Canada H.C. - Alaska
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DEPARTMENT OF THE INTERIOR US. GEOLOGICAL SURVEY TO ACCOMPANY MAP MF-1874-B LlTHOTECTONIC TERRANES OF WESTERN CANADA AND SOUTHEASTERN ALASKA INTRODUCTION 3.W.H. Monger Geologiml Survey of Canada and H.C. Berg US. Geological Suwey This map shows the distribution of lithotectonic terranes in western Canada and southeastern Alaska. It is one of four such maps (see index map), covering the North American Cordillera from Alaska through Mexico, prepared a t 1:2,500,000 scale as a cooperative project of the U.S. Geological Survey, Geological Survey of Canada, and Petroleos Mexicanos. Each terrane preserves a geologic record different from those of its neighbors and from rocks deposited on or adjacent to cratonic North America. The boundaries of terranes are discontinuities, generally major faults, across which the geologic record changes abruptly. While some of these changes may be due to structural telescoping of different facies, there is sufficient paleontologic and paleo- magnetic evidence to show or suggest that many terranes were originally widely separated from one another and (or) from cratonic North America by distances of up to thousands of kilometers. Thcre are five categories of terranes. I. Coherent terranes are the simplest type, with either "layer-cake" stratigraphy or else demonstrable internal facies changes. They are commonly little rnetamor- phosed and some contain distinctive paleontologic and paleomagnetic records. Examples are the Alexander, Cassiar, Quesnellia, Stikinia, and Wrangellia terranes. 2. Disrupted terranes are commonly ophiolitic terranes, whose internal homogeneity derives both from their relatively limited range of lithologies, mostly indica- tive of deposition in ocean basins, and from their characteristic deformational style, which includes melange and broken formation. This category contains subterranes with internally coherent stratigraphy dispersed between other subterranes that show extreme stratigraphic disruption. Examples are the Bridge River, Cache Creek, and Pacific Rim terranes,, with, for example, the Nakina subterrane as a subter- rane that has coherent stratigraphy within the ~ a c & Creek terrane. 3. Metamorphic terranes are derived mainly from stratified sequences, but their integrity is provided by a metamorphic and structural overprint that largely or wholly conceals the stratigraphic record. Enough characteristics of the protolith of a metamorphic terranc (such as Yukon-Tanana terrane) may be preserved to distinguish it on stratigraphic grounds from adjacent terranes. Other metamorphic terranes (such as the Skagit terrane) are partly or wholly the metamorphosed equivalents of adjacent terranes; still others (such as the Tracy Arm terrane) are of uncertain primary affinity, 4. Subterranes are divisions of terranes, denoted by three-letter symbols, and their use commonly indicates lithotectonic affinity but not necessarily stratigraphic continuity. For example, the Cache Creek terrane (CC), with its limited range of lithologies and distinc- tive Permian faunas, clearly constitutes a terrane that is very different from the adjacent, coeval Quesnellia (QN) and Stikinia (ST) terranes, yet within it are subterranes with different stratigraphies, lor example, the French Range (CCF) and Nakina (CCN) subter- ranes, whose original relations to one another are unknown. Similarly, the Alexander terrane (AX) contains two, probably three subterranes, the Admiralty (AXA), Annette (AXN), and Craig (AXC), that appear to have had independent histories prior to the Permian. 5. Superterranes are composite terranes, composed of major terranes amalgamated with others prior to their accretion to the ancient continental margin. There appear to be two superterranes in this segment of the Cordillera, an eastern and a western. The eastern superterrane consists of the Cache Creek, Quesnellia, Stikinia, and Slide Mountain terranes, which were amalgamated in the early Mesozoic, and it began its accretion in Jurassic time. It was called "Composite Terrane I" by Monger and others (1982) and "Stikinian superterrane" by Saleeby (1983). Middle and late Mesozoic overlap assemblages of the Bowser Basin (map unit KI-3u) and of the Spences Bridge and Kingsvale Groups (map unit Kum) may have undergone substantial displacement with respect to North America