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Computer-assisted mass spectrometry and its application to rubidium-strontium geochronology Blenkinsop, John 1972

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COMPUTER-ASSISTED MASS SPECTROMETRY AND ITS APPLICATION TO RUBIDIUM-STRONTIUM GEOCHRONOLOGY by JOHN BLENKINSOP B.Sc., U n i v e r s i t y o f B r i t i s h Columbia, 1964 M.Sc., U n i v e r s i t y o f B r i t i s h Columbia, 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department o f Geophysics and Astronomy We accept t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA August, 1972 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e H e a d o f my D e p a r t m e n t o r b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a D a t e A B S T R A C T An o n - l i n e data a c q u i s i t i o n system, c e n t r e d around an I n t e r d a t a Model 4 computer, has been designed f o r a mass spectrometer used p r i m a r i l y f o r r u b i d i u m - s t r o n t i u m geochron-ol o g y . The d i g i t a l system has been used f o r an i n v e s t i g a t i o n of the ages o f c e r t a i n gneisses w i t h i n the southern Omineca C r y s t a l l i n e B e l t o f B r i t i s h Columbia. With the system, i t has proved p o s s i b l e to achieve a p r e c i s i o n o f 0.02% (95% c o n f i d e n c e l i m i t ) i n the measurement o f S r 8 7 / S r 8 6 r a t i o s , a p r e c i s i o n which was n e c e s s a r y f o r the i n v e s t i g a t i o n d e s c r i b e d . The system employs a d i g i t a l v o l t m e t e r at the mass spectrometer f o r a n a l o g - d i g i t a l c o n v e r s i o n o f the ion beam. The " c o n v e r s i o n complete" s i g n a l from the v o l t m e t e r i s used to i n t e r r u p t the computer. At each i n t e r r u p t , the computer reads the mass spectrometer, f i l t e r s the v o l t m e t e r r e a d i n g , and a d j u s t s the magnet scan speed as r e q u i r e d . At the end o f each mass spectrum, the data are processed and the i s o t o p i c r a t i o s are c a l c u l a t e d . They can be output to a d i g i t a l d i s p l a y at the mass spectrometer as requested by the o p e r a t o r . Rock samples from the gneisses were o b t a i n e d from areas near R e v e l s t o k e , Quesnel Lake, and Malton Range i n order to t e s t suggestions t h a t they r e p r e s e n t Precambrian c r y s t a l l i n e basement. Samples from the f i r s t two l o c a t i o n s e x h i b i t e d a r e s t r i c t e d range of Rb/Sr r a t i o s , and r e q u i r e d the p r e c i s e d e t e r m i n a t i o n o f t h e i r S r 8 7 / S r 8 6 r a t i o s i n o r d e r to be deter-mined. A l l areas appear to have experi e n c e d an event about 700 m.yr. ago, and a r e , t h e r e f o r e , Precambrian i n age. The event can p o s s i b l y be c o r r e l a t e d w i t h the East Kootenay Orogeny. In a d d i t i o n , the gneiss at Revelstoke i s c l e a r l y o l d e r than i t s s u r r o u n d i n g metasediments, an o b s e r v a t i o n which supports the t h e s i s o f J . V. Ross that i t was t e c t o n i c a l l y emplaced. T h i s l a t t e r f i n d i n g has r e g i o n a l i m p l i c a t i o n s i n t h a t Precambrian c r y s t a l l i n e basement has a p p a r e n t l y been i n v o l v e d i n the deformation of the r e g i o n . TABLE OF CONTENTS A b s t r a c t i i L i s t o f Tables v i L i s t o f Fi g u r e s v i i Acknowledgments v i i i CHAPTER I INTRODUCTION 1 1-1 Background 1 1-2 O b j e c t i v e s 2 1-3 B a s i c theory o f r u b i d i u m - s t r o n t i u m 6 geochronology CHAPTER II INSTRUMENTATION 13 I I - l I n t r o d u c t i o n 13 11-2 Hardware 15 II-3 F i l t e r i n g 20 II-4 Spectrum scanning 23 II-5 The d i g i t a l data system 24 II-6 Conclusions 27 CHAPTER I I I ANALYTICAL TECHNIQUES 28 I I I - l I n t r o d u c t i o n 28 III-2 Measurement o f rubidium and 2 8 s t r o n t i u m c o n c e n t r a t i o n s I I I - 3 Chemical p r e p a r a t i o n o f samples 34 III-4 Mass spectrometry 35 I I I - 5 P r e c i s i o n 38 V CHAPTER IV THE GEOLOGICAL PROBLEM 42 IV-1 Background 42 IV-2 Theories of o r i g i n of the gneiss domes 46 IV-3 The Revelstoke gneiss 48 IV-4 The Quesnel Lake gneiss 54 IV-5 The Malton gneiss 57 IV-6 Calculation of isochrons 60 CHAPTER V CONCLUSIONS 64 V- l Ages of the gneisses and t h e i r 64 implications V-2 Regional considerations 67 V-3 Timing of the Shuswap metamorphism 69 V-4 Relationship to plate tectonics 69 V-5 Summary 70 References 72 Appendix A - l 78 Appendix A-2 80 v i LIST OF TABLES Tabl e I I - l I n t e r f a c e f u n c t i o n s 19 Table I I I - l O p e r a t i n g parameters f o r the x-ray 29 f l u o r e s c e n c e u n i t Table 111-2 Rubidium and s t r o n t i u m c o n c e n t r a t i o n s 32 of s t a n d a r d rocks Table 111 -3 y values f o r U.S.G.S. standar d rocks 33 Tabl e 111 -4 R e p l i c a t e measurements o f Eimer and 40 Amend s t r o n t i u m carbonate T a b l e I I I - 5 D u p l i c a t e S r 8 7 / S r 8 6 measurements 40 f o r rock samples T a b l e 111-6 R e p l i c a t e s o f rubidium and s t r o n t i u m 41 c o n c e n t r a t i o n measurements Table IV-1 S i m p l i f i e d g e o l o g i c a l t i m e - s c a l e 45 Table IV-2 Rubidium and s t r o n t i u m measurements 49 f o r the Revelstoke gneiss Table IV-3 Rubidium-strontium measurements 57 o f the Quesnel Lake gneiss T a b l e IV-4 Rubidium-strontium measurements 60 of the Malton gneiss v i i LIST OF FIGURES Fi g u r e 1-1 G e o l o g i c a l elements of s o u t h e a s t e r n B r i t i s h Columbia 5 F i g u r e 1-2 Compston-Jeffery p l o t 8 F i g u r e 1-3 BPI p l o t 10 F i g u r e 1-4 S i n g l e event model 11 F i g u r e 1-5 Two event model 12 Fi g u r e I I - 1 Computer b l o c k diagram 17 Fi g u r e I I - 2 F i l t e r r e p r e s e n t e d i n time and frequency domains 21 F i g u r e I I - 3 Power spectrum of b a s e l i n e n o i s e 22 Fi g u r e IV- 1 G e o l o g i c a l elements o f s o u t h e a s t e r n B r i t i s h Columbia 43 Fi g u r e IV- 2 Sample l o c a t i o n s f o r the Revelstoke gneiss 51 Fi g u r e IV- 3 BPI p l o t f o r Revelstoke gneiss 52 F i g u r e IV- 4 Sample l o c a t i o n s f o r the Quesnel Lake gneiss 55 Fig u r e IV- 5 BPI p l o t f o r Quesnel Lake gneiss 58 Fi g u r e IV- 6 Sample l o c a t i o n f o r the Malton gneiss 61 Fi g u r e IV- 7 BPI p l o t f o r the Malton gneiss 62 v i i i ACKNOWLEDGEMENTS I t i s a p l e a s u r e to acknowledge the, a s s i s t a n c e p r o v i d e d the w r i t e r i n the course o f h i s s t u d i e s . The work was s u p e r v i s e d by R. D. R u s s e l l , whose enthusiasm and i n t e r e s t at a l l stages of the p r o j e c t are much a p p r e c i a t e d . Other c o l l e a g u e s who p r o v i d e d a s s i s t a n c e and encouragement i n c l u d e R. D. Meldrum, D. L. M i t c h e l l , J . M. Ozard and W. F. Slawson. The capable t e c h n i c a l a s s i s t a n c e o f E. J . B e l l i s , C. J . C u r t i s , K. D. S c h r e i b e r , and H. Verwoerd i s r e c o g n i z e d w i t h thanks. I t i s a l s o a p l e a s u r e to acknowledge the a s s i s t a n c e and support p r o v i d e d by members of the Department o f G e o l o g i c a l S c i e n c e s . P. C. Le Couteur, J . V. Ross, and B. D. Ryan p r o v i d e d guidance e s s e n t i a l f o r the completion o f t h i s r e s e a r c h . In a d d i t i o n , B. D. Ryan shared w i t h the w r i t e r the task o f s e t t i n g up the r u b i d i u m - s t r o n t i u m f a c i l i t y . The generous c o o p e r a t i o n of the Computing Centre o f the U n i v e r s i t y of B r i t i s h Columbia was s i n c e r e l y a p p r e c i a t e d . F i n a n c i a l a i d i n the form o f a U n i v e r s i t y o f B r i t i s h Columbia Graduate F e l l o w s h i p , and an H. R. MacMillan Family F e l l o w s h i p i s g r a t e f u l l y acknowledged. The t h e s i s was typed by Rosanne Rumley. T h i s r e s e a r c h and the mass spectrometer l a b o r a t o r y have been f i n a n c i a l l y supported by the N a t i o n a l Research C o u n c i l o f Canada through grants A720 to R. D. R u s s e l l and A5131 to W. F. Slawson, and i n p a r t by the N a t i o n a l Science Foundation of the U n i t e d S t a t e s through grant GA-737 to W. F. Slawson. CHAPTER I INTRODUCTION I -1 Background Isotope geophysics s t u d i e s began at the U n i v e r s i t y o f B r i t i s h Columbia i n 1960, w i t h the completion o f a gas source mass spectrometer which was used to measure the v a r i -a t i o n s i n the i s o t o p i c composition o f l e a d i n ores ( K o l l a r et a l . , 1960). During the next few y e a r s , a major e f f o r t a f the r e s e a r c h group was to improve the measurement of l e a d i s o -tope r a t i o s by the gas source method (Stacey, 1962; O s t i c , 1963; S i n c l a i r , 1964; Weichert, 1965; S m a l l , 1968) and to extend i t to m a t e r i a l s o f low l e a d c o n c e n t r a t i o n ( U l r y c h , 1962; W h i t t l e s , 1964; Reynolds, 1967). S o l i d source techniques were l a t e r i n t r o d u c e d to supplement the gas source t e t r a m e t h y l e a d technique (Ozard, 1970; Hay l e s , i n p r e p a r a t i o n ) , and have now r e p l a c e d i t . During 1962-64, a potassium-argon d a t i n g f a c i l i t y was added to the l a b o r a t o r y (White et a l . , 1967) as a j o i n t p r o j e c t w i t h the Department of G e o l o g i c a l S c i e n c e s . I t has s i n c e been used to determine the chronology o f d i f f e r e n t p a r t s o f B r i t i s h Columbia. Potassium-argon ages, however,, are q u i t e e a s i l y a f f e c t e d by subsequent events, and s i n c e the p r o v i n c e has undergone s e v e r a l orogenies s i n c e the l a t e P a l e o z o i c , the ages have i n many cases been e i t h e r p a r t i a l l y o r t o t a l l y r e s e t . The e a r l i e r g e o c h r o n o l o g i c h i s t o r y o f the p r o v i n c e has t h e r e f o r e been at l e a s t p a r t l y obscured. Ages determined 2 by the r u b i d i u m - s t r o n t i u m method are not so e a s i l y a f f e c t e d by subsequent a c t i v i t y so, i n o r d e r to look beyond the r e l a t i v e l y r e c e n t events, i t was d e c i d e d to add a rubidium-s t r o n t i u m geochronology f a c i l i t y to the l a b o r a t o r y , again w i t h c o o p e r a t i o n from the Department of G e o l o g i c a l S c i e n c e s . Rubidium-strontium geochronology i s based on the 8 decay o f R b 8 7 to S r 8 7 , a process which has a h a l f - l i f e o f n e a r l y 5 x 1 0 1 0 y r . An age d e t e r m i n a t i o n e n t a i l s measuring the rubidium and s t r o n t i u m c o n c e n t r a t i o n s of a sample i n o r d e r to determine i t s Rb/Sr r a t i o . The i s o t o p i c composition of the s t r o n t i u m i s a l s o measured, the important r a t i o b e i n g S r 8 7 / S r 8 6 . An age i s normally o b t a i n e d from a p l o t o f the R b 8 7 / S r 8 6 and S r 8 7 / S r 8 6 r a t i o s of a group of samples. Under c e r t a i n c o n d i t i o n s the samples w i l l d e f i n e a s t r a i g h t l i n e , the s l o p e o f which i s r e l a t e d to the age o f the group ( S e c t i o n 1-3). M a t e r i a l s dated are e i t h e r m i n e r a l s such as b i o t i t e or muscovite, or whole r o c k s . 1-2 Obj e c t i v e s The two major o b j e c t i v e s o f t h i s t h e s i s a r e : 1) to extend the range o f problems t h a t can be s t u d i e d by r u b i d i u m - s t r o n t i u m geochronology by improving the p r e c i s i o n o f the measurement o f S r 8 7 / S r 8 6 r a t i o s , and 2) to determine whole-rock ages o f c e r t a i n gneisses w i t h i n the southern p a r t o f the Omineca C r y s t a l l i n e B e l t of B r i t i s h Columbia i n order to a s c e r t a i n i f they are o f Precambrian age. 3 The f i r s t objective arose from consideration of some of the l i m i t a t i o n s of rubidium-strontium geochronology. Since the h a l f - l i f e of Rb 8 7 i s large, about ten times the age of the earth, radiogenic S r 8 7 accumulates slowly, so that a suite of samples often exhibits a small range i n S r 8 7 / S r 8 6 r a t i o s . Consequently, the pre c i s i o n of the measurement of this r a t i o determines the minimum spread i n S r 8 7 / S r 8 6 r a t i o s a suite of samples must have i n order to be dated with acceptable p r e c i s i o n . The range i n S r 8 7 / S r 8 6 r a t i o s i s i n turn related to the age of the s u i t e , and to the range of Rb/Sr r a t i o s , so that suites with l i m i t e d variations i n Rb/Sr ra t i o s or suites with small ages often cannot be dated. It is apparent that more precise measurement of the S r 8 7 / S r 8 6 r a t i o reduces the range in S r 8 7 / S r 8 6 required, and allows rubidium-strontium geochronology to be applied to a greater v a r i e t y of problems. The approach adopted i n this thesis has been to improve the p r e c i s i o n of S r 8 7 / S r 8 6 r a t i o s , to some extent by using improved instrumentation, but large l y through the use of more sophisticated data reduction techniques. The improvements in instrumentation included an A.C. filament supply (Russell and B e l l i s , 1971) and a hybrid s o l i d state measuring system, both designed by R. D. Russell. The data reduction techniques made use of a d i g i t a l computer, and were a primary r e s p o n s i b i l i t y of the writer. The second objective arose from remarks made by Wheeler (1970) i n his summary of a conference on structure 4 of the southern Canadian C o r d i l l e r a . In his discussion of future work to be done i n the region, he states: "One of the most important problems concerns whether Precambrian c r y s t a l l i n e basement i s involved i n the deformation of the Eastern Core Zone. Several areas of gra n i t o i d gneiss that may possibly represent Precambrian basement have been recognized. These are the Malton gneiss stra d d l i n g the Rocky Mountain Trench, the gneiss wedge i n northern Kootenay Arc, the granitoid gneisses i n the cores of Thor-Odin and Frenchman's Cap gneiss domes, and a b e l t of gr a n i t o i d gneiss i n the western Cariboo Mountains. These areas require d e t a i l e d and comprehensive radiometric age determination studies by several d i f f e r e n t methods, e s p e c i a l l y on zircons from the gneisses, to determine which, i f any, are of Precambrian age." (Figure 1-1) Whether Precambrian basement has been involved i n the extensive deformation and accompanying metamorphism of southeastern B r i t i s h Columbia is a controversial question. Ross (1968, 1970) has proposed a model for the Paleozoic and Mesozoic h i s t o r y of part of the region, i n which he suggests that Precambrian basement has been involved i n the deformation of the region. His ideas have been disputed by Wheeler (1970) and Reesor (1970), among others. Samples were c o l l e c t e d from the gneissic wedge in northern Kootenay Arc (Revelstoke gneiss) and the granitoid gneiss i n the western Cariboo Mountains (Quesnel Lake gneiss). Some samples from the Malton gneiss were c o l l e c t e d by C. A. FIGURE 1-1 Geological elements of southeastern B r i t i s h Columbia. Q L F C TO Quesnel Lake Gneiss Frenchman 1s Cap Thor-Odin MG Malton Gneiss RG Revelstoke Gneiss V V a l h a l l a 6 G i o v a n e l l a o f the G e o l o g i c a l Survey o f Canada. I t was a n t i c i p a t e d t h a t the samples would e x h i b i t a r e s t r i c t e d range i n Rb/Sr r a t i o s , and hence would r e q u i r e p r e c i s e measurement o f t h e i r S r 8 7 / S r 8 6 r a t i o s i n order to be dated. 1-3 B a s i c t h e o r y of r u b i d i u m - s t r o n t i u m geochronology In common w i t h other methods, r u b i d i u m - s t r o n t i u m geochronology i s based on the well-known eq u a t i o n N = N . e ~ U , (1) where N i s the number of atoms p r e s e n t at time t , i s the number of atoms i n i t i a l l y p r e s e n t at t=0 , and X , the decay c o n s t a n t , r e p r e s e n t s the p r o b a b i l i t y o f decay o f an atom i n u n i t time. The equation i s r e - a r r a n g e d to give N t = N e X t , (2) where the q u a n t i t y t i s the time p e r i o d from f o r m a t i o n o f the rock to the p r e s e n t , i . e . i s the age, and N i s the number of atoms i n the rock at p r e s e n t . Let the symbols D and P r e p r e s e n t the number of daughter and parent atoms now observed i n the sample, and l e t and P^ r e p r e s e n t the number of atoms at the time the sample was formed. I f the system remained c l o s e d from t h a t time u n t i l the p r e s e n t (no daughter or parent atoms are removed or added), then D + P = P± + D i . (3) 7 From equation 2, D " D i = e X t - l ( 4 ) and 1 .. r n ^ D-D. , t = T l n [ 1 + I ] For rubidium and strontium. 1 S r 8 7 * t = - In [ 1 + ^TTT ] where S r 8 7 * i s the radiogenic strontium accumulated i n time t ( i . e . S r 8 7 - S r ^ 8 7 ) . This equation was used for several 8 7 years before the d i f f i c u l t y of evaluating S r ^ 8 was f u l l y appreciated. Equation ( 4 ) can be rearranged, and each side divided by a suitable index isotope (one that i s neither radioactive nor radiogenic). For rubidium-strontium geo-chronology, S r 8 6 i s the most useful index isotope because i t occurs i n about the same abundance as S r 8 7 . Equation ( 4 ) then becomes 8 7 Sr Sr*"5" Sr 8 7 + S T ^ " • C e X t - l ) • (5) The quantities S r 8 7 / S r 8 6 and R b 8 7 / S r 8 6 are measurable i n the laboratory, and X i s known1, leaving only t and ( S r 8 7 / S r 8 6 ) ^ to be determined. The evaluation of the two quantities requires, of course, data from at least two oogenetic samples. U n c e r t a i n t i e s i n X are discussed i n Appendix A - l . 