0.30  2404.7  240.5  10.00  44.2  17.3  5.33  88.4  0.81  0.67  0.23  1.77  0.13  0.29  0.22  1.04  0.0  0.04  0.02 0.27  10.2  9.75  0.54  1.67  1.02  1.71  41.3  0.36  534.7  95.2  5.62  14.2  12.0  5.15  89.4  0.81  0.66  0.22  1.71  0.12  0.29  0.19  1.02  0.4  0.02  0.01  6.27  8.31  0.44  1.87  25.4  0.41  0.30  115.0  3.76  1.49 18.3  0.80  432.1  7.50  5.11  88.6  0.80  0.66  0.22  1.79  0.11  0.31  0.21  1.01  0.1  0.01  0.01  4.19  6.42  0.35  1.18  0.62  1.90  21.7  0.41  0.31  592.7  94.1  6.30  14.6  13.0  5.91  90.0  0.83  0.69  0.17  1.58  0.10  0.25  1.03  0.0  0.03  0.02  3.57  6.51  0.35  1.19  0.18 0.62  1.98  25.0  0.43  0.32  190.0  60.9  3.15  11.4  6.05  13.2  89.9  0.92  0.82  0.17  1.52  0.11  0.25  0.16  1.03  0.0  0.03  0.02  5.95  7.60  0.45  1.31  0.84  1.57  34.1  0.32  0.23  166.9  64.3  2.84  10.9  5.84  89.8  0.80  0.13  1.33  0.10  0.23  0.19  4.96 1.02  0.1  0.02  0.66 0.01 0.23  6.24  7.85  0.48  1.36  0.89  1.55  31.3  0.32  194.9  55.4  3.58  10.3  6.55  4.95  89.8  0.80  0.66  0.19  1.53  0.12  0.27  0.22  1.01  0.0  0.01  0.01  4.22  6.61  0.37  1.19  0.66  1.74  26.7  0.38  0.28  149.0  57.2  2.72  10.5  4.58  4.82  90.0  0.79  0.65  0.15  1.59  0.06  0.27  0.16  1.01  0.0  0.01  0.01  5.52  7.90  0.45  1.40  0.81  1.74  29.3  0.37  0.27  337.1  84.5  3.99  14.9  7.19  4.70  89.0  0.79  0.64  0.23  1.80  0.13  0.26  1.02  0.1  0.02  0.01  10.3  10.1  0.58  0.28 1.74  1.09  1.62  35.9  0.33  0.24  332.9  81.1  4.10  14.5  7.31  4.84  88.1  0.79  0.65  0.23  1.77  0.13  0.29  0.22  1.02  0.5  0.02  0.01  7.28  8.22  0.45  1.46  0.82  1.79  28.3  0.39  0.29  396.4  81.2  4.88  13.9  9.09  7.80  89.9  0.87  0.14  1.35  0.10  0.24  0.19  1.03  0.0  0.03  0.75 0.02  6.83  7.78  0.45  1.37  0.82  1.66  31.6  0.35  0.26  212.2  64.1  3.31  12.3  6.34  3.49  90.0  0.71  0.57  0.17  1.47  0.05  0.26  0.21  1.01  0.1  0.01  0.01  C(%)  M (%)  47  53  59  41  54  46  49  51  47  53  52  48  46  54  45  55  56  44  59  41  51  49  52  48  43  57  ' N = number of particles; E = volume strain estimated from oblateness (1 -c/a); E = pure shear strain estimated from oblateness (1 - c / a ) 2  3  V  M  S  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 (e ), pure shear strain (e ), and % of clasts (C) and matrix (M) by area. Standard deviations (la) are shown where appropriate. v  STM A (cm ) 2  x  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 !  175.8 133.7 124.4 113.5 106.4 147.0 157.7 159.0 111.5 113.3 108.1 113.9 122.7 88.7 78.3 124.5  N  1  s  A (cm ) a (cm ) P(cm) A/P a (cm) a (cm) c (cm) o (cm) a/c Orientation (°) « ( ) 2  0.08 0.11 0.07 0.07 0.14 0.04 0.07 0.08 0.09 0.11 0.07 0.06 0.09 0.08 0.07 0.06  838 399 598 305 181 468 634 653 289 340 304 234 284 226 288 590  4  2  0.322 0.477 0.254 0.208 0.470 0.079 0.324 0.358 0.642 0.699 0.152 0.213 0.564 0.196 0.279 0.254  116.40 111.61 112.04 116.45 106.17 129.77 112.53 114.73 118.34 114.28 105.23 107.23 114.52 108.67 120.79 119.79  0.05 0.06 0.05 0.05 0.06 0.04 0.05 0.05 0.04 0.05 0.05 0.05 0.05 0.05 0.05 0.04  0.16 0.20 0.16 0.15 0.19 0.12 0.15 0.15 0.13 0.15 0.16 0.14 0.15 0.16 0.15 0.14  0.176 0.228 0.142 0.143 0.212 0.085 0.156 0.166 0.178 0.238 0.119 0.124 0.177 0.143 0.140 0.149  0.08 0.10 0.09 0.09 0.11 0.07 0.08 0.09 0.08 0.08 0.09 0.09 0.08 0.10 0.08 0.07  0.076 0.079 0.070 0.066 0.108 0.042 0.071 0.077 0.0970.096 0.067 0.072 0.103 0.074 0.071 0.070  1.91 1.98 1.73 1.79 1.67 1.75 1.71 1.72 1.73 1.77 1.90 1.70 1.85 1.71 1.81 1.94  22.77 21.34 28.58 26.66 32.32 31.19 27.03 25.76 35.98 31.23 25.60 30.38 28.33 32.75 34.37 32.83  21.147 18.338 23.716 23.164 22.956 22.584 21.897 21.967 25.315 23.746 22.463 24.104 23.633 26.046 25.325 22.535  £  V  0.41 0.43 0.37 0.38 0.35 0.37 0.36 0.37 0.37 0.37 0.41 0.36 0.39 0.36 0.38 0.41  es C (%) M (%) 0.30 44 56 0.32 39 61 0.27 40 60 0.28 54 46 0.26 58 42 0.27 52 48 0.27 49 51 0.27 51 49 0.27 68 32 0.27 56 44 0.31 45 55 0.26 61 39 0.29 69 31 0.27 62 38 0.28 55 45 0.31 44 56 5  N = number of particles; e = volume strain estimated from oblateness (1-c/a); £ = pure shear strain estimated from oblateness (l-c/a ) 2  3  v  2/3  s  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 30  a  25  3 20  FTM 02  FTM 03  Limit of observation 121  IL  8  a is  i SI A Claat area (cm )  Clast area (cm ) FTM OS  30 25 £ S 20  3 o  113  "5  15 10  HP". Clast area (cm )  Clast area (cm)  1  1  Clast area (cm)  Clast area (cm )  1  1  25 .2 20 u  a 15 o 5 10  I  10  9  Clast area (cm ) 2  Figure 10: FTM grain size distribution by clast area as calculated by image analysis. The distribution is truncated below 0.1 cm 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. 2  27  STM 01  STM 02  STM 03  Clast araa (cm ) 1  STM 16  Figure 11: STM grain size distribution by clast area as calculated by image analysis. The distribution is truncated below 0.01cm 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. 2  28  - • - densely welded • unwelded (basal)  CN>  cv>  <*  - * - indurated (upper, oxidized) -e- unwelded (upper)  J>  o>  N  &  NFC  &  Clast area (cm ) • Block#1  #  ^  • Block#3  • Block#4  • Block#5  ^ Clast area (cm )  Figure 12: Cumulative grain size distribution for (a) F T M s , 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 w e l d i n g intensity (Quane and R u s s e l l , 2005a) and it is calculated using the f o l l o w i n g f o rmul a:  Oblateness = 1  Q  a  (1)  where c = m i n i m u m clast diameter, and a = m a x i m u m 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. A n o t h e r indicator o f w e l d i n g intensity may be clast orientation; Sheridan and R a g a n (1976) reported that mechanical deformation (i.e., non-viscous, b e l o w T ) was insufficient to change the orientation g  and alignment o f particles. T h e y argued that a compactional load d r i v i n g viscous deformation (i.e., above T ) was responsible for producing elongated clasts that then rotate towards the g  horizontal (Ragan and Sheridan, 1972; Sheridan and Ragan, 1976). Alternatively, clasts i n nonw e l d e d deposits are expected to have random orientations averaging 45° from the horizontal. T h u s , a plot o f averages o f these two properties for each F T M ( F i g . 13a) might serve to numerically distinguish between facies observed i n the field. A s evident i n Figure 13a, each facies o f this b l o c k and ash f l o w plots i n order o f increasing w e l d i n g intensity from the bottom right to the top left i n terms o f orientation and oblateness. Upper non-welded deposits near K e y h o l e F a l l s 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 l o c k and ash f l o w deposits, o n average, have h i g h clast orientations (32 - 34°), and l o w values o f clast oblateness (0.32 - 0.35). Incipiently w e l d e d deposits show a decrease i n average clast orientation (27 29°), and as expected, an increase in average clast oblateness (0.37 - 0.39). F i n a l l y , the densely w e l d e d b l o c k and ash f l o w 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 i n 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 m u c h greater ranges in these properties (Fig. 13b), suggesting that on the centimeter scale, w e l d i n g intensity is h i g h l y heterogeneous. N o t o n l y are the b l o c k s o f densely welded material indistinguishable f r o m one another, but the ranges o f average oblateness and orientation for a l l S T M s nearly span the f u l l range o f oblateness (0.35 0.43) and orientation (21 - 36°) for the entire deposit. T h i s is an indication that strain is m u c h more l o c a l i z e d at this scale.  31  20  30  40  50  Orientation (°) 0.8 0.7  b)  • Block #1 A Block #3 • Block #4  0.6  • Block #5 0.5 0.4  1  0.3  2  5  0.2  i  0.1 0 10  20  3 0  40  50  Orientation (°) Figure 13: Average clast orientation is plotted against average clast oblateness f o r (a) F T M s , and (b) S T M s . F T M s are grouped b y facies: (1) densely w e l d e d facies, (2) upper, incipiently welded facies, (3) non-welded basal facies, (4) upper, nonw e l d e d facies and, (5) densely w e l d e d facies mapped i n the plane o f flattening. W e l d i n g is expected to promote h i g h clast oblateness and l o w clast orientation due to compaction. Non-welded deposits w o u l d have a l o w clast oblateness (e.g. nearspherical), and a random clast orientation o f 45°. The deposit remains heterogeneous at the sub-metre scale as indicated b y data f r o m the S T M s . S T M samples originate f r o m the densely w e l d e d 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, £ ), then oblateness is mathematically equal to strain for spherical particles: v  (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 nonwelded 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  0.5  Strain (volume or pure shear) F i g u r e 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 initially spherical. M a i n figure accounts for an original oblateness o f 0.3, w h i c h is a conservative estimate based on non-welded deposits (Figure 13). I f this is the case, values o f strain incurred b y the welded b l o c k and ash f l o w deposit are approximately 1 2 % for volume strain and 9 % for pure shear strain.  34  3.2.1. E m p i r i c a l Experiment w i t h Image A n a l y s i s  The w e l d i n g trajectory is defined b y average values o f oblateness and orientation for F T M s , but they provide a substantially lower estimate o f strain ( 1 2 % ) than expected. A n e m p i r i c a l experiment was devised to investigate the progression o f v o l u m e strain using the least w e l d e d F T M . F T M 0 8 , a texture map deriving f r o m a section o f the basal non-welded facies was digitally reduced i n its vertical dimension b y 10, 20, 30, 40 and 5 0 % w h i c h is exactly equivalent to a v o l u m e strain o f 10, 2 0 , 30, 40 and 5 0 % (Fig. 15). F T M s f r o m the densely w e l d e d facies ( F T M 0 5 , 06) were then compared to the digitally 'strained' images o f F T M 08. T h e images o f F T M 05 and 06 most closely resembled F T M 08 after a 'strain' o f 30 - 4 0 % . T h i s experiment and v i s u a l comparison o f images implies that the densely welded facies have undergone 30 4 0 % v o l u m e strain, relative to the non-welded facies. This is a value m u c h 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. S c i o n I m a g e ™ revealed F T M 08 had an average oblateness o f o n l y 0.54 after being d i g i t a l l y 'strained' b y 5 0 % . Thus, an accommodation o f 5 0 % v o l u m e strain only resulted i n a 0.22 increase i n average oblateness. T h i s is consistent w i t h the lower-than-expected average oblateness values associated w i t h the densely w e l d e d F T M s and S T M s .  35  F i g u r e 1 5 : D i g i t a l images produced f r o m computersimulated shortening o f F T M 08, w h i c h represents the unwelded b l o c k and ash f l o w deposit. Simulations show incremental shortenings (e.g., v o l u m e strains) o f 10, 2 0 , 30, 40, and 5 0 % . F T M 05 and 06 are displayed to show their similarity to F T M 08 after undergoing 3 0 - 4 0 % v o l u m e strain. O f note is that average oblateness should parallel values o f v o l u m e strain incurred, but e = 5 0 % produces a l o w e r than expected average oblateness o f 0.54.  