along with the amalgamated terranes of this superterrane. The western superterrane is composed of the Alexander and Wrangellia terranes, which were amalgamated in the Late Jurassic and accreted in the Cretaceous. It was designated 'tComposite Terrane 11" by Monger and others (1982) and "Wrangellian super- terrane" by Saleeby (1983). The Upper Jurassic to mid-Cretaceous Gravina-Nutzotin overlap assemblage (GN) was deposited upon the amalgamated Alexander and Wrangellia terranes prior to their accretion. The boundary between the eastern superterrane and the ancient western margin of North America corresponds - with a major metamorphic and structural welt, the Omineca Crystalline Belt. The boundary between the eastern and western superterranes coincides with a second welt,,the Coast Plutonic Complex, within which deformation and metamorphism were concentrated. The process of accretion of these superterranes to the ancient western margin of North America in Jurassic and Cretaceous times may be responsible for the two major metamorphic and structural culminations. The evidence for amalgamation is enumerated in table 1, which follows the descriptions of terranes, and the location of the evidence is shown by corresponding numbers on the terrane map. All of these terranes are suspect (Coney and others, 1980) in the sense that their original paleogeographic 'positions relative to the North American craton are uncertain. tiowever, there are indications that they exhibit widely differing amounts of displacement. Some terranes, as determined by paleontologic or paleomagnetic data or by extreme stratigraphic dissimilarities, are probably exotic (for example, the Alexander and Wrangellia terranes and parts of the Cache Creek terrane). Others could have formed offshore of western North America but were later displaced
Transcript of Canada H.C. - Alaska
DEPARTMENT OF THE INTERIOR U S . GEOLOGICAL SURVEY
T O ACCOMPANY MAP MF-1874-B
LlTHOTECTONIC TERRANES OF WESTERN CANADA AND SOUTHEASTERN ALASKA
INTRODUCTION
3.W.H. Monger Geolog iml Survey of Canada
and
H.C. Berg U S . Geological Suwey
This m a p shows t h e dis t r ibut ion of l i t ho tec ton ic t e r r anes in western Canada a n d sou theas t e rn Alaska. I t is o n e of f o u r such m a p s (see index map), cover ing t h e Nor th Amer i can Cordi l lera f rom Alaska through Mexico, prepared a t 1:2,500,000 sca l e a s a coope ra t ive p ro j ec t of t h e U.S. Geological Survey, Geological Survey of Canada , and Pe t ro l eos Mexicanos.
Each t e r r a n e preserves a geologic record d i f f e ren t f rom those of i t s neighbors and f rom rocks deposi ted on o r ad j acen t t o c r a t o n i c North America . The boundaries of t e r r anes a r e discont inui t ies , generally ma jo r faul ts , a c ros s which the geologic record changes abruptly. While s o m e of t hese changes may be due to s t ruc tu ra l te lescoping of d i f f e r e n t f ac i e s , t h e r e i s suff ic ient paleontologic and paleo- magne t i c evidence to show or suggest t h a t many t e r r anes were originally widely sepa ra t ed f rom one ano the r and (or) f r o m c ra ton ic Nor th Amer i ca by d i s t ances of up t o thousands of k i lometers .
T h c r e a r e f ive ca t egor i e s of ter ranes . I. Cohe ren t t e r r anes a r e t h e s imples t type, with e i t h e r
"layer-cake" s t ra t igraphy o r e l s e demons t r ab le in ternal f ac i e s changes. They a r e commonly l i t t l e rnetamor- phosed a n d s o m e con ta in dis t inct ive paleontologic and paleomagnet ic records. Examples a r e t h e Alexander , Cass iar , Quesnellia, St ik inia , and Wrangellia ter ranes .
2 . Disrupted t e r r anes a r e commonly ophiolitic t e r r anes , whose in ternal homogenei ty der ives both f rom thei r re la t ively l imi ted range of l i thologies, most ly indica- t ive of deposition in ocean basins, and f rom thei r cha rac t e r i s t i c deformat ional style, which includes melange and broken fo rma t ion . This ca t egory con ta ins sub te r r anes with in ternal ly cohe ren t s t r a t i g raphy dispersed between o the r sub te r r anes tha t show e x t r e m e s t r a t ig raph ic disruption. Examples a r e t h e Bridge River , C a c h e Creek , and Pac i f i c R im terranes , , with, f o r example , t h e Nakina sub te r r ane a s a subter- rane t h a t has cohe ren t s t ra t igraphy within the ~ a c & Creek terrane.