8 In p r a c t i c e , s e v e r a l samples from each rock u n i t are a n a l y z e d , and the r e s u l t s are pr e s e n t e d g r a p h i c a l l y . The f i r s t method o f g r a p h i c a l p r e s e n t a t i o n , proposed by Compston and J e f f e r y (1959) , made use o f the i d e n t i t y Sr B 7 Sr 8 6 Sr 8 7 ) Sr 8 6 R b 8 7 S r 8 7 * Sr 8 6 Rb 8 7 Rearranging terms leads t o S r 8 7 * _ Sr Rb 8 6 Rb 7 7" s F 5 ^ Sr 8 7 Sr 8 7 Sr 8 6 which i s the eq u a t i o n o f a s t r a i g h t l i n e between S r 8 7 * / R b 8 7 and ( S r 8 7 / S r 8 6 ) ^ . A sample thus d e f i n e s a s t r a i g h t l i n e on the graph, w i t h the i n t e r c e p t on the S r 8 7*/Rb 8 7 a x i s b e i n g the known S r 8 7 / R b 8 7 r a t i o o f the sample, and the i n t e r c e p t on the ( S r 8 7 / S r 8 6 ) i a x i s b e i n g the measured S r 8 7 / S r 8 6 r a t i o ( F i g u r e 1-2). The s l o p e of the l i n e i s the n e g a t i v e o f the S r 8 6 / R b 8 7 r a t i o ( i . e . i t i s always n e g a t i v e ) . Figure 1-2 S r 8 7 * R b 8 7 ( S r 8 7 / S r 8 6 ) 9 Samples from a oogenetic suite w i l l define a number of l i n e s on such a graph, one l i n e for each sample. I f the closed system assumption has been s a t i s f i e d , the l i n e s w i l l i n t e r s e c t at a common point, the coordinates of which give the S r 8 7 * / R b 8 7 and ( S r 8 7 / S r 8 6 ) i r a t i o s for the suite (Figure 1 - 2 ) . The age of the rocks can be calculated from the equation S r 8 7 * Xt , = e -1 Rb e 7 An a l t e r n a t i v e graphical presentation of rubidium-strontium data was proposed by workers at the Bernard Price I n s t i t u t e (Hales, 1960), and t h i s BPI plot i s the method i n general use today. They pointed out that equation (5) Sr 8 7 Sr 8 6 Sr 8 71 Sr 8 6 A Rb 8 7 , Xt + ~ iT * (e -1) Sr i s also an equation of a st r a i g h t l i n e , i n this case between S r 8 7 / S r 8 6 and R b 8 7 / S r 8 6 , where each sample defines a point on the graph. I f a l l samples are cogenetic, and i f the closed system assumption has been s a t i s f i e d , the points w i l l define a str a i g h t l i n e of slope e X t - l and intercept ( S r 8 7 / S r 8 6 ) i . (Figure 1-3) This l a t t e r plot i s probably preferred because the f i t of points to a l i n e i s easier to judge than the common in t e r s e c t i o n of a family of l i n e s , and because recognized procedures exist for estimating uncertainties. Since i t i s i n 10 wider use, i n t e r p r e t a t i o n of r u b i d i u m - s t r o n t i u m data w i l l be made i n terms o f t h a t r e p r e s e n t a t i o n . Figure 1-3 R b 8 7 / S r 1-4 I n t e r p r e t a t i o n s The s i m p l e s t model to i n t e r p r e t i s one i n which a s u i t e of samples has r e c o r d e d o n l y one event, such as i t s i n t r u s i o n or a severe metamorphism. As a r e s u l t o f the event, a l l t o t a l rocks and m i n e r a l s i n the s u i t e had the same s t r o n t i u m i s o t o p i c c o mposition, but v a r i e d i n t h e i r Rb/Sr r a t i o s . At t h i s i n i t i a l time, a l l samples d e f i n e d a h o r i z o n -t a l l i n e on the BPI diagram. As R b 8 7 decayed to S r 8 7 , a l l p o i n t s moved along l i n e s w i t h s l o p e of -1 , but maintained t h e i r c o l i n e a r i t y , as shown i n F i g u r e 1-4. A f t e r a time t ^ , the p o i n t s , both t o t a l rocks and m i n e r a l s , l i e on an i s o c h r o n of s l o p e e X t i - l . 11 A more c o m p l i c a t e d model i s r e q u i r e d i f a second, l e s s i n t e n s i v e , event has a f f e c t e d the samples. One p o s s i b l e e f f e c t of the event i s t h a t , although the t o t a l rock system remained c l o s e d , the m i n e r a l s exchanged s t r o n t i u m and p o s s i b l y rubidium. I f exchange was complete, the m i n e r a l s l o s t a l l memory of t h e i r p r e v i o u s h i s t o r y and once again l a y on a h o r i z o n t a l l i n e ( d o t t e d l i n e i n F i g u r e 1-5). When the samples are a n a l y z e d , the whole rocks and the m i n e r a l s d e f i n e two i s o c h r o n s , w i t h s l o p e s of e X t l - l and e X t 2 - l r e s p e c t i v e l y . The ages of the two events can thus be determined. 12 I t i s q u i t e p o s s i b l e t h a t the t o t a l rock systems w i l l g ain or l o s e rubidium and s t r o n t i u m as w e l l , i n which case i t w i l l be d i f f i c u l t o r i m p o s s i b l e to date the primary event. I f s t r o n t i u m i n the m i n e r a l s i s not p r o p e r l y homogenized, the m i n e r a l data w i l l not p r o v i d e a u s e f u l d e t e r m i n a t i o n o f the secondary event. More co m p l i c a t e d models, such as continuous d i f f u -s i o n or m u l t i p l e event models are p o s s i b l e , but t h e r e i s seldom enough i n f o r m a t i o n to apply them u s e f u l l y . The remainder of the t h e s i s c o n s i s t s of a d e s c r i p -t i o n o f the d i g i t a l data system i n Chapter I I , the a n a l y t i c a l t echniques i n Chapter I I I , and the g e o l o g i c a l problem i n Chapter IV. The c o n c l u s i o n s reached i n t h i s study are summarized i n Chapter V. CHAPTER II INSTRUMENTATION II-1 I n t r o d u c t i o n In the past few y e a r s , many mass spectrometer l a b o r a t o r i e s have moved toward some form of d i g i t a l p r o c e s s i n g o f t h e i r d ata. In a s i m p l e r c o n f i g u r a t i o n , i t has taken the form o f o f f - l i n e p r o c e s s i n g - d i g i t i z a t i o n o f the mass s p e c t r a i n the course o f the a n a l y s i s , f o l l o w e d l a t e r by computer p r o c e s s i n g (Weichert et a l . , 1967; Cumming et a l . , 1971; Stacey et a l . , 1971, 1972). More complex systems i n v o l v e o n - l i n e p r o c e s s i n g o f s p e c t r a , i n which data are t r a n s m i t t e d d i r e c t l y to a computer, so t h a t r e d u c t i o n o f the s p e c t r a i s c a r r i e d out d u r i n g the a n a l y s i s (Wasserburg et a l . , 1969; R u s s e l l e t a l . , 1971). The primary advantages o f a d i g i t a l system are convenience, and improvement of p r e c i s i o n and r e p r o d u c i b i l i t y . In a d d i t i o n , an o n - l i n e system p r o v i d e s a means o f m o n i t o r i n g the q u a l i t y o f an a n a l y s i s d u r i n g the run, so t h a t a l l analyses can be made to a s p e c i f i e d degree of p r e c i s i o n . The f i r s t d i g i t a l data system at the U n i v e r s i t y o f B r i t i s h Columbia was an o f f - l i n e system designed by Weichert (1965) f o r the l a b o r a t o r y ' s gas source mass spectrometer (Weichert et a l . , 1967). The measuring system at that time was an i o n c u r r e n t a m p l i f i e r o f the s e r v o - v o l t m e t e r type, i t s output b e i n g the s h a f t r o t a t i o n o f a motor-driven p o t e n t i -ometer (Stacey et a l . , 1965). A n a l o g - d i g i t a l c o n v e r s i o n was 14 conveniently provided by a shaft p o s i t i o n encoder. Twice per second, the four decimal d i g i t s from the encoder were read into a buffer and subsequently punched s e r i a l l y onto paper tape. A f i f t h character indicated the magnet scan d i r e c t i o n (up-mass, down-mass or no scan) and the measuring system attenuation, or shunt. In this way, a complete representation of the trimethylead-ion spectrum was stored on the tape. A study of signal and noise spectra showed that the paper tape contained a l l the useful information i n the mass spectrum (Weichert et a l . , 1967). A mass spectrometer run consisted of several scans of the spectrum, each scan beginning at the high-mass end. F i r s t , baseline readings (zero signal level) were recorded, then the magnetic f i e l d was varied to scan down the spectrum. More baselines were taken at the low-mass end of the spectrum, before the peaks were scanned again, this time i n the reverse order. Baselines were recorded once more, and the scan terminated. Processing of the tape was ca r r i e d out using the f a c i l i t i e s of the Computing Centre. Each scan was treated as a complete unit. Data were f i r s t f i l t e r e d d i g i t a l l y , then searched for maxima and minima. Baselines were calcu-lated from the appropriate data, and subtracted from the maxima and minima to produce the peak heights. The peaks were i d e n t i f i e d and stored, together with t h e i r time of occurrence. Pressure scattering calculations were determined, and output, together with the peak heights and times. F i n a l l y , 15 the l e a d i s o t o p e r a t i o s were c a l c u l a t e d . The system, w i t h minor m o d i f i c a t i o n s , was i n use u n t i l l a t e 1969, when the e l e c t r o n i c s u p p l i e s f o r the gas source mass spectrometer were r e - b u i l t . By l a t e 1968, the l a b o r a t o r y had two s o l i d - s o u r c e mass spectrometers i n o p e r a t i o n , as w e l l as the gas source instrument, though on l y the l a t t e r was p r o v i d e d w i t h d i g i t a l o utput. I n s t e a d o f extending Weichert's system to the s o l i d source machines, i t was d e c i d e d to s e t up a more s o p h i s t i c a t e d system, capable of p r o v i d i n g simultaneous data r e d u c t i o n f o r a l l t h r e e mass spe c t r o m e t e r s . Since the system i n c o r p o r a t e d a d i g i t a l computer, i t was expected t h a t f u l l o n - l i n e p r o c e s s -i n g o f s p e c t r a c o u l d be a c h i e v e d , at l e a s t f o r the s o l i d source machines, and t h a t the computer c o u l d s u p e r v i s e the o p e r a t i o n of the mass spectrometers. The p r e s e n t w r i t e r was r e s p o n s i b l e f o r the o v e r a l l d e s i g n and implementation o f the system as i t now e x i s t s . With h i s h e l p , D. L. M i t c h e l l (1971) designed and b u i l t the computer-mass spectrometer i n t e r f a c e , and R. D. Meldrum designed and b u i l t the t a p e - d r i v e i n t e r f a c e and a s e l e c t o r channel. T h i s w r i t e r was e n t i r e l y r e s p o n s i b l e f o r the computer programming, a l l of which was done i n assembly language. 11- 2 Hardware The equipment to be d i s c u s s e d i n t h i s s e c t i o n i n c l u d e s the hardware at the mass spectrometer, the computer, and the i n t e r f a c e between the two d e v i c e s . 16 The hardware at each mass spectrometer c o n s i s t s o f the measuring system, a d i g i t a l v o l t m e t e r , a d i g i t a l d i s p l a y and an output request s w i t c h . The measuring system i s c u r r e n t l y a h y b r i d D.C. a m p l i f i e r , c o n s i s t i n g o f an e l e c t r o m e t e r vacuum-tube p r e a m p l i f i e r and a c o n v e n t i o n a l D.C. a m p l i f i e r . The v o l t m e t e r d i g i t i z e s the output o f the measuring system, and i s d i s c u s s e d more f u l l y i n the f o l l o w i n g paragraph. The d i g i t a l d i s p l a y i s used i n c o n j u n c t i o n w i t h the 8 - p o s i t i o n output request s w i t c h to d i s p l a y data from the computer. The d i g i t a l v o l t m e t e r i s a Data Technology DT-344-2 4 - d i g i t meter, 1.000 v o l t s f u l l s c a l e , o f the d u a l - s l o p e i n t e g r a t i n g type. The input s i g n a l d i s c h a r g e s a c a p a c i t o r f o r a p e r i o d o f 50 msec (10,000 counts o f a 200 khz i n t e r n a l o s c i l l a t o r ) . At the c o n c l u s i o n of the i n t e r v a l , the input s i g n a l i s d i s c o n n e c t e d , and a p r e c i s e c u r r e n t source i s used to re-charge the c a p a c i t o r . The time taken f o r the r e c h a r g i n g o p e r a t i o n i s measured by c o u n t i n g the c y c l e s o f the i n t e r n a l o s c i l l a t o r . The number o f counts i s p r o p o r t i o n a l to the input v o l t a g e , and i t i s t h i s number which i s d i s p l a y e d at the c o n c l u s i o n o f the measurement. B i n a r y coded decimal (BCD) outputs are a l s o p r o v i d e d , t o g e t h e r w i t h a s i g n a l to i n d i c a t e the o p e r a t i o n i s complete (the PRINT s i g n a l ) . The measure-ment c y c l e i s repeated 5 times each second. The computer used i n the study i s an I n t e r d a t a Model 4, manufactured by I n t e r d a t a Inc. o f Oceanport, New J e r s e y . I t s major components are the p r o c e s s o r , the memory, and the p e r i p h e r a l d e v i c e s ( F i g u r e I I - l ) . The c e n t r a l pro-17 FIGURE I I - l Computer b l o c k diagram. MEMORY MEMORY BUS CONTROLLER MEMORY BUS PROCESSOR TAPE DRIVE TTY MS 1 MS 2 MS 3 A/D 360/67 18 c e s s o r , under c o n t r o l of a program r e s i d e n t i n a r e a d - o n l y memory, decodes and executes user i n s t r u c t i o n s , performs l o g i c a l and a r i t h m e t i c o p e r a t i o n s , supervises, communication w i t h e x t e r n a l d e v i c e s , and performs a v a r i e t y o f tasks a s s o c i ated w i t h the running o f programs. The memory, which c u r r e n t c o n s i s t s of 8,192 1 6 - b i t words, p r o v i d e s storage f o r user programs and data. The p e r i p h e r a l d e v i c e s i n c l u d e an ASR-33 T e l e t y p e , t h r e e mass spectrometers, and an a n a l o g - d i g i t a l c o n v e r t e r , a l l of which are connected to the m u l t i p l e x o r bus. A s e l e c t o r channel, designed and b u i l t i n the l a b o r a t o r y , p r o v i d e s data access independent o f the c e n t r a l p r o c e s s o r f o r a magnetic tape d r i v e . As t h i s t h e s i s was being w r i t t e n , a l i n k to the Computing Centre's IBM Duplex 360/67 was complete The p r o c e s s o r r e c o g n i z e s an e x t e n s i v e i n s t r u c t i o n s e t (about 65 user i n s t r u c t i o n s ) . I t has s i x t e e n 1 6 - b i t r e g i s t e r s , a l l of which can be used as accumulators. An i n t e r n a l program s t a t u s word (PSW) s u p e r v i s e s sequencing of i n s t r u c t i o n s , masks i n t e r r u p t s of v a r i o u s t y p e s , and c o n t a i n s s t a t u s i n f o r m a t i o n . The general a r c h i t e c t u r e o f the computer matches t h a t of the IBM 360 s e r i e s . Communication between the computer and e x t e r n a l d e v i c e s a t t a c h e d to the m u l t i p l e x o r bus i s e i t h e r program-c o n t r o l l e d or i n t e r r u p t - c o n t r o l l e d . The former r e q u i r e s t h a t the computer wait f o r the p a r t i c u l a r device to become ready b e f o r e i n i t i a t i n g a data t r a n s f e r , so t h a t the computer i s f u l l y d e d i c a t e d to the i n p u t / o u t p u t o p e r a t i o n . I n t e r r u p t -c o n t r o l l e d i n p u t / o u t p u t , however, all o w s the computer to 19 proceed w i t h o t h e r t a s k s . When a d e v i c e i s ready f o r a data t r a n s f e r , i t i n t e r r u p t s the computer, which immediately s e r v i c e s the de v i c e and then r e t u r n s t o i t s p r e v i o u s t a s k when the in p u t / o u t p u t o p e r a t i o n i s complete. The i n t e r r u p t -c o n t r o l l e d form o f communication was used i n t h i s study, as i t permits a g r e a t e r f l e x i b i l i t y i n programming. The mass spectrometer-computer i n t e r f a c e ( M i t c h e l l , 1971) c o n t r o l s the flow o f i n f o r m a t i o n between the tv/o d e v i c e s . The i n t e r f a c e c o n s i s t s o f the standard l o g i c r e q u i r e d f o r m u l t i p l e x o r bus o p e r a t i o n s , and s p e c i a l l o g i c r e q u i r e d f o r the mass spec t r o m e t e r s . The parameters read by the computer i n c l u d e the d i g i t a l output of the measuring system, and the s e t t i n g o f the output request s w i t c h . Output to the mass spectrometers i n c l u d e s BCD data to the 5-decade d i g i t a l d i s p l a y , and frequency c o n t r o l o f an o s c i l l a t o r t h a t determines the speed o f the magnetic scan d r i v e . A l l these f u n c t i o n s are summarized i n Table I I - 1 . TABLE I I - l INPUT MODE READ 1) 5 BCD d i g i t s from measuring system 2) shunt number 3) scan d i r e c t i o n 4) output request s w i t c h STATUS r e s e r v e d f o r f u t u r e use OUTPUT MODE WRITE 1) 5 BCD d i g i t s to d i g i t a l d i s p l a y 2) decimal p o i n t s on d i s p l a y 3) magnet scan speed OUTPUT COMMAND 1) decade s e l e c t i o n f o r rea d / w r i t e 2) scan speed m o d i f i c a t i o n s 20 I I - 3 F i l t e r i n g The d i g i t a l output of the measuring system lends i t s e l f to the use o f d i g i t a l f i l t e r s f o r improving the s i g n a l -t o - n o i s e r a t i o o f the data. The i n f o r m a t i o n content o f the s i g n a l occurs at low f r e q u e n c i e s , hence i t i s advantageous to employ a low pass f i l t e r (Weichert et a l . , 1967; R u s s e l l et a l . , 1971). The f i l t e r used i n t h i s study i s shown i n F i g u r e I I - 2 , r e p r e s e n t e d i n both the time and frequency domains. I t i s apparent t h a t f r e q u e n c i e s above about 0.6 hz. are almost co m p l e t e l y r e j e c t e d . The f i l t e r i s a p p l i e d by f i r s t a v eraging a l l p o s s i b l e c o n s e c u t i v e sets o f seven p o i n t s . A l t e r n a t e p o i n t s are d i s c a r d e d , and those remaining are averaged w i t h a t h r e e - p o i n t f i l t e r . The t h i r d stage i s f i l t e r i n g w i t h a f i v e - p o i n t f i l t e r , a f t e r which a l t e r n a t e p o i n t s are again d i s c a r d e d . For each summation, the end-points are h a l v e d . The r e p e t i t i v e averaging i s e n t i r e l y e q u i v a l e n t to m u l t i p l y i n g each o f the 19 p o i n t s i n c l u d e d i n the f i l t e r window by i t s a p p r o p r i a t e weight ( F i g u r e I I - 2 a ) , but i s c o m p u t a t i o n a l l y f a s t e r , s i n c e m u l t i p l i c a t i o n s are avoided. An a l i a s e d power spectrum o f the measuring system b a s e l i n e n o i s e i s shown i n F i g u r e I I - 3 , both b e f o r e and a f t e r f i l t e r i n g . Since the d i g i t i z a t i o n r a t e i s 5 per second (5 h z . ) , n o i s e at f r e q u e n c i e s above the Nyquist frequency ( f ^ ) of 2.5 hz. i s f o l d e d back to lower f r e q u e n c i e s . Noise at f r e q u e n c i e s (5 n ± 0.6) hz. (n = 1,2,*••) w i l l contaminate the s i g n a l i n the r e g i o n passed by the f i l t e r , but such c o n t r i b u t i o n s are 2 1 FIGURE I I - 2 F i l t e r r e p r e s e n t e d i n time and frequency domains. 