FTM 08 basal unwelded £ =0% oblateness = 0.32 v  £ = 10% (volume strain by collapsing pores) v  v  e = 20%  £ = 50% oblateness = 0.54 v  FTM 06 (oblateness = 0.43) 36  3.2.2. Distributions o f Oblateness and Orientation  Distributions o f clast oblateness and orientation were examined i n the F T M s i n an effort to further examine the nature o f strain. The distributions were created u s i n g plots o f n o r m a l i z e d frequency vs. oblateness (bin size = 0.1) or orientation (bin size = 10°). Oblateness shows nearn o r m a l distributions whereby the degree o f skewness to the right (towards larger values o f oblateness) defines the degree o f w e l d i n g (Fig. 16). The densely welded facies ( F T M s 0 1 , 02, 04 - 06) show the most skewness towards the right, whereas non-welded facies ( F T M s 0 7 , 0 8 , 13) show more normal distributions or even a skewness towards the left. Incipiently w e l d e d facies ( F T M s 09, 10, 12) show intermediate trends. In most cases, a w e l l defined peak also appears i n those distributions representing densely w e l d e d 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  w e l d e d sections, once again, show intermediate results. The peak values o f oblateness are also significantly higher than the averages calculated for each F T M . O n average, the densely w e l d e d facies show a m a x i m u m frequency at 0.4 - 0.5, whereas the incipiently w e l d e d facies peak at 0.3 - 0.5, and the non-welded facies peak at 0.2 - 0.4. The distribution o f oblateness seen i n the digitally deformed F T M 08 ( 5 0 % v o l u m e strain) is a prime example o f these three features i n a densely w e l d e d deposit (Fig. 17). F T M 0 3 , drawn o f the densely w e l d e d facies i n the plane o f flattening; it shows a sharp peak but it is skewed to the left at a m a x i m u m 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 i g u r e 1 6 : D i s t r i b u t i o n o f oblateness for each F T M . M o s t display a n o r m a l or nearn o r m a l distribution w h i c h becomes progressively more skewed to the right as w e l d i n g intensity and the peak oblateness values increase. N u m b e r s indicate the c h r o n o l o g i c a l order i n w h i c h the f i e l d texture maps were completed (e.g., not w e l d i n g intensity).  38  FTM 08 (-50%)  N 0.2  Q-  <a"  cs-  fcfcfc fcfcfc- fc- fc- fc- fc- fc- fc> fc- fcv  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 i g u r e 1 7 : D i s t r i b u t i o n o f (a) oblateness and (b) orientation for a 5 0 % volumereduced F T M 08. Oblatess shows a near-normal distribution skewed to the right, w i t h a peak oblateness o f 0.6 - 0.7. Orientation shows a negative exponential distribution w i t h less than 1 % o f clasts at angles greater than 40° f r o m the horizontal.  39  A s w e l d i n g intensifies, orientation shows an increasingly negative exponential distribution from l o w to h i g h clast orientations (Fig. 18). Densely w e l d e d F T M s show the most pronounced exponential distributions w i t h a strong peak at 0 - 10°. Incipiently w e l d e d facies c o m m o n l y show a more subtle or irregular curve w i t h a m a x i m u m frequency at 0 - 10 °. N o n - w e l d e d deposits show an irregular or nearly flat trend, although the m a x i m u m frequency still occurs at 0 - 10°. The F T M drawn o f the densely w e l d e d facies i n the plane o f flattening ( F T M 03) demonstrates a nearly flat trend, w i t h a m a x i m u m frequency o f 30 - 4 0 °. The distribution o f orientation seen i n the digitally deformed F T M 08 shows an extremely steep negative exponential curve, w i t h less than 1 % o f clasts having an orientation greater than 4 0 ° ( F i g . 17).  40  FTM 01  0-10  10-20  20-30  30-40  40-50  F T M 02  50-60  60-70  70-80  60-90  0-10  10-20  20-30  Orientation f )  0-10  10-20  20-30  30-40  40-50  50-60  10-20  20-30  30-40  40-50  50-60  60-70  70-80  80-90  0-10  10-20  20-30  30-40  50-60  50-60  60-70  n.n  70-80  80-90  0-10  10-20  20-30  II  60-70  70-60  80-90  0-10  0-10  10-20  20-30  70-80  0-10  n.n n.n  10-20  20-30  40-50  50-60  60-70  70-80  80-90  Orientation (°)  "111 I M l fl 0-10  10-20  20-30  30-40  P 40-50  60-70  70-60  80-90  30-40  40-50  50-60  60-70  70-60  80-90  0-10  10-20  20-30  _ln 30-40  40-50  n nnn  50-60  60-70  70-80  80-90  Orientation (*)  nn nn n n  30-40  50-60  Orientation (°)  Orientation (°)  60-70  40-50  1, II , n , n , n  n . n . n  10-20 20-30 30-40 40-50 50-60 60-70 70-60 80-90  Orientation (°)  30-40  Orientation f )  Orientation {")  1 n.n n.n  40-50  40-50  10-20 20-30 30-40 40-50 50-60 60-70 70-80 60-90  Orientation f>  0-10  1 nn  30-40  Orientation O  Orientation (°)  0-10  F T M 03  0-10  10-20  20-30  l.n.n  30-40  40-50  50-60  n n.n  60-70  70-60  Orientation (°)  n n  50-60  60-70  nn  70-60  80-90  Orientation (°)  F i g u r e 1 8 : Distribution o f orientation for each F T M . T h e distributions become progressively more exponential i n shape as w e l d i n g intensity increases. N u m b e r s indicate the chronological order i n w h i c h the f i e l d texture maps were completed (e.g., not w e l d i n g intensity).  41  CHAPTER FOUR PETROGRAPHY & SEM ANALYSIS OF TEXTURES Petrography and analysis using the scanning electron microscope ( S E M ) are used to provide a description o f the K e y h o l e Falls M e m b e r at the micro-scale. These observations reinforce the fact that this deposit is a w e l d e d b l o c k and ash f l o w . The textural observations provide evidence o f w e l d i n g 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 w e l d e d deposits. L a s t l y , these observations constrain the mechanisms i n v o l v e d i n w e l d i n g the b l o c k and ash f l o w deposits. F o r a detailed description o f Pebble C r e e k F o r m a t i o n mineralogy, refer to Stasiuk et a l . (1996).  4.1.  Petrography  Petrographic descriptions derive f r o m 36 thin sections ranging from non-welded to densely w e l d e d facies o f the b l o c k and ash f l o w deposit. T h i n section analysis records the development o f a foliation, progressive deformation o f the clasts, and a reduction i n total porosity i n both clasts and matrix w i t h increasing w e l d i n g 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 darkercoloured, 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 upwardsfrom0.5 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 lathshaped 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 ( F O V = 3.9 mm);(b) vesicular pumice-like clast in incipiently welded deposits ( F O V = 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.  W e l d e d Facies  The componentry and mineralogy o f the w e l d e d facies parallels that described for the nonw e l d e d and incipiently w e l d e d facies. H o w e v e r , deformation due to compaction and v o l u m e strain is prominent. Clasts are noticeably more elongate i n shape ( F i g . 20a), i n comparison to their less w e l d e d counterparts. In addition, elongate clasts show a particle alignment (perpendicular to flattening), resulting i n a foliation ( F i g . 20b). L o s s o f porosity due to v o l u m e strain is most evident i n the clasts, where collapsed pores have left behind w i s p y structures ( F i g . 20c). These w i s p y structures also have formed parallel to the length o f the flattened clast ( F i g . 20a). W h e r e these w i s p y structures are absent, the collapsed pores may have been completely obliterated b y the w e l d i n g process. W h e r e these structures are not aligned parallel to fabric, the clasts' groundmass has collapsed around a crystal/crystal fragment ( F i g . 20d). O p t i c a l l y , there is very little discernable porosity remaining i n the clasts (<5%) (Fig. 20e), and only slightly more remaining i n the matrix (5-10%). Deformation i n the matrix is less noticeable due to its glassy nature, but can be observed i n areas between larger clasts. In these areas, the matrix has been reduced i n v o l u m e to the extent that clasts i n close p r o x i m i t y are interacting and d e f o r m i n g ( F i g . 20f).  46  F i g u r e 20: W e l d i n g textures observed i n thin section: (a) elongated clast formed due to loss o f porosity ( F O V = 3.9 m m ) . It is important to note that the collapsed vesicles are consistently parallel to the length o f the clast. (b) elongated clasts f o r m i n g a parallel fabric ( F O V = 3.9 m m ) ; (c) close-up o f collapsed vesicles around a small crystal fragment ( F O V =1.0 m m ) ; and, (d) compacted vitrophyric rhyodacite clast s h o w i n g collapsed vesicles (wispy structures) and localized strain i n p r o x i m i t y to crystals ( F O V = 3.9 m m ) ; (e) dense vitrophyric glassy clast l a c k i n g porosity ( F O V = 7.8 m m ) ; and, (f) deformation i n matrix evident between two larger clasts ( F O V = 2.0 m m ) .  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 shardsfromsamples 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 (matrixfromnon-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  T a b l e 4. Sample suite chosen for S E M study o f a variably w e l d e d b l o c k and ash flow deposit, and expectations according to parallel research i n ignimbrites. Sample  Format  W e l d i n g facies *  Expectation i n ignimbrites  KM-04-018  loose grains  KM-04-031  loose grains  non-welded non-welded  no deformation  KM-04-015c  thin section  incipiently w e l d e d  little to no deformation  KM-04-017  r o c k fragment  incipiently welded*  little to no deformation  KM-05-063  thin section  moderately welded  moderate deformation  KM-05-017c  r o c k fragment  densely w e l d e d  extensive deformation  KM-05-012  thin section  densely w e l d e d  extensive deformation  o x i d i z e d sample  49  no deformation  4.2.1 N o n - w e l d e d Facies  S E M analysis o f non-welded samples o f the b l o c k and ash f l o w deposit, allows the study o f primary, non-welded pyroclasts. Samples are o f loose to barely consolidated ash o f the b l o c k and ash f l o w deposit, and they comprise four m a i n types o f shards. M o s t ( 6 0 % ) o f the particles are b l o c k y i n habit; others are bubble-wall ( 2 0 % ) , platy ( 1 0 % ) , and pumiceous ( 1 0 % ) shards ( F i g . 21). The shards show little evidence o f mechanical abrasion during transport as their overall shapes remain sharp, arcuate, curvilinear, or angular. Shard size varies f r o m approximately 5 p m to several hundred u m , w i t h most shards i n the 50 - 500 p m range ( F i g . 19c). The non-welded to incipiently w e l d e d section o f the b l o c k and ash f l o w deposit comprise euhedral crystals o f plagioclase, pyroxene, and amphibole enclosed b y glass selvages. S o m e crystal and glass selvage ensembles are fragmented (Fig. 19d). Finer particles (5 - 50 pm) tend to adhere i n a moss-like manner to the larger glass shards (Fig. 19e). Larger ash particles (500 1500 pm) c o m m o n l y contain multiple vesicles w h i c h are stretched i n the same general orientation ( F i g . 19d). Otherwise, b l o c k y , platy and bubble w a l l shards show vesicles that are dominantly spherical to d i s c o i d i n shape ( F i g . 