3. Metamorphic t e r r anes a r e derived mainly f rom s t r a t i f i ed sequences , but t he i r i n t eg r i ty is provided by a me tamorph ic and s t ruc tu ra l overpr int t h a t largely o r wholly concea l s t h e s t r a t ig raph ic record. Enough c h a r a c t e r i s t i c s of the protol i th of a me tamorph ic t e r r a n c (such a s Yukon-Tanana t e r r ane ) may be preserved t o distinguish i t on s t r a t ig raph ic grounds f rom ad jacen t ter ranes . O t h e r me tamorph ic t e r r anes (such a s the Skag i t t e r r ane ) a r e par t ly or wholly t h e metamorphosed equivalents of ad j acen t ter ranes; s t i l l o the r s (such a s the Tracy Arm t e r r ane ) a r e of uncer ta in p r imary aff in i ty ,
4. Sub te r r anes a r e divisions of t e r r anes , denoted by th ree - l e t t e r symbols, a n d the i r use commonly ind ica t e s l i t ho tec ton ic a f f in i ty b u t not necessarily s t r a t ig raph ic cont inui ty . F o r example , t h e C a c h e Creek t e r r a n e (CC), with i t s l imi ted range of l i thologies and distinc- t ive Pe rmian faunas , c l ea r ly cons t i t u t e s a t e r r a n e t h a t i s ve ry d i f f e ren t f rom the ad jacen t , coeva l Quesnellia
(QN) and St ik inia (ST) t e r r anes , y e t within i t a r e sub te r r anes with d i f f e ren t s t ra t igraphies , l o r example , t h e F rench Range (CCF) and Nakina (CCN) subter- ranes, whose original re la t ions t o one ano the r a r e unknown. Similar ly , t he Alexander t e r r a n e (AX) con ta ins two, probably t h r e e subterranes , t h e Admi ra l ty (AXA), A n n e t t e (AXN), and C r a i g (AXC), t h a t a p p e a r t o have had independent h is tor ies pr ior t o t h e Permian.
5. Supe r t e r r anes a r e compos i t e t e r r anes , composed of ma jo r t e r r anes ama lgamated with o t h e r s prior t o t he i r acc re t ion t o t h e anc ien t con t inen ta l margin. T h e r e a p p e a r t o b e t w o supe r t e r r anes in t h i s s egmen t of t h e Cordi l lera , a n eas t e rn and a western . The e a s t e r n supe r t e r r ane consis ts of t h e C a c h e Creek , Quesnellia, St ik inia , a n d Slide Mountain t e r r anes , which w e r e a m a l g a m a t e d in t h e ea r ly Mesozoic, and i t began i t s a c c r e t i o n in Jurass ic t ime. I t was cal led "Composi te T e r r a n e I" by Monger and o t h e r s (1982) and "Stikinian super terrane" by Saleeby (1983). Middle and l a t e Mesozoic ove r l ap a s semblages of t h e Bowser Basin (map un i t KI-3u) and of t he Spences Bridge and Kingsvale Groups (map uni t Kum) m a y have undergone substant ia l d isplacement with r e spec t t o North Amer i ca a long with t h e a m a l g a m a t e d t e r r anes of t h i s super terrane. The wes t e rn supe r t e r r ane is composed of t h e Alexander and Wrangellia t e r r anes , which w e r e a m a l g a m a t e d in t h e L a t e Jurass ic and a c c r e t e d in t h e Cre t aceous . I t was des ignated ' tComposi te T e r r a n e 11" by Monger and o t h e r s (1982) and "Wrangellian super- t e r r ane" by Saleeby (1983). T h e Upper Ju ra s s i c t o mid-Cretaceous Gravina-Nutzot in over lap a s semblage (GN) was deposi ted upon t h e a m a l g a m a t e d Alexander and Wrangellia t e r r a n e s prior t o t he i r accre t ion. The boundary be tween t h e e a s t e r n supe r t e r r ane and t h e anc ien t wes t e rn margin of North Amer i ca corresponds