6 r 0 1 2 Frequency (hz) 22 FIGURE I I - 3 2 Frequency (hz) 8 I Frequency (hz) 23 b e l i e v e d to be n e g l i g i b l e . The l a r g e peak at low f r e q u e n c i e s i n the power spectrum i s p r o b a b l y a r e s u l t o f b a s e l i n e d r i f t d u r i n g the time the raw data were taken. I I - 4 Spectrum scanning Two a l t e r n a t i v e s were c o n s i d e r e d f o r scanning of the spectrum. One o f these was peak s w i t c h i n g , i n which the magnet c u r r e n t i s a l t e r e d i n d i s c r e t e s t e p s , l a r g e enough to move d i r e c t l y from one peak to the next. The primary advantage of t h i s method i s speed o f a n a l y s i s , s i n c e v i r t u a l l y a l l measure-ment time i s spent m o n i t o r i n g the peaks, w h i l e i t s primary disadvantage i s the problem of r e c o v e r y o f p o s i t i o n on the peak t o p s . I f the peak tops are not completely f l a t , t h i s problem i n t r o d u c e s an a d d i t i o n a l u n c e r t a i n t y i n t o the data. Wasserburg et a l . (1969) have, however, used t h i s approach w i t h remarkable s u c c e s s . The o t h e r a l t e r n a t i v e i s magnetic f i e l d s canning, s i m i l a r to t h a t employed by Weichert (1965). The problem of r e c o v e r i n g peak p o s i t i o n and the requirement o f f l a t peak tops are removed, but c o n s i d e r a b l e time i s spent c o l l e c t i n g i n f o r m a t i o n between the peaks, e s p e c i a l l y i f the mass spectrometer has r e l a t i v e l y h i g h r e s o l u t i o n . With mag-net s c anning, t h e r e f o r e , a l o n g e r time i s r e q u i r e d t o o b t a i n the same amount o f data, which means th a t demands on the long-term s t a b i l i t y o f the i o n beam are g r e a t e r . The method used i n t h i s study i s magnetic f i e l d s c a nning, but the computer i s used to a l t e r the scanning r a t e . 24 In the r e g i o n between peaks, the scanning r a t e i s g r e a t l y i n c r e a s e d , but when a peak i s d e t e c t e d by the computer, the scan r a t e i s slowed, so t h a t an a c c u r a t e d e t e r m i n a t i o n o f the peak amplitude can be made. The computer d e t e c t s peaks by comparing two c o n s e c u t i v e d i g i t a l v o l t m e t e r r e a d i n g s , and a l t e r s the r a t e i f they d i f f e r by more than 0.51 o f f u l l s c a l e . The s i g n of the d i f f e r e n c e between the p o i n t s d e t e r -mines whether the r a t e i s i n c r e a s e d or decreased. 1 1 - 5 The d i g i t a l data system The system as i t p r e s e n t l y e x i s t s i s capable o f o p e r a t i n g i n t h r e e modes - f i l t e r i n g , data a c q u i s i t i o n , and o n - l i n e r e d u c t i o n . The f i r s t two were not used i n t h i s study, so they w i l l be d i s c u s s e d o n l y b r i e f l y . F i l t e r i n g mode: Th i s i s the s i m p l e s t mode of o p e r a t i o n , and the o n l y one t h a t can c u r r e n t l y be used by a l l t h r e e mass spec-trometers s i m u l t a n e o u s l y . The PRINT s i g n a l from a d i g i t a l v o l t m e t e r i s used to i n t e r r u p t the computer, whereupon the meter i s read, and i t s r e a d i n g f i l t e r e d as d e s c r i b e d i n the p r e v i o u s s e c t i o n . When a f i l t e r e d p o i n t becomes a v a i l a b l e ( a f t e r every f o u r i n t e r r u p t s ) , i t i s w r i t t e n onto the d i g i t a l d i s p l a y at the mass spectrometer. The o p e r a t o r records the a p p r o p r i a t e readings from the d i s p l a y . T h i s mode i s , i n p r a c t i c e , seldom used, except f o r r a t h e r u n s t a b l e s i g n a l s , where i t i s advantageous to make peak measurements as q u i c k l y as p o s s i b l e . 25 Data a c q u i s i t i o n mode: T h i s mode i s used o n l y w i t h the gas source mass spectrometer, and i s a m o d i f i c a t i o n o f the procedures des-c r i b e d by Weichert (1965). Data are f i l t e r e d as i n the f i l t e r i n g mode, but a d d i t i o n a l i n f o r m a t i o n such as magnet scan d i r e c t i o n and measuring system a t t e n u a t i o n i s a l s o r e q u i r e d . I t i s combined w i t h the f i l t e r e d d ata and s t o r e d i n a b u f f e r , which, when f u l l , i s output onto magnetic tape. T h i s tape i s p r o c e s s e d l a t e r at the Computing Centre by updated v e r s i o n s o f the program d e s c r i b e d by Weichert et a l . (1967). O n - l i n e r e d u c t i o n : T h i s mode p r o v i d e s f o r o n - l i n e r e d u c t i o n o f s o l i d source s p e c t r a o f both l e a d and s t r o n t i u m . Since i t was used i n t h i s study f o r measurement of s t r o n t i u m i s o t o p e r a t i o s , i t w i l l be d i s c u s s e d i n terms of t h i s element. Only one mass spectrometer c o u l d be p r o v i d e d w i t h o n - l i n e r e d u c t i o n at any one time, because of computer memory l i m i t a t i o n s . (The memory s i z e has r e c e n t l y been doubled, and t h i s l i m i t a t i o n no l o n g e r a p p l i e s . ) The program begins by s e t t i n g c onstants and c l e a r i n g a r r a y s , and prompting the user to e n t e r a sample i d e n t i f i c a t i o n and to s e l e c t program o p t i o n s through the t e l e t y p e . The computer then waits f o r an i n t e r r u p t from the mass spectrometer. The o p e r a t o r begins the a n a l y s i s at the up-mass end o f the spectrum by p e r m i t t i n g the PRINT commands from the d i g i t a l v o l t m e t e r to i n t e r r u p t the computer. At each i n t e r -2 6 r u p t , the mass spectrometer i s read and the data are f i l t e r e d , as d e s c r i b e d p r e v i o u s l y . The f i r s t data t h a t are taken are b a s e l i n e p o i n t s , which the computer r e c o g n i z e s by the absence o f a magnet scan i n d i c a t i o n . The f i l t e r e d b a s e l i n e p o i n t s f o r each shunt are summed and s t o r e d i n an a r r a y from which the average b a s e l i n e values are l a t e r c a l c u l a t e d . When the o p e r a t o r begins to scan, the computer r e c o g n i z e s the f a c t and t r e a t s the p o i n t s somewhat d i f f e r e n t l y . The raw p o i n t s are compared to determine i f the scan r a t e needs to be a l t e r e d . F i l t e r e d p o i n t s are searched f o r r e l a t i v e maxima by summing them i n c o n s e c u t i v e groups o f t h r e e , and examining the sums under a f i v e - p o i n t window. I f one i s found, the thr e e p o i n t s c o m p r i s i n g the sum are examined, and the l a r g e s t o f them i s taken as the maximum. I t , t o g e t h e r w i t h i t s time, i s s t o r e d i n a t a b l e o f maxima. (Times are d e r i v e d from a f i l t e r e d p o i n t counter.) B a s e l i n e s are taken again at the low-mass end o f the spectrum, and the spectrum i s scanned i n the up-mass d i r e c t i o n . B a s e l i n e s are again measured, and the end-of-scan b u t t o n i s p r e s s e d to i n i t i a t e scan p r o c e s s i n g . T h i s begins w i t h the s u b t r a c t i o n o f b a s e l i n e s , c o r r e c t e d f o r d r i f t , from a l l the maxima i n the t a b l e . The peaks are a u t o m a t i c a l l y i d e n t i f i e d , a l i n e a r c o r r e c t i o n f o r growth or decay i s a p p l i e d to them, and the i s o t o p i c r a t i o s are c a l c u l a t e d . The S r 8 7 / S r 8 6 r a t i o i s c o r r e c t e d f o r f r a c t i o n a t i o n . Peak h e i g h t s , t h e i r times, and the i s o t o p i c r a t i o s are p r i n t e d on the t e l e -27 type and serve as a permanent r e c o r d o f the a n a l y s i s . The i s o t o p i c r a t i o s can a l s o be output on the d i s p l a y at the mass spectrometer at the request o f the o p e r a t o r . At the o p t i o n o f the o p e r a t o r , the f i l t e r e d data may be s t o r e d on magnetic tape. Each scan r e q u i r e s about three minutes. I I - 6 C o n c l u s i o n s The system d e s c r i b e d i n the pre v i o u s s e c t i o n s has been used e x t e n s i v e l y i n the l a b o r a t o r y f o r analyses o f l e a d (by gas and s o l i d s o u r c e ) , rubidium, and s t r o n t i u m . Over 1000 analyses have been made w i t h i t i n the l a s t two y e a r s . The p r e c i s i o n o b t a i n e d w i t h the system depends on the element b e i n g analyzed. For s t r o n t i u m , a p r e c i s i o n o f 0.02% f o r the S r 8 7 / S r 8 6 r a t i o i s r o u t i n e l y a c hieved (Chapter 1 1 1 - 5 ) , a value which i s q u i t e adequate f o r the purposes of t h i s study. Perhaps the p r i n c i p a l advantage o f the system i s i t s great f l e x i b i l i t y . With minor m o d i f i c a t i o n s to the hard-ware, i t should be p o s s i b l e f o r the computer to c o n t r o l a l l aspects o f the a n a l y s i s . The r e c e n t completion of an o n - l i n e c o n n e c t i o n to the IBM Duplex 360/6 7 at the Computing Centre enables the system to employ the much l a r g e r computing re s o u r c e s o f the IBM computer. CHAPTER I I I ANALYTICAL TECHNIQUES I I I - l I n t r o d u c t i o n The a n a l y t i c a l techniques employed i n t h i s study are mostly c o n v e n t i o n a l ones, the most n o t a b l e e x c e p t i o n b e i n g the d e t e r m i n a t i o n o f rubidium and s t r o n t i u m concentra-t i o n s by an x-ray f l u o r e s c e n c e method. Since the procedures are an important p a r t o f o b t a i n i n g r e s u l t s o f h i g h p r e c i s i o n , they are d e s c r i b e d i n t h i s c h a pter. I I I - 2 Measurement o f rubidium and s t r o n t i u m c o n c e n t r a t i o n s The samples were prepared as f o l l o w s : Rocks were f i r s t examined f o r weathered or d i s -c o l o u r e d s u r f a c e s , which were chipped o f f . About 2-5 kgm of the rock were passed through a jaw c r u s h e r , and then through a cone c r u s h e r . At t h i s p o i n t , the sample was s p l i t , and a p o r t i o n o f about 200 gm was taken f o r whole rock a n a l y s i s . T h i s p o r t i o n was crushed to pass 100 mesh by running i t through a p u l v e r i z e r two or three times. Any p a r t i c l e s t h a t d i d not pass 100 mesh (mostly p l a t y m i n e r a l s ) were crushed i n a Spex m i l l u n t i l they were s u f f i c i e n t l y f i n e . Approximate Rb/Sr r a t i o s were determined by x-ray f l u o r e s c e n c e f o r a l l samples i n order to s e l e c t those best s u i t e d f o r d a t i n g . The machine used was a P h i l i p s u n i t , operated by the Department of G e o l o g i c a l S c i e n c e s . I t c o n s i s t s of a PW1011/60 h i g h v o l t a g e generator, a PW1050/85 x-ray 29 ge n e r a t o r , a PW4025 s c i n t i l l a t i o n c o u n t e r , a PW4231 s c a l e r , a PW4261 t i m e r , a PW1365 p u l s e shaper, a PW4280 a m p l i f i e r / a n a l y s e r , and a PW1362 ratemeter. A few grams o f rock powder were i n t r o d u c e d i n t o the x-ray f l u o r e s c e n c e u n i t , and the p o r t i o n o f the x-ray spectrum i n c l u d i n g the rubidium and s t r o n t i u m peaks was scanned. An estimate o f the Rb/Sr r a t i o o f a sample was o b t a i n e d from the spectrum by comparing i t to t h a t o f a sta n d a r d . The u n c e r t a i n t y o f the estimate was about 5 p e r c e n t . Rubidium and s t r o n t i u m c o n c e n t r a t i o n s were a l s o i n d i v i d u a l l y e s t i m a t e d , but s u b s t a n t i a l e r r o r s o f t e n o c c u r r e d u n l e s s the standard and unknown were c h e m i c a l l y q u i t e s i m i l a r . The o p e r a t i n g parameters o f the x-ray f l u o r e s c e n c e u n i t are g i v e n i n Table I I I - l . TABLE I I I - l O p e r a t i n g parameters f o r the x-ray f l u o r e s c e n c e u n i t . (Ryan, i n p r e p a r a t i o n ) Target m a t e r i a l : Tube v o l t a g e : Tube amperage: Pulse h e i g h t a n a l y s e r : molybdenum 50 kV 30 mA a t t e n u a t i o n : 5 C r y s t a l : C o l l i m a t o r s e t t i n g : window: time c o n s t a n t : 2.70 (lower l e v e l ) 4.00 (width) 0.5 seconds l i t h i u m f l u o r i d e (200) f i n e 30 Once the approximate Rb/Sr r a t i o s were known, samples w i t h a s u i t a b l e spread i n t h a t r a t i o were s e l e c t e d f o r d a t i n g . T h e i r R b 8 7 / S r 8 6 r a t i o s were determined more p r e c i s e l y by an x-ray f l u o r e s c e n c e technique developed by Ryan ( i n p r e p a r a t i o n ) , and t h e i r S r 8 7 / S r 8 6 r a t i o s were measured mass s p e c t r o m e t r i c a l l y w i t h the a i d o f the o n - l i n e system d e s c r i b e d i n Chapter I I . Rubidium and s t r o n t i u m c o n c e n t r a t i o n s have conven-t i o n a l l y been determined by i s o t o p e d i l u t i o n . The technique e n t a i l s adding a known amount of rubidium or s t r o n t i u m o f r a d i c a l l y d i f f e r e n t i s o t o p i c composition (spike) to a weighed q u a n t i t y o f rock powder. The powder i s p r o c e s s e d c h e m i c a l l y to separate the rubidium or s t r o n t i u m , and the i s o t o p i c com-p o s i t i o n of the mixture of spike and sample i s measured on the mass spectrometer. S i n c e the i s o t o p i c composition of both s p i k e and sample i s known, as i s the amount o f s p i k e added and the weight o f rock used, the c o n c e n t r a t i o n of rubidium or s t r o n t i u m i n the sample can e a s i l y be c a l c u l a t e d . R e c e n t l y , the i s o t o p e d i l u t i o n technique has been r e p l a c e d to some extent by x-ray f l u o r e s c e n c e methods (Doering, 1968; Compston et a l . , 1969; F a i r b a i r n and H u r l e y , 1971). The primary advantages are speed and s i m p l i c i t y ; ten to f i f t e e n samples can e a s i l y be analyzed i n a few hours, and no sample d i s s o l u t i o n i s r e q u i r e d . About three or f o u r grams of rock powder are formed i n t o a p e l l e t , which i s surrounded by a 50-50 mixture o f b o r i c a c i d and b a k e l i t e powder, and the sample i s compressed 31 h y d r a u l i c a l l y . The r e s u l t i n g p e l l e t i s about 3 cm i n diameter, and about 0.8 cm t h i c k . The measurement i s made by comparing the unknown samples w i t h a group of fou r U n i t e d S t a t e s G e o l o g i c a l Survey s t a n d a r d s . For each p e l l e t , readings are taken at s p e c i f i c p o i n t s i n the x-ray spectrum, the p o i n t s b e i n g the in c o h e r -e n t l y (Compton) s c a t t e r e d molybdenum peak, the rubidium and s t r o n t i u m peaks and a b a s e l i n e p o s i t i o n . In a d d i t i o n , the molybdenum peak i t s e l f i s measured on a b a k e l i t e d i s c f o r 20 seconds i n order to monitor the s t a b i l i t y o f the x-ray beam. At a l l other p o s i t i o n s , counts are taken f o r 100 seconds. A t y p i c a l a n a l y s i s i n v o l v e s measuring the fou r s t a n d a r d s , u s u a l l y i n d u p l i c a t e , and the unknowns. Most samples r e p o r t e d i n the t h e s i s were analyzed i n d u p l i c a t e , and on d i f f e r e n t days, but measurements were made on the same p e l l e t s . The c a l c u l a t i o n o f the rubidium and s t r o n t i u m con-c e n t r a t i o n s , and the Rb/Sr r a t i o s , were done by computer. The s t a n d a r d s , f o r which rubidium and s t r o n t i u m c o n c e n t r a t i o n s and the mass a b s o r p t i o n c o e f f i c i e n t (u) were known, were f i r s t used to d e f i n e a l i n e r e l a t i n g u to the r e c i p r o c a l o f the Compton s c a t t e r e d peak h e i g h t . The u-values f o r the unknown samples were determined from the l i n e . L i n e s were computed f o r the standards by comparing the rubidium or s t r o n t i u m c o n c e n t r a t i o n s and the a d j u s t e d peak h e i g h t (peak h e i g h t m u l t i p l i e d by u). The rubidium and s t r o n t i u m c o n c e n t r a t i o n s were o b t a i n e d from the l a t t e r p l o t s , and were used t o c a l c u l a t e 32 the Rb/Sr r a t i o s . The p r e c i s i o n of the r e s u l t s w i l l be d i s c u s s e d i n a l a t e r s e c t i o n , but was not worse than 31 f o r the Rb/Sr r a t i o s . The standards used f o r the x-ray f l u o r e s c e n c e d e t e r m i n a t i o n o f Rb/Sr r a t i o s were standar d rocks d i s t r i b u t e d by the U n i t e d S t a t e s G e o l o g i c a l Survey. The samples are a b a s a l t , BCR-1, an a n d e s i t e , AGV-1, a g r a n i t e , G-2, and a g r a n o d i o r i t e , GSP-1. Values f o r t h e i r rubidium and s t r o n t i u m c o n c e n t r a t i o n s were o b t a i n e d from F a i r b a i r n and H u r l e y (1971) and De L a e t e r and Abercrombie (1970), and are g i v e n i n Table I I I - 2 , t o g e t h e r w i t h the values used i n t h i s study, which are denoted by an a s t e r i s k . The apparent d i f f e r e n c e s between the samples are not s i g n i f i c a n t . TABLE III-2 Rubidium and s t r o n t i u m c o n c e n t r a t i o n s of s t a n d a r d r o c k s . Sample Rubidium S t r o n t i u m Rb/Sr Reference (ppm) (ppm) BCR-1 48.2 * 331 * .146 1 48.0 332 .145 2 AGV-1 67.7 663 * .102 1 67.0 657 .102 2 GSP-1 253 235 1.08 1 255 * 235 A 1.09 2 G-2 171 480 * .356 1 169 * 475 .356 2 * Values used i n t h i s study , References: 1 - F a i r b a i r n and H u r l e y (1971) 2 - De L a e t e r and Abercrombie (1970) 33 The y v a l u e s f o r the rock standards were o b t a i n e d by d i r e c t measurement and by c a l c u l a t i o n . The d i r e c t measure-ment, c a r r i e d out by B. D. Ryan, employed the x-ray technique p r e v i o u s l y d e s c r i b e d , except t h a t chemical standards o f known y's were used to d e f i n e the l i n e r e l a t i n g y and the r e c i p r o c a l o f the Compton-scattered peak h e i g h t . The y valu e s f o r the rock standards were o b t a i n e d from t h i s l i n e , s i n c e t h e i r Compton-scattered peak h e i g h t s were known. The c a l c u l a t i o n of the y - v a l u e s , c a r r i e d out by the w r i t e r , made use o f chemical analyses o f the r o c k s , and t a b l e s of the y valu e s o f t h e i r c o n s t i t u e n t elements. The weight p e r c e n t o f each element was m u l t i p l i e d by i t s y va l u e and the products summed to y i e l d the y v a l u e . The r e s u l t s o b t a i n e d are summarized below. TABLE I I I - 3 y v a l u e s f o r the U.S.G.S. standar d rocks Standard ^llll^r.