19f). The more pumiceous shards c o m m o n l y host abundant tubular vesicles (Fig. 2 I d ) .  50  F i g u r e 2 1 : Shard types observed i n the non-welded to incipiently welded b l o c k and ash f l o w deposits at M o u n t Meager: (a) blocky, (b) bubble-wall/cuspate, (c) platy, and (d) pumiceous.  51  4.2.2.  W e l d e d Facies  T h e examination o f the densely w e l d e d b l o c k and ash f l o w deposits at M o u n t M e a g e r under the S E M a l l o w for a contrast w i t h the non-welded deposits. It also a l l o w s for features that are o n l y associated w i t h the w e l d i n g process to be isolated f r o m those brought about b y earlier processes such as fragmentation and transportation.  In general, there are five m a i n types o f glass shards identified i n the ash o f the densely w e l d e d deposits: (a) larger (>50 um) b l o c k y shards ( 5 0 % ) , (b) bubble-wall shards ( 1 0 % ) and (c) platy ( 5 % ) shards ( F i g . 22a-c), as w e l l as smaller shards (<50 um) that are (d) dendritic to moss-like ( 7 5 % ) , or (e) acicular ( 2 5 % ) (Fig. 22d). The shards remain angular, curvilinear, and arcuate i n shape, but tend to be more elongated than the non-welded samples (Fig. 22e). Shard size varies from less than 5 u m to approximately 1500 u m , where the b u l k o f the glass shards are 50 - 500 u m . The densely w e l d e d b l o c k and ash f l o w deposit samples comprise euhedral crystals o f plagioclase, pyroxene, and amphibole enclosed w i t h i n glass selvages. The amount o f glass encompassing the crystals does not appear to be any thicker or thinner than the selvages observed i n the non-welded to incipiently w e l d e d samples. The crystal and glass selvage assemblages, however, are fragmented more frequently than those i n the non-welded samples. Finer particles, especially those less than 50 u m , tend to adhere i n a moss-like fashion to the larger glass shards, and accumulate i n the depressions o f the larger shards ( F i g . 22d). S o m e pitting and irregular surfaces are evident i n larger shards (Fig. 22a, d) and vesicles are less c o m m o n . Some larger ash particles (500 - 1500 um) contain multiple vesicles that are stretched i n the same direction. Otherwise, the b l o c k y , platy and bubble w a l l shards show very f e w  52  vesicles. A p p r o x i m a t e l y 1 0 % o f shards larger than 500 p m contain vapor-phase crystallization o f feldspars w i t h i n their isolated pores (Fig. 22f).  4.2.3.  S E M A n a l y s i s o f Porosity  A t the outcrop or hand sample scale, the b l o c k and ash f l o w deposit shows a v i s i b l e densification o f the material w i t h w e l d i n g intensity. A n a l y s i s o f porosity at the micro-scale w i l l a i d i n determining whether this densification is due to a loss i n porosity or whether shear stresses also contributed to the w e l d i n g process. Twenty S E M images o f three thin sections analyzed w i t h Image J revealed that the non-welded samples have an average o f 2 9 % total porosity (range = 26 - 3 2 % ) ( F i g . 23a). Densely w e l d e d samples have an average o f 1 9 % total porosity (range = 13 2 3 % ) ( F i g . 23c). O n e sample o f moderately w e l d e d b l o c k and ash f l o w 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. B o t h types are observed i n the welded and non-welded deposits, and both are destroyed as w e l d i n g intensity increases. Isolated porosity is identified qualitatively as voids that are completely hosted b y shards or clasts, and where there is a lack o f i n f i l l i n g material. In addition, vapour-phase crystallization occurs w i t h i n some pores, suggesting that these pores were also sealed o f f f r o m the surrounding environement (e.g., isolated). Pores that are f i l l e d w i t h smaller ash or shard particles are c o m m o n , and these are assumed to represent connected pores. U s i n g these parameters, isolated porosity is visible o n l y i n the larger glass shards (> 50 pm). Connected porosity appears i n a l l ash size fractions as both intra- and inter-shard porosity.  53  F i g u r e 22: Attributes o f the densely welded b l o c k and ash f l o w deposit: (a) large, b l o c k y shard s h o w i n g pitting or irregular surface textures, (b) platy shard w i t h bubble-wall remnants, (c) bubble-wall/cuspate shard, (d) dendritic/acicular/moss-like fine ash f i l l i n g depressions i n larger shards, (e) elongated shards, (f) vapour-phase crystallization o f feldspars w i t h i n isolated pores o f large shards.  54  F i g u r e 2 3 : Output images f r o m Image J ™ , where black = porosity and white = shards/crystals. There is a substantial decrease i n average porosity f r o m (a) the unwelded/incipiently w e l d e d sections ( 2 9 % ) to (c) the densely welded sections ( 1 9 % ) . O n average, however, the moderately welded section (b) conserves its h i g h porosity ( 2 8 % ) . A l l scale bars represent 200 u m .  55  CHAPTER FIVE PHYSICAL PROPERTIES Density and porosity are strongly coupled properties o f pyroclastic rocks, and vary strongly w i t h w e l d i n g and compaction (Ragan and Sheridan 1972; Streck and Grunder 1995; Rust and R u s s e l l 2 0 0 0 ; Quane and R u s s e l l , 2005a). A suite o f more than 100 samples was collected from a l l facies o f the b l o c k and ash f l o w deposits. Sample selection was done such that both matrix and clast components o f the deposits are w e l l represented. Density and porosity were measured for a l l samples and are used b e l o w to investigate the w e l d i n g process. Specific methods and procedures for measuring density are summarized i n A p p e n d i x D.  In this study, measurements o f density and porosity involve three separate experiments. B u l k density ( p ) is used here to denote the density o f the rock and a l l o f its pores, i n c l u d i n g both B  connected and isolated pore space. B u l k density o f consolidated samples derives f r o m measurements o f sample mass and geometrical v o l u m e (e.g., w i t h digital calipers) calculated for c y l i n d r i c a l cores. F o r unconsolidated materials, a graduated cylinder was packed w i t h sample to a specified v o l u m e and the mass was recorded ( A p p e n d i x D ) . Skeletal density (ps) is the density o f the r o c k and its isolated (non-penetrated) porosity. Skeletal density o f both c y l i n d r i c a l cores and unconsolidated materials was measured by h e l i u m pycnometry ( K l u g and C a s h m a n , 1994; R u s s e l l and Stasiuk, 1997). Lastly, an aliquot o f each sample was crushed into a powder and the r o c k p o w d e r density ( p ) was measured using He-pycnometry (Rust et a l . , 1999). The r o c k R  powder density represents the density o f the s o l i d material (powdered rock) only. These three  56  values o f density are useful metrics o f w e l d i n g intensity but can also be used to calculate three forms o f porosity (O): total (T), connected (C), and isolated (I):  O  r  = l - — PR  ®c=l-—  Ps  4> =1-^ 7  PR  (2)  (3)  (4)  These calculated values o f porosity can also be validated b y equating total porosity to the s u m o f connected and isolated porosity:  ® *® +®, T  C  The p h y s i c a l properties for a l l samples are summarized i n Tables 5-8. p h y s i c a l property data can be found i n A p p e n d i x E.  57  (5)  Complete tables o f  Table 5. Summary of physical property measurements on bulk samples of unconsolidated block and ash flow deposits, including: bulk density (p ), and isolated porosity (O,). Standard deviations are reportec as lo. skeletal density (p ), rock density (p ), total porosity (O ), connected porosity B  s  R  t  PB (g/cm )  o  Ps (g/cm )  c  PR (g/cm )  a  0> (%)  a  KM-04-018  1  1.47  0.003  2.50  0.003  2.54  0.006  42.1  0.17  KM-04-019'  1.48  0.012  2.52  0.002  2.55  0.002  42.1  1  KM-04-020  1.52  0.014  2.52  0.002  2.53  0.002  2  KM-04-031  1.59  0.025  2.54  0.002  2.55  3  KM-05-023  1.54  0.028  2.52  0.003  KM-05-032  1  1.39  0.028  2.52  KM-05-036  1.43  0.057  2.53  Sample  3  2  3  a  0>, (%)  <T  41.2  0.13  1.65  0.25  0.48  41.3  0.49  1.42  0.12  39.8  0.57  39.5  0.57  0.41  0.10  0.002  37.8  0.98  37.4  0.98  0.68  0.10  2.55  0.003  39.5  1.11  38.7  1.13  1.32  0.14  0.001  2.53  0.004  45.0  1.09  44.8  1.09  0.34  0.15  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  3  T  ®  c  (%)  Table 6. Summary of measured densities listed by welding facies of the block and ash flow deposit. Rock Density (g/cm ) Max Min Avg. a  Facies  N  Bulk Density (g/cm ) Max Min Avg. a  Skeletal Density (g/cm ) Max Min Avg. o  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  3  3  3  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. Bulk Density Skeletal Density Rock Density Total Porosity Isolated Connected Component/Welding N Porosity (%) Porosity (%) (g/cm ) (g/cm ) (g/cm ) (%) Intensity Avg. a Avg. o Avg. a Avg. o Avg. o Avg. o 3  Clasts  Matrix  Mixed  3  3  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  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  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  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  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  AU samples  5.1.  The 'Proto-deposit'  In order to relate variations i n density and porosity to strain accumulated during w e l d i n g , a n estimate o f the b l o c k and ash f l o w deposit properties w h e n it was initially emplaced is required (e.g., prior to sintering and compaction). O u r best estimate o f this state derives f r o m measurements o n samples o f the unconsolidated facies o f the b l o c k and ash f l o w deposits (Table 5). A total o f seven b u l k samples f r o m non-welded to incipiently welded facies were collected ( F i g . 4d). V a l u e s o f b u l k densities (graduated cylinder technique) for the matrix vary b y 1 5 % between 1.39 - 1.59 ± 0.057 g/cm . Skeletal density, based on h e l i u m pycnometry, show less 3  variation ( 1 . 5 % ) , and range f r o m 2.50 - 2.54 ± 0.003 g/cm . L a s t l y , the densities o f powdered 3  samples measured b y h e l i u m pycnometry vary b y less than 1 % and return values between 2.53 2.55 ± 0.006 g/cm . F r o m these three values o f density, porosity can be inferred. The resulting 3  values o f total porosity for the non-welded/unconsolidated matrix range f r o m 3 8 - 4 5 ± 2 . 2 6 % , where 37 - 45 ± 2 . 2 7 % is connected, and 0.3 - 1.7 ± 0 . 2 5 % is isolated. The average values o f O = 41.4%, O t  = c  4 0 . 9 % , and O i = 0. 8 5 % are used as a baseline for subsequent calculations and  analysis o n matrix samples o f b l o c k and ash f l o w deposit.  L a r g e clasts sampled f r o m the unconsolidated and incipiently w e l d e d facies were also sampled to estimate o r i g i n a l conditions o f the b l o c k and ash f l o w deposit. B u l k density values (geometric v o l u m e technique) for clasts vary 2 6 % , ranging from 1.50 - 1.89 ± 0.020 g/cm . 