- with a major me tamorph ic a n d s t ruc tu ra l we l t , t h e Omineca Crysta l l ine Belt. The boundary be tween t h e e a s t e r n and wes t e rn supe r t e r r anes coincides with a second wel t , , the C o a s t P lu ton ic Complex, within which de fo rma t ion and me tamorph i sm were concen t r a t ed . The process of a c c r e t i o n of t hese supe r t e r r anes t o t h e anc ien t wes t e rn margin of North Amer i ca in Ju ra s s i c a n d C r e t a c e o u s t imes may be responsible fo r t h e t w o ma jo r me tamorph ic and s t ruc tu ra l culminat ions . T h e ev idence fo r ama lgamat ion i s enumera t ed in t a b l e 1, which fol lows t h e descr ipt ions of t e r r anes , and t h e locat ion of t h e evidence i s shown by corresponding numbers on the t e r r a n e map. All of t hese t e r r a n e s a r e suspec t (Coney and o the r s ,
1980) in t h e sense t h a t t he i r original paleogeographic ' pos i t i ons re la t ive t o t h e North American c r a t o n a r e
uncer ta in . t iowever , t h e r e a r e indicat ions t h a t t hey exh ib i t widely d i f f e r ing a m o u n t s of d isplacement . Some t e r r anes , a s de t e rmined by paleontologic or paleomagnet ic d a t a or by e x t r e m e s t r a t ig raph ic dissimilarities, a r e probably exo t i c (for example , t h e Alexander and Wrangellia t e r r a n e s and p a r t s of t h e C a c h e C r e e k terrane) . O t h e r s could have fo rmed o f f sho re of wes t e rn Nor th Amer i ca bu t w e r e l a t e r d isplaced
northwards (for example, the Chilliwack, Quesnellia, Slide Mountain, and Stikinia t e r r anes and p a r t s of t h e C a c h e Creek terrane). O the r s (such a s the Cassiar t e r r ane ) a r e f r agment s of t h e cont inental t e r r a c e wedge, slivered off during Cre taceous and Ter t i a ry dex t ra l strike-slip motion, and s t i l l o the r s a r e suspect because they contain f e a t u r e s unknown on the c ra ton ic margin and yet exhibit possible s t r a t ig raph ic s imilar i t ies (for example, t h e Barkeruille, McLeod, Monashee, Kootenay, and Yykon-Tanana terranes): The evidence f o r displacement is given i n t h e descriptions of t h e terranes .
T h e basic ou tc rop pa t t e rn and e x t e n t of postaccret ion or postamalgamation cover &posits and bathol i thic g ran i t i c rocks shown on our t e r r ane map i s adap ted f rom Tipper and o the r s (1981). T h e line weight and s ty l e of c o n t a c t s shown on t h e m a p ' represent di f ferent f ea tu res f rom those conven t~ona l ly used on geologic maps. Heavy lines on t h e t e r r a n e map represent only those f au l t s t h a t a r e t e r r ane boundaries. Light-weight lines represent f au l t s t h a t only bound postaccret ion o r postamalgamation cover deposi ts or bathol i thic igneous rocks a s well a s depositional and int rusive con tac t s .
ACKNOWLEDGMENTS
Advice and ass is tance i n compiling th i s m a p have been received from colleagues mainly in the Geological Surveys of Canada and t h e United S ta t e s , notably P.J. Coney, Huber t Gabrielse, S.P. Gordey, D.L. Jones , A.V. Okulitch, George P la fke r , N.J. Silberling, L.C. Struik, D.J. Tempelman-Kluit, H.W. Tipper , G.J. Woodsworth and J.O. Wheeler. P.B. Read, Geo tex Consul tants , gave advice on a spec t s of t h e southeastern p a r t of the Canadian Cordillera. These geolo- gis ts may or may not a g r e e with t h e m a p pa t t e rn , which i s t h e responsibility of the authors .