* C a l c u l a t e d measurement GSP-1 6.76 6.67 AGV-1 7.41 7.33 BCR-1 9.65 9.50 G-2 6.07 6.04 The d i r e c t l y measured r e s u l t s were used f o r t h i s study, because they are b e l i e v e d to be b e t t e r determined. The c a l c u l a t e d y's are q u i t e s e n s i t i v e to u n c e r t a i n t i e s i n the measurement of elements w i t h h i g h y v a l u e s , such as i r o n . However, both s e t s o f y v a l u e s gave e s s e n t i a l l y 34 s i m i l a r Rb/Sr r a t i o s f o r the unknowns. I I I - 3 Chemical p r e p a r a t i o n of samples The chemical procedure f o r the p r e p a r a t i o n o f samples f o r i s o t o p i c a n a l y s i s was m o d i f i e d from U n i t e d S t a t e s G e o l o g i c a l Survey procedures by Ryan ( i n p r e p a r a t i o n ) . About 0.5 gm of rock powder were d i s s o l v e d i n 10 ml o f 48% hydro-f l u o r i c a c i d and about 1 ml of 9M s u l p h u r i c a c i d . D i s s o l u t i o n s were c a r r i e d out i n 50 ml T e f l o n beakers, and u s u a l l y r e q u i r e d 24 to 48 hours. A f t e r the sample was i n s o l u t i o n , the beaker was heated s t r o n g l y to d r i v e o f f excess s u l p h u r i c a c i d . The r e s i d u e i n the beaker was d i s s o l v e d i n about 10 ml o f 6N h y d r o c h l o r i c a c i d , and c e n t r i f u g e d . The s o l u t i o n was t r a n s -f e r r e d to an i o n exchange column, c o n s i s t i n g of about 20 gm o f Dowex 50 X-8 i o n exchange r e s i n . The sample was e l u t e d through the column w i t h 6N h y d r o c h l o r i c a c i d . C o l l e c t i o n o f the e l u a n t began a f t e r 25 ml o f s o l u t i o n had passed through the columns. About 40 ml o f s o l u t i o n , which c o n t a i n e d both rubidium and s t r o n t i u m , were c o l l e c t e d . A second, s i m i l a r column was used to separate the rubidium and s t r o n t i u m . The 40 ml o f s o l u t i o n c o l l e c t e d from the f i r s t column were taken to dryness and r e - d i s s o l v e d i n a minimum volume of 2N h y d r o c h l o r i c a c i d . The sample was t r a n s f e r r e d to the column, and e l u t e d w i t h 2N h y d r o c h l o r i c a c i d . A f t e r 85-90 ml o f a c i d had passed through the column, about 40 ml of s o l u t i o n were c o l l e c t e d . T h i s r e p r e s e n t e d the s t r o n t i u m f r a c t i o n . The sample was reduced i n volume, 35 t r a n s f e r r e d to a 5 ml beaker, and taken to dryness. I I I-4 Mass spectrometry The mass spectrometer used was a 30 cm, 90°, s i n g l e -f o c u s i n g i n s t r u m e n t . Samples were an a l y z e d u s i n g the t r i p l e f i l a m e n t t e c h n i q u e , w i t h f i l a m e n t s o f .75 mm x .025 mm rhenium r i b b o n . The s t r o n t i u m c h l o r i d e was d i s s o l v e d i n a s m a l l amount o f h y d r o c h l o r i c a c i d and t r a n s f e r r e d t o the outgassed f i l a -ments w i t h a d i s p o s a b l e g l a s s p i p e t t e . A drop was p l a c e d on each o f the s i d e f i l a m e n t s and a c u r r e n t o f about 0.8 A was passed through them. Another drop was added a f t e r the sample had d r i e d , and the procedure repeated u n t i l a l l the sample was on the f i l a m e n t s . The c u r r e n t through them was i n c r e a s e d to about 1.2-1.4 A f o r a minute, a f t e r which time i t was i n c r e a s e d u n t i l the f i l a m e n t s glowed a d u l l r e d , (about 1.7 to 2.1 A) and was h e l d t h e r e f o r about a minute. The f i l a m e n t s were p l a c e d i n a f i l a m e n t b l o c k , a c e n t r e f i l a m e n t was added, and the b l o c k i n t r o d u c e d i n t o the mass spectrometer. The mass spectrometer was l e f t to pump u n t i l the p r e s s u r e , measured at the i o n s o u r c e , f e l l below 5 x 10" 7 t o r r . The mass spectrometer s u p p l i e s were switched on about 15-20 minutes b e f o r e the a n a l y s i s began. The a c c e l e r -a t i n g v o l t a g e was s e t at 5 kV, and the magnet c u r r e n t to about 250 mA. The c e n t r e f i l a m e n t supply was s e t to about 2 A (approx. 1300° C) then turned s l o w l y up to 3 A (approx. 1500° C) over a p e r i o d o f about 15 minutes. The slow i n c r e a s e i n c u r r e n t was n e c e s s a r y because at temperatures above about 36 1000° C, the samples outgassed s i g n i f i c a n t l y and the p r e s s u r e r o s e . More r a p i d h e a t i n g gave r i s e to a very h i g h p r e s s u r e i n the source r e g i o n ( > l x l 0 " s t o r r . ) . Above a f i l a m e n t c u r r e n t o f about 3 A, the r e g i o n o f the s t r o n t i u m spectrum was searched f o r the rubidium peaks. The f i l a m e n t c u r r e n t was i n c r e a s e d i n steps o f 0.1 A u n t i l the rubidium was d e t e c t e d . (Rubidium i s e a s i l y i o n i z e d - 1 ugm o f rubidium w i l l produce an i n t e n s e s i g n a l . ) At t h i s p o i n t , the behaviour of the rubidium peaks was observed i n order to o b t a i n an i d e a o f the amount of rubidium contamina-t i o n p r e s e n t . A s l o w l y growing or decaying peak i n d i c a t e d r e l a t i v e l y l i t t l e rubidium, w h i l e continuous r a p i d growth f o r at l e a s t t e n minutes suggested c o n s i d e r a b l e rubidium. Samples w i t h low contamination were u s u a l l y heated s t r o n g l y f o r about 5 minutes, or u n t i l the rubidium s i g n a l was <^10" 1 S A, by r a i s i n g the c e n t r e f i l a m e n t temperature to about 2500° C. Samples w i t h s i g n i f i c a n t rubidium c o n t a m i n a t i o n were l e f t to heat f o r an hour or so at 1500° C, then heated s t r o n t l y u n t i l the rubidium peak was s u i t a b l y s m a l l . A f t e r the s t r o n g h e a t i n g s t e p , the f i l a m e n t c u r r e n t was reduced to 2.5 to 3 A f o r a few minutes i n order to a l l o w the source r e g i o n to c o o l and the machine p r e s s u r e to drop. The next step i n the a n a l y s i s was to i n c r e a s e the c e n t r e f i l a m e n t c u r r e n t u n t i l a s t r o n t i u m spectrum was d e t e c t e d . Focus c o n d i t i o n s f o r the source were o p t i m i z e d , and the c u r r e n t was s l o w l y i n c r e a s e d . The c u r r e n t was r a i s e d u n t i l the S r 8 8 i o n c u r r e n t was about 2x10" 1 1 A, or u n t i l the c e n t r e f i l a m e n t 37 temperature was about 1850° C. I f the s i g n a l s t r e n g t h was i n s u f f i c i e n t , the s i d e f i l a m e n t c u r r e n t supply was turned on, and the c u r r e n t was i n c r e a s e d u n t i l the S r 8 8 s i g n a l was s u f f i c i e n t l y l a r g e . The s i g n a l was allowed to s t a b i l i z e f o r a few minutes, d u r i n g which time a check was made f o r the R b 8 5 peak. I f one was found, and the S r 8 8 s i g n a l was i n c r e a s -i n g , the sample was again heated s t r o n g l y w i t h the c e n t r e f i l a m e n t as d e s c r i b e d p r e v i o u s l y . I f a R b 8 5 peak was found, and the s t r o n t i u m s i g n a l was deca y i n g , no attempt to remove the rubidium was made, and the a n a l y s i s was cont i n u e d . For most runs i t was p o s s i b l e t o remove the Rb 8 5 peak completely ( R b 8 5 < 1 0 " 1 5 A). The S r 8 8 i o n beam was then monitored, and i f i t appeared s t a b l e on the c h a r t r e c o r d e r , the a n a l y s i s was begun. The a n a l y s i s i t s e l f c o n s i s t e d o f at l e a s t f i v e complete scans o f the s t r o n t i u m spectrum. I f a rubidium peak was p r e s e n t , but was too smal l to be d e t e c t e d by the computer ( < 2 .5x10" 1 , 1 A ) , i t s peak h e i g h t was reco r d e d on the c h a r t so t h a t a c o r r e c t i o n c o u l d l a t e r be a p p l i e d . The peaks u s u a l l y scanned were the S r 8 8 , S r 8 7 and S r 8 6 peaks and, i f ne c e s s a r y , R b 8 5 . S r 8 1 f was measured only i f a Sr 8"* s p i k e was used. , During the a n a l y s i s the n o r m a l i z e d S r 8 7 / S r 8 6 r a t i o was rec o r d e d , and a running estimate kept o f i t s standard d e v i a t i o n o f the mean (o) . The run was u s u a l l y t e r m i n a t e d when 2a f o r the r a t i o f e l l below 0.03%, but not b e f o r e f i v e scans had been taken. For some a n a l y s e s , a s t a b l e beam was d i f f i c u l t to o b t a i n , p r o b a b l y due to a poor sample l o a d i n g . It was found 38 t h a t i f the sample was heated s t r o n g l y by the c e n t r e f i l a m e n t f o r a few minutes, the s t r o n t i u m s i g n a l was u s u a l l y more s t a b l e a f t e r w a r d s . An a l t e r n a t i v e procedure was to i n c r e a s e the s i d e f i l a m e n t c u r r e n t b r i e f l y to produce the same e f f e c t . I I I - 5 P r e c i s i o n As was s t a t e d i n the p r e v i o u s s e c t i o n , a l l s t r o n t i u m analyses were c o n t i n u e d u n t i l 2o f o r the run f e l l below 0.03%. I f the e r r o r s are random and n o r m a l l y d i s t r i b u t e d , r epeated analyses o f a s t a n d a r d should a l s o f a l l below t h i s v a l u e . R e p l i c a t e analyses o f an i n t e r - l a b o r a t o r y s t a n d a r d , the Eimer and Amend s t r o n t i u m carbonate, are shown i n T a b l e III-4 and have a 95% c o n f i d e n c e l i m i t o f .01 6%, which compares f a v o r a b l y w i t h the average value f o r the i n d i v i d u a l analyses of about 0.02%. The agreement of estimates suggests the e r r o r s are indeed random. A more s t r i n g e n t t e s t of p r e c i s i o n i s d u p l i c a t e analyses o f rock samples, which i n c l u d e s s e p a r a t e chemical p r e p a r a t i o n o f the samples. S i x rocks were analyzed i n d u p l i c a t e , and the r e s u l t s are shown i n Table I I I - 5 . An e s t i m a t e o f p r e c i s i o n from these r e s u l t s i s 0.02 ?% (95% c o n f i d e n c e l e v e l ) , i n reasonable agreement w i t h the p r e v i o u s v a l u e s . On the b a s i s o f the three d i f f e r e n t e stimates o f p r e c i s i o n , a v a l u e o f 0.02% f o r a l l analyses r e p o r t e d i n t h i s t h e s i s i s i n d i c a t e d . T h i s v a l u e may be compared to t h a t o b t a i n e d at the C a l i f o r n i a I n s t i t u t e o f Technology by Wasserburg and co-workers. 39 Papanastassiou and Wasserburg (1969) have d i s c u s s e d the pre-c i s i o n o f t h e i r system, which i s g e n e r a l l y regarded as r e p r e s e n t i n g the s t a t e o f the a r t . T h e i r v a l u e appears to average about 0.01%, as e s t i m a t e d from i n d i v i d u a l analyses and from r e p l i c a t e analyses of a sea-water standard. The p r e c i s i o n o b t a i n e d i n t h i s study i s thus w i t h i n a f a c t o r o f two o f t h a t o b t a i n e d at C.I.T. I t s h o u l d be noted t h a t o n l y about 10 scans were taken f o r each a n a l y s i s r e p o r t e d i n t h i s t h e s i s , whereas Wasserburg and a s s o c i a t e s u s u a l l y r e q u i r e about 100. For g e o c h r o n o l o g i c a l s t u d i e s of B r i t i s h Columbia, such as are d e s c r i b e d i n t h i s t h e s i s , the l a r g e r number o f scans was c o n s i d e r e d u n a c c e p t a b l e , whereas the 0.02% p r e c i s i o n appears s a t i s f a c t o r y . Ryan ( i n p r e p a r a t i o n ) has estimated the p r e c i s i o n o f Rb/Sr r a t i o s determined by x-ray f l u o r e s c e n c e to be 3% at the 95% c o n f i d e n c e l e v e l . D u p l i c a t e analyses of some samples are t a b u l a t e d i n T a b l e II1-6, and c o n f i r m Ryan's e s t i m a t e . For the samples s t u d i e d i n t h i s r e s e a r c h , the i s o t o p i c analyses and x-ray f l u o r e s c e n c e analyses make comparable c o n t r i b u t i o n s to the age u n c e r t a i n t i e s . 40 TABLE III- 4 R e p l i c a t e measurements o f Eimer and Amend s t r o n t i u m carbonate. Date S r 8 7 / S r S 6 1971 May 13 May 15 May 16 June 5 June 7 J u l y 3 0.7083 0.7079 0.7080 0.7083 0.7082 0.7082 1972 May 19 May 22 0.7083 0.7082 average: 0.7082 2 a 0 . 0 0 0 ^ TABLE I I I - 5 D u p l i c a t e S r 8 7 / S r 8 6 measurements f o r rock samples. Sample 401-10 401-11 R2-1 Rl-T-1 18AF71 R6-2 S r 8 7 / S r 0.7196 0.7197 0.7304 0.7304 0.7101 0.7099 0.7148 0.7149 0.7127 0.7128 0.7176 0.7178 41 TABLE II I - 6 R e p l i c a t e s o f rubidium § s t r o n t i u m c o n c e n t r a t i o n measurements. Sample Rb (ppm) Sr (ppm) Rb/Sr 2BF71 143 460 0.311 143 459 0.312 141 457 0.309 142 460 0.309 Rl-4 76.1 266 0.286 75.7 266 0.285 75.6 272 0.278 76.5 271 0.282 Rl-T-1 101 201 0.502 - 101 199 0.508 3F71 127 327 0.388 126 327 0.385 R5-2 86.5 210 0.412 87.4 210 0.416 87.2 211 0.413 5F71 109 521 0.209 110 522 0.211 R2-1 79.7 427 0.189 79.9 432 0.185 R3-1 85.0 228 0.373 85.6 229 0.374 R3-T 73.7 230 0.320 74.8 234 0.320 CHAPTER IV THE GEOLOGICAL PROBLEM IV-1 Background The g e n e r a l g e o l o g i c a l elements o f s o u t h e a s t e r n B r i t i s h Columbia are shown on F i g u r e IV-1, t o g e t h e r w i t h the l o c a t i o n s o f areas s t u d i e d . The major elements are the P u r c e l l A n t i c l i n o r i u m , the Kootenay A r c , and the Shuswap Metamorphic Complex. The l a t t e r two are i n c l u d e d i n the Omineca C r y s t a l l i n e B e l t , which extends northwestward i n t o the Yukon. To the south i t disa p p e a r s beneath younger r o c k s . The P u r c e l l A n t i c l i n o r i u m i s composed p r i m a r i l y o f sediments o f the B e l t - P u r c e l l Supergroup. Where the base of the sequence i s exposed, i t i s seen to r e s t on c r y s t a l l i n e basement, which i s 1600-1800 m.yr. o l d (Obradovich and P e t e r -man, 1968). The B e l t - P u r c e l l sediments are unconformably o v e r l a i n by the l a t e Precambrian Windermere sequence i n some p l a c e s , and by Cambrian rocks i n o t h e r s . The comprehensive r u b i d i u m - s t r o n t i u m study by Obradovich and Peterman (1968) i n d i c a t e d an age o f about 850 m.yr. f o r the youngest sediments, w i t h o t h e r p e r i o d s o f s e d i m e n t a t i o n at 1050 m.yr. and 1250 m.yr. The E a s t Kootenay Orogeny (White, 1959) t e r m i n a t e d the P u r c e l l s e d i m e n t a t i o n . The Kootenay Arc i n c l u d e s rocks o f l a t e Precambrian to T r i a s s i c age. I t i s a b e l t of h i g h l y deformed rocks which have been v a r i a b l y metamorphosed. I t s s t r u c t u r e and s t r a t i g -raphy have r e c e n t l y been d e s c r i b e d by F y l e s (1964, 1967, 1970a), 4 3 FIGURE IV-1 G e o l o g i c a l elements o f s o u t h e a s t e r n B r i t i s h Columbia. QL FC TO Quesnel Lake Gneiss Frenchman's Cap Thor-Odin mg RG v Malton Gneiss Revelstoke Gneiss V a l h a l l a 44 Read (1966) , Crosby (1968) , Ross and Kell e r h a l s (1968) , and Ross (1970). The Nelson and Kuskanax Batholiths are major intrusions within the arc; the former has been dated at about 165 m.yr. (Nguyen et a l . , 1968). A lead isotope study of galenas from the Arc ( S i n c l a i r , 1966; Reynolds and S i n c l a i r , 1971) indicated that, i n i t s southern part, i t may be under-l a i n by 1500-1700 m.yr. basement. The Shuswap Complex i s an extensive b e l t of high-grade, highly deformed metamorphic rocks. Its boundaries generally coincide with the s i l l i m a n i t e isograd. The time of metamorphism has long been i n dispute, estimates ranging from Mesozoic (Cairnes, 1929; Wheeler, 1970) to Precambrian (Jones, 1959), though recent mapping favours a la t e Paleozoic or Mesozoic age (Ross and K e l l e r h a l s , 1968; Reesor and Moore, 1971). (A generalized geological time scale i s shown i n Table IV-1.) It was stated i n the f i r s t chapter that a major objective of thi s study was to date cert a i n gneisses within the southern Omineca C r y s t a l l i n e Belt of B r i t i s h Columbia. Proposals have been made that these gneisses represent Pre-cambrian c r y s t a l l i n e basement. Their complex metamorphic and deformational h i s t o r y make them d i f f i c u l t to date from geologic evidence, so an attempt was made to date some of them radi o m e t r i c a l l y . The presence of Precambrian c r y s t a l l i n e basement i s important for several reasons. One concerns a hypothesis proposed by Ross (1968, 1970) o u t l i n i n g a deformational 45 h i s t o r y o f the are a , a c e n t r a l p a r t o f which i s the p a r t i c i p a -t i o n o f Precambrian basement i n the r e g i o n a l d e f o r m a t i o n . Another reason concerns p l a t e t e c t o n i c r e c o n s t r u c t i o n s f o r the r e g i o n , which r e q u i r e g e o c h r o n o l o g i c a l data. A t h i r d reason i s r e l a t e d to the evidence t h a t the area was once a c o n t i n e n t a l margin ( f o r p a r t o f i t s h i s t o r y ) , which, i f t r u e , c o u l d p l a c e severe c o n s t r a i n t s on the occurrence o f Precambrian c r y s t a l l i n e basement. TABLE IV-1 S i m p l i f i e d g e o l o g i c a l t i m e - s c a l e . ERA PERIOD TIME (m.yr.) CENOZOIC Quaternary 0 - 10 T e r t i a r y 10 - 70 Cretaceous 70 - 135 MESOZOIC J u r a s s i c 135 - 190 T r i a s s i c 190 - 225 Permian 225 - 280 Car b o n i f e r o u s 280 -. 