3  Skeletal  density based o n h e l i u m pycnometry shows less variation ( 1 3 % ) , and ranges f r o m 2.24 - 2.52 ± 0.007 g/cm . L a s t l y , the densities o f powdered samples measured b y h e l i u m pycnometry vary b y 3  5 % and return values o f 2.46 - 2.59 ± 0.009 g/cm . F r o m these three values o f density, porosity 3  62  can be inferred. The values o f total porosity for these non-welded/unconsolidated clasts range f r o m 24 - 40 ± 4 . 7 5 % , where 1 9 - 3 4 ± 3 . 8 3 % is connected, and 0 - 12 ± 3 . 4 8 % is isolated. The average values o f O  t  = 32.4%, O  c  = 2 8 . 9 % , and O i = 5 . 2 6 % are used as a baseline for  subsequent calculations and analysis o f clasts belonging to the b l o c k and ash f l o w deposit at M o u n t Meager.  5.2.  Bulk D e n s i t y  B u l k densities were calculated for all 106 samples, representing the f u l l w e l d i n g spectrum o f the deposit. T h e y were calculated i n order to determine the overall sample density ( i n c l u d i n g a l l its porosity), and h o w it varies throughout the w e l d i n g facies (Table 6), as w e l l as h o w it varies between components o f the b l o c k and ash f l o w deposit (Fig. 24a; Table 8). B u l k density values, i n combination w i t h other density measurements, are also used i n obtaining total porosity values (Tables 7, 8).  63  Volume - skeletal (cm )  c)  120 range- p - - - range - p o matrix • clasts x mixed range- p B  100 8 0  TO I  s  R  60  S 40 20  10  20  30  40  50  Volume - rock (cm )  F i g u r e 2 4 : Mass-volume plots for a l l samples showing total ranges of: (a) b u l k density ( p ) , (b) skeletal density ( p ) , and (c) rock density (p ) for clasts (solid circle), matrix (open circles), and m i x e d samples (x's). In each case, the m i n i m u m and m a x i m u m densities are represented b y s o l i d lines. G r e y shaded regions i n (b) and (c) represent the range i n b u l k density shown i n (a). Dashed line i n (c) represents the variation i n skeletal density. In (a), clasts show a w i d e range o f b u l k densities, but they are generally lower than the matrix. The matrix shows a tighter but higher overall range i n b u l k density. In (b), the same pattern is observed, except ranges o f skeletal density are m u c h smaller than the ranges i n b u l k density. T h e range o f rock powder densities seen i n (c) is extremely narrow, and is independent o f componentry. B  s  R  64  5.2.1. N o n - w e l d e d vs. W e l d e d  Distinct variations i n b u l k density exist between non-welded and w e l d e d facies o f the b l o c k and ash f l o w deposit. A n average o f fifteen basal non-welded samples resulted i n a b u l k density o f I. 64 ± 0.126 g/cm . Sixteen upper non-welded samples averaged a b u l k density o f 1.70 ± 0.122 3  g/cm . The incipiently w e l d e d facies shows a slight increase i n b u l k density, but are more 3  variable, averaging 1.83 ± 0.275 g/cm for twelve samples. S i x samples o f a moderately w e l d e d 3  b l o c k o f material revealed a significantly higher average b u l k density o f 2.08 ± 0.041 g/cm , 3  whereas the densely w e l d e d samples ( N = 57) had the highest average w i t h 2.19 ± 0.113 g/cm . 3  T o t a l porosity is inversely related to b u l k density. The basal non-welded section contains an average total porosity o f 33.9 ± 5 . 6 4 % , whereas the upper, non-welded section averages o n l y slightly less at 32.7 ± 4 . 8 8 % . The incipiently welded facies maintains a total porosity o f 27.4 ± II. 9 6 % . M o d e r a t e l y w e l d e d samples show a m u c h lower total porosity o f 17.6 ± 1.59%, and the densely w e l d e d samples have the lowest porosity at 13.5 ± 5 . 4 1 % .  5.2.2. Clasts vs. M a t r i x  A s w i t h the trends seen i n the different facies o f the b l o c k and ash f l o w deposit, the b u l k density trends between clasts and matrix are the most distinctive. B o t h clasts and matrix show an increase i n b u l k density as w e l d i n g intensifies. A v e r a g e clast density progresses from 1.68 ± 0.120 g/cm (non-welded) to 2.01 ± 0.059 g/cm i n the incipiently w e l d e d facies, and f i n a l l y to 3  3  2.34 ± 0.035 g/cm for the welded facies. The matrix begins w i t h a b u l k density o f 1.52 ± 0.081 3  g/cm , averages 1.46 ± 0.054 g/cm where incipiently welded, and ends w i t h a w e l d e d b u l k 3  3  65  density o f 2.13 ± 0.082 g/cm . M i x e d samples reveal an intermediate w e l d e d density o f 2.26 ± 3  0.078 g/cm . T o t a l porosity again mirrors b u l k density w i t h an inverse relationship. N o n 3  w e l d e d clasts start w i t h an average total porosity o f 32.4 ± 4 . 7 5 % , decreasing to 18.9 ± 2 . 2 5 % where incipiently welded, and f i n a l l y decrease to 5.35 ± 1.070% where they have become densely welded. The matrix contains 40.3 ± 2 . 9 6 % total porosity w h e n non-welded, and remains similar at 42.2 ± 2 . 1 6 % where incipiently w e l d e d , but decreasing to 16.6 ± 2 . 9 5 % i n the densely w e l d e d facies. M i x e d samples show an intermediate average total porosity o f 9.63 ± 3 . 3 2 9 % where welded.  5.3.  Skeletal Density  Skeletal density has been measured b y h e l i u m pycnometry o n a l l 106 samples i n order to determine the amount o f connected porosity i n the samples, and h o w it varies throughout the deposit and its components (Tables 5, 7). O v e r a l l , values o f skeletal density are m u c h higher than the values obtained for b u l k density (Fig. 24b).  5.3.1 N o n - w e l d e d vs. W e l d e d  M u c h less variation i n skeletal density is observed w h e n comparing non-welded and w e l d e d facies o f the b l o c k and ash f l o w deposit. B a s a l non-welded samples resulted i n a skeletal density o f 2.31 ± 0.069 g/cm , and averaged 28.9 ± 5 . 3 0 % connected porosity. The upper non-welded 3  samples had an average skeletal density o f 2.46 ± 0.061 g/cm w i t h a connected porosity o f 31.0 3  ± 4 . 7 6 % . The incipiently w e l d e d facies shows a similar average skeletal density o f 2.44 ± 0.062 66  g/cm , but has a corresponding connected porosity o f 25.4 ± 1 3 . 0 7 % . The large variation i n this 3  section is largely due to the presence o f dense clasts, w h i c h represent only a small proportion o f this facies. The basal section is therefore distinct f r o m the upper non-welded to incipiently w e l d e d sections i n terms o f skeletal density, but not i n terms o f connected porosity. The moderately w e l d e d and densely welded samples show near identical values o f 2.52 ± 0.030 g/cm and 2.51 ± 0.040 g/cm , respectively. Connected porosity values are similar, w i t h an 3  3  average o f 17.2 ± 2 . 1 6 % for the moderately w e l d e d samples, and 13.1 ± 5 . 5 1 % for the densely w e l d e d samples. Therefore, the upper non-welded facies o f b l o c k and ash f l o w deposit has the most connected porosity, and, as expected, the densely w e l d e d intermediate facies retains the least amount o f connected porosity. In addition, there is a general increase i n skeletal density and decrease i n connected porosity as w e l d i n g progresses.  5.3.2..Clasts vs. M a t r i x  B o t h the clast and matrix components show very little variation i n skeletal density despite their transition f r o m the non-welded to the densely welded state. Clasts show a small increase i n skeletal density as w e l d i n g intensifies, but this increase is small relative to analytical uncertainty. Clasts, o n average, have a starting skeletal density o f 2.37 ± 0.091 g/cm i n the non-welded 3  facies, w h i c h increases slightly to 2.41 ± 0.041 g/cm i n the incipiently w e l d e d section, and 3  f i n a l l y to a skeletal density o f 2.46 ± 0.022 g/cm where welded. M a t r i x samples show minute 3  variations that are also w i t h i n measurement error. The non-welded matrix has an average skeletal density o f 2.53 ± 0.011 g/cm , averages 2.51 ± 0.012 g/cm w h e n incipiently w e l d e d , and 3  3  ends w i t h a w e l d e d skeletal density o f 2.52 ± 0.082 g/cm . M i x e d samples reveal an 3  67  intermediate skeletal density o f 2.49 ± 0.046 g/cm w h e n welded. Connected porosity shows a 3  more significant change as the components become welded. Non-welded clasts start w i t h an average connected porosity o f 29.0 ± 3 . 8 3 % , decreasing to 16.0 ± 1 . 5 8 % w h e n incipiently w e l d e d , and are reduced to 4.79 ± 0 . 9 9 2 % once the clasts have undergone w e l d i n g . The matrix contains 39.9 ± 3 . 2 2 % connected porosity w h e n non-welded, stays fairly constant at 41.7 ± 2 . 2 5 % w h e n incipiently welded, and finishes o f f at 16.3 ± 3 . 0 3 % w h e n welded. M i x e d samples show an intermediate average connected porosity o f 9.10 ± 3 . 5 1 9 % w h e n welded. N o t e that values o f total porosity and connected porosity for the matrix samples are very similar.  5.4.  R o c k Powder Density  R o c k powder density is the final step i n characterizing the p h y s i c a l properties o f the M o u n t M e a g e r b l o c k and ash f l o w deposit, and is important i n c o n f i r m i n g the presence o f isolated porosity. O v e r a l l observations reveal there is a further reduction i n range for r o c k powder density, as we are measuring the rock only (i.e., accounting for a l l pore space) ( F i g . 24c). T h i s s h o u l d remain constant throughout a deposit unless there is a geochemical or crystal content change during its eruption f r o m the source.  5.4.1. N o n - w e l d e d vs. W e l d e d  V a l u e s o f rock powder density for a l l facies show very little variation, and o n average, range f r o m 2.49 ± 0.040 g/cm to 2.53 ± 0.040 g/cm i n the basal non-welded and moderately w e l d e d 3  3  facies, respectively. The powder pycnometry does, however, c o n f i r m the presence o f isolated 68  porosity. The basal non-welded facies contains the highest average isolated porosity, w i t h 7.02 ± 2 . 6 1 0 % . The upper non-welded facies possesses 2.38 ± 1 . 9 5 3 % isolated porosity, whereas the incipiently w e l d e d facies possess 2.54 ± 1 . 8 2 1 % . The w e l d e d facies contain little to no isolated porosity, w i t h values o f 0.53 ± 1 . 2 3 1 % and 0.37 ± 1.268% for the moderately and densely samples, respectively. Therefore, there is a general decrease i n isolated porosity w i t h increasing w e l d i n g intensity.  5.4.2. Clasts vs. M a t r i x  Clasts and matrix are nearly indistinguishable f r o m each other o n the basis o f the results o f powder pycnometry. Clasts, o n average, range f r o m 2.48 ± 0.026 g/cm to 2.50 ± 0.029 g/cm 3  3  regardless o f their w e l d i n g intensity. M a t r i x samples show minute variations w i t h i n analytical uncertainty, but are slightly denser than the clasts. The matrix has an overall average r o c k p o w d e r density o f 2.54 ± 0.025 g/cm to 2.55 ± 0.010 g/cm . M i x e d samples contain a similar 3  3  r o c k powder density o f 2.50 ± 0.028 g/cm . Isolated porosity shows a slightly more evident 3  trend. N o n - w e l d e d clasts start w i t h an average isolated porosity o f 4.90 ± 3 . 1 3 3 % , decreasing slightly to 3.45 ± 1 . 6 2 3 % w h e n incipiently welded, and end up w i t h 0.98 ± 1 . 0 7 1 % isolated porosity (essentially none) once the clasts have been densely welded. The matrix and m i x e d samples a l l demonstrate average isolated porosities o f less than 1 % .  