DESCRIPTION OF TERRANES AND NAMED OVERLAP ASSEMBLAGES
[ Arranged alphabet ical ly by name I
AX ALEXANDER TERRANE--The Alexander t e r r ane comprises l a t e P recambr ian t o Triass ic s t ra ta . Where l i t t l e metamorphosed, AX is divided in to th ree sub te r ranes (Admiral ty , AXA; Craig , AXC; and Anne t t e , AXN), a t l eas t two of which (AXA, AXC) appea r t o have had an independent his tory until Pe rmian time, when they f i r s t sha re common rock uni ts (Brew and o the r s , 1966; Berg and o the r s 1972, 1978). Rocks of Mississippian t o Triass ic a g e (AXN?) I cca ted 35 km northwest of P r ince Ruper t , British Columbia, Canada (M.J. Orchard, oral commun., 1982; Hutchison, 19821, a r e provisionally co r re l a t ed with Alexander t e r r ane rocks in southeastern Alaska on t h e basis of s t ra t igraphic similarities. Metamorphosed s t r a t a in the C o a s t Plutonic Complex south of P r ince Ruper t a r e shown on the map as undivided Alexander t e r r ane (AX). They consist mainly of greenschist- to amphibolite-facies schis t and gneiss, derived largely f rom feldspathic sediments and fe ls ic t o maf i c volcanics and in small p a r t f rom shale, graywacke, and ca rbona te rocks. Regional metamorphism of these rocks is of mid-Cretaceous a g e (Woodsworth and o the r s , 1983).
ADMIRALTY SUBTERRANE--The Admiral ty subterrane of the Alexander t e r r ane i s dis- tinguished by a coheren t Paleozoic sequence of Devonian marine- me tabasa l t and ca rbona te rocks (Gambier Bay Format ion) over la in by la te Devonian and Mississipian basal t ic tuff and radiolarian c h e r t (Cannery Formation). Ordovician carbonaceous flysch and minor basal t ic tuff (Hood Bay Format ion) a r e in f a u l t c o n t a c t with t h e younger
Paleozoic units. The s t ra t igraphic basemen t of t h e sub te r rane is not exposed. Pebbles of Cannery c h e r t a r e present a s c l a s t s in the Pe rmian Hal leck Format ion of t h e C r a i g subterrane, t hus linking t h e t w o sub te r ranes by Pe rmian t ime (Berg and others , 1978; loc. 3, t ab le I), Pe rmian ca rbona te rocks (Pybus Format ion) and Triass ic volcanic and ca rbona te rocks (Hyd Group) over lap f rom AXA on to t h e Cra ig subterrane.
A XN ANNETTE SUBTERRANE--The Anne t t e subter- rane comprises a heterogeneous assemblage of variably metamorphosed, Ordovician o r Silurian t o Triass ic intrusive, extrusive, c l a s t i c , and ca rbona te rocks, and i t i s char- ac t e r i zed by t h e absence of any known post-Middle Devonian Paleozoic s t r a t a (Berg and others , 1978). R e c e n t invest igat ions by Gehrels and o the r s (1983a, b) show t h a t AXN con ta ins a n Ordovician-Silurian volcanoplu- tonic complex similar t o the one in the southern pa r t of Cra ig subterrane. These d a t a suggest t h a t t he t w o subterranes may have been in re la ted tectonic environments during Ordovician-Silurian t ime, b u t the marked d i f f e rences in their Devonian and l a t e r Palevzoic history support re ta ining their c lass i f icat ion a s dis t inct ive subdivisions of the Alexander terrane.
