Provenance of North American Phanerozoic ... - GeoScienceWorld

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Framework modes of terrigenous sandstones reflect derivation from various types of provenance terranes that depend upon plate- tectonic setting. Triangular ...
Provenance of North American Phanerozoic sandstones in relation to tectonic setting W I L L I A M R. D I C K I N S O N L. S U E B E A R D G. R O B E R T B R A K E N R I D G E J A M E S L. E R J A V E C R O B E R T C. F E R G U S O N K E R R Y F. I N M A N R E X A. K N E P P F. A L A N L I N D B E R G P A U L T. R Y B E R G

Laboratory of Geotectonics, Arizona 85721

Department

ABSTRACT F r a m e w o r k m o d e s of terrigenous s a n d s t o n e s reflect derivation f r o m various types of p r o v e n a n c e terranes that depend u p o n platetectonic setting. T r i a n g u l a r Q F L a n d Q m F L t c o m p o s i t i o n a l diag r a m s f o r plotting point c o u n t s of s a n d s t o n e s can be subdivided into fields t h a t are characteristic of s a n d s t o n e suites derived f r o m the different kinds of p r o v e n a n c e terranes controlled by plate tectonics. T h r e e m a i n classes of p r o v e n a n c e a r e termed " c o n t i n e n t a l blocks," " m a g m a t i c arcs," a n d "recycled o r o g e n s . " S a n d s t o n e suites f r o m each include three variants, of which the subfields lie within the larger subdivisions. Average m o d e s f o r s a n d s t o n e suites can be classified provisionally a c c o r d i n g to tectonic setting using the subdivided Q F L and Q m F L t plots. T o test t h e validity of t h e classification, average m o d e s f o r 233 P h a n e r o z o i c s a n d s t o n e suites f r o m N o r t h America were plotted on the t r i a n g u l a r c o m p o s i t i o n a l d i a g r a m s a n d a c c o m p a n y i n g paleotectonic m a p s . Paired m a p s and ternary d i a g r a m s were p r e p a r e d for eight d i f f e r e n t time slices, f o r each of which the tectonic setting of each m a j o r region within the c o n t i n e n t remained relatively u n c h a n g e d . T i m e slices are u n e q u a l in length but are controlled by the timing of m a j o r orogenic and rifting events that affected N o r t h America d u r i n g the Phanerozoic. C o m p a r i s o n of the sandstone c o m p o s i t i o n s with inferred tectonic setting t h r o u g h the P h a n e r o zoic indicates that t h e p r o p o s e d classification scheme is generally valid a n d yields satisfactory results when applied on a b r o a d scale. Its a p p l i c a t i o n , together with other a p p r o a c h e s , in regions of the world where over-all trends of geologic history are less well known could lead to i m p o r t a n t conclusions a b o u t the timing a n d n a t u r e of m a j o r tectonic events. INTRODUCTION Relative p r o p o r t i o n s of different types of terrigenous sand grains a r e guides t o the n a t u r e of the source rocks in the provenance t e r r a n e f r o m which sandy detritus was derived. P r o v e n a n c e terranes

of Geosciences,

University

of Arizona,

Tucson,

a n d related basins of d e p o s i t i o n can be classified a c c o r d i n g to their plate-tectonic settings. C o n s e q u e n t l y , detrital f r a m e w o r k m o d e s of s a n d s t o n e suites p r o v i d e i n f o r m a t i o n a b o u t the tectonic setting of basins of deposition a n d associated provenances. This p a p e r evaluates t h e diverse c o m p o s i t i o n s of P h a n e r o z o i c s a n d s t o n e suites f r o m N o r t h America as a f u n c t i o n of c h a n g i n g tectonic setting. O u r c o m p i l a t i o n s generally s u p p o r t previous inferences a b o u t the regional relations between s a n d s t o n e c o m p o s i t i o n s a n d plate settings ( D i c k i n s o n a n d Suczek, 1979; D i c k i n s o n a n d Valloni, 1980). T h e over-all f r a m e w o r k that o u r general analysis provides can serve as a basis f o r f u r t h e r specific investigations. In this study, we used published a n d u n p u b l i s h e d d a t a on detrital m o d e s d e t e r m i n e d by point c o u n t s of s a n d s t o n e suites f r o m t h e United States, s o u t h e r n C a n a d a , a n d n o r t h e r n Mexico. O u r t r e a t m e n t here is c o n f i n e d accordingly to N o r t h America exclusive of A l a s k a , the Arctic, and M e s o a m e r i c a . A b u n d a n t d a t a f r o m coastal Alaska a r e discussed elsewhere ( D i c k i n s o n , 1982). FRAMEWORK