69  CHAPTER SIX DISCUSSION The a i m o f this study is to document the w e l d i n g trajectory o f the K e y h o l e Falls M e m b e r and recover the conditions and mechanism(s) under w h i c h this unique deposit formed. In previous chapters, I have described a w e l d e d b l o c k and ash f l o w deposit and presented data collected from f i e l d m a p p i n g , petrography, image analysis, S E M analysis and p h y s i c a l property measurements. In this chapter, those data sets and observations are used to: (a) document the w e l d i n g process at M o u n t M e a g e r , (b) discern the mechanism(s) i n v o l v e d , and (c) calculate the amount o f strain accommodated b y the deposit. T h i s chapter w i l l also compare the w e l d i n g process as evidenced i n the K e y h o l e Falls M e m b e r against w e l d i n g features c o m m o n l y found i n ignimbrites.  6.1 Analysis of Porosity W e l d i n g intensity is evaluated relative to the o r i g i n a l properties i n the non-welded b l o c k a n d ash f l o w deposit. These properties are represented b y p h y s i c a l property measurements o n the unconsolidated facies o f the K e y h o l e Falls M e m b e r . Non-welded clasts reveal an i n i t i a l b u l k density o f 1.50 - 1.89 ± 0.020 g/cm ; given a rock powder density o f 2.50 ± 0.029 g/cm , this 3  3  corresponds to a total porosity o f 24 - 40 ± 4 . 7 5 % . Non-welded matrix shows an initial b u l k density o f 1.39 - 1.59 ± 0.057 g/cm ; g i v e n a r o c k powder density o f 2.55 ± 0.010 g/cm , this 3  3  corresponds to a porosity range o f 38 - 45 ± 2 . 2 6 % .  70  Porosity can be further broken d o w n into two categories: isolated and connected. The presence o f isolated porosity is first demonstrated i n Figure 25a, i n w h i c h connected porosity is plotted against b u l k density. The y-intercepts i n this plot represent the range i n skeletal density (2.24 2.57 g/cm ) i f there is no isolated porosity. The m a x i m u m y-intercept corresponds to a 3  reasonable value; however, the m i n i m u m y-intercept is m u c h lower than the density o f the rock (2.49 - 2.53 g/cm ). It can therefore be inferred that isolated porosity is the cause o f the lower 3  density samples. R o c k powder pycnometry confirms this hypothesis, as illustrated i n Figure 25b, i n w h i c h r o c k powder density is plotted against skeletal density for a l l samples. Samples plotting b e l o w the 1:1 line, and outside the 9 5 % confidence limits represent samples w i t h apparent isolated porosity. It is further reinforced b y a plot o f total porosity vs. connected porosity ( F i g . 25c), whereby several samples demonstrate total porosities greater than their connected porosities.  In terms o f b l o c k and ash f l o w componentry, m i n i m a l isolated porosity exists i n the matrix ( < 1 . 6 5 % ) , regardless o f w e l d i n g intensity; most is connected (Fig. 25d). O v e r a l l , the matrix experiences a - 2 4 % reduction i n porosity, f r o m the non-welded to the densely w e l d e d facies o f the b l o c k and ash f l o w deposit. The i m p l i c a t i o n is that as the deposit undergoes c o m p a c t i o n during w e l d i n g , the o r i g i n a l interstitial gas contained w i t h i n matrix porosity was a l l o w e d to escape out o f the deposit and, thus, the matrix o f the deposit maintained connected pathways (e.g., permeability) until the very end o f w e l d i n g .  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). O n average, both types o f porosity are drastically reduced during the w e l d i n g process: connected porosity is reduced to 5 % and isolated  71  porosity is reduced to 1 % i n the dense, vitrophyric clasts. T h i s is unforeseen, as it was expected that compaction and w e l d i n g w o u l d cut o f f existing connected porosity pathways and create isolated porosity, and the same effect w o u l d be observed i n the matrix. Thus, there must be additional processes acting u p o n these deposits causing isolated pores to collapse. F o r isolated porosity to collapse, however, is slightly more complicated because there are no existing gas escape pathways. A s compaction and w e l d i n g proceed, isolated pores c o u l d become connected b y cracks f o r m i n g w i t h i n the deposit that are created mechanically during compaction. A l t e r n a t i v e l y , they c o u l d be infinitely flattened, due to pure shear strain. A n o t h e r p o s s i b i l i t y is that the volatiles may be resorbed back into the glass rather than escaping f r o m the compacting b l o c k and ash f l o w deposit (Sparks et al., 1999). T h i s occurs w h e n the isolated pore pressures remain h i g h despite the deposit as a w h o l e having degassed subsequent to eruption. T h i s w o u l d create a pressure gradient, possibly a l l o w i n g the gas to dissolve back into the v i s c o u s l y d e f o r m i n g deposit, and the empty pores to collapse.  72  F i g u r e 2 5 : Plots o f p h y s i c a l properties i n c l u d i n g : (a) connected porosity (<J> ) vs. bulk density (p ); y-intercepts define B  C  m i n i m u m and m a x i m u m values o f density where there is no isolated porosity (O,); (b) R o c k powder density (p ) plotted vs. R  skeletal density (p ). Samples w i t h no isolated porosity plot on the 1:1 line (solid line); samples with isolated porosity plot s  b e l o w the line ( p > p ). 9 5 % confidence limits on 1:1 line are also shown as dashed lines; (c) Total porosity (O ) R  s  connected porosity (O ). C  T  vs.  Samples l y i n g b e l o w the 1:1 line (solid line) have isolated porosity represented b y the vertical or  horizontal distance to the 1:1 line; (d) Isolated porosity (O,) vs. total porosity ( 0 ) , showing that the isolated porosity content T  is positively correlated to total porosity.  6.2 W e l d i n g M e c h a n i s m s  P h y s i c a l property measurements demonstrate that porosity decreases w i t h increasing w e l d i n g intensity. T h i s decrease i n porosity can be used to compute strain. The strain estimate is the total strain i f a l l strain is v o l u m e strain (e.g., no shear strain) or is a m i n i m u m estimate o f total strain i f there is appreciable shear strain (e.g., constant v o l u m e strain). Quane and R u s s e l l (2006) use the original and final values o f porosity to define total strain as:  <D -<D,  —  o  (6)  where it is assumed that (a) all strain is accommodated b y 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 h o w porosity is affected b y an increasing w e l d i n g intensity, and can reveal h o w i n d i v i d u a l components accommodate strain. The resulting graph reveals two k e y aspects o f the w e l d i n g process occurring at M o u n t M e a g e r ( F i g . 26). First, clasts and matrix show parallel pathways w i t h increasing strain (e.g., w e l d i n g intensity). It therefore appears as though both components are simultaneously losing porosity at the same rate. T h i s is contrary to observations o f Sheridan and R a g a n (1972) w h o state that pumiceous clasts i n ignimbrites d e f o r m more rapidly than the surrounding matrix due their l o w relative viscosities and h i g h initial porosities. Ross and S m i t h (1961) also observed that glass viscosity is very sensitive to volatile content and that pumice clasts i n ignimbrite appear to retain a higher proportion o f volatiles than the particulate ash.  74  0.5  a) 0.4  0.3  0>T O Matrix • Clasts 0.1  0.2  0.3  0.4  0.5  0.5  b)  ' o 0.4  • •• 0.1  So  H  ]  0.1  0.2  0.3  0.4  0  0.5  c)  0.4  0.3 H  0,  0.2 H  0.1  -T  At.  <  -0.1  0.1  0.2  0.3  0.4  0.5  F i g u r e 2 6 : Values o f calculated total strain (£ = 0 - 0 / l - O ) are plotted vs. (a) observed total porosity (0 ), (b) observed connected porosity (0 ), and (c) observed isolated porosity (O,) for clasts (closed circles) and matrix (open circles). Values o f £ are calculated assuming: (i) a l l strain is due to v o l u m e loss, and (ii) clasts and matrix each had a single starting porosity ( 4 0 % and 4 5 % , respectively). T  T  0  f  C  T  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: U n c o m m o n textures indicating m i n i m a l effects o f shear strain: (a) glassy pull-apart clast; (b) extreme flattening o f glassy clasts near a lithic Plinth clast (P).  77  6.3 Original Thickness and Average Strain Calculations  The strain calculations depicted i n Figure 26 can also be used to determine the deposit thickness prior to w e l d i n g , as w e l l as the average strain over the entire deposit. A c c o r d i n g to Stewart (2002), there is roughly 20 m o f a l l u v i a l deposits, and 20 m o f r o c k avalanche deposits o v e r l y i n g the w e l d e d b l o c k and ash f l o w deposits (Fig. 2a). O v e r l y i n g these non-volcanic deposits is a further 60 m o f non-welded to incipiently welded b l o c k and ash f l o w deposits. Because the deposits are not stratigraphically comformable, o n l y the lower section w i l l be used i n this calculation. The lower section is currently a total o f 112 m at K e y h o l e Falls, w h i c h can be broken d o w n into thicknesses o f the three i n d i v i d u a l w e l d i n g facies distinguished i n 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 w e l d e d facies. V a l u e s o f strain calculated using equation 6 are then averaged over the three w e l d i n g facies to produce a strain profile ( F i g 28). The facies thicknesses and average strain values are then c o m b i n e d to give an estimate o f the original deposit thickness using the formulae b e l o w (Quane and R u s s e l l , 2005a).  