AXC CRAIG SUBTERRANE--The Cra ig sub te r rane i s distiguished by a relatively comple te and undeformed sequence of Ordovician to Triass ic , basal t ic t o silicic volcanic and volcaniclas t ic rocks and terr igenous c l a s t i c and ca rbona te rocks (Brew and o the r s , 1966; Berg and others , 1972, 1978) and by a pre- Middle Ordovician me tamorph ic complex (Wales Group). R e c e n t mapping and geo- chronologic s tudies (Eberlein and others , 1983; Gehrels and others , 1983 a , b) show t h a t t he southern p a r t of the C r a i g subter- r ane is underlain by a n Ordovician-Silurian volcanoplutonic basemen t complex of dior i te and t rondhjemite and by cogene t i c volcanic and volcaniclas t ic rocks. This complex i s in f au l t c o n t a c t with Wales Group me tabas i t e and me taca rbona te . Pa leomagne t i c d a t a indicate t h a t t he t e r r ane has undergone abou t 15, o f nor thward movement re la t ive t o c ra ton ic North Amer ica s ince Pennsylvanian t i m e (Van de r Voo and others , 198O), bu t no apparen t change in l a t i t ude . s ince L a t e Triass ic t i m e (Hillhouse and Gromme, 19801, if a n origin in t h e nor thern hemisphere i s assumed.
ARCTIC ALASKA TERRANE
AAN NORTH SLOPE SUBTERRANE--This sub te r rane of the A r c t i c Alaska t e r r ane consis ts o f P recambr ian t o lower Paleozoic basemen t rocks overlain by the Kekiktuk Cong lomera te (Mississippian), Lisburne Group (Mississippian and ~ e n n s ~ l v a n i a n ) , Sadlerochi t Croup (Permian and Triassic), and younger Mesozoic s t r a t a . In general , t he Carboniferous through ear ly Mesozoic rocks a r e miogeoclinal shelf deposits, a s a r e t h e North American s t r a t a of th is general a g e in t h e Mackenzie pla t form and Richardson Mountains, which, however , have a very d i f f e ren t s t ra t igraphic sect ion and substra te . AAN cont inues ac ross north- e r n Alaska, where i t f o r m s t h e s t ructural ly lowest rocks beneath successive over thrust s h e e t s composed of o the r sub te r ranes of t h e A r c t i c Alaska t e r r ane and the r e s t of t h e
t e r r anes t h a t c h a r a c t e r i z e t h e major sha re of t h e Brooks Range.
BV BARKERVLLE TERRANE--The Barkervi l le t e r r a n e is composed of in terbedded g r i t and pe l i t e which locally con ta ins volcanic las t ic rocks, l imestone, and quar tz i te-c las t conglomerate . I t i s complexly de fo rmed a n d metamorphosed to g reensch i s t t o amphibol i te f ac i e s and is of possible P ro t e rozo ic t o l a t e Pa l eozo ic pre- me tamorph ic a g e s (Struik, 1981, and oral commun., 1982). I t con ta ins a body of ortho- gneiss of possible Devonian a g e (A.V. Okulitch, ora l commun., 1982). In both gross composition and regional s t ruc tu ra l s e t t i ng BV i s similar to t h e Kootenay and Yukon-Tanana ter ranes .
BR BRIDGE RIVER TERRANE--The Bridge River t e r r a n e is a d isrupted t e r r ane composed of bedded radiolarian c h e r t , argi l l i te , basal t , minor sandstone and ca rbona te rocks, and alpine- type u l t r amaf i c rocks (Roddick and Hutchison, 1973). The me tamorph ic g rade commonly i s subgreenschis t and the rocks typical ly a r e chaot ic (broken f orrnation, melange) or , a t bes t , have a weakly developed foliation. S t ruc tu ra l ly in ter leaved wi th these a r e higher grade me tamorph ic rocks, namely siliceous schis t , amphibol i te , local marble , and ul t ramafics , which a r e assumed on compositional grounds to have been der ived f rom the low-grade Bridge River rocks (Po t t e r , 1983). Paleontologic a g e s range f rom Middle Tr iass ic t o l a t e Ear ly Jurass ic (Cameron and Monger, 1971; D,L. Jones , ora l commun., 1978; M,J. Orchard, ora l commun., 1981), and isotopic a g e s f r o m associa ted gabbro a r e a s old a s Pe rmian (R.L. Armstrong, ora l commun., 1981).