350 PALEOZOIC Devonian 350 - 400 S i l u r i a n 400 - 440 O r d o v i c i a n 440 - 500 Cambrian 500 -^600 PRECAMBRIAN >600 4 6 IV-2 Theories of o r i g i n of the gneiss domes Ross's hypothesis for the deformational h i s t o r y of the region, among other things, accounts for the origi n s of three domal complexes that l i e within the eastern edge of the Shuswap Complex at about 80 km in t e r v a l s (Figure IV-1). From north to south they are Frenchman's Cap (Wheeler, 1965; Fyles, 1970; McMillan, 1970) , Thor-Odin (Reesor, 1970 ; Reesor and Moore, 1971), and V a l h a l l a (Reesor, 1965). An opposing view regarding t h e i r origins has been put forward by Reesor and Moore (1971). These views w i l l now be discussed. Ross (1968, 1970) and Ross and Kellerhals (1968) have proposed that the domes were produced as a r e s u l t of interference between two d i f f e r e n t directions of f o l d i n g . In t h e i r view, sediments that had been deposited on a gneissic basement were f i r s t deformed when a s l i c e of basement was detached and was thrust into them. This f i r s t phase of deformation thus produced large recumbent f o l d s , cored i n t h e i r a n t i c l i n a l parts by basement gneiss. The folds were l a t e r refolded about d i f f e r e n t a x i a l planes, giving r i s e to the domal structures. The f i r s t phase of deformation, which began at some time a f t e r the early Cambrian, saw the formation of large recumbent folds or nappes, most of which closed towards the east. At some l a t e r time, probably a f t e r the early Permian, but before the la t e T r i a s s i c , structures of the second phase developed as a resu l t of reaction between the easterly move-ment of the nappes and the more r i g i d P u r c e l l mass. The t h i r d 4 7 and f i n a l phase of deformation was backfolding of the nappes, again as a r e s u l t of reaction against the Pu r c e l l Anticlinorium. The timing of t h i s l a s t phase i s post T r i a s s i c , but before the intrusion of the Nelson Batholith. Metamorphism accompanied a l l three phases of defor-mation, reaching a maximum during the second phase. Ross and Ke l l e r h a l s (1968) suggest that the metamorphism affected most, i f not a l l , of the Shuswap Complex, and that the major metamorphism of the Shuswap was post early Permian. They do not f i n d structures r e l a t e d to the f i r s t two phases of defor-mation within the T r i a s s i c Slocan Group, and therefore conclude that the major Shuswap metamorphism had ended by the T r i a s s i c . Reesor (1970) and Reesor and Moore (1971) have pro-posed a somewhat d i f f e r e n t o r i g i n for the domes. In t h e i r view, the f i r s t step was the appearance of a narrow, north-northwesterly trending zone of high heat flow. Migmatization and metamorphism followed, occurring synchronously with i n t e r -f o l d i n g and penetration of the mobile migmatites into meta-sedimentary gneisses. The folds permitted l o c a l upwelling of migmatite and g r a n i t i c gneiss, thus concentrating hotter materials beneath easterly-trending antiforms. D i a p i r i c uprise of migmatite and g r a n i t i c gneiss took place beneath the antiforms and gave r i s e to the domal structure. Reesor and Moore (1971) have also discussed the possible timing of the Shuswap metamorphism. They point out that, although i t is rather d i f f i c u l t to correlate metamorphic rocks with t h e i r unmetamorphosed equivalents, some s t r u c t u r a l 48 s u c c e s s i o n s can be found w i t h i n the Shuswap Complex t h a t appear to correspond to known sequences o u t s i d e i t . On t h i s b a s i s , rocks which range i n age from l a t e Precambrian to M i s s i s s i p p i a n are p r e s e n t i n the Shuswap Complex, so the main metamorphism cannot be e a r l i e r than l a t e P a l e o z o i c . F u r t h e r -more, the T r i a s s i c S l o c a n Group may a l s o extend i n t o the Complex, i n d i c a t i n g t h a t the b e g i n n i n g o f the Shuswap metamor-phism i s p o s t T r i a s s i c . The age o f the g n e i s s e s thus becomes an important t e s t of these hypotheses. A c c o r d i n g to Ross, the g n e i s s e s r e p r e s e n t c r y s t a l l i n e basement and are Precambrian i n age, perhaps as o l d as 1600-1800 m.yr. Reesor and Moore, on the o t h e r hand, argue t h a t the gneisses were formed, f o r the most p a r t , from Windermere sediments at the time o f the Shuswap metamorphism, which they p l a c e at about 150 to 250 m.yr. ago. IV-3 The Revelstoke gneiss In o r d e r to date the g n e i s s e s , samples were o b t a i n e d from the g n e i s s i c wedge n o r t h e a s t o f R e v e l s t o k e , an area mapped by Ross (1968). The major s t r u c t u r e i n the area i s an e a s t e r l y - v e r g i n g recumbent a n t i c l i n e w i t h a g n e i s s i c c o r e . I t has undergone at l e a s t t h r e e episodes of deformation. The h y p o t h e s i s proposed f o r the e v o l u t i o n o f the area has a l r e a d y been d i s c u s s e d . On the b a s i s o f the r e l a t i o n s h i p between the gneiss and a m p h i b o l i t i c b o d i e s , Ross has suggested t h a t the amphibo-l i t e s were emplaced as b a s i c dikes w i t h i n the gneiss p r i o r to 49 the f i r s t phase o f deformation. The gneiss t h e r e f o r e must have had a metamorphic h i s t o r y p r i o r to the time o f the f i r s t phase, which f o l l o w s the e a r l y Cambrian. Furthermore, S i n c l a i r (1966) had p o s t u l a t e d t h a t a 1700 m.yr. basement e x i s t e d beneath the southern p a r t o f the Kootenay A r c , and s i m i l a r ages aTe found f o r rocks from boreholes 200 km to the e a s t . Ross (1968) t h e r e f o r e suggested t h a t the gneiss c o u l d be as o l d as 1700 m.yr., and t h a t i t formed a basement upon which metasediments now found i n the Shuswap Complex were o r i g i n a l l y d e p o s i t e d . TABLE IV-2 Rubidium § s t r o n t i u m measurements from the Revelstoke g n e i s s . Sample Rb (ppm) Sr (ppm) R b 8 7 / S r 8 6 S r 8 7 / S r 8 6 Rl-T-1 101 200 1.46 0.7148 Rl-T-2 64.2 277 0.671 0.7120 Rl-1 55.5 342 0.470 0.7095 Rl-2 113 225 1.45 0.7147 Rl-4 76.0 269 0.818 0.7137 Rl-5 86.7 205 1.23 0.7139 R2-1 79. 8 430 0.537 0.7100 R3-T 74.2 232 0.926 0.7130 R3-1 85.3 229 1.08 0.7131 R4-T 92.3 217 1.23 0.7139 R5-T 86.5 217 1.15 0.7168 R5-1 * 85.9 195 1.28 0.7175 R5-2 87.0 210 1.20 0.7170 R6-1 84.9 211 1.17 0.7173 R6-2 * 104 183 1.65 0.7177 *Not used f o r i s o c h r o n c a l c u l a t i o n The w r i t e r , w i t h the a s s i s t a n c e o f B. D. Ryan, c o l l e c t e d samples o f the g r a n i t i c gneiss from l o c a t i o n s along 50 the Trans-Canada Highway and Laforme Creek ( F i g u r e IV-2). The r e s u l t s are g i v e n i n T a b l e IV-2 and p l o t t e d on F i g u r e IV-3. Two i s o c h r o n s have been o b t a i n e d , one w i t h an age o f 740 ± 30 m.yr., and the o t h e r o f age 240 ± 30 m.yr. ( A l l u n c e r t a i n t i e s are 95% c o n f i d e n c e l i m i t s . ) The p a t t e r n shown i n F i g u r e IV-3 i s unusual i n t h a t two i s o c h r o n s have a p p a r e n t l y been o b t a i n e d f o r the same rock u n i t . The samples on the 740 m.yr. i s o c h r o n have remained c l o s e d systems w i t h r e s p e c t to exchange o f rubidium and s t r o n t i u m s i n c e t h a t time, w h i l e those on the younger i s o c h r o n became homogeneous i n t h e i r S r 8 7 / S r 8 6 r a t i o s 240 m.yr. ago. No s i g n i f i c a n t d i f f e r e n c e s are r e c o g n i z e d between the two groups o f samples, except t h a t Rl-T-2, R l - 1 , Rl-4, and R2-1 a l l have h i g h e r and more v a r i a b l e s t r o n t i u m c o n c e n t r a t i o n s when compared to the o t h e r s . The remaining samples, i n f a c t , are remarkably u n i f o r m i n t h e i r s t r o n t i u m c o n c e n t r a t i o n s . However, samples R5-T, R5-2, and R6-1, which are from the Laforme Creek a r e a , a l l l i e on the o l d e r i s o c h r o n , so the d i s t i n c t i o n based on s t r o n t i u m c o n c e n t r a t i o n s may be meaning-f u l o n l y f o r the samples c o l l e c t e d along the Trans-Canada Highway. Problems r e l a t i n g to the r e - d i s t r i b u t i o n of rubidium and s t r o n t i u m d u r i n g metamorphism have been c o n s i d e r e d by Lanphere et a l . (1963), A r r i e n s et a l . (1966), and Ryan and B l e n k i n s o p (1971), among o t h e r s . There i s g e n e r a l agreement t h a t d u r i n g metamorphism, s t r o n t i u m - r i c h m i n e r a l s such as e p i d o t e , a p a t i t e and p l a g i o c l a s e w i l l g a i n r a d i o g e n i c s t r o n -FIGURE IV-2 Sample l o c a t i o n s f o r the Revelstoke g n e i s s . 52 S3 tium from r u b i d i u m - r i c h , s t r o n t i u m - p o o r m i n e r a l s such as the micas. In o t h e r words, s t r o n t i u m - r i c h m i n e r a l s w i l l e x p e r i e n c e an i n c r e a s e i n t h e i r S r 8 7 / S r 8 6 r a t i o s , w h i l e strontium-poor m i n e r a l s w i l l have t h e i r r a t i o s lowered. As long as no s t r o n t i u m i s l o s t from the t o t a l rock system, under these c o n d i t i o n s the rock w i l l p r e s e r v e i t s o r i g i n a l age. I t i s suggested t h a t t h i s s i t u a t i o n p r e v a i l e d f o r the samples on the o l d e r i s o c h r o n , a s u g g e s t i o n t h a t r u b i d i u m - s t r o n t i u m a n a l y s i s o f the m i n e r a l s c o u l d c o n f i r m . Samples R5-1 and R6-2 p r o b a b l y r e p r e s e n t rocks which have l o s t r a d i o g e n i c s t r o n t i u m and t h e r e f o r e have not remained c l o s e d systems. For the younger samples, homogenization of S r 8 7 / S r 8 6 r a t i o s must have o c c u r r e d . The process by which t h i s happened i s not c l e a r , i n p a r t because r u b i d i u m - s t r o n t i u m analyses o f the s e p a r a t e m i n e r a l s are not a v a i l a b l e , but some p o s s i b i l i -t i e s can be c o n s i d e r e d . One o f these i s complete e x p u l s i o n o f r a d i o g e n i c s t r o n t i u m from a l l samples, a p o s s i b i l i t y which can be d i s c o u n t e d because the two i s o c h r o n s have d i f f e r e n t i n i t i a l r a t i o s . P a r t i a l l o s s o f r a d i o g e n i c s t r o n t i u m i s p o s s i b l e , but the l i k e l i h o o d o f the samples l o s i n g j u s t enough r a d i o g e n i c s t r o n t i u m so t h a t they were a l l l e f t at the time o f a l t e r a t i o n w i t h the same S r 8 7 / S r 8 6 r a t i o i s not very h i g h . I t seems more l i k e l y t h a t exchange o f both common and r a d i o -g e n i c s t r o n t i u m o c c u r r e d . In t h i s c o n n e c t i o n , Ross (1968) has observed t h a t the metamorphism was q u i t e v a r i a b l e throughout the a r e a , so i t may have been i n t e n s e enough i n some p a r t s to b r i n g about homogenization o f the S r 8 7 / S r 8 6 r a t i o s , perhaps 54 through r e c r y s t a l l i z a t i o n o f the m i n e r a l s . IV-4 The Quesnel Lake gneiss The Quesnel Lake gneiss r e p r e s e n t s another area which may be c r y s t a l l i n e basement. The gneiss has been d e s c r i b e d by Campbell (1961, 1963), Campbell and Campbell (1970), and F l e t c h e r (1972). I t i s exposed along the n o r t h shore o f the east arm o f Quesnel Lake ( F i g u r e IV-4), where i t forms an elongate t o p o g r a p h i c r i d g e . The s t r u c t u r e o f the g n e i s s , a c c o r d i n g to F l e t c h e r (1972) , i s t h a t o f a t i g h t a n t i f o r m o v e r t u r n e d to the south-west. F u r t h e r deformation has caused warping and a r c h i n g o f the s t r u c t u r e to produce the p r e s e n t outcrop p a t t e r n . The g n e i s s plunges beneath surrounding metasediments, to the northwest and s o u t h e a s t . Minor s t r u c t u r e s w i t h i n the gneiss are concordant w i t h those i n the metasediments, i n d i c a t i n g t h a t the gneiss and metasediments have experi e n c e d the same d e f o r m a t i o n a l h i s t o r y . No s t r u c t u r e s p r e - d a t i n g the e a r l i e s t d eformation o f the metasediments have been found w i t h i n the g n e i s s . Campbell (1961, 1963) c o n s i d e r e d the gneiss to be an e x o t i c body o f unknown age, but l a t e r (1970) suggested t h a t i t c o u l d r e p r e s e n t c r y s t a l l i n e basement on which s e d i -ments were d e p o s i t e d p r i o r to f o l d i n g . F l e t c h e r (1972) has d i s c u s s e d f o u r p o s s i b l e o r i g i n s f o r the g n e i s s . I t may r e p r e s e n t : FIGURE IV-4 Sample locations for the Quesnel Lake gneiss. 56 1) a metamorphosed P r o t e r o z o i c sedimentary u n i t . 2) basement exposed i n the core o f an a n t i c l i n e . 3) basement t h r u s t i n t o o v e r l y i n g sediments. 