78  avalanche deposits  840 -820  non-welded & incipiently welded block and ash avalanche deposits  6:0  CP :  avalanche deposits alluvial deposits  700 4  variably welded block and ash avalanche deposits  112 m 600  incipiently welded block and ash flow deposits  h =12 m £,=18.5  densely welded block and ash flow deposits  h =90 m £,=34.7  non-welded block and ash flow deposits  h =10 m £ =9.8%  average total strain = 30.8%  600 A  3  F i g u r e 28: Strain profile o f the lower welded b l o c k and ash f l o w deposits at M o u n t Meager, southwestern B r i t i s h C o l u m b i a , based on the stratigraphy o f Stewart (2002). O n l y the lower section was used for the calculations due to the avalanche and a l l u v i a l deposits separating the upper and lower b l o c k and ash f l o w deposits. A total o f 112 m o f block and ash f l o w deposits exists i n the lower section, consisting of: i) 12 m o f incipiently welded deposits with an average strain o f 1 9 % ; ii) 90 m o f densely welded deposits w i t h an average total strain o f 3 5 % ; and, iii) 10 m o f basal, non-welded block and ash f l o w deposits bearing an average total strain o f 1 0 % . U s i n g the procedure f o l l o w e d in Quane and R u s s e l l (2005a), these values correspond to an overall average total strain o f 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 ) accommodated by T  the deposit as a whole:  £ =E£, r  (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  °~\-E  {Q\ ( 9 )  T  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 (<D ), connected T  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 0.8  0.2  0.3  0.4  0.5  0.6  0.7  0.8  b)  0.7 0.6 0.5  4>  r  0.4 0.3 0.2 0.1 0  • Pumice  • Jr V 0.1,  x Breadcrust bombs  0.2,  0.3,  0.4 ,  0.5r-  0.6  0.7  0.8  0.8  c)  0.7  cp C  +  0.4 0.3  A Lava  0.2  V*  0.1  0  0.1  + Lava blocks from pyroclastic flows - Scoria  0.2  0.3  0.4  0.5  0.6  0.7  0.8  Figure 29: Plots of total porosity (0 ) vs. connected porosity (<3>) 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. T  c  82  Samples f r o m the matrix f r o m the M o u n t M e a g e r b l o c k and ash f l o w deposits contain negligible isolated porosity (Fig. 29a). In contrast, the blocks w i t h i n the deposit contain up to 1 2 % isolated porosity. The m a x i m u m value o f isolated porosity is found i n the non-welded to incipiently welded facies, i n w h i c h clasts contain 20 - 4 0 % total porosity. H o w e v e r , as w e l d i n g proceeds, that isolated porosity is destroyed along w i t h most o f the connected porosity. P u m i c e f r o m M o u n t Meager, Lascar V o l c a n o , and Soufriere H i l l s develop a m a x i m u m o f 1 1 % isolated porosity, but possess 52 - 7 5 % total porosity (Fig. 29b). Breadcrust bombs f r o m G u a g u a P i c h i n c h a have total porosities o f 32 - 7 1 % , and develop up to 1 2 % isolated porosity w h e n total porosity values are a m i n i m u m o f 4 0 % (Fig. 29b). Thus, the b l o c k and ash f l o w deposits at M o u n t M e a g e r develop an isolated porosity at lower total porosities than typical pumices or breadcrust bombs.  W i t h the exception o f one location ( M o u n t St. Helens), lava f l o w deposits, lava b l o c k s f r o m dome-collapse pyroclastic f l o w deposits and scoria deposits show no development o f isolated porosity. Despite their broad range i n total porosities (2 - 5 9 % ) , only deposits f r o m a disrupted cryptodome blast deposit at M o u n t St. Helens show any departure f r o m the 1:1 line (up to 5 % isolated porosity, w i t h total porosities - 5 0 % ) (Fig. 29c). Thus, b l o c k and ash f l o w deposits at M o u n t M e a g e r develop isolated porosities w h e n lava f l o w deposits and dome-collapse pyroclastic f l o w deposits o f similar densities fail to do so.  These trends i n porosity can be explained b y bubble nucleation events occurring prior to eruption. A l l pumice samples f r o m fountain-collapse pyroclastic f l o w s possess an isolated porosity, as do the non-welded to incipiently welded clasts f r o m the b l o c k and ash f l o w deposits at M o u n t Meager. B l o c k s from dome-collapse pyroclastic f l o w s o n l y 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 domecollapse 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 resultfromthe 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 84  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 E x c e l l e n t outcrops and exposures at M o u n t M e a g e r provide an opportunity to study a unique, w e l d e d b l o c k and ash pyroclastic f l o w deposit. Texture m a p p i n g and image analysis at two scales were completed as independent and objective means o f quantifying the change i n fabric and flattening o f particles i n the K e y h o l e F a l l s M e m b e r . Results indicate the f o l l o w i n g :  •  Image analysis o f F T M s demonstrate a w e l d i n g trajectory whereby average oblateness increases and average orientation decreases w i t h increasing w e l d i n g intensity.  •  T h i s w e l d i n g trajectory is more subtle than expected due to an o r i g i n a l clast oblateness o f approximately 3 0 % ; this results i n an estimated m a x i m u m v o l u m e strain o f 1 2 % i n the deposit or a m a x i m u m o f 8 % pure shear strain.  •  Conversely, S T M s show heterogeneity or strain localization i n terms o f average orientation and oblateness.  •  A n e m p i r i c a l experiment w i t h image analysis reveals average oblateness does not reflect total v o l u m e strain for these deposits due to the original clast oblateness; however, the most w e l d e d F T M s visually correspond to experimental results h a v i n g undergone a total v o l u m e strain o f 30 - 4 0 % .  •  Distributions o f oblateness and orientation for each F T M are more accurate i n indicating w e l d i n g 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 w i t h the w e l d i n g o f the b l o c k and ash deposit. In addition, deposit components and porosity were examined to document the changes f r o m non-welded to welded facies.  •  W e l d i n g textures observed i n thin section include: (a) v i s i b l y flattened clasts, (b) collapsed vesicles, (c) deformation around clasts/crystals, and (d) parallel alignment o f clasts, clast length, and collapsed vesicles.  •  Shards observed i n the b l o c k and ash f l o w deposit are (in decreasing order f r o m most abundant): (a) b l o c k y , (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 w e l l to values obtained i n physical property measurements.  P h y s i c a l property measurements were used to elucidate the progression from non-welded to welded facies o f the b l o c k and ash f l o w deposit. U s i n g values o f density and porosity, several inferences can be made regarding the w e l d i n g process i n v o l v i n g the 2360 B.P. eruption o f the K e y h o l e Falls M e m b e r :  •  Non-welded clasts reveal an original b u l k 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 o r i g i n a l b u l k density o f 1.39 - 1.59 ± 0.057 g/cm , w i t h a corresponding porosity o f 38 - 45 ± 3  2.26%. •  B o t h clasts and matrix record strain equally, unlike i n ignimbrites whereby clasts accommodate more strain than the surrounding matrix.  •  The m a x i m u m total (volume) strain accommodated by the deposit is approximately 3 8 % .  87  Isolated porosity exists i n highly-porous, non-welded clasts o n l y , and is reduced along w i t h connected porosity during the w e l d i n g process; possible vehicles for this are volatile resorption or connection o f isolated porosity during compaction. V o l u m e strain i n the viscous regime is the dominant strain mechanism, reducing the o r i g i n a l thickness o f the K e y h o l e Falls M e m b e r b y 50 m (from 162 - 112 m ) ; this corresponds to an average o f 3 1 % v o l u m e strain over the entire deposit. Pure shear strain (constant volume) i n the viscous regime is a m i n i m a l component, only occurring l o c a l l y as pull-apart clasts or shearing i n p r o x i m i t y to lithic clasts. C o m p a r i s o n o f porosity data f r o m other volcanic deposits demonstrates that the b l o c k and ash f l o w was most l i k e l y generated by an explosive dome collapse triggered b y a V u l c a n i a n event, as evidenced b y the presence o f isolated porosity i n clasts, and the presence o f breadcrust bombs o f the b l o c k and ash f l o w deposit at M o u n t Meager.  88  REFERENCES A b d u r a c h m a n , E.K., Bourdier, J.-L., V o i g h t , B., 2000. 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B u l l e t i n o f V o l c a n o l o g y 69(3), 281-300.  98  APPENDIX A DETAILED DESCRIPTIONS OF FIELD TEXTURE MAPS  99  F I E L D 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% o f 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 l o c k #3, 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%) 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 MAP # 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, 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%) • 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  F I E L D 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  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 o  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 i e l d Site 1) Clast types: o Black: • Glassy • Dense • Variably welded showing different shades o f 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 • U p 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  F I E L D 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:  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  Plinth: • 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?) o  108  Poorly sorted Slightfining-upwardtrend see at the outcrop scale  109  F I E L D 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 N E 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 • U p to 6 cm in diameter o Dark grey: • Welded • Porphyritic, with (avg. 2 mm) phenos of plag/hbl/pyx (10-20%) • Subangular • 4 2 % o f clasts • U p 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 • U p 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 • U p 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  110  F I E L D 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 o f 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?  Ill  F I E L D 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 N o breadcrusting observed Apparent thickness of indurated section: 2 m with a -10 m talus slope  112  F I E L D 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 o f hbl/pyx visible (~5-15%) • 15-20% of clasts " • N o 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  F I E L D 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  F I E L D T E X T U R E M A P #13 (Basal, non-welded block and ash flow deposit, Field Site 1 (3 m N E 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 • N o flow banding observed • Up to 50 cm in diameter, but mostly 10-15 cm o N o 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 f o l l o w i n g sequences o f photos document the process o f recovering data f r o m the f i e l d to obtaining results f r o m image analysis (e.g. f r o m S c i o n Image™, Image J™). T h e F T M s represent the f u l l spectrum o f w e l d i n g intensity observed i n the K e y h o l e Falls M e m b e r . The process for each F T M is as f o l l o w s : (a) a field photo is taken o f the mapped area overlain b y the 1 m  2  grid,  where " T " represents the top o f the f i e l d texture map; (b) clasts greater than 0.5 c m are handdrawn w i t h the aid o f the g r i d and graph paper; (c) the original F T M is retraced and scanned into a digital image; (d) the image i n (c) is run through image analysis software and the output image is created based o n clast recognition w i t h i n the 1 m area. 2  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 i g u r e B6: F T M 06 - Densely welded facies  123  F i g u r e B7: F T M 07 - B a s a l non-welded facies  124  125  126  1  A-  .  -  ' -  -Ji -  >—• •  P,.  b)  c)  d)  Figure BIO: F T M 10 - Incipiently welded facies  127  •  *  *  *  f  •«  -  *  •- •  Figure B l l :  FTM  11 - U p p e r non-welded facies  128  129  F i g u r e B13: F T M 13 - B a s a l non-welded facies  130  APPENDIX  C  IMAGE ANALYSIS METHODS:  131  STMs  The f o l l o w i n g 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 r o m S c i o n Image™, Image J™). A l l S T M s were created f r o m slabs o f densely w e l d e d material due to its' competence. The process for each S T M is as f o l l o w s : (a) a photo is taken o f the p o l i s h e d slab; (b) clasts greater than 0.5 m m are hand-drawn w i t h the aid o f an acetate and permanent marker; (c) the o r i g i n a l F T M is retraced and scanned into a digital image; (d) the image obtained i n (c) is run through image analysis software where the output image is created based o n clast recognition.  