MODES

T h e most significant c o m p o s i t i o n a l v a r i a t i o n s a m o n g terrigen o u s s a n d s t o n e s can be displayed as t e r n a r y plots on t r i a n g u l a r d i a g r a m s . T h e three apices, or poles, represent recalculated p r o p o r tions of key categories of g r a i n types d e t e r m i n e d by m o d a l p o i n t c o u n t s . T w o a l t e r n a t e sets of poles ( Q F L a n d Q m F L t ) a r e u s e f u l ( G r a h a m and others, 1976): A. F o r Q F L d i a g r a m s , the poles are (1) total q u a r t z o s e grains (Q), including polycrystalline lithic f r a g m e n t s such as chert a n d quartzite; (2) m o n o c r y s t a l l i n e f e l d s p a r grains (F); a n d (3) u n s t a b l e polycrystalline lithic f r a g m e n t s (L) of either igneous or s e d i m e n t a r y parentage, including m e t a m o r p h i c varieties. B. F o r Q m F L t d i a g r a m s , t h e poles are (1) q u a r t z grains ( Q m ) t h a t a r e exclusively monocrystalline; (2) feldspar grains (F), as before; a n d (3) total polycrystalline lithic f r a g m e n t s (Lt), including q u a r t z o s e varieties. S u c h t e r n a r y d i a g r a m s d o not a d e q u a t e l y display t h e c o m p o s i -

Compilations of and references for data used to construct the figures in this article are available as an appendix in tabular form by requesting supplementary material 83-2 from Documents Secretary, Geological Society of America, P.O. B o x 9140, Boulder, Colorado 80301. There are 233 data lines and 145 references included in the data summary. Geological Society of America Bulletin, v. 94, p. 222-235, 10 figs., February 1983.

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NORTH AMERICAN PHANEROZOIC SANDSTONES

CRAT0N INTERIOR

PROVENANCE CATEGORIES

TRANSITIONAL CONTINENTAL

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Figure 1. Q F L (upper) and Q m F L t (lower) plots for framework modes of terrigenous sandstones showing provisional subdivisions according to inferred provenance type, modified after Dickinson and Suczek (1979). Geometric symbols (filled, open, and half-filled triangles, circles, and squares) in various compositional fields indicate inferred provenance type on Q F L / Q m F L t plots and on paleotectonic maps (Figs. 3 - 1 0 ) . Numbered ticks on legs of triangle denote positions of empirical provenance division lines in percentage units measured from nearest apical pole.

BASEMENT UPLIFT

fields characteristic of s a n d s t o n e s derived f r o m different types of provenances. T h e positions of the b o u n d a r y lines of subdivision are empirical. T h e y were d e t e r m i n e d initially by inspection of the diag r a m s in D i c k i n s o n a n d Suczek (1979, Figs. 1 a n d 2) and were then a d j u s t e d slightly, so as best to a c c o m m o d a t e the a d d i t i o n a l d a t a reported here w i t h o u t altering the assignment of a n y suites treated originally by D i c k i n s o n and Suczek (1979). Figure 1 thus represents a w o r k i n g d i a g r a m by means of which the a p p r o x i m a t e type of p r o v e n a n c e can be inferred for a n y terrigenous s a n d s t o n e suite. F u r t h e r a d j u s t m e n t s in the positions of the b o u n d a r y lines could doubtless be m a d e as even m o r e i n f o r m a t i o n becomes available in the f u t u r e .

%

LITHIC RECYCLED

UNDISSECTED ARC • tions of s a n d s t o n e s in which special kinds of grains are i m p o r t a n t f r a m e w o r k constituents. F o r example, only the terrigenous f r a c t i o n of hybrid s a n d s t o n e s c o n t a i n i n g b o t h c a r b o n a t e and silicate grains can be s h o w n properly by the Q F L and Q m F L t d i a g r a m s ( Z u f f a , 1980). In o u r study, we have t h u s ignored s a n d s t o n e s rich in limeclasts or other unusual grain types (for example, glauconite). PROVENANCE TYPES D i c k i n s o n and Suczek (1979) showed that mean compositions of s a n d s t o n e suites derived f r o m different kinds of p r o v e n a n c e terranes controlled by plate tectonics tend to lie within discrete and s e p a r a t e fields on Q F L a n d Q m F L t d i a g r a m s . T h e three main categories of p r o v e n a n c e terranes thus distinguished were those within c o n t i n e n t a l blocks, m a g m a t i c arcs, and recycled orogens. Variants of each can be related to specific plate settings. Figure 1 is a modification of this provenance classification. Both Q F L a n d Q m F L t d i a g r a m s are subdivided into c o m p o s i t i o n a l