4) a metamorphosed igneous i n t r u s i o n . F l e t c h e r has excluded the f i r s t p o s s i b i l i t y on chemical and p e t r o g r a p h i c grounds, and because no s i m i l a r u n i t has been r e c o g n i z e d elsewhere w i t h i n the Kaza Group. Of those remaining, he d i s c o u n t s the second and t h i r d hypotheses because both would r e q u i r e an e x t r a p e r i o d o f defo r m a t i o n , f o r which no evidence i s observed. However, he c o n s i d e r s t h a t these hypotheses can be no means be completely excluded. In support o f h i s p r e f e r r e d i n t e r p r e t a t i o n , t h a t the gneiss r e p r e s e n t s a metamorphosed igneous i n t r u s i o n , F l e t c h e r (1972) c i t e s the f o l l o w i n g evidence: r e g i o n a l l y metamorphosed skarns at the gneiss-metasediment c o n t a c t ; a p l i t e d i k es i n the gneiss and metasediments; mafic i n c l u s i o n s w i t h i n the gneiss which c o u l d be x e n o l i t h s ; and the igneous t r e n d o f the chemical a n a l y s e s . A l l o f these p o i n t s suggest i n t r u s i o n o f the gneiss i n t o the sediments. Thus, two d i f f e r e n t modes o f o r i g i n f o r the gneiss are suggested - that i t r e p r e s e n t s an igneous i n t r u s i o n i n t o Windermere sediments, or t h a t i t i s c r y s t a l l i n e basement upon which these sediments were d e p o s i t e d . The w r i t e r o f t h i s t h e s i s c o l l e c t e d , w i t h the a s s i s t a n c e o f C.J.N. F l e t c h e r , a s u i t e o f samples from the Quesnel Lake g n e i s s . The i s o t o p i c r e s u l t s f o r these samples, 57 o b t a i n e d w i t h the techniques a l r e a d y d e s c r i b e d , are g i v e n i n T a b l e IV-3. An i s o c h r o n ( F i g u r e IV-5) based on the i n d i c a t e d samples has an age o f 740 ± 150 m.yr. TABLE IV-3 Rubidium-strontium measurements o f the Quesnel Lake g n e i s s . Sample Rb (ppm) Sr (ppm) R b 8 7 / S r 8 6 S r 8 7 / S r 8 6 1F71 117 448 0.756 0.7121 2F71 133 321 1.20 0.7158 2AF71 143 338 1.23 0.7161 2BF71 142 459 0.896 0.7142 3F71 126 327 1.12 0.7156 4F71 140 581 0.698 017110 5F71 109 521 0.606 0.7097 8AF71 * 94.6 307 0.892 0.7058 18F71 * 8 490 0.05 0.7148 18AF71* 91.9 395 0.674 0.7127 20F71 107 36 3 0.854 0.7120 *Not used f o r i s o c h r o n c a l c u l a t i o n The two samples from the e a s t e r n end of the gneiss 18F71 and 18AF71 were not used to determine the i s o c h r o n because they came from an e x t e n s i v e zone o f pegmatites. Sample 8AF71, which was a l s o excluded, was from the c o n t a c t between the gneiss and the metasediments. The s i g n i f i c a n c e o f the age and the i n i t i a l S r 8 7 / S r 8 6 r a t i o of .7033 ± .0020 w i l l be d i s c u s s e d i n the next chapter. IV-5 The Malton gneiss G i o v a n e l l a (1968) d e s c r i b e d the Malton gneiss ( F i g u r e IV-6), a g n e i s s i c t e r r a i n s t r a d d l i n g the Rocky Mountain Trench, 58 59 as "a heterogeneous assemblage o f l a y e r e d g n e i s s e s and s c h i s t s which range i n c o m p o s i t i o n from l e u c o g r a n i t e t o a m p h i b o l i t e . " Rocks o f the l a t e Precambrian Kaza Group occur s t r u c t u r a l l y above and to the south o f the gneiss on the west s i d e o f the Trench. The gneiss on the east s i d e of the Trench i s sur-rounded by Cambrian q u a r t z i t e s (Gog Group) and l a t e Precambrian s c h i s t s ( M i e t t e Group). The M i e t t e and Kaza Groups are regar-ded as e q u i v a l e n t . G i o v a n e l l a (1968) c o n s i d e r s t h a t the g n e i s s i s o l d e r than the e n c l o s i n g sediments, and i s a l s o a l l o c h t h o n o u s . Samples of the gneiss and s c h i s t s f o r a rubidium-s t r o n t i u m age study were c o l l e c t e d by C. A. G i o v a n e l l a , and made a v a i l a b l e to the w r i t e r through the kindness o f R. K. Wanless o f the G e o l o g i c a l Survey o f Canada. P r e l i m i n a r y attempts by the G e o l o g i c a l Survey at d a t i n g the samples were i n c o n c l u s i v e . From G i o v a n e l l a ' s f i e l d d e s c r i p t i o n s , the w r i t e r grouped the samples a c c o r d i n g to l i t h o l o g i c a l s i m i l a r -i t i e s , but o n l y two groups c o n t a i n e d more than two samples. The analyses o f these samples are g i v e n i n T a b l e IV-4, and they are p l o t t e d on F i g u r e IV-7. From the graph i t i s apparent t h a t the p o i n t s s c a t t e r about a r a t h e r poor i s o c h r o n ; i t s age was c a l c u l a t e d to be 680 ± 80 m.yr. The estimate o f pre-c i s i o n o f the age i s not c o n s i d e r e d r e l i a b l e f o r reasons to be d i s c u s s e d l a t e r , although the age i t s e l f i s p r o b a b l y a v a l i d e s t i m a t e . 60 TABLE IV-4 Rubidium-strontium measurements o f the Malton g n e i s s . Sample Rb (ppm) Sr (ppm) R b 8 7 / S r 8 6 S r 8 7 / S r 8 6 401-8 47.9 49.0 2.84 0.7335 401-9 70.6 55.8 3.68 0.7499 401-10 * 20 138 0.420 0.7197 401-11 109 156 2.03 0.7304 401-12 70.2 41.4 4.93 0.7560 401-13 48.5 302 0.465 0.7137 401-14 82.2 319 0.747 0.7156 401-17 100 245 1.18 0.7198 *Not used f o r i s o c h r o n c a l c u l a t i o n IV-6 C a l c u l a t i o n o f i s o c h r o n s In a r e c e n t paper, Brooks et a l . (1972) have reviewed the problem of i s o c h r o n c a l c u l a t i o n , and i n p a r t i c u l a r the e s t i m a t i o n o f e r r o r s . The authors proposed t h a t the term " i s o c h r o n " be r e s t r i c t e d to those cases i n which the data p o i n t s f i t the l i n e w i t h i n experimental p r e c i s i o n . They pro-pose the term " e r r o r c h r o n " f o r i n s t a n c e s i n which the s c a t t e r about the l i n e exceeds experimental e r r o r . They p o i n t out t h a t i n the l a t t e r case, the estimate of age and i n i t i a l r a t i o may s t i l l be v a l i d , but the estimates o f e r r o r s are p r o b a b l y poor. By t h e i r c r i t e r i a , the two Revelstoke l i n e s are i s o -chrons, but the Quesnel Lake and Malton l i n e s are e r r o r c h r o n s . The c a l c u l a t e d u n c e r t a i n t i e s f o r the l a t t e r s hould be viewed w i t h c a u t i o n . The s l o p e s and i n t e r c e p t s were a l l c a l c u l a t e d from the method proposed by York (1969). F o l l o w i n g a s u g g e s t i o n by Brooks e t a l . (1972), the e r r o r s i n R b 8 7 / S r 8 6 and S r 8 7 / S r 8 6 61 FIGURE IV - 6 Sample l o c a t i o n f o r the Malton g n e i s s . 62 FIGURE IV-7 Malton g n e i s s . Il 63 were c o n s i d e r e d t o be u n c o r r e l a t e d . For the e r r o r c h r o n s , the u n c e r t a i n t i e s i n age and i n i t i a l r a t i o are based on the f i t o f the p o i n t s to the l i n e , and take no account of experimental u n c e r t a i n t i e s , which would make the estimates lower. For the i s o c h r o n s , u n c e r t a i n t i e s are es t i m a t e d by t a k i n g experimental u n c e r t a i n t i e s i n t o c o n s i d e r a t i o n , the procedure recommended by Brooks et a l . (1972). The s i g n i f i c a n c e o f these f i n d i n g s w i l l be d i s c u s s e d i n the next chapter. CHAPTER V CONCLUSIONS V - l Ages o f the gneisses and t h e i r i m p l i c a t i o n s The r e s u l t s o b t a i n e d i n t h i s study are summarized below: Area I n i t i a l R a t i o Age (m.yr.) Revelstoke .7044 ± .0007 740 ± 30 .7095 ± .0009 240 ± 30 Quesnel Lake .7033 ± .0020 740 ± 150 Malton Range .7086 ± .0014 680 ± 80 I t i s apparent t h a t each area was a f f e c t e d by an event about 700 m.yr. ago. I t w i l l be r e c a l l e d from the p r e v i o u s chapter that Ross's h y p o t h e s i s i m p l i e s t h a t the g n e i s s e s are o l d e r than t h e i r e n c l o s i n g sediments. The o l d e s t sediments known to be i n v o l v e d i n the deformation of the southern p a r t of the Omineca C r y s t a l l i n e B e l t are those o f the Windermere sequence o f age 600-800 m.yr. ( G a b r i e l s e , 1972). On a r e g i o n a l b a s i s , t h e r e f o r e , these g n e i s s e s and the o l d e s t sediments are i n d i s t i n g u i s h a b l e i n age, so t h a t the age data alone n e i t h e r support nor r e f u t e Ross's h y p o t h e s i s . In the o r i g i n a l paper, Ross (1968) proposed t h a t the o l d e s t sediments p r e s e n t at Revelstoke were those o f the Windermere H o r s e t h i e f Creek Group. More r e c e n t l y , however, he has concluded t h a t the metasediments surrounding the gneiss 65 belong to the middle H a m i l l Group (Ross, p e r s o n a l communica-t i o n , 1971), which i s Lower Cambrian, i . e . , p o s t Windermere. Wheeler (1963) has made a s i m i l a r o b s e r v a t i o n . I f these c o n c l u s i o n s are c o r r e c t , the gneiss at Revelstoke i s demon-s t r a b l y o l d e r than the e n c l o s i n g sediments, and the age data are c o n s i s t e n t w i t h the h y p o t h e s i s t h a t the gneiss was t e c h n -i c a l l y emplaced i n t o the sediments. Thus, at l e a s t at R e v e l s t o k e , Ross's hypothesis can be defended, although the gneiss i s a p p a r e n t l y not o f Hudsonian age (1600-1800 m.yr.). I t i s p o s s i b l e t h a t the age o f the gneiss r e p r e s e n t s a metamorphic age, i n which case the arguments p r e s e n t e d here are o n l y strengthened. The r a t h e r low i n i t i a l r a t i o o f 0.7044 ± .0007 f o r the gneiss i n d i c a t e s , however, t h a t the body i s p r o b a b l y an i n t r u s i o n , and t h a t the date r e p r e s e n t s the time of i n t r u s i o n . The low i n i t i a l r a t i o does not p r e c l u d e the p o s s i b i l i t y of the age b e i n g metamorphic, but any metamorphism would have had to r e s u l t i n q u i t e complete e x p u l s i o n o f r a d i o g e n i c s t r o n t i u m from the rock u n i t . The age r e l a t i o n s h i p s , t o g e t h e r w i t h the s t r u c t u r a l d a t a , are t h e r e f o r e seen to be c o n s i s t e n t w i t h the mode o f dome fo r m a t i o n proposed by Ross. His h y p o t h e s i s w i l l have to be m o d i f i e d s l i g h t l y i n t h a t the gneiss i s p r o b a b l y not Hudsonian (1600-1800 m.yr.) i n age. I f the gneiss at Revel-stoke and the gneiss i n the cores o f the domes are e q u i v a l e n t , as appears q u i t e l i k e l y , then the age data p r e s e n t s e r i o u s problems f o r the model proposed by Reesor and Moore (1971) , s i n c e they c o n s i d e r t h a t the core g n e i s s e s were d e r i v e d from 66 Windermere sediments at some time a f t e r the Permian. The gneiss i s o l d e r than t h i s , however, and the low i n i t i a l r a t i o f o r the i s o c h r o n i s not compatible w i t h d e r i v a t i o n o f the gneiss from sediments, at l e a s t by any simple p r o c e s s . The r e s u l t s f o r the o t h e r two areas are l e s s con-c l u s i v e . The Quesnel Lake gneiss appears to be about the same age as the Windermere sediments which surround the gneiss ( F l e t c h e r , 1972). F l e t c h e r c o n s i d e r s i t to be an i n t r u s i o n i n t o the Windermere Kaza Group, an i n t e r p r e t a t i o n which i s supported by the low i n i t i a l r a t i o o f 0.7033 ± .0020. Campbell and Campbell (1970) d e s c r i b e the gneiss as c r y s t a l l i n e basement upon which the sediments were d e p o s i t e d . The s i m i l a r i t y i n age o f gneiss and metasediments make i t im p o s s i b l e t o choose between these a l t e r n a t i v e s on the b a s i s o f the g e o c h r o n o l o g i c a l d a t a . The age o b t a i n e d f o r the Malton gneiss must be regarded w i t h c a u t i o n i n view o f the c o n s i d e r a b l e s c a t t e r o f p o i n t s about the i s o c h r o n . Nonetheless, the age i s c o n s i s t e n t w i t h t h a t o f the o t h e r g n e i s s e s . Again, the gneiss i s about the same age as some o f i t s e n c l o s i n g sediments, but i s pro b a b l y o l d e r than the q u a r t z i t e s o f the Gog Group. The gneiss i s g e n e r a l l y regarded as a l l o c h t h o n o u s , and the age i s c e r t a i n l y c o n s i s t e n t w i t h t h i s i n t e r p r e t a t i o n , i n t h a t the l a t e Precambrian gneiss and Kaza sediments surround the Lower Cambrian Gog q u a r t z i t e s . 6 7 V-2 Regional c o n s i d e r a t i o n s I t seems reasonable to suggest that a l l areas were a f f e c t e d by the same event. I t may t h e r e f o r e be p o s s i b l e to c o r r e l a t e t h i s 700 m.yr. event w i t h the East Kootenay Orogeny, which was f i r s t d e s c r i b e d by White (1959). He c i t e d the presence of a r e g i o n a l unconformity between the Windermere and B e l t - P u r c e l l sediments as evidence f o r orogeny, and some m i l d f o l d i n g and t i l t i n g o f the B e l t - P u r c e l l r o c k s . From t h i s and o t h e r evidence, the East Kootenay Orogeny i s u s u a l l y regarded as post B e l t - P u r c e l l , but pre-Windermere. Approximate l i m i t s f o r the time of the E a s t Kootenay Orogeny can be o b t a i n e d from the maximum age o f the Windermere sediments. An age o f about 850 m.yr. (Obradovich and Peterman, 1968) f o r the youngest formations of the B e l t - P u r c e l l Super-group i s an upper bound f o r the time of orogeny. A minimum age cannot be determined from the Windermere sediments, because they are not f o s s i l i f e r o u s , but they are o v e r l a i n , i n p l a c e s conformably, by Lower Cambrian r o c k s . The d e p o s i t i o n of the Windermere was a c c o r d i n g l y completed about 600 m.yr. ago, but no estimate can be made o f the time i t s t a r t e d . The orogeny must be o l d e r than 600 m.yr., but younger than 850 m.yr. G e o c h r o n o l o g i c a l data from s e v e r a l sources suggest a time between 700 and 800 m.yr. f o r the East Kootenay Orogeny. S e v e r a l potassium-argon ages o f metamorphism b e l i e v e d a s s o c i -a t e d w i t h the orogeny f a l l w i t h i n t h a t range ( G o l d i c h et a l . , 1959; Leech, 1962; Leech, 1967). S i m i l a r ages were o b t a i n e d f o r s tocks thought to be i n t r u d e d d u r i n g the orogeny, but one 6 8 o f them has s i n c e been dated by the r u b i d i u m - s t r o n t i u m method, and was shown to have an age o f 1300 ± 100 m.yr. (Ryan and B l e n k i n s o p , 1971). I t i s t h e r e f o r e not c l e a r whether any i n t r u s i o n accompanied the orogeny. The p r o p o s a l t h a t the event observed i n the gneisses c o r r e l a t e s w i t h the East Kootenay Orogeny i s thus seen to be c o n s i s t e n t w i t h independent g e o l o g i c a l and g e o c h r o n o l o g i c a l evidence. I f the c o r r e l a t i o n i s v a l i d , then the orogeny appears to be more e x t e n s i v e than p r e v i o u s l y thought. The contemporaneous Racklan Orogeny ( G a b r i e l s e , 1967, 1972) a f f e c t e d P u r c e l l - e q u i v a l e n t rocks i n n o r t h e r n B r i t i s h Columbia and the Yukon, and i t i s p o s s i b l e t h a t both are evidence f o r a much l a r g e r event. F l e t c h e r ' s i n t e r p r e t a t i o n of the Quesnel Lake gneiss as an i n t r u s i v e i n t o Windermere sediments c a s t s doubt on the c o r r e l a t i o n o f the 700 m.yr. event w i t h the East Kootenay Orogeny because the orogeny i s c o n s i d e r e d pre-Windermere. A a l t o (1971) argues f o r an i n i t i a l orogeny, which was pre-Windermere, f o l l o w e d by p e r i o d s o f u p l i f t d u r i n g s e d i m e n t a t i o n . Perhaps the Quesnel Lake gneiss was emplaced d u r i n g one o f the l a t e r events. I t seems q u i t e p o s s i b l e t h a t the E a s t Kootenay Orogeny encompassed m u l t i p l e events extending over a c o n s i d e r -able p e r i o d o f time, perhaps o f the order of 100 m.yr. A s i m i l a r s i t u a t i o n has p r e v a i l e d more r e c e n t l y i n B r i t i s h Columbia i n the i n t e r v a l from about 50 to 250 m.yr. ago. A c c e p t i n g t h i s i n t e r p r e t a t i o n , the orogeny p r o b a b l y began 69 about 800 m.yr. ago w i t h u p l i f t t h a t l e d to the r e g i o n a l unconformity between the B e l t - P u r c e l l and Windermere sediments, and c o n t i n u e d d u r i n g the accumulation o f Windermere sediments. V-3 Timing o f the Shuswap metamorphism The 240 ± 30 m.yr. i s o c h r o n f o r the Revelstoke gneiss r e q u i r e s some c a u t i o n i n i n t e r p r e t a t i o n . U n t i l m i n e r a l data c o n f i r m the age, or more whole rock data are o b t a i n e d , the i s o c h r o n s h o u l d be regarded as p r o v i s i o n a l . N e v e r t h e l e s s , the i s o c h r o n i s w e l l determined, and i t i s tempting to r e g a r d the age as s i g n i f i c a n t . I t presumably r e f l e c t s the time o f maximum metamorphism. The age i s c o n s i s t e n t w i t h the estimates by Ross and K e l l e r h a l s (1968) and by Reesor and Moore (1971) f o r the age o f Shuswap metamorphism. V-4 R e l a t i o n s h i p to p l a t e t e c t o n i c s Papers p r e s e n t i n g g e o l o g i c a l h i s t o r i e s o f B r i t i s h Columbia i n terms o f p l a t e t e c t o n i c t h e o r y are o n l y now s t a r t i n g to appear ( D e r c o u r t , 1972; Monger et a l . , i n p r e s s ) , and perhaps i t i s premature to l i n k the r e s u l t s o b t a i n e d i n t h i s study to these i d e a s . Nonetheless, i t i s i n t e r e s t i n g to note t h a t a s u b d u c t i o n zone i s thought to have e x i s t e d i n the r e g i o n d u r i n g Permian and/or T r i a s s i c time (Monger et a l . , i n p r e s s ) , which would p r o v i d e a mechanism f o r i n t r u s i o n , meta-morphism and t h r u s t i n g w i t h i n t h a t time span. The 240 m.yr. age c o u l d , t h e r e f o r e , be r e l a t e d to s u b d u c t i o n . A subduction zone may a l s o have e x i s t e d d u r i n g the 70 l a t e Precambrian (Monger et a l . , i n p r e s s ) . The g n e i s s e s may have been emplaced as i n t r u s i o n s w h i l e s u b d u c t i o n was occur-r i n g , so the 700 m.yr. event may date the time o f s u b d u c t i o n . I t i s i n t e r e s t i n g to observe t h a t the A t l a n t i c may have been opening at about the same time ( D i e t z , 1972). V-5 Summary I t w i l l be r e c a l l e d from Chapter I t h a t the major aims o f t h i s study were t w o f o l d . The f i r s t purpose was to improve the p r e c i s i o n o f measurement o f S r 8 7 / S r 8 6 r a t i o s as a means o f extending the v a r i e t y of problems t h a t can be s t u d i e d by r u b i d i u m - s t r o n t i u m geochronology. To t h i s end, a p r e c i s i o n of 0.02% (95% c o n f i d e n c e l i m i t ) has been achieved on a r o u t i n e b a s i s , p r i m a r i l y by means of an o n - l i n e data a c q u i s i t i o n system f o r the mass spectrometer. The system has been used to o b t a i n ages f o r s u i t e s of samples which have a range i n S r 8 7 / S r 8 6 r a t i o s o f o n l y about 1%, i n c o n t r a s t w i t h a spread o f 5% or more f o r most i s o c h r o n s i n the l i t e r a t u r e . I f the S r 8 7 / S r 8 6 r a t i o s f o r the younger Revelstoke i s o c h r o n had been measured to a p r e c i s i o n of 0.1%, the age determined would be 240 ± 110 m.yr., which has an u n a c c e p t a b l y l a r g e u n c e r t a i n t y . The second purpose o f t h i s study was to determine the ages o f c e r t a i n g n e i sses w i t h i n the southern Omineca C r y s t a l l i n e B e l t o f B r i t i s h Columbia i n order to determine i f any were Precambrian i n age. A l l three areas gave ages o f about 700 m.yr. ( l a t e Precambrian), a r e s u l t which l e a d to 71 p o s s i b l e c o r r e l a t i o n w i t h the E a s t Kootenay Orogeny. 