132  133  134  135  136  SSSEB&  ktw-CT-B'ii  It-d-fl)  t$IMM«o  c)  d)  Figure C 5 : S T M 05 - Densely w e l d e d 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 s o l i d r o c k samples are cut into cores using a d r i l l press and a 30 m m diameter 2. ) 3. ) 4. ) 5. )  c y l i n d r i c a l d r i l l bit. The ends o f the cored samples are cut w i t h a rock saw and ground d o w n u s i n g a lap and 240 AI2O3 grit to make a cylinder. Individual cores are placed i n a sonic bath for 5-10 minutes to remove any residual grit or r o c k fragments. C o r e d samples (mass = 26-101 g) are dried i n an oven at 120°C for a m i n i m u m o f 12 hours and cooled to r o o m temperature. R e s i d u a l materials ( m i n i m u m 10 g) from each cored sample are powdered i n a tungsten carbide r i n g m i l l for 20-60 seconds.  Bulk Density - Consolidated Samples  ;  .  1. ) D i g i t a l calipers are used to obtain average values o f core height and diameter based on at least six measurements o f each. 2. ) U s i n g the c y l i n d r i c a l shape o f the core, the b u l k density is calculated u s i n g the geometrical equation for the v o l u m e o f a cylinder:  V  b u  ik  = rcr h.  3. ) T h i s value o f v o l u m e is then used to calculate b u l k density:  2  p ik b u  =  m  s a m p  /  Vbuik-  Quality Control Issues Accuracy: D i g i t a l calipers were used, w h i c h are accurate to 0.01 m m ; ends were  flattened to A h < 0.5 m m . The balance used is accurate to w i t h i n 0.001 (<40 g) o r 0.01 (>40g). Precision: Measurements used are averages o f at least six measurements o f height and diameter. Results are precise w i t h i n ± 4 % .  Bulk Density - Unconsolidated Samples 1. ) The mass o f a 500 m L graduated cylinder is determined. 2. ) The graduated is f i l l e d carefully w i t h a precise volume o f the unconsolidated material (250-500 m L ) . 3. ) The sample and graduated cylinder (tempered glass) are placed i n an oven at 120°C for a m i n i m u m o f 12 hours, and then c o o l e d to r o o m temperature. 4. ) The mass o f the graduated cylinder and sample are determined ( F i g . D l ) 5. ) The mass and volume are then used to calculate b u l k density: pbuik m p / V s a m p =  sam  Quality Control Issues Accuracy: The graduated cylinder 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 w i t h i n ± 4 % .  150  Skeletal Density 1. ) Skeletal density is determined using the cored sample and an automated h e l i u m pycnometer (Fig. D 2 i , D 3 ) . The largest a l u m i n u m cell insert is placed inside the sample and reference cells to m a x i m i z e the sample to v o i d ratio. Smaller cores require an additional filler (Fig. D 2 i i ) to achieve this result. 2. ) E a c h o f the four sample cells and the reference c e l l o f the pycnometer are calibrated against steel spheres o f a k n o w n volume (Fig. D 2 i i i ) . The sample c e l l and reference c e l l volumes are thus determined b y the f o l l o w i n g equations: V  cell  CE  ( F ^ v J C ^ l -jP2 )  =  "  ( P I -P2 )-(P2  w  h  e  r  e  y  = 2 2 . 1 8 8 0 c m (with filler) or 3  q w  /P2)(Pl-P2)  • 31.0082 c m (without 3  V  ' ref  =V  filler)  (P\-P?  ' cell  The resulting values o f V i i and V f are calibration factors for each cell. These values are unique to each c e l l and depend on temperature. T h e y represent an average o f five consecutive measurements. 3.) The core is placed i n the pycnometer to acquire an averaged value o f v o l u m e (over five consecutive measurements): c e  V  skeletal  =V  cell  r e  V -• (pyp2)-\ re/  4.) The v o l u m e acquired is used to calculate skeletal density (that is, the density o f r o c k ± isolated porosity):  p  ske  ietai  =m  s a m p  /  V  s k e  ietai.  Quality Control Issues A c c u r a c y : Experiments were performed o n various combinations o f steel spheres ( o f k n o w n volume) prior to running samples, i n order to check the accuracy o f the pycnometer; results were w i t h i n 1 % relative error. The temperature was controlled i n such a w a y ( d w e l l time = 1-2 hrs.) that it varied <1°C f r o m time o f calibration to the final run o f the day. The smallest possible configuration o f inserts was used i n order to m a x i m i z e the sample to v o i d space ratio.  P r e c i s i o n : C a l i b r a t i o n values are averages o f five measurements (five w i t h the c e l l empty, five w i t h the k n o w n volume i n the cell); sample volumes are also averages o f five consecutive measurements. Results are precise w i t h i n ± 0 . 3 % .  Rock Powder Density 1.) R o c k powder density is determined u s i n g the powdered sample and an automated h e l i u m pycnometer ( F i g . D 2 i , F i g D 3 ) . T h e largest a l u m i n u m c e l l insert and the a c c o m p a n y i n g filler (Fig. D 2 i i ) are placed inside the sample and reference cells i n order to a l l o w large amounts o f powder to be used ( m a x i m u m powder mass = -45-60 g), thus m i n i m i z i n g the v o i d space to sample ratio. 151  2.) E a c h o f the four sample cells o f the pycnometer is calibrated against steel spheres o f a k n o w n v o l u m e (Fig. D 2 i i i ) . T h e sample c e l l and reference c e l l volumes are thus determined b y the f o l l o w i n g equations: Kell  =  1  ( kno n)( \ V  =V ref  )  fa  y  =  ^  l  g  g  3  (P2 /P2)(P\ - P2)  (PI -P2)V  ^  P  W  (P\-P2^  cell ^  p2  These calibration values are unique to each cell and depend on temperature. T h e y represent an average o f five consecutive measurements. 3.) The powder (-15-60 g) is placed i n the pycnometer to acquire an averaged value o f v o l u m e (over five consecutive measurements):  V  y  rock  ' cell  (Pl/P2)-1  4.) T h e v o l u m e acquired is used to calculate matrix density (that is, the density o f the r o c k 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 o n various combinations o f steel spheres ( o f k n o w n volume) prior to running samples, i n order to check the accuracy o f the pycnometer; results were w i t h i n 1 % relative error. The temperature was controlled i n such a w a y ( d w e l l time =1-2 hrs.) that it varied <1°C f r o m time o f calibration to the f i n a l run o f the day. T h e m a x i m u m amount o f powder was used i n order to ensure that the powder is representative o f the sample, and to m a x i m i z e the sample to v o i d space ratio. A l s o , a standard powder is measured w i t h the other samples i n order to monitor the variability f r o m day to day, run to run. P r e c i s i o n : C a l i b r a t i o n values are averages o f five measurements (five w i t h the c e l l empty, five w i t h the k n o w n v o l u m e i n the cell); sample volumes are also averages o f five consecutive measurements. Results are precise w i t h i n ± 0 . 6 % .  152  Figure D l : Measurement of bulk density for unconsolidated samples. A 500 m L graduated cylinder is packed full with material and mass is acquired with a digital balance precise to 0.1 g.  153  Figure D 2 : H e l i u m pycnometry setup: (i) automatic h e l i u m pycnometer; (ii) a l u m i n u m c e l l insert (left) and filler (right) for use w i t h smaller samples; (iii) steel balls o f k n o w n v o l u m e used for calibration.  154  vent rate  low voltage switch  regulator  vent ,  y e  reference cell circuit board  cell #4  cell #3  cell #2  cell #1  valve  connector valve  ©  to He tank  ©  to serial port on computer  ®  to parallel port on computer  ©  to power source  overpressure valve  F i g u r e D 3 : Schematic diagram o f automated h e l i u m pycnometer, indicating major components and connections.  155  APPENDIX E COMPLETE TABLES OF PHYSICAL PROPERTY DATA  156  T a b l e E l . F u l l summary o f core pycnometry, i n c l u d i n g : component measured ( C = clast, M = matrix), mass (m), volume b y geometry ( V ) , v o l u m e b y core pycnometry ( V s ) , bulk density ( p ) , skeletal density (ps), and connected porosity (O )- Standard deviations are reported as l a . g e o  B  FIELD SITE  LITHOFACIES  1  Intermediate, densely welded block and ash flow deposit  LOCATION  Block #3  Block #4  c  SAMPLE #  C/M  m(g)  V (cm )  0  V (cm)  a  KM-05-059a(2)  M  52.15  0.010  23.705  0.4932  KM-05-060a(l)  M  78.14  20.277  0.0243  0.010  38.061  0.1532  30.350  0.0226  KM-05-060a(2)  M  84.22  0.010  40.126  0.3822  33.103  0.0254  KM-05-060a(3)  M  76.27  0.010  36.283  0.4518  30.191  KM-05-060a(4)  M  44.62  0.010  20.905  0.1165  KM-05-012(l)  M  46.68  0.010  22.566  KM-05-012(2)  M  44.93  0.010  20.109  o  3  eto  o  Ps (g/cm)  2.20  0.046  2.572  2.05  0.008  2.575  2.10  0.020  2.544  0.0255  2.10  0.026  17.715  0.0200  2.13  0.1968  18.181  0.0320  0.2605  17.733  0.0355  3  s  p (g/cm)  a  4>c (%)  o  0.0031  14.46  1.337  0.0019  20.38  1.241  0.0020  17.46  1.412  2.526  0.0021  16.87  1.427  0.012  2.519  0.0028  15.44  1.125  2.08  0.018  2.568  0.0045  18.99  1.760  2.23  0.029  2.534  0.0051  11.99  1.981  16.20 ' 0.541  3  B  3  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  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  00  Block #5  Near Classic  Basal, non-  Base of  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  0.0019  7.68  1.476  KM-05-058d(3)  M  86.05  0.010  37.140  0.3433  34.242  0.0262  2.32  0.021  2.513  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  0.0019  16.24  1.439 1.282  KM-05-017b(2)  M  88.00  0.010  41.283  0.2432  34.574  0.0259  2.13  0.013  2.545  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  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  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 1.334  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  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  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  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 and ash flow deposit  Classic Section  KM-05-024(l)  C  68.39  0.010  44.833  0.1092  30.032  0.0215  1.53  0.004  2.277  KM-05-024(2a)  c c c c c c c c c c c c  46.30  0.010  29.589  0.3119  20.028  0.0471  1.56  0.016  47.46  0.010  31.559  0.2277  21.164  0.0122  1.50  0.011  KM-05-024(2b) KM-05-024(3) KM-05-024(4a) KM-05-024(4b) KM-05-026(l) KM-05-026(2) KM-05-026(3) KM-05-026(4) KM-05-046(1) KM-05-046(2) KM-05-046(3)  Oxidized Roadcut  2  Upper, incipiently welded (oxidized) block and ash flow deposit  NearTM#10  NearTM#12  3  Upper, nonwelded, block and ash flow deposit  Keyhole Falls  0.0016  32.81  2.312  0.0054  32.52  2.882  2.243  0.0013  33.11  0.771 1.920  1.335  70.94  0.010  45.541  0.3387  31.486  0.0306  1.56  0.012  2.253  0.0022  30.76  41.75  0.010  27.613  0.2063  18.501  0.0232  1.51  0.011  2.257  0.0028  33.09  1.457  49.16  0.010  31.335  0.2383  21.808  0.0334  1.57  0.012  2.254  0.0035  30.35  2.095  49.46  0.010  30.197  0.1215  21.629  ' 0.0267  1.64  0.007  2.287  0.0028  28.28  1.651  60.37  0.010  36.435  0.2000  26.006  6.0238  1.66  0.009  2.321  0.0021  28.49  1.450 2.245  68.37  0.010  40.454  0.2160  29.183  0.0372  1.69  0.009  2.343  0.0030  27.90  42.33  0.010  27.015  0.2276  18.692  0.0202  1.57  0.013  2.265  0.0025  30.67  1.264  26.14  0.001  15.926  0.1661  11.401'  0.0349  1.64  0.017  2.293  0.0070  28.47  2.155  60.37  0.010  28.130  0.2520  26.006  0.0238  1.80  0.016  2.335  0.0021  22.92  1.441  89.09  0.010  47.503  • 0.4274  37.535  0.0662  1.88  0.017  2.374  0.0042  20.79  3.946 1.616  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  KM-04-018  bulk  56.14  0.010  -  -  22.504'  0.0267  1.47  0.003  2.495  0.0030  41.15  1.516  KM-04-019  bulk  52.16  0.010  -  -  20.735.  