C A CASSLAR TERRANE--The cohe ren t Cass iar t e r r a n e comprises sedimentary rocks, ranging in a g e f rom l a t e P recambr ian t o Devonian, similar in p a r t t o North American pla t formal s t r a t a in t h e Rocky Mountains b u t s epa ra t ed f rom t h e m by offshelf Cambr ian , Ordovician, Silurian and Devonian facies . Silurian and Devonian s t r a t a in bo th Rocky Mountains and Cass iar successions include a re la t ively condensed sequence of ca rbona te and c l ean sandstone. A t ransi t ional f ac i e s in t he Cass i a r t e r r a n e includes g rap to l i t i c Ordovician and Silurian rocks like those in t h e wes t e rnmos t Rocky Mountains. T h e Cass iar t e r r a n e appea r s t o have been dis- p laced nor thward 500-1,000 km along t h e wes t e rn margin of ances t r a l North Amer i ca , a t l e a s t in pa r t by l a t e Mesozoic and ea r ly Te r t i a ry r ight- la tera l strike-slip faul ts , so t h a t p l a t fo rma l s t r a t a t o t h e wes t a r e juxta- posed with off-shelf f ac i e s t o the e a s t (Gabrielse, 1963, 1985).
CC CACHE CREEK TERRANE--The und i f f e ren t i a t ed pa r t of t h e C a c h e Creek t e r r ane , l oca t ed in c e n t r a l British Columbia, comprises s t ruc- tura l ly complex radiolarian che r t , argi l l i te , and basal t , extensive bodies of shallow-water ca rbona te rocks, alpine-type u l t r amaf i c rocks, melange conta ining these components , and, n e a r Pinchi Lake, local high-grade blueschis t and ec log i t e (Armstrong, 1949; P a t e r ~ n , 1977). Ca lca reous s t r a t a a r e of Pennsylvanian and Pe rmian ages , and blue- schis t y ie lds L a t e Tr iass ic isotopic a g e s (Paterson and Harakal , 1974).
Mid- and Upper Pe rmian fusulinid a n d co ra l f aunas in a l l C a c h e Creek rocks a r e s imilar t o coeval faunas in Japan, China, Indonesia, and t h e Himalayan region and a r e d i f f e ren t f rom coeval faunas of c r a ton ic Nor th Amer i ca and o t h e r Cordi l leran t e r - ranes. The local presence of more cosmo- pol i tan arnmonoid f aunas in t h e C a c h e C r e e k t e r r a n e a l lows i t s exo t i c f aunas t o be cor- r e l a t ed with those of t h e North Amer i can (West Texas) Pe rmian (Ross and Nassichuk, 1971). T h e C a c h e C r e e k f aunas suggest t h a t Pe rmian (and presumably older) rocks in t h e C a c h e C r e e k Group a r e t ru ly e x o t i c with r e spec t t o North Amer i ca (Ross and Ross, 1983). By l a t e s t Tr iass ic t ime, however , C C w a s evident ly linked t o t h e Quesnellia and St ik inia t e r r anes , which have Pe rmian f aunas t h a t a r e displaced bu t not obviously e x o t i c (Monger and others , 1982; Ross and Ross, 1983). Pa l eomagne t i c d a t a f rom a discordant Ear ly C r e t a c e o u s anor thosi t ic gabbro emplaced in C a c h e C r e e k suggests t ha t t h e C a c h e C r e e k t e r r a n e lay m o r e than 10' t o t he south r e l a t ive t o t h e North Amer i can c ra ton a s l a t e a s mid-Cretaceous t i m e (Monger and Irving, 1980).