Within c o n t i n e n t a l blocks, sediment sources are either on stable shields and p l a t f o r m s or in uplifts m a r k i n g plate b o u n d a r i e s and trends of i n t r a p l a t e d e f o r m a t i o n that transect the continental blocks. T h e basement uplifts occur a l o n g incipient rift belts, transf o r m r u p t u r e s , deep-seated thrusts, and zones of wrench tectonism. Figure 1 d e n o t e s three g r a d a t i o n a l kinds of sand f r a m e w o r k s of which the p r o v e n a n c e s are within continental blocks. All are q u a r t z o f e l d s p a t h i c sands pooi in lithic f r a g m e n t s , a l t h o u g h recycling of cover rocks overlying basement can i n t r o d u c e a n o m a l o u s lithic f r a g m e n t s in variable a m o u n t s locally. T h e most q u a r t z o s e sands are derived f r o m stable c r a t o n interiors having low relief, somewhat m o r e feldspathic sands f o r m a transitional g r o u p , a n d the most feldspathic sands are arkoses derived f r o m basement uplifts where erosion has cut deep into the continental crust. Within active m a g m a t i c arcs, sediment sources are mainly in the volcanic c a r a p a c e c a p p i n g the igneous belt and in granitic plutons of the arc roots. S u b o r d i n a t e debris is derived f r o m b o u n d i n g envelopes of m e t a m o r p h i c rock and f l a n k i n g sediment cover. Derivative sands f o r m a s p e c t r u m of lithofeldspathic a n d feldspatholitic types of which the c o m p o s i t i o n s typically spread across the central a n d lower parts of Q F L and Q m F L t plots (Fig. 1). T h e most lithic f r a m e w o r k s are largely volcaniclastic sands derived f r o m essentially undissected arcs, s o m e w h a t less lithic sands f o r m a t r a n sitional g r o u p , and the most q u a r t z o f e l d s p a t h i c f r a m e w o r k s are v o l c a n o p l u t o n i c s a n d s derived f r o m dissected arcs where erosion has e x p o s e d b a t h o l i t h s beneath volcanic cover. Arkosic sands derived mainly f r o m the p l u t o n s of m a g m a t i c arcs are g r a d a t i o n a l to similar sands derived f r o m basement uplifts that e x p o s e granite and gneiss elsewhere within continental blocks. Where compositional overlap occurs, the two kinds of arkosic suites are indistinguishable by p e t r o g r a p h i c methods. Within recycled orogens, sediment sources are sedimentary strata and s u b o r d i n a t e volcanic rocks, in p a r t m e t a m o r p h o s e d , exposed to erosion by t h e orogenic uplift of fold belts and thrust

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DICKINSON AND OTHERS

sheets. Varied tectonic settings include the s u b d u c t i o n complexes of a r c orogens, highlands a l o n g the s u t u r e belts of collision orogens, a n d thin-skinned f o r e l a n d f o l d - t h r u s t belts a l o n g the flanks of arc o r collision o r o g e n s ( D i c k i n s o n a n d Suczek, 1979, Fig. 7). S a n d s derived f r o m such p r o v e n a n c e s a r e generally low in feldspar because igneous rocks a r e not prime sources. T h r e e g r a d a t i o n a l kinds of f r a m e w o r k m o d e s a r e d e n o t e d on the Q m F L t plot (Fig. 1): q u a r t z o s e a n d lithic varieties plus a transitional variety intermediate in c o m p o s i t i o n . T h e three variants c a n n o t be distinguished on the Q F L plot because m a n y lithic f r a g m e n t s a r e chert grains that plot together with q u a r t z at t h e s a m e pole. T h e q u a r t z o s e variants of sands having orogenic provenances a r e doubtless recycled f r o m sediments whose ultimate sources were cratonic. C o m p o s i t i o n s of the first-cycle a n d second-cycle materials a r e clearly g r a d a t i o n a l . Recycling of such q u a r t z o s e sands typically involves d e f o r m a t i o n and uplift of miogeoclinal successions. By c o n t r a s t , m a n y of t h e chert-rich lithic variants had sources in uplifted oceanic terranes of eugeosynclinal belts where radiolarian cherts occur. C h e r t grains m a y also be derived, however, f r o m n o d u l e s in c a r b o n a t e sequences or f r o m p h o s p h a t i c shelf deposits, to n a m e but t w o c o m m o n occurrences. S e d i m e n t o l o g i c a l f a c t o r s m a y locally e n h a n c e t h e q u a r t z c o n tent of s a n d s such as beach-barrier deposits by selective removal of lithic grains a n d feldspars. C a u t i o n should t h u s always be exercised when i n t e r p r e t i n g the p r o v e n a n c e of q u a r t z - r i c h sands. In particular, t h e d a t a compiled here show g r a d a t i o n a l relationships between s o m e s a n d s t o n e suites interpreted as having been derived f r o m c r a t o n interiors a n d recycled orogenic belts. F o r such lithic-bearing q u a r t z o s e sands, few, if any, strictly p e t r o g r a p h i c criteria are infallible as p r o v e n a n c e indicators.

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