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APPENDIX A-1 The d e t e r m i n a t i o n o f the h a l f - l i f e o f the rubidium-s t r o n t i u m decay scheme i s o b v i o u s l y important i n o b t a i n i n g a b s o l u t e ages. However, although the maximum energy o f the 8 p a r t i c l e s e m i t t e d by R b 8 7 i s 2 75 keV, t h e i r average value i s o n l y about 45 keV, so t h a t d i f f i c u l t i e s are encountered i n measuring the h a l f - l i f e by d i r e c t c ounting methods. None-t h e l e s s , numerous attempts have been made to use d i r e c t c o u n t i n g , one o f the more s u c c e s s f u l b e i n g by Flynn and Glendenin (1959), who ob t a i n e d a va l u e o f 4.7 * 10 1 0 y r . ± 21. T h e i r value i s used i n many l a b o r a t o r i e s today. An a l t e r n a t i v e method has been to compare age det e r m i n a t i o n s by d i f f e r e n t methods on the same samples. A l d r i c h et a l . (1956) measured uranium-lead and rubidium-s t r o n t i u m ages on s e v e r a l samples, and concluded t h a t a h a l f -l i f e o f 5.0 x 10 1 0 y r . p r o v i d e d the best agreement between the ages. Kulp and Engels (1963) compared potassium-argon and r u b i d i u m - s t r o n t i u m ages f o r a group o f m i n e r a l s , and concluded t h a t a h a l f - l i f e o f 4.7 x 1 0 1 0 y r . p r o v i d e d the best concordance between the ages. The value o f 5.0 x 1 0 1 0 y r . o b t a i n e d by A l d r i c h e t a l . i s a l s o w i d e l y used today. A t h i r d method of determ i n i n g the h a l f - l i f e was r e p o r t e d by McMullen et a l . (1966). They measured the accumulation o f S r 8 7 produced i n a rubidium s a l t over a known p e r i o d o f time. T h e i r value f o r the h a l f - l i f e i s 4.72 x i o 1 0 y r . 79 The value used i n t h i s t h e s i s i s 4.7 * 1 0 1 0 y r . , w i t h an accompanying decay constant X of 1.47 * 1 0 " 1 1 y r . " 1 . T h i s value was chosen l a r g e l y because two d i f f e r e n t methods, d i r e c t c o u n t i n g and d i r e c t measurement, gave the same r e s u l t , and the r e s u l t i s not i n c o n s i s t e n t w i t h t h a t o b t a i n e d by g e o l o g i c comparison. The l a t t e r method, though, s u f f e r s from the problem o f d e c i d i n g whether or not the r u b i d i u m - s t r o n t i u m , potassium-argon, and uranium-lead methods are a l l d a t i n g pre-c i s e l y the same event. C e r t a i n l y i n the case o f a sample which has c o o l e d s l o w l y , the r e t e n t i o n o f r a d i o g e n i c argon i s not l i k e l y to occur u n t i l l o n g a f t e r the oth e r " c l o c k s " have s t a r t e d . A l l r u b i d i u m - s t r o n t i u m ages r e f e r r e d to i n t h i s t h e s i s have been r e - c a l c u l a t e d t o a X of 1.47 x 1 0 " 1 1 y r . " 1 where n e c e s s a r y . 80 APPENDIX h-2 L i s t i n g of Computer Program * STRONTIUM ISOTOPE PROGRAM VERSION 15/07/71 * INITIALIZE ROUTINE L3 ORG X'80« LPSW *+4 HALT COMPUTES DC X '8000 • DC A (*+2) LHI 3, H'13 • BAL 15,DISPL ZERO DISPLAY DC A(ZERO) XHR 14,14 LHI 15, GO STM 14,X'0044' SET UP INTERRUPT STH 14,TAPEHR+2 ! RESET TAPEWR LHI 14,X'482F» STH 14,TAPEWR LHI 14,X'41F0» STH 14,STOP+8 STH 14,FCALC LHI 14,PREND2 STH 14,PRSW+2 LHI 8,H'8' DEVICE NO. OF T&PEDRIVE BAL 15,OUPT IDENTIFY PROGRAM DC A(MESS0) DC H«54» LHI 12,4 INITIALIZE SOME COUNTERS STH 12,11 STH 12,L3 STH 12,L4 LHI 12,H'20« STH 12,L2 XHR 11,11 ZERO ID LHI 12, ID LHI 13,H»2« LHI 14,IDEND STH 11,0 (12) BXLE 12,*-4 BAL 15,OUPT ASK IF TAPE OUTPUT DESIRED DC A(HESS11) DC H«28' BAL 15,INPT GET REPLY DC A(BTEMP) DC H»4« LH 4,BTEMP CLHI 4,X»4E4F* IS REPLY 'NO' ? BNE TSTAT NO, IT ISN'T 81 Appendix A-2 Program L i s t i n g TSTAT REW L1 SPIKE A SKID L2 LHI STH LHI STH LHI STH B SSR BFC BAL DC DC LPSW DC DC LHI OCR BAL DC DC BAL DC DC LH CLHI BNE BAL BAL DC DC BAL DC DC LH CLHI BE LHI STH LHI STH BAL DC DC BAL DC DC LH AHI LHI STB STB 9,X »430F' 9 , TAPEWR 9,X»0004' 9,TAPEWR+2 9,X«U200' 9,STOP+8 SPIKE 8,0 9, REW 15,OUPT A (MESS 1) H'22' * + 4 X'COOO* A(TSTAT) 0,X»0020' 8,0 15,OUPT A(MESS2) H*44* 15,INPT A (BTEMP) H'4 ' 4,BTEMP 4, X'UE4F' * + 8 15,SKIP 15,OUPT A(MESS12) H'22' 15,INPT a(BTEMP) H«4« 5, BTEMP 5,X'4E4F« ASKID 5,X'4200» 5,FCALC 4,PREND1 4, PRSW+2 15,0UPT A(MESS3) H'2U« 15,INPT A(ID+1) H'20« 5, *-2 5,1 4,X'0027» 4, ID 4,ID<5) SET 'TAPEWR ' TO SKIP TAPE WRITE STATUS OF TAPE DRIVE BRANCH IF TAPE DRIVE READY OUTPUT MESSAGE IF NOT STOP COMPUTER REWIND TAPE ASK IF FIRST SAMPLE ON TAPE GET RESPONSE IS IT 'NO• ? IF *N0', SEARCH FOR 2 CONSECUTIVE EOF'S ASK IF SAMPLE SPIKED GET REPLY IS IT * NO * ? SUPPRESS NORMALIZATION IF SAMPLE IS SPIKED ASK FOR I. D. GET IT FIND LENGTH OF ID DELIMITING CHARACTER 32 Appendix A-2 Program L i s t i n g WAIT * ZERO HESSO MESS11 MESS12 MESS 1 MESS2 MESS3 BAL 15,TAPEWR WRITE ID ON TAPE DC A (ID) DC A(IDEND) SSR 8,4 OPERATION SUCCESSFUL ? BTC 1 ,*+8 SKIP STATUS CHECK IF DRIVE OFF BTC 4, TPERR NO, GO TO * TPERR' BAL 15,ODPT OUTPUT «GO» MESSAGE DC A (MESS4) DC H'28' XHR 12,12 ZERO SOME VARIABLES STH 12,CHECKPT STH 12,NPTS STH 12,SW STH 12,PTR1 STH 12,PTR2 STH 12,PTR3 STH 12,NSCAN STH 12,TOTAL LHI 13,PTR LHI 14,2 LHI 15,BEND STH 12,0 (13) ZERO BUFFER BXLE 13,*-4 LHI 12,X'2020' BLANK RATIO OUTPUT AREA LHI 13,RATI01- 4 LHI 15,PR0UT2- 2 STH 12,0(13) BXLE 13,*-4 LHI 12,X'420O' INITIALIZE SWITCHES STH 12,CNTRL STH 12,BASES STH 12,MAXMUM LPSW * + 4 WAIT FOR INTERRUPT DC X'COOO' DC A(*-6) DC 3X '30 30 • DC X•8D0 AO AO A i DC C i *** STRONTIUM ISOTOPE PROGRAM • DC C•VERSION B-71 ***' DC X'8D0 A ' DC C»IS TAPE OUTPUT DESIRED' DC X '8D0 A8D3F i DC X»8D0A« DC C I S SAMPLE S PIKED * DC X f8D0A8D3F • DC X »8D0A I DC C'PLEASE READY TAPE • DC X '8D0 A • DC C I S THIS THE FIRST SAMPLE ON THIS TAPE « DC X '8D0A8D3F i DC X * 8D0 A• 83 Appendix A-2 Program L i s t i n g DC C'PLEASE ENTER I. D. » DC X'8D0A8D3F t MESSM DC X '8D0A' DC C'THANKS. • DC X '49274D20 • DC C ' ALL READY • DC X'8D0A0A0A * BTEMP DS 6C ID DC 6X'00000000« IDEND EQU *-2 STOP LPSW *+4 DISABLE INTERRUPT DC X'0000' DC A(*+2) BAL 15,EOF WRITE EOF'S AND REWIND TAPE LPSW * + 4 HALT COMPUTER DC X'80000080 i * INTERRUPT SERVICING ROUTINE GO STM 0,SAVR STORE ALL REGISTERS AIR 3,a CLHI 3,H'8» TAPE DRIVE PROBLEMS ? BE TPERR YES ! CLHI 3, H • 1 3 ' RB-SB MASS SPECTROMETER ? BNE END NO, RETURN TO NORMAL PROCESSING LHI 1,1 LOOK FOR 'END RUN' INDICATION RDR 1.0 READ DISPLAY PANEL NHR 1,0 SW 15 SET ? BNZ STOP YES, PREPARE TO TERMINATE RUN LH 1,NPTS INCREMENT RAW POINT COUNTER AHI 1,1 STH 1 ,NPTS BAL 15,READ READ MASS SPECTROMETER BB IN DS H DVM READING (BINARY) RSW DS H SCANB EQU *-1 LB 6,SCANB GET SCAN BYTE LH 5,RBIN GET NEW POINT LBR 7,6 LOAD SCAN BYTE NHI 7,X '0007' STRIP OFF SCANNING INDICATION CLHI 1,2 FIRST POINT ? BL * + 12 YES, HO PREVIOUS SHUNT TO COMPARE CLH 7,LAST COMPARE SHUNT TO PREVIOUS BE CHECK NO SHUNT CHANGE STH 7 ,LAST STORE NEW SHUNT STH 1 ,RESET STORE NO. OF RAW POINTS LH 4,SW SET SWITCH TO INDICATE SHUNT CHANGE OHI 4,X '0001 • STH 4,SW CHECK SH 1,RESET CLHI 1,H'12' 0 K TO RESET SW ? 84 Appendix A-2 Program L i s t i n g BL *+16 NO, BRANCH LH 4,SW YES, RESET SW NHI 4,X »00FE« STH 4, SW BAL 15,CNTRL GO TO SCAN RATE CONTROL ROUTINE SSR 3,0 IS DVM 0VER-RAN3 E ? BFC 4,*+8 NO, BRANCH AHI 5,H'10000* YES, ADD 10000 BAL 15,FILTER GO TO FILTER CALLING ROUTINE STH 5,FILPT STORE FILTERED POINT BAL 15,SIBTOD CONVERT TO DECIMAL DC A (FILPT) DC A(BUFF 1) LB 7,CBYTE + 1 MOVE SCAN BYTES STB 7 ,CBYTE LB 7,CBYTE+2 STB 7,CBYTE+1 STB 6, CBYTE+2 LB 6,CBYTE LH 4,SW IS SW ON ? NHI 4,X '0001 • BZ CRSW NO, BRANCH LB 6,SCANB YES, SO FILL CBYTE WITH NEW BYTE STB 6,CBYTE STB 6,CBYTE+1 STB 6,CBYTE+2 OHI 6,X'0080« AND FLAG SCAN BYTE TO STB 6,SCANB INDICATE SW ON CRSW BAL 15,SWITCH OUTPUT TO DISPLAY B STATUS CONTINUE END LM 0,SAVR RESTORE REGISTERS LPS W X'0040' RETURN TO NORMAL PROCESSING CBYTE DS 2H NPTS DS H LAST DS H RESET DS H SW DS H FILPT DS H BUFF1 DS 6C SAVR * DS 16H * SCAN RATE CONTROL ROUTINE CNTRL BTC 0,HERE NORMALLY BRANCH TO 'HERE' STH 5,PREV EXECUTE THIS SEQUENCE AT STAI LB 4,FAST OF EACH SCAN STB 4,RATE SET RATE TO FAST LHI 9,X*4300» SET CNTRL SWITCH STH 9,CNTRL HERE LH 9,SW CHECK SW NHI 9,X '0009' 85 Appendix A-2 Program L i s t i n g BZ * + 14 BRANCH IF SW OFF LHI 9,X»4200» RESET CNTRL SWITCH STH 9 , CNTRL BR 15 EXIT LHR 9,5 R5 CONTAINS NEW POINT SH 9,PREV R9 CONTAINS CHANGE IN DVM READING STH 5,PREV BP PLUS CHECK SIGN OF DIFFERENCE BM MINUS RTRN LH 0,NPTS SH 0,CHECKPT SPEED SET TO * FAST' 16 SECS. CLHI 0,H'80' AFTER PEAK IS DETECTED BL *+12 LB 0,FAST STB 0,RATE OC 3,SPEED SET FOR SCAN RATE CONTROL WD 3,RATE BR 15 PLUS CLH 9,CRIT IS DIFFERENCE SIGNIFICANT ? BL RTRN NO LB 4,RATE CLHI WAS RATE SET TO 'FAST * ? BL RTRN NO, PEAK ALREADY DETECTED LH 4,NPK YES, SO FIND POSITION IN SPECTRUM AHI 4,1 NPK IS NO. OF PEAKS SO FAR STH 4,NPK LH 0,NPTS STORE TIME OF SPEED CHANGE STH 0,CHECKPT CLHI 4,2 BNL * + 16 PAST 1ST PEAK - SPEED SHOULD BE SLOW LB 4,MED SPEED SHOULD BE MEDIUM STB 4,RATE SET RATE B RTRN LB 4,SLOW SET SPEED TO SLOW STB 4,RATE B RTRN MINUS XHI 9,X«FFFF» TAKE TWO'S COMPLEMENT AHI 9,1 CLH 9,CRIT IS DIFFERENCE SIGNIFICANT ? BL RTRN NO LB 4,FAST SET RATE TO FAST STB 4,RATE B RTRN FAST DC X'0403' MED DC X '0201 ' SLOW EQU *-1 NPK DS H RATE DS H CRIT DC H'50 • 86 Appendix A-2 Program L i s t i n g PREV DS CHECKPT DS * * ROUTINE * STATUS H H TO CHECK STATUS BYTE * * RI * REJECT LH 8,SW CHECK SW NHI 8,X«0001« BZ * + 10 BRANCH IF OFF XHH 5,5 STORE ZERO IN BUFFER IF SW ON B STOKE LBR 7,6 GET SCAN BYTE HHI 7,X«0007« SET UP SHUNT FOR INDEXING AHR 7,7 SHI 7,2 LH 8,CRUDE (7) GET CRUDE BASE BNZ * + 8 IF ZERO, THIS POINT IS CRUDE STH 5,CRUDE (7) SO STORE IT se 5,CRUDE (7) SUBTRACT CRUDE BASE LHI 15,STORE SET R15 FOR RETURN FROM STORE LBR 7,6 CHECK SCAN CHARACTER NHI 7,X«0070» SCANNING ? BNZ *+20 YES, BRANCH LHI 1 ,X'4200» NO, SO RESET CNTRL AND BCALC STH 1 ,CNTRL SWITCHES AND BRANCH TO BASES STH 1 ,*+8 B BASES BFC 0,*+2<4 FIRST NON-BASELINE POINT BAL 15,BCALC CAUSES BRANCH TO «BCALC« LHI 1,X'U300» THEN BCALC SWITCH IS RESET STH 1 ,*-12 LHI 1,X «4200« AND MAXMUM SWITCH IS INITIALI! STH 1 , MAX MUM LHI 15,STORE CLHI 7,X'0070» CHECK FOR SCAN REJECT BE REJECT REJECT FOUND - REJECT SCAN CLHI 7,X»0030« CHECK FOR END OF SCAN BE EOS END OF SCAN FOUND B MAXMUM OTHERWISE GO TO MAXMUM !CT ROUTINE STH 15,RTEMP0 BAL 15,DISPL WRITE ZERO ON DISPLAY DC A(ZERO) LH 15,RTEMP0 LHI 7,X'8000' INDICATE REJECT STH 7,BOUT OC 3,SPEED SET SCAN SPEED TO FAST WD 3,FAST LH 7,SW SET SW OHI 7,X»0008' STH 7,SW 87 Appendix A-2 Program L i s t i n g BR 15 CONTINUE * HAXHUM ROUTINE TO SEARCH FOR MAXIMA NORM MAXI SHIFT BTC XHR LHI LHI LHI STH BXLE LHI STH LH AHI STH XHR LH STH LH STH AHI CLHI BL STH STH LH AH AHR STH CLHI BL LH XHR LH LHR SH BM BNZ CLHI BNL AHI CLHI BE CLHI BL B XHR LH STH 0 , NORM 11,11 12,WRK 13,2 14,COUNT 11,0 (12) 12,*-4 10,X»4300* 10,MAXMUM 10,COUNT 10,1 10, COUNT 8,8 11 ,CRNT+4 (8) 11, CRNT (8) 11 ,CRNT+6 (8) 11 ,CRNT+2 (8) 8,4 8, HM 6' *-24 5, CRNT+16 6, CRNT+18 9, CRNT+8 9 ,CRNT + 12 9,5 9, WRK+8 10,5 SHIFT 10, NFPTS NORMALLY BRANCH PAST FOLLOWING INSTRUCTIONS ZERO MAXMUM WORK AREA SET MAXMUM SWITCH INCREMENT COUNT MOVE POINTS IN CRNT BUFFER BRANCH IF NOT ALL MOVED ADD NEWEST POINT AND SCAN BYTE ADD LAST THREE POINTS STORE SUM IN WORK AREA IF < 5 POINTS, SKIP MAXIMUM CHECK 4,4 8,WRK+4 13,8 13,WRK (4) SHIFT * + 12 4,4 SHIFT 1,2 4,4 *-8 4,10 MAXI+6 YES R10 CONTAINS TIME GET POINT TO BE TESTED (CENTRE POINT OF FIVE) SUBTRACT ONE OF THE OTHER POINTS IF < 0, NO MAXIMUM CENTRE POINT > OTHER POINT IF POINTS ARE EQUAL, AND OTHER POINT COMES AFTER CENTRE POINT, BRANCH DON'T COMPARE POINT WITH ITSELF! DONE ? NO, SO BRANCH FOUND A MAXIMUM! 4,4 7,WRK+2 (4) 7,WRK{4) MOVE POINTS OVER IN WORK AREA Appendix A-2 Program L i s t i n g * YES MAXLP * XS WRK CRNT COUNT * * I * EOS AHI 4,2 CLHI 4,8 ALL DONE ? BL SHIFT+2 NO, CONTINUE BR 15 BRANCH TO STORE LH 9,NMAX GET MAXIMA COUNTER CLH 9,XS OVERFLOW TABLE ? BNL SHIFT YES, SO SKIP IT XHR 11,11 LHI 12,4 LHI 13,8 LHI 14,-10000 LH 1 ,CENT (11) SEARCH FOR MAXIMUM OF THE THREE SHR 1,14 SUBTRACT PREVIOUS MAXIMUM BM * + 10 PREVIOUS MAXIMUM BIGGER LH 14,CRNT (11) THIS POINT BIGGER LHR 2,11 STORE MAXIMUM POINTER BXLE 11,MAXLP LH 11,CRNT+2(2) GET SCAN BYTE OF MAXIMUM STB 11 ,SHMAX (9) AND STORE IT AHR 9,9 LH 1 1 ,CRNT (2) GET POINT ITSELF AND STH 11 ,MAX (9) STORE SRHA 2,2 AHI 10,-3 (2) STH 10, IMAX (9) STORE TIME OF MAXIMUM SRHA 9,1 AHI 9,1 INCREMENT COUNTER STH 9 ,NMAX B SHIFT PREPARE TO EXIT DC H'32' DS 5H DS 10H DS H ROUTINE FOR SCAN PROCESSING LPSW * + 4 ENABLE INTERRUPT DC X '4000 ' DC A (*+2) STH 15,RTEMP0 BAL 15,DISPL ZERO DISPLAY DC A (ZERO) LH 15,RTEMP0 LH 8,NFPTS CARRY-OVER FROM PREVIOUS SCAN ? CLHI 8,H'10» BNL * + 10 NO, SO BRANCH NHI 6,X'008F» YES, REMOVE EOS INDICATION BR 15 LH 9,SW SET SW TO INDICATE END OF SCAN OH I 9,X'0080« Appendix A-2 Program L i s t i n g FCALC * TOTAL TOTALS NSCAN * * E BASES STH 9 , SW BAL 15,STORE BRANCH TO STORE LH 9,TOTAL STH 9,TOTAL2 LH 8 ,NPPTS AHR 8,9 INCREMENT TOTAL POINT COUNTER STH 8,TOTAL XHR 8,8 CLEAR CERTAIN COUNTERS STH 8,NPTS XHR 11,11 STH 11 ,NFPTS STH 1 1 ,CRUDE (8) AHI 8,2 CLHI 8,10 BL *-12 LHI 9,X'U200» RESET SOME SWITCHES STH 9,CNTRL STH 9 ,BASES STH 9 ,MAXMUM LH 8,SW SKIP PROCESSING IF SCAN REJECTED NHI 8,X '0008' BNZ * + 32 BAL 15,REFINE SUBTRACTS TRUE BASELINES BAL 15,PEAK PICKS PEAKS BAL 15,CALC CALCULATES RATIOS BAL 15,CONVRT PREPARE FOR PEAK PRINTOUT LH 8,NSCAN INCREMENT SCAN NO. AHI 8,1 STH 8,NSCAN XHR 8,8 LHI 9,NMAX LHI 10,2 LHI 11,BOUT-2 STH 8,0(9) ZERO MAXIMUM TABLE BXLE 9,*-4 LH 8,SW LHR 9,8 R8 AND R9 CONTAIN SW NHI 8,X'0007» REMOVE REJECT INDICATION FROM SW STH 8,SW NHI 9,X»0008« IF SCAN WAS REJECTED, NO RATIOS BNZ WAIT TO OUTPUT BAL 15,FRACT CALCULATE NORMALIZED SR87/SR86 B PRINT PRINT SCAN SUMMARY DS H DS H DS H FINE ! TO STORE BASELINES BTC 0, BYPASS SKIP FOLLOWING SECTION IF NOT XHR 11,11 FIRST CALL 90 appendix A-2 Program L i s t i n g BYPASS TEMP FIRST NBASE BASE * * I * BCALC LHI 12,TEMP ZERO BASELINE MATRIX LHI 13,2 LHI 14,BASE+8 STH 11,0(12) BXLE 12,*-4 LHI 7,X»4300» SET SWITCH STH 7,BASES LH 0,NFPTS LBR 7,6 NHI 7,X»0007» GET SHUNT AND ADJUST AHR 7,7 FOR ADDRESSING SHI 7,2 LH 4,NBASE (7) ANY POINTS ON THIS SHUNT YET ? BNZ * + 12 YES, SKIP STH 0,FIRST (7) NO, SO STORE TIME B * + 16 LHR 1,0 CHECK THAT POINTS ARE CONSECUTIVE SH 1, TEMP (7) CLHI 1,1 BNER 15 EXIT IF THEY AREN'T STH 0,TEMP (7) CLHI 4,H'50« >5 0 POINTS ON THIS BASE ? BNLR 15 YES, SO RETURN AHI 4,1 STH 4 ,NBASE (7) INCREMENT NBASE LHR 1,5 AH 1 ,BASE (7) ADD CURRENT POINT TO TOTAL STH 1,BASE (7) FOR THIS SHUNT BR 15 GO TO 'STORE• DS 5H DS 5H DS 5H DS 5H 'INE TO CALCULATE BASELINES XHR 4,4 STH 4,NPK ZERO NPK IN CNTRL LH 2,NBASE (4) GET NO. OF BASELINE POINTS BNZ * + 18 IF ZERO, NO POINTS ON THIS SHUNT AHI 4,2 CLHI 4 , H * 10 * BNLR 15 EXIT POINT B BCALC+6 TRY ANOTHER SHUNT XHR 8,8 LHR 1,2 CALCULATE CORRECTION SRHA 1,1 FOR ROUNDING LH 9,BASE (4) GET SUM OF POINTS BNM * + 14 SKIP IF NUMBER POSITIVE LHI 8,X'FFFF» GENERATE 32 BIT NEGATIVE NUMBER SHR 9,1 Appendix A-2 Program L i s t i n g B * + 6 AHR DHR 8,2 DIVIDE SUM BY NUMBER OF POINTS AH 1 ,FIRST (4) CALCULATE TIME FOR POINT CLHI 7,X'0020» DETERMINE WHICH PART OF SCAN BNE * + 12 LHI 8,BHD SCANNING DOWN B *+20 BNL * + 12 LHI 8,BLO SCANNING UP B * + 8 LHI 8,BHU END OF SCAN SLHA 4,1 AHR 8,4 CALCULATE WHERE TO STORE RESULT SRHA 4,1 LH 10,2 (8) SOMETHING ALREADY THERE ? BNZ *+12 YES, SO DON'T STORE THESE NUMBERS STH 9,0 (8) STORE AVERAGED POINT STH 1,2(8) STORE TIME XHR 2,2 STH 2,BASE (4) ZERO BASE AND NBASE FOR STH 2 ,NBASE (4) THIS SHUNT STH 2,FIRST (4) ALSO ZERO FIRST B BCALC+14 DO ANOTHER SHUNT UTINE TO STORE FILTERED POINTS LH 2/NFPTS INCREMENT FILTERED POINT COUNTER AHI 2,1 STH 2,NFPTS LH 7,PTR GET INDICATOR STH 5,BOUT (7) STORE POINT IN OUTPUT BUFFER STH 6,BOUT+2 (7) STORE SCAN BYTE AHI 7,4 INCREMENT INDICATOR STH 7,PTR LHR 8,7 LH 7,SW NHI 7,X '0080' IS EOS BIT ON ? BNZ * + 12 YES, OUTPUT RECORD CLHI 8,H'256* 64 POINTS ? BL END NO, RETURN TO NORMAL PROCESSING STH 15,RTEMP1 YES, SO BAL 15,TAPEWR OUTPUT RECORD DC A(BOUT) DC A (BEND) LH 15,RTEMP1 XHR 1,1 STH 1 ,PTR ZERO INDICATOR LHR 7,7 WAS SW ON ? BNZR 15 YES, RETURN B END RETURN TO NORMAL PROCESSING Appendix A-2 Program L i s t i n g PRINT ROUTINE TO OUTPUT RATIOS, ETC ON TELETYPE TSENS PRSW * W RT * * R( CONVRT CONLP BAL 15,SIBTOD CONVERT SCAN NO. TO ASCII DC A(NSCAN) DC A(BTEMP) LH 1,BTEMP+4 LOAD NO. OF SCANS (MAX. OF 99) STH 1 ,PROUT+14 STORE IN PRINT OUTPUT AREA LHI 3,PROUT LH 4,PRE8D LHI 2,2 SSR 2,0 CHECK STATUS OF TELETYPE BTC 1,WAIT EXIT IF TELETYPE POWERED DOWN OC 2 , WRT SET WRITE MODE SSR 2,0 BTC 8,TSENS LOOP IF TELETYPE BUSY WD 2,0 (3) OUTPUT A BYTE AHI 3,1 CLHR 3,4 ALL DONE ? BL TSENS NO CLH 4,PREND2 BE WAIT CLH 4,PREND1 BE * + 16 LHI 3,PROUT1 LH 4,PREND1 B TSENS OUTPUT SECOND PRINT BUFFER LHI 3,PROUT2 LH 4,PREND2 B TSENS OUTPUT THIRD PRINT BUFFER DC X «9898« 'INE TO GENERATE OUTPUT BUFFER STH 15,RTEMP2 LH 12,NPEAKS R12 CONTAINS NO. OF PEAKS FOUN AHR 12,12 SHI 12,1 ADJUST R12 FOR ADDRESSING XHR 2,2 LHI 13,HTS LHI 11 ,X«8D0A» LB 8, POINT (2) GET POINTER BYTE LH 7,IMAX (8) GET TIME OF MAXIMUM AH 7,TOTAL2 CALCULATE TIME FROM START OF R STH 7,BTEMP STH 13,WHERE ADDRESS OF ASCII NUMBER LHI 14,*+8 RETURN ADDRESS B CONV CONVERT TIME TO ASCII LH 7,MAX (8) GET MAXIMUM STH 7,BTEMP AHI 13,8 93 appendix A-2 Program L i s t i n g STH 13,WHERE INCREMENTED ADDRESS OF ASCII NUMBER LHI 14,*+8 B CONV CONVERT PEAK HEIGHT TO ASCII LHR 7,8 LB 8,POINT (12) GET POINTER FOR UPMASS SECTION CLHR 7,8 DONE UPMASS AND DOWNMASS PEAK ? BE WHERE+4 YES, SO BRANCH AHI 13,8 NO, SO DO UPMASS PEAK B CONLP+4 CONV BAL 15,SIBTOD DC A (BTEMP) WHERE DS H BR 14 AHI 13,6 STH 11,0(13) INSERT