CCB BONAPARTE SUBTERRANE--The disrupted Bonapa r t e sub te r r ane in southern British Columbia consis ts of me lange with Pe rmian to Upper Tr iass ic radiolarian c h e r t and argi l l i te m a t r i x (DL. Jones , ora l commun., 1981) and blocks of c h e r t , basal t , u l t r amaf i c rock, and Middle Pennsylvanian and Lower Pe rmian limestone. Local blocks of vol- can ic l a s t i c s within t h e melange a r e li tho- logically ident ical t o rocks in t h e western- mos t f ac i e s of t h e Upper Tr iass ic Nicola Group to t h e c a s t within the Quesnel l ia t e r r a n e (Monger, 1981; Shannon, 198 I, 1982). Norian s t r a t a of t he Nicola Group a d j a c e n t t o C a c h e Creek rocks include cong lomera t e of che r t , greenstone, lirne- s tone, and u l t r amaf i c c l a s t s (Travers , 1978; Monger, 1981). C h e r t c l a s t s f rom th i s con- g lomera t e yield probable Middle Tr iass ic conodonts (M.3. Orchard, ora l cornmun, 19821, o lder t han those in any Nicola rocks. These observat ions suggest t h a t t h e Bonapa r t e sub te r r ane was associa ted with Quesnellia by L a t e Tr iass ic t i m e (loc. 13, t ab l e I).
C C F FRENCH RANGE SUBTERRANE--The cohe ren t F r e n c h R a n g e sub te r r ane of nor thern British Columbia consis ts of Pe rmian shallow-water ca rbona te rocks (Teslin Fo rma t ion ) conform- ably , and locally gradat ional ly , overlying rnafic o r sil iceous flows and pyroclas t ics (French Range Format ion) . These rocks a r e locally confo rmab le on, and gradat ional with, a sequence of c h e r t y pelite, che r t , and in t e rca l a t ed volcanic g raywacke (Kedahda Format ion) , b u t e lsewhere they l ie on t h e s a m e sequence with unknown ( thrust?) rela- t ions (Monger, 1969, 1975). A t t he no r thwes t end of t h i s subterrane, radiolarian c h e r t in terbedded with g raywacke has yielded L a t e Tr iass ic (Norian) conodonts (M.3'. Orchard, ora l commun, , 1982; loc. 7 , t ab l e I), Because th i s g raywacke i s l i thologically ident ical with coeval g raywacke in t h e St ik inia t e r r ane , i t suggests t h a t i n l a t e s t Tr iass ic t i m e t h e F rench Range sub te r r ane was a f ac i e s equivalent of Stikinia. C a c h e C r e e k de t r i t u s was shed o n t o St ik inia in l a t e Middle Ju ra s s i c t i m e ( for example , loc. 9 , t ab l e 1) and C a c h e
CCN
CCP
CCS
Creek s t ra ta subsequently were structurally superpoped on Stikinia (for example, loc. 8, table 1) (Monger and others, 1978).
MARBLE RANGE SLIBTERRANE-The Marble Range subterrane of southern British Columbia comprises extensive shallow-water mid and Upper Permian carbonate rocks along with minor interbedded basalt and local chert (Trettin, 1980). Associated with these rocks a r e thin-bedded radio!adan limestone and calcareous tuff of Early Triassic age (M.J. Orchard, oral commun., 1982). This subterrane is in thrust(?) fault contact with the Bonaparte subterrane to the eas t and the Pavilion subterrane to the west.
NAKINA SUBTERRANE--The coherent Nakina subterrane contains the most complete stratigraphic section known in the Cache Creek terrane. Its base is Mississippian basalt (Nakina Formation) containing pods of Upper Mississippian carbonate rocks in the uppermost part. On one side basalt is in fau l t contact with the Nahlin ultrarnafic body, mainly tectonized harzburgite but locally cumulate ultramafic rocks, gabbro, and trondjhemite, tha t possibly represents the oceanic crust on which the Nakina sub- terrane was deposited. Conformably and gradationally overlying the basalt a r e thick (2,000 m), shallow-water to intertidal, reefoidal Upper Mississippian to Upper Permian carbonate rocks (Horsefeed Formation). These a re overlain, with regional angular unconf orrnity, by Middle or Upper Triassic chert (Monger, 1975, 1977a; Terry, 1977).
PAVLION SUBTERRANL-The Pavilion sub- terrane comprises interbedded silicified argillite, siltstone, and chert of Early and L a t e Triassic ages, and minor Permian and Upper Triassic limestone, volcaniclastic rocks and local metabasalt. The volcaniclas- t ic rocks resemble those of La te