0.0185  1.48  0.012  2.516  0.0022  41.25  1.042  1.52  0.014  2.515  0.0016  39.51  0.905  KM-04-020  bulk  61.94  0.010  -  •-  24.633 •  0.0161  KM-05-032  bulk  59.87  0.010  -  -  23.723' .  0.0062  1.39  0.028  2.524  0.0007  44.84  0.349  KM-05-033(l)  C  100.18  0.010  47.711  0.2490  40.772  0.0215  2.10  0.011  2.457  0.0013  14.53  1.236  KM-05-033(2)  C  60.29  0.010  29.393  0.2772  24.745  0.0296  2.05  0.019  2.437  0.0029  15.86  1.719  KM-05-033(3)  C  60.07  0.010  28.759  0.1722  24.566  0.0168  2.09  0.013  2.445  0.0017  14.53  0.969  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  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  KM-04-031  bulk  68.14  0.010  -  -  26.868  0.0212  1.59  0.025  2.536  0.0020  37.35  1.184  KM-05-036  bulk  45.49  0.010  17.964 '  0.0076  1.43  0.057  2.532  0.0011  43.49  0.422  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  !  as  o  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  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  1.262  T a b l e E2. F u l l summary o f r o c k powder pycnometry, including: f i e l d site (FS), lithofacies ( L F ) , location ( L O C ) , component measured ( C = clast, M = matrix), mass o f powder ( m ) , v o l u m e o f powder ( V ) , rock powder density ( p ) , total porosity (O ), connected porosity R  (<l>c), FS 1  R  R  T  and isolated porosity (Oi). Standard deviations are reported as l a .  LF Intermediate, densely welded block and ash flow deposit  LOC  SAMPLE #  Block #1  KM-05-061(l)  Block #3  Block #4  C/M m (g)  g  V (cm )  g  p (g/cm )  a  28.51 46.75 26.87 45.04 33.22 38.69  0.001 0.010 0.001 0.010 0.001 0.001  11.245 18.674  0.0302 0.0168 0.0117 0.0059 0.0092  2.535 2.504 2.600 2.536 2.549  0.0068  37.51 45.33 28.60 24.03  0.001 0.010 0.001 0.001  9.396  0.0140 0.0130 0.0092 0.0132 0.0260  2.523 2.550 2.524 2.542 2.557  25.10 24.43 21.00  0.001 0.001 0.001  9.773 9.429 8.350 12.599 14.039  0.0158 0.0348 0.0280 0.0250 0.0197  2.568 2.591 2.515 2.558 2.496  15.187" 10.779 11.530 10.966  0.0111 0.0061 0.0031 0.0206 0.0231 0.0048 0.0107 0.0211 0.0171 0.0021  R  KM-05-062(3) KJVI-05-059a(l) KM-05-059a(2) KM-05-060a(l) KM-05-060a(2) KM-05-060a(3)  M M M M M M M  KM-05-060a(4) KM-05-012(l) KM-05-012(2) KM-05-012(3) KM-05-057a(l) KM-05-057a(2)  M M M M M M  KM-05-057a(3) KM-05-057b(l)  M M  32.23 ,0.001 35.04 0.001  KM-05-057b(2) KM-05-057b(3) KM-05-057b(4)  M M M  38.09 27.26 28.76  0.001 0:001 0.001  KM-05-057b(5) KM-05-057b(6)  M M  28.08 46.38  0.001 0.010  KJVl-05-057c(l) KM-05-057c(2) KM-05-057c(3) KM-05-057c(4) KM-05-057c(5)  C C C/M C/M C/M  26.61 37.87 28.75 40.08 37.21  0.001 0.001 0.001 0.010 0.001  3  R  10.335 17.763 13.032 15.333 14.713 17.963 11.252  18,207 10.634 15.331 11.496 16.035 15.135  3  R  0.0023 0.0029 0.0010 0.0018 0.0023 0.0023 0.0014  «P (%) T  +/-  a»i (%)  . 1.08 -1.43 -1.00  0.163 0.128 0.104  0.717 1.156 3.378 0.772  -0.83 0.91 0.19 -1.01 0.93 1.97 3.89  0.120 0.121 0.126 0.213 0.339 0.168 0.378  0.965 1.577  -0.20 1.45  0.340 0.303  0.372 0.632 0.417  -0.45 -0.28 0.74  0.156 0.123 0.124  0.789 0.265  -0.45 1.69  0.124 0.189  15.38 13.23 19.58 16.77  1.763 1.805 0.329 0.796  1.782 1.782 0.326 0.788  1.029 0.474 0.719 1.157  1.039 0.482  0.0030 0.0071  17.63 15.60 18.17 12.80  0.0041 0.0096  17.85 22.43  3.313 0.789  0.0084 0.0051 0.0035  18.49 22.60 17.46  1.004 1.552 0.387  2.508 2.529 2.494 2.561 2.547  0.0018 0.0014  19.86 19.73  0.632 0.407  0.0007 0.0048 0.0033  18.21 21.50 21.09  0.786 0.297 1.076  2.502 2.470 2.501 2.500 2.459  0.0011 0.0017  6.49 5.68  0.374 0.265  1.088 0.380 0.262  1.24 1.75 0.95  0.169 0.054 0.079  0.0046 0.0027 0.0003  7.63  0.684 0.483 0.504  0.673 0.477 0.507  1.20  9.98 7.26  0.82 -0.28  0.190 0.114 0.075  KM-05-057c(6) KM-05-057c(7) KM-05-057c(8) KM-05-058a(l) KM-05-058a(2) KM-05-058a(3) KM-05-058b(l) KM-05-058b(2) KM-05-058d(l) KM-05-058d(2) KM-05-058d(4) KM-05 058d(5) KM-05-058d(6) KM-05-058d(7) KM-05-058d(8) KM-05-017b(l) KM-05-017b(2) KM-05-017b(3) KM-05-017b(4) KM-05-017b(5) KM-05-017b(6) Block #5 KM-05-017b(7) . KM-05-017c(l) KM-05-018d(l) KM-05-018d(2) KM-05-018d(3) KM-05-019b(l) KM-05-019b(2) KM-05-063(l) KM-05-063(2) Near KM-05-063(3) Classic KM-05-063(4) KM-05-063(5) KM-05-063(6) 7  Intermediate, moderately welded block and ash flow deposit  C C C/M C M C/M M M M M M M M M M M M M M M C C/M M M C C  c c M M M M M M  32.58 19.07 31.07 31.36 28.43 25.13 37.07 39.16 45.69 37.93 34.40 48.95 40.83 48.78 44.97 45.58 45.01 15.20 46.03 43.08 32.11 47.69 22.84 16.78 23.21 19.61 35.58 34.75 45.37 45.37 41.15 45.47 45.66 45.39  0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.010 0.001 0.001 0.010 0.010 0.010 0.010 0.010 0.010 0.001 0.010 0.010 0.001 0.010 0.001 0.001 0.001 0.001 0.001 0.001 0.010 0.010 0.010 0.010 0.010 0.010  13.314 7.647 12.374 12.530 11.112 10.043 14.596 15.438 18.153 14.903 13.454 19.442 16.250 18.998 17.814 17.981 17.713 6.047 18.183 17.003 13.040 18.737 8.807 6.684 9.368 7.968 14.308 13.697 17.957 17.976 16.164 17.985 18.056 18.108  0.0144 0.0056 0.0303 0.0185 0.0114 0.0173 0.0104 0.0067 0.0345 0.0216 0.0176 0.0288 0.0112 0.0104 0.0233 0.0318 0.0212 0.0180 0.0084 0.0244 0.0204 0.0235 0.0566 0.0169 0.0418 0.0210 0.0378 0.0434 0.0079 0.0164 0.0075 0.0130 0.0136 0.0285  2.447 2.494 2.511 2.503 2.559 2.502 2.540 2.537 2.517 2.545 2.557 2.518 2.513 2.568 2.524 2.535 2.541 2.514 2.532 2.534 2.462 2.545 2.594 2.510 2.478 2.461 2.487 2.537 • 2.527 2.524 2.546 2.528 2.529 2.507  0.0027 0.0018 0.0061 0.0037 0.0026 0.0043 0.0018 0.0011 0.0048 0.0037 0.0033 0.0038 0.0018 0.0015 0.0033 0.0045 0.0031 0.0075 0.0013 0.0037 0.0038 0.0032 0.0167 0.0063 0.0111 0.0065 0.0066 0.0080 0.0012 0.0024 0.0013 0.0019 0.0020 0.0040  3.56 5.37 15.97 5.30 12.45 7.29 14.56 12.88 12.20 15.92 15.52 10.63 10.85 12.76 15.23 15.77 16.10 15.43 16.26 16.45 4.04 9.64 18.37 16.99 4.63 6.75 5.10 6.55 16.88 18.78 17.12 20.10 15.77 16.62  0.533 0.381 1.279 1.642 0.759 0.938 0.592 1.768 0.748 0.626 0.350 0.960 0.739 0.385 0.472 0.773 0.505 0.611 0.440 0.910 1.276 0.530 1.347 0.837 0.798 1.154 0.687 0.862 1.339 1.032 0.683 0.573 1.184 1.337  0.521 0.381 0.078 0.045 0.082 0.947 0.599 1.783 0.730 0.624 0.342 0.954 0.744 0.389 0.454 0.755 0.497 0.551 0.443 0.905 1.273 0.542 1.283 0.809 0.686 1.149 0.638 0.829 1.356 1.054 0.692 0.565 1.194 1.331  -0.51 1.53 1.12 1.58 2.96 2.04 0.83 0.76 -0.23 0.95 1.75 0.04 0.64 1.73 -1.18 -0.46 -0.17 -2.02 0.16 -0.07 0.20 -1.30 1.11 -1.53 1.38 1.62 -0.98 2.33 0.77 1.86 1.26 -1.69 0.41 -0.42  0.115 0.075 0.258 0.153 0.133 0.185 0.115 0.092 0.205 0.164 0.144 0.171 0.109 0.062 0.138 0.182 0.143 0.318 0.087 0.176 0.185 0.246 0.711 0.304 0.445 0.276 0.279 0.311 0.173 0.156 0.068 0.124 0.170 0.216  Basal, nonwelded block and ash flow  Base of Classic  deposit  2  Upper, incipiently welded (oxidized) block and ash flow deposit  Near TM#10 (oxidized roadcut) Near TM#12 (oxidized roadcut) Oxidized Roadcut  3  Upper, nonwelded, block and ash flow deposit  Keyhole Falls  KM-05-023 KM-05-024(l) KM-05-024(2) KM-05-024(3) KM-05-024(4) KM-05-026(l) KM-05-026(2) KM-05-026(3) KM-05-026(4) KM-05-046(l) KM-05-046(2) KM-05-046(3) KM-05-046(4) KM-05-031 KM-05-032 KM-05-033(l) KM-05-033(2) KM-05-033(3) KM-05-056(l) KM-05-056(2) KM-05-056(3a) KM-05-056(3b) KM-04-018 KM-04-019 KM-04-020 KM-04-031 KM-05-036 KM-05-043(l) KM-05-043(2) KM-05-043(3) KM-05-043(4) KM-05-044(l) KM-05-044(2)  bulk C  C C C C  C C C  C C C  C C  bulk C C C  C C C  C bulk bulk bulk bulk bulk C  C C C C  C  47.15 35.07 33.13 45.93 31.50 46.74 35.91 35.22 40.60 28.64 45.61 45.65  0.010 0.001 0.001 0.010 0.001 0.010 0.001 0.001 0.010 0.001 0.010 0.010  18.501 14.024 13.175 18.381 12.643 18.715 14.476 14.212 16.509 11.570 18.387 18.331  0.0190 0.0404 0.0225 0.0135 0.0369 0.0225 0.0165 0.0238 0.0228 0.0110 0.0083 0.0226  2.549 2.501 2.515 2.499 2.492 2.498 2.481 2.478 2.459 2.475 2.481 2.490  0.0026 0.0072 0.0043 0.0019 0.0073 0.0031 0.0028 0.0041 0.0035 0.0024 0.0012 0.0031  39.53 38.82 40.35 37.57 39.40 34.33 33.08 31.80 36.16 33.75 27.44 24.51  1.112 0.041 0.231 0.170 0.443 0.485 0.466 0.519 0.487 0.508 0.277 0.301 0.374 0.397 0.382 0.396 0.544 0.588 0.694 0.778 0.650 0.833 0.684 0.724  1.30 8.94 10.82 9.83 9.43 8.44 6.42 5.45 7.92 7.37 5.86 4.69  0.145 0.270 0.161 0.112 0.288 0.159 0.137 0.199 0.163 0.297 0.098 0.206  45.72 50.45 41.22 50.43 47.49 49.15 42.44 21.73 48.21 46.09 50.06 50.28  0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.001 0.010 0.010 0.010 0.010  18.513 20.407 16.277 20.149 18.985 19.737 17.096 8.680 19.502 18.737 19.741 19.709  0.0173 0.0101 0.0239 0.0193 0.0041 0.0078 0.0132 0.0128 0.0056 0.0175 0.0436 0.0162  2.470 2.472 2.532 2.503 2.501 2.490 2.482 2.504 2.472 2.460 2.536 2.551  0.0024 0.0013 0.0038 0.0025 0.0008 0.0011 0.0020 0.0037 0.0009 0.0024 0.0056 0.0022  23.87  0.534  0.573  4.85  0.187  -  -  -  -  45.03 16.10 18.05 16.07 21.05 21.71 19.90 19.51 42.11 42.07  1.092 0.445 0.774 0.504 0.444 0.674 0.691 0.698 0.170 0.479  0.014 0.448 0.800 0.515 0.463 0.708 0.731 0.731 0.070 0.053  0.34 1.83 2.59 1.81 2.53 5.55 5.17 4.70 1.62 1.40  0.151 0.109 0.120 0.080 0.151 0.164 0.090 0.124 0.248 0.121  37.45 51.63 50.55 40.40 40.49 30.80 42.31 18.28 40.76  0.001 0.010 0.010 0.010 0.010 0.001 0.010 0.001 0.010  14.832 20.220 19.941 16.146 16.136 12.264 16.962 7.047 15.973  0.0112  2.525 2.553 2.535 2.502 2.509 2.512 2.494 2.594 2.552  0.0019 0.0016 0.0013 0.0033 0.0043 0.0029 0.0034 0.0088 0.0021  39.76 37.77 43.55 34.06 29.86 35.50 27.84 33.69 32.20  0.568 0.040 0.976 0.050 2.265 0.024 0.202 0.203 0.317 0.313 0.361 0.382 0.316 0.323 0.401 0.345 0.223 0.227  0.41 0.68 0.11 3.08 3.73 5.73 3.61 3.65 2.38  0.100 0.100 0.065 0.168 0.191 0.150 0.168 0.329 0.110  0.0119 0.0090 0.0210 0.0273 0.0142 0.0225 0.0239 0.0126  KM-05-044(3) KM-05-044(4) KJVl-05-045(l) KM-05-045(2) KM-05-054(l) KM-05-054(2) KM-05-054(3) KM-05-054(4)  C C  c c c c c c  28.68 38.11 43.41 19.58 36.63 36.45 46.46  0.001 0.001 0.010 0.001 0.001 0.001 0.010  11.393 15.023 17.114 7.885 14.832 14.622 18.619  0.0145 0.0142 0.0107 0.0096 0.0072 0.0120 0.0397  2.517 2.537 2.537 2.483 2.470 2.493 2.495  0.0032 0.0024 0.0017 0.0030 0.0012 0.0021 0.0053  30.48 28.26 25.49 24.29 34.00 33.81 35.08  0.234 0.688 0.429 0.590 0.145 0.246 0.741  0.220 0.692 0.431 0.580 0.155 0.252 0.770  -0.12 1.01 0.64 -1.08 3.04 2.73 4.77  0.141 0.102 0.084 0.154 0.089 0.109 0.241  46.25  0.010  18.449  0.0364  2.507  0.0050  36.57  0.256  0.237  4.15  0.203  

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