CARRIAGE RETURN/LINE FEED * INTO TEXT AHI 13,6 ADJUST REGISTERS TO DO NEXT PEAK AHI 2,1 SHI 12,1 CLHR 2,12 PEAKS ALL DONE ? BL CONLP NO, MORE PEAKS TO DO SHI 13,4 STH 13,PREND STORE ENDING ADDRESS OF FIRST LH 15,RTEMP2 BUFFER •6: BR 15 EXIT PROUT DC X '8D0A' DC C'SCAN NUMBER » DS H DC X'8D0A8D0A» DC C PEAK DATA: ' DC X '8D0A' DC C ' HTS DC 90X»2020» PROUT1 DC X«8D0A» DC C» RATIOS: * DC X»8D0A* DS 2H RATI01 DS 12C RATI02 DS 12C RATI03 DS 12C RATI04 DS 12C PROOT2 DC X'8D0A» DC C NORMALIZED RATIO: • NRATIO DC 4X»2020» DC X '8D0A» PREND DS H PREND1 DS H PREND2 DS H * * OUTPUT ROUTINE FOR MAGNETIC TAPE Appendix A-2 Program L i s t i n g TAPEWR LH 2,0 (15) GET STARTING ADDRESS STH 2,X'0000« AND STORE LH 2,2(15) GET ENDING ADDRESS STH 2,X'0002' AND STORE LHI 2,8 DEVICE NUMBER OF TAPE DRIVE OC 2,TWRT OUTPUT RECORD * B 4(15) RETURN TWRT DC X '4802 » WEF EQU *-1 EOF LHI 2,8 DEVICE NUMBER OF TAPE DRIVE SSR 2,0 DEVICE BUSY ? BTC 8,*-2 YES, WAIT OC 2,WEF WRITE AN END OF FILE SSR 2,0 BTC 8,*-2 WAIT AGAIN OC 2,WEF WRITE ANOTHER LHI 1 ,X'0020« REWIND COMMAND BYTE SSR 2,0 BTC 8,*-2 OCR 2,1 REWIND TAPE BR 15 RETURN * ROUTINE TO ADJUST MAXIMA FOR BASELINE DRIFT REFINE STH 3,RTEMP2 SAVE R3 AND R15 STH 15,RTEMP3 XHR 1,1 LHI 7,DELTD ZERO WORK AREA LHI 8,2 LHI 9,CORR+18 STH 1,0(7) BXLE 7,*-4 LHI 14,DELTD ADDRESS FOR STORING RESULTS LHI 10,BHD ADDRESS OF FIRST SET OF BASELINES LHI 11,BLO ADDRESS OF SECOND SET XHR 4,4 SLOOP LHR 12,10 SET UP REGISTERS FOR ADDRESSING AHR 12,4 LHR 13,11 AHR 13,4 LHR 15,14 AHR 15,4 LH 7,2(12) GET TIME OF FIRST SET BZ NONE NO POINTS ON THIS SHUNT STH 7,TIMES (1) STORE TIME OF SET LH 8,2(13) GET TIME OF SECOND SET BZ NONE IF ZERO, TROUBLE ! SHR 8,7 FIND DELTA T STH 8,2(15) STORE IT LH 7,0(12) GET BASELINE VALUE FOR FIRST SET 9 5 A p p e n d i x a-2 Program L i s t i n g NONE SPIN MORE STH 7,CORR(1) LH 8,0(13) SHR 8,7 STH 8,0(15) AHI 1,2 AHI 4,4 CLHI 4,H'20» BL SLOOP CLHI 14,DELTO BE SPIN LHI 14,DELTO LHR 10,11 LHI 11,BHD B SLOOP-2 XHR 11,11 LHI 12,IMAX LHI 13,MAX LHI 14,SHMAX LHR 8,12 AHR 8,11 LHR 9,13 AHR 9,11 SRHA 11,1 LHR 10,14 AHR 10,11 AHR 11,11 LB 7,0(10) NHI 7,X'0007» BZ DON AHR 7,7 SHI 7,2 LH 6,0(8) CLH 6,TIMES+10 BNL * + 14 XHR 0,0 LHI 4,DELTD B * + 12 LHI 0 , 1 LHI 4,DELTU AHR 4,7 AHR 4,7 LH 3,2(4) BZ NOBASE LHR 0,0 BNZ *+12 SH 6,TIMES (7) B *+8 SH 6/TIMES+10 LHR 3,6 MH 2,0(4) LH 6,2(4) GET OTHER BASELINE VALUE FIND DELTA H STORE IT ALL SHUNTS DONE ? NO, CONTINUE DONE BOTH BLOCKS ? YES SET UP TO DO UPMASS BLOCK GO AROUND AGAIN SET UP REGISTERS FOR PEAK HEIGHT ADJUSTMENT 88 IS TIME POINTER R9 IS HEIGHT POINTER R 1 0 IS SCAN BYTE POINTER GET BYTE GET SHUNT ZERO SHUNT MEANS aLL PEAKS DONE USE SHUNT FOR aDDRESSING GET TIME FOR MAXIMUM (7) COMPARE TO TIME AT CENTRE OF SCAN I F GREATER, WANT UPMASS BLOCK IF LESS, WANT DOWNMASS BLOCK FLAG RO TO INDICATE BLOCK ADJUST POINTER GET DELTA T FOR BASELINES NO BASELINES FOR THIS MAXIMUM ! SET CONDITION CODE GET TIME OF RIGHT BLOCK CALCULATE DELTA T FOR MAXIMUM (7) CALCULATING ADJUSTMENT ROUND-OFF FACTOR Appendix A-2 Program L i s t i n g SRHA 6,1 LHR 2,2 BNM * + 14 SHR 3,6 SCH 2, NIL B * + 10 AHR 3,6 ACH 2,NIL DH 2,2(4) LHR 0,0 BNZ * + 12 AH 3,CORR (7) B * + 8 AH 3,CORR+10 LH 1,0 (9) SHR 1,3 STH 1,0(9) AHI 11,2 B MORE DON LH 3,RTEMP2 LH 15,RTEMP3 BR 15 * NOBASE LH 7,SW OHI 7,X «0008« STH 7,SW LH 3,RTEMP2 LH 15,RTEMP3 B 24(15) * DELTD DS 5F DELTU DS 5F TIMES DS 10H CORR DS 10H * * ROUTINE TO IDENTIFY * DECAY * PEAK XHR 10,10 STH 10,NPEAKS LH 9,NMAX BZ ERRET AHR 9,9 XHR 2,2 XHR 1,1 MAJOR LH 7,MAX (10) BM * + 12 CLHI 7,H'25» BNL OK AHI 10,2 CLHR 10,9 BL MAJOR CHECK SIGN OF PRODUCT POSITIVE NEGATIVE CALCULATE ADJUSTMENT CALCULATE CORRECTION (7) GET MAXIMUM APPLY CORRECTION RETURN IT TO MAXIMUM TABLE MORE POINTS TO DO RESTORE REGISTERS EXIT NO BASELINES FOR A PEAK, SO REJECT SCAN AND FLAG IT RESTORE REGISTERS SKIP SCAN PROCESSING PEAKS, AND ADJUST FOR GROWTH ZERO NPEAKS NO MAXIMA ! GET A MAXIMUM BIG ENOUGH ? YES NO DONE ALL MAXIMA ? 97 Appendix A-2 Program L i s t i n g OK FIX DONE ERRET PLOOP B DONE STB 10,POINT (2) LH 0,IMAX(10) SHE 0,1 LH 1,IMAX(10) CLHI 0,H'18' BL FIX AHI 2,1 LH 4,NPEAKS AHI 4,1 STH 4,NPEAKS B MAJOR+16 LHR 4,2 SHI 4,1 LB 8, POINT (4) CLH 7,MAX (8) BL MAJOR+16 BE MAJOR+16 STB 10,POINT (4) B MAJOR+16 LH 12,NPEAKS BZ ERRET SRHA 12,1 BFC 8,*+20 LH 9,SW OHI 9,X'0008« STH 9,SW B 20(15) STH 12,NPEAKS AHR 12,12 SHI 12,1 LB 8,POINT+2 GET POINTERS FOR SR86 PEAK, R8 FOR LB 9,POINT-2 (12) DOWNMASS PEAK, R9 FOR UP MASS LH 13,IMAX(8) AH 13,IMAX(9) AHI 13,1 SRHA 13,1 R13 HOLDS TIME FOR SR86 PEAK SRHA 8,1 LB 3,SHMAX(8) R3 CONTAINS SHUNT FOR SR86 PEAK NHI 3,X»0007' XHR 11,11 XHR 2,2 LB 8, POINT (2) LB 9,POINT(12) LH 5,MAX (8) GET DOWNMASS PEAK HEIGHT LH 7,MAX (9) GET UPMASS PEAK HEIGHT SRHA 8,1 SRHA 9,1 LB 0,SHMAX(8) GET CORRESPONDING SHU8T BYTES LB 1,SHMAX(9) AHR 8,8 YES STORE MAXIMUM POINTER GET TIME OF MAXIMUM FIND TIME DIFFERENCE FROM PREVIOUS MAXIMUM TWO MAXIMA ON ONE PEAK ! ALL OK INCREMENT NPEAKS CONTINUE R4 NOW POINTS TO PREVIOUS MAXIMUM COMPARE THE MAXIMA PREVIOUS MAXIMUM IS BEST USE NEW MAXIMUM GET NUMBER OF PEAKS NO PEAKS ! DIVIDE BY TWO EVEN NO. OF PEAKS SET SW FOR REJECT -ERROR HAS OCCURRED SKIP REST OF PROCESSING 98 appendix A-2 Program L i s t i n g AHR 9,9 NHI 0,X»0007» REMOVE SCANNING INDICATION NHI 1,X'0007« SHR 1,0 COMPARE BYTES BZ ADD PEAKS ON SAME SHDNT AHR 1,1 PEAKS ON DIFFERENT SHUNTS BNM ADD-4 UPMASS PEAK ON HIGHER SHUNT LH 14,FACT (1) GET SUITABLE SHUNT FACTOR SRHA 14,1 THESE INSTRUCTIONS ADJUST PEAKS AHR 7,14 TO SAME SHUNT LH 14,FACT{1) XHR 6,6 DHR 6,14 B ADD MH 6,FACT (1) ADD CLHI 2,2 BE SR86 BRANCH IF DOING SR86 PEAK SHR 7,5 FIND HEIGHT DIFFERENCE BETWEEN PEAKS LH 4,IMAX(8) TIME OF DOWNMASS PEAK LH 1,IMAX(9) TIME OF UPMASS PEAK SHR 1,4 FIND TIME DIFFERENCE LHR 14,13 TIME OF SR86 PEAK SHR 14,4 TIME DIFFERENCE FROM SR86 PEAK MHR 6,14 CALCULATE ADJUSTMENT LHR 4,1 SRHA 4,1 LHR 6,6 BNM *+14 SHR 7,4 SCH 6,NIL B * + 10 AHR 7,4 ACH 6, NIL DHR 6,1 AHR 5,7 ADJUST PEAK HEIGHT XHR 4,4 LHR 1,0 SHR 1,3 COMPARE PEAK SHUNT WITH SR86 SHUNT BZ STPKS PEAKS ON SAME SHUNT AHR 1,1 PEAKS ON DIFFERENT SHUNTS - ADJUST BNM SR86-8 TO SR86 SHUNT LH 14,FACT (1) PEAK ON LOWER SHUNT LHR 1,14 SRHA 1,1 AHR 5,1 DHR 4,14 XHR 4,4 B STPKS MH 4,FACT (1) PEAK ON HIGHER SHUNT B STPKS SR86 AHR 5,7 CALCULATE SR86 PEAK HEIGHT AHI 5,1 Appendix A-2 Program L i s t i n g SRHA 5,1 XHR 4,4 STPKS STH 4,PEAKS (11) STORE PEAK HEIGHT ( 32 BITS ) STH 5,PEAKS+2 (11) AHI 11,4 AHI 2,1 SHI 12,1 CLHR 2,12 DONE ALL PEAKS ? BL PLOOP NO, GO ROUND AGAIN BR 15 EXIT POINT DS 10C PEAKS DS 5F NPEAKS DS H DC H«81 • DC H«27« DC H«9 « DC H'3 » FACT DC H«1 » DC H«3 « DC H'9 » DC H»27» * DC H'81 » * ROUTINE CALCULATES ISOTOPE RATIOS AND CONVERTS THEM * TO ASCII CALC STH 15,RTEMP5 LHI 13,RATI01- 4 BLANK RATIO OUTPUT AREA LHI 14,2 LHI 15,PROUT2- 2 LHI 12,X'2020» STH 12,0(13) BXLE 13,*-4 LHI 14,PEAKS LH 13, 10 (14) GET SR86 PEAK LHR 7,13 ADJUSTMENT FOR ROUNDING SRHA 7,1 LHI 12,RATI01 ADDRESS OF OUTPUT AREA XHR 6,6 LH 11,NPE AKS R11 IS LOOP COUNTER SHI 11,1 AROUND LH 0,0(14) GET PEAK HEIGHT LH 1,2(11) GET OTHER HALF DHR 0,13 CALCULATE INTEGER PART OF RATI LHR 3,0 MOVE REMAINDER CLHI 1,3 INTEGER PART < 3 ? BNL *+16 NO LHI 8,4 FOUR DECIMAL PLACES LH 4 ,TENM SCALE FACTOR = 10000 B SCALE CLHI 1,H«30» INTEGER PART < 30 ? 100 Appendix A-2 Program L i s t i n g BNL *+16 NO LHI 8,3 THREE DECIMAL PLACES LH 4,ONEM SCALE FACTOR = 1000 B SCALE CLHI 1,H»300* INTEGER PART < 300 ? BNL *+16 NO LHI 8,2 TWO DECIMAL PLACES LH 4,ONEC SCALE FACTOR = 100 B SCALE CLHI 1,H«3000» INTEGER PART < 3000 ? BNL *+16 NO LHI 8,1 ONE DECIMAL PLACE LH 4,TEN SCALE FACTOR = 10 B SCALE XHR 8,8 INTEGER PART > 3000 ! B *+18 SCALE FACTOR = 1, SO SKIP SCALING SCALE MHR 0,4 SCALE INTEGER PART OF RATIO MHR 2,4 SCALE FRACTIONAL PART AHR 3,7 FOR RODNDING ACH 2,NIL DHR 2,13 CALCULATE FRACTIONAL PART OF RATIO AHR 1,3 STH 8,NDEC(6) STORE NO. OF DECIMAL PLACES STH 1,BIN STH 1,BRATIO(6) STORE BINARY RATIO STH 12,*+10 BAL 15,SIBTOD CONVERT RATIO TO DECIMAL NUMBER DC A (BIN) DS H ADDRESS OF ASCII RATIO LHR 8,8 BZ NODEC NO DECIMAL POINT LHR 10,12 DLOOP LB 9,5(10) MOVE BYTES TO RIGHT OF DECIMAL CLHI 9,X«0020» A BLANK ? BNE *+8 NO LHI 9,X'0030 1 YES, REPLACE BY ZERO STB 9,6(10) SHI 8,1 DECREMENT COUNTER BZ * + 12 MOVED ALL BYTES SHI 10,1 B DLOOP MORE TO MOVE LHI 9,X»002E« A DECIMAL POINT STB 9,5(10) NODEC AHI 14,4 CLHI 14,PEAKS+8 NO NEED TO CALCULATE BE *-8 SR86/SR86 RATIO AHI 6,2 AHI 12,12 SHI 11,1 DONE ALL PEAKS ? BNZ AROUND NO LHI 11,X*8D0A* YES SHI 12,2 101 Appendix A-2 Program L i s t i n g STH 12,PREND1 ADDRESS OF BUFFER END STH 11,-2 (12) STORE CARRIAGE RETURN/LINE FEED LH 15,RTEMP5 BR 15 YES, RETURN TEN DC H' 10' ONEC DC H'100 • ONEM DC H'1000* TENM DC H'10000 ' BIN DS H BRATIO DS UH NDEC DS UH * ROUTINE * NORMALIZES SR87/SR86 FRACT STH 15,RTEMP2 LHI 10,X«2020' BLANK NRATIO AREA STH 10,NRATIO+6 LHI 10 , H' 83 75' ACCEPTED SR88/SR86 RATIO LHR 9,10 SH 9,BRATIO SUBTRACT MEASURED SR88/SR86 RATIO MH 8,TENM SCALE LHR 8,8 BM * + 1U ROUND-OFF PROCEDURE AHR 9,10 ACH 8, NIL B * + 10 SHR 9,10 SCH 8,NIL AHR 10, 10 DIVISOR DHR 8,10 AH 9,TENM R9 CONTAINS THE ONE-MASS FACTOR LH 1,BRATIO+2 GET SR87/SR86 RATIO MHR 0,9 AND NORMALIZE IT AHI 1,H'5000' MORE ROUND-OFF ACH 0,NIL DH 0,TEN M STH 1,BRATIO+2 BAL 15,SIBTOD CONVERT NORMALIZED RATIO TO ASCII DC A(BRATIO+2) DC A (NRATIO) LH 8,NDEC+2 NUMBER OF DECIMAL PLACES BNZ DSHIFT NOT ZERO, SO BRANCH LH 15,RTEMP2 EXIT POINT BR 15 DSHIFT LHI 10,NRATIO LB 9,5(10) MOVE BYTES TO RIGHT OF DECIMAL CLHI 9,X'0020« INSERT ZEROES TO RIGHT OF DECIMAL BNE *+8 IF NEEDED LHI 9,X '0030' STB 9,6(10) SHI 8,1 LOOP COUNTER 102 Appendix A-2 Program L i s t i n g BZ * + 12 ALL DONE SHI 10,1 B DSHIFT+4 CONTINUE LHI 9,X»002E» DECIMAL POINT STB 9,5(10) STORE IT IN NUMBER LHI 9,NRATIO+10 STH 9,PREND2 ADDRESS OF BUFFER END B DSHIFT-6 GO TO EXIT POINT * ROUTINE TO READ MASS SPECTROMETER READ XHR 4,4 LHI 5,1 LHI 6,6 OC 3,IN (4) READ MASS SPECTROMETER RD 3,BUFF+2 (4) BXLE 4,*-8 LOOP TILL ALL READ STH 15,RTEMP4 BAL 15,SIDTOB CONVERT DVM READING TO BINARY DC A (BUFF) DC A (RBIN) LH 15,RTEMP4 LB 2,BUFF+6 FORM SCAN BYTE LB 4,BUFF+7 SLHL 4,4 OHR 2,4 STB 2,3(15) STORE IT LB 2,BUFF+8 GET OUTPUT REQUEST SWITCH SETTING STB 2,2(15) AND STORE IT * B 4(15) RETURN IN DC ; X «0809« DC ' X «0A0B» DC X'OCOD* DC X 'OEOF* OUT DC X «0001 » DC X '0203 • DC X'0405« SPEED DC X '0607* BUFF DC X'2B30« DS 8C * * * ROUTINE OUTPUTS TO DIGITAL DISPLAY DISPL LH 1,0 (15) ADDRESS OF NUMBER TO BE OUTPUT LHR 2,1 AHI 2,5 ENDING ADDRESS XHR 4,4 DISLP LB 0,0 (1) GET BYTE TO BE DISPLAYED CLHI 0,X •002E' IS IT A DECIMAL POINT ? BE DECOUT YES OC 3,OUT (4) OUTPUT DIGIT Appendix A-2 Program L i s t i n g DECOUT * * R( SWITCH DUMP WDR 3,0 SEND BYTE TO DISPLAY AHI 4,1 AHI 1,1 CLHR 1,2 DONE ? BL DISLP NO, CONTINUE B 2(15) YES, RETURN LHR 0,1 GET ADDRESS OF CURRENT BYTE SH 0,0(15) CALCULATE DECADE FOR DECIMAL OC 3,ODT+5 WDR 3,0 WRITE DECIMAL POINT AHI 2,1 B DECOUT-14 CONTINUE 'INE DETERMINES DESIRED OUTPUT FOR DISPLAY STH 15,RTEMP6 LHI 7,DUMP LB 2,RSW GET SWITCH POSITION CLHI 2,1 IF 1, OUTPUT FILTERED POINT BNE * + 20 LHI 4,5 OC 3,OUT+5 WDR 3,4 LHI 4,BUFF1+1 BR 7 CLHI 2,2 IF 2, OUTPUT FIRST RATIO BNE * + 10 LHI 4,RATI01+1 BR 7 CLHI 2,4 IF 4, OUTPUT SECOND RATIO BNE * + 10 LHI 4,RATI02+1 BR 7 CLHI 2,5 IF 5, OUTPUT NORMALIZED RATIO BNE * + 10 LHI 4,NRATIO+1 BR 7 CLHI 2,6 IF 6, OUTPUT THIRD RATIO BNE * + 10 LHI 4,RATI03+1 BR 7 CLHI 2,8 IF 8, OUTPUT FOURTH RATIO BNE * + 10 LHI 4,RATI04+1 BR 7 LHI 4,ZERO IF NONE OF ABOVE, OUTPUT ZERO STH 4,*+8 BAL 15,DISPL OUTPUT DESIRED INFORMATION DS H LH 15,RTEMP6 BR 15 RETURN appendix A-2 Program L i s t i n g * FILTER CALLING SUBROUTINE * FILTER PTB1 * PTE 2 PTE 3 * * WSP1 WSP2 WSP3 * FILT STH 15,RTEMP7 BAL 15,FILT DC tt'Ol* DC A(WSP1) DC A(WSP1+14) DC H'02« DS H BAL 15,FILT DC H'03» DC A(WSP2) DC A(WSP2+6) DC H*01» DS H BAL 15,FILT DC H«05» DC A(WSP3) DC A(WSP3 + 10) DC H ^ ' DS H LH 15,RTEMP7 BB 15 DS 7H DS 3H DS 5H FILTEB SUBBOUTINE * NXT STM 0,SAVE1 LH 11,0(15) LH 6,2 (15) LH 3,4(15) LHI 2,2 SHE 3,2 LHB 1,6 LH 14,SW NHI 14,1 BZ NXT STH 5,0(1) BXLE 1 ,*-4 B * + 20 LH 0,2(1) STH 0,0 (1) AHB 1,2 CLHB 1,3 SEVEN POINT FILTEB KEEP EVERY SECOND POINT THBEE POINT FILTER KEEP ALL POINTS FIVE POINT FILTER KEEP EVERY SECOND POINT SAVE REGISTERS GET FILTER LENGTH GET ADDRESS OF WORK AREA ENDING ADDRESS AND LOAD SW TEST FOR SHUNT CHANGE SW OFF SW ON - FILL BUFFER WITH NEW POINT SKIP MOVE OPERATION IF SW WAS SET MOVE POINTS IN WORK AREA appendix A-2 Program L i s t i n g LP CONT * FINISH SAVE1 * * BINJ * SIBTOD FB BL NXT STH 5,0(3) STORE NEW POINT LH 9,8(15) FILTER THIS TIME ? AHI 9,1 STH 9,8(15) CLH 9,6(15) BNE FINISH NO, SO SKIP CaLCULATION XHR 4,4 YES STH 4,8(15) AH 5,0(6) ADD NEWEST AND OLDEST POINT AHI 5,1 SRHA 5,1 DIVIDE BY 2 (TAPERED ENDPOINTS) XHR 10,10 AHR 6,2 INCREMENT R6 BY 2 SHR 3,2 DECREMENT R3 BY 2 CLHR 6,3 ARE THEY EQUAL ? BE CONT YES, FILTERING ALMOST DONE AH 5,0(6) NO, CONTINUE ACHR 4,10 ADD POINTS aH 5,0(3) ACHR 4,10 B LP AH 5,0 (6) ADD CENTRE POINT ACHR 4,10 LHR 9,11 R9 WILL CONTAIN DIVISOR SRHa 11,1 DIVIDE BY 2 AHR 5,11 AND ADD FOR ROUNDING ACHR 4,10 SHI 9,1 R9 CONTAINS FILTER WEIGHT DHR 4,9 NORMALIZE POINT STH 5,SAVE1+10 STORE IT LM 0,SAVE1 RESTORE REGISTERS B 10(15) RETURN LM 0,SAVE1 EXIT HERE IF FILTERING IS SKIPPED B END DS 16H TO/FROM ASCII BCD CONVERSION ROUTINES STM 10,SAVE SAVE REGISTERS XHR 10,10 LH 14,0(15) A (ARGUMENT) LH 15,2(15) A (RESULT) LHI 12,X'0020 • BLANK SIGN LH 13,0(14) GET ARGUMENT STB 12,0(15) STORE SIGN LHI 14,8 LH 11,TABLE- 2 (14) GET DIVISOR XHR 12,12 DHR 12,11 106 Appendix A-2 Program L i s t i n g SAVE TABLE * SIDTOB LOOPZ LHR 10, 10 SET CONDITION CODE BUZ *+18 SUPPRESS LEADING ZEROS LHR 10,13 LOAD RESULT INTO R10 BNZ * + 12 NOT LEADING ZERO LHI 13,X«0020' REPLACE LEADING ZERO WITH B * + 8 OHI 13,X»0030' ADD ASCII ZONE STB 13,1 (15) AND STORE CHARACTER LHR 13,12 GET REMAINDER AHI 15,1 INCREMENT POINTERS AHI 14,-2 BNZ FB OHI 12,X'0030' GENERATE LAST CHARACTER STB 12,1 (15) LM 10,SAVE RESTORE REGISTERS B 4(15) EXIT DS 6H DC H» 10 • DC H'100' DC H'1000» DC H'10000' STM 10,SAVE SAVE REGISTERS LH 14,0(15) A(ARGUMENT) LHI 15,4 (14) END OF BCD NO. XHR 10,10 LHI 11,H*10' MULTIPLIER LB 13,1 (14) GET FIRST DIGIT NHI 13,X*OO0F' REMOVE ZONE AHR 13,10 ADD RESULT MHR 12,11 * 10 LHR 10,13 AHI 14,1 INCREMENT POINTER CLHR 14,15 END YET? BL LOOPZ NO, BRANCH LB 13,1 (14) GET LAST DIGIT, NHI 13,X»000F» STRIP ZONE, AND AHR 10,13 ADD TO RESULT LB 12,-4 (14) GET SIGN NHI 12,X»007F« REMOVE EXTRA BIT CLHI 12,X'002D» MINUS SIGN? BNE * + 12 NO, BRANCH XHI 10,X«FFFF» TWO'S COMPLEMENT AHI 10,1 LH 15,SAVE+10 RESTORE R15 LH 14,2(15) GET A (RESULT) STH 10,0(14) STORE RESULT LM 10,SAVE RESTORE REGISTERS B 4(15) EXIT A BLANK * * INPUT AND OUTPUT ROUTINES FOR TELETYPE 107 OUPT * INPT SENSE SET DELLN DELCH Appendix A-2 Program L i s t i n g STM 12,SAVE SAVE REGISTERS LH 12,0 (15) GET A (MESSAGE) LHR 13,12 AH 13,2 (15) ADD LENGTH AND SHI 13,1 ADJUST FOR WB INSTRUCTION LHI 14,2 DEVICE NO, OF TELETYPE OC 14,BLOK SET WRITE MODE WBR 14,12 OUTPUT MESSAGE LM 12,SAVE RESTORE REGISTERS B 4(15) RETURN STM 11,SAVE STORE REGISTERS LH 12,0 (15) A (BUFFER) LHR 13,12 AH 13,2 (15) CALCULATE BUFFER END LHI 14,2 DEVICE NO. OF TELETYPE OC 1 4,DNBL SET READ MODE SSR 14,11 SENSE STATUS OF TELETYPE BTC 15,SENSE BRANCH IF STATUS NOT ZERO RDS 14,11 READ ONE CHARACTER NHI 11,X'007F* STRIP EXTRA BIT CLHI 11,X»007F» RUB-OUT CHARACTER? BE DELLN YES, BRANCH CLHI 11,X»005F' DELETE LAST CHARACTER? BE DELCH YES, BRANCH CLH 12,0 (15) FIRST CHARACTER? BNE * + 12 NO, BRANCH CLHI 11,X«0020» LEADING BLANK? BE SENSE YES, IGNORE IT CLHI 11,X'000D' END OF TEXT INDICATED? BE RET YES, BRANCH STB 11,0(12) STORE CHARACTER AHI 12,1 INCREMENT R12 CLHR 12,13 END OF BUFFER? BL SENSE-4 NO, GET NEXT CHARACTER SH 12,0 (15) CALCULATE TEXT LENGTH STH 12,2 (15) STORE LENGTH IN CALLING PROGRAM OC 14,BLOK SET WRITE MODE LHI 12,MS+1 LHI 13,MS+2 WBR 14,12 ADVANCE LINE AND RETURN CARRIAGE LM 11,SAVE RESTORE REGISTERS B 4(15) RETURN OC 14,BLOK SET WRITE MODE LHI 12,MS SET UP REGISTERS FOR WB LHI 13,MS+3 WBR 14,12 OUTPUT CONFIRMATION MESSAGE B INPT+4 START AGAIN SHI 12, 1 DELETE LAST CHARACTER CLH 12,0(15) WAS IT FIRST CHARACTER? Appendix A-2 Program L i s t i n g BL DELLN YES BRANCH B SENSE-4 NO, GET ANOTHER CHARACTER HS DC X'A38D0A3F i BLOK DC X »98A4 « UNBL * EQU *-1 * ROUTINE TO SEARCH TAPE FOR TWO CONSECUTIVE FILE * MARKS *• SKIP XHR 7,7 STB 7,FILESW FILESW INITIALLY ZERO LHI 1,1 LHI 6,X'0004« FORWARD SPACE COMMAND AGAIN OCR 8,6 FORWARD SPACE ONE RECORD SSR 8,0 WAIT TILL FINISHED BTC 8,*-2 BRANCH IF BUSY BTC 2,*+12 FILE MARK FOUND! STB 7,FILESW RESET FILESW B AGAIN DO ANOTHER RECORD LB 0,FILESW DETERMINE STATUS OF FILESW LHR 0,0 SET CONDITION CODE BNZ FOUND TWO CONSECUTIVE FILE MARKS STB 1 ,FILESW SET FILESW ON - FILE MARK FOUND B AGAIN LOOK FOR ANOTHER FOUND LHI 6,X«0010« BACKSPACE COMMAND OCR 8,6 BACKSPACE TAPE * BR 15 FILESW DS H * ROUTINE IDENTIFIES TAPE ERRORS LPSW * + 4 DISABLE EXTERNAL DEVICE INTERRUPT DC X '0000 • DC A (*+2) NHI 4,X '0080' FIND OUT WHAT'S WRONG BZ FPV MUST BE FILE PROTECT VIOLATION BAL 15,OUPT INDICATE TAPE FULL DC A(TAPE1) DC H«24« B STOP TERMINATE RUN LHI 8,H'8' SSR 8,0 BTC 8,*-2 LHI 9,X«0020« REWIND COMMAND BYTE OCR 8,9 BAL 15,OUPT INDICATE FILE PROTECT VIOLATION DC A(TAPE2) DC H«44» LPS W * + 4 HALT COMPUTER 109 Appendix A-2 Program L i s t i n g TAPE 1 TAPE2 NIL RTEMPO RTEMP1 RTEMP2 RTEMP3 RTEMP4 RTEMP5 RTEMP6 RTEMP7 PTR CRUDE NFPTS NMAX MAX SHMAX IMAX BHD BLO BHU BOUT BEND DC DC DC DC DC DC DC DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS DS EQU END X'80000080» X'8D0A» C'END OF TAPE REACHED ' X»8D0A» C'ATTEMPT TO WRITE ON FILE PROTECTED TAPE!' X«8D0A» H«0 H H H H H H H H H 5H H H 32H 32C 32H 10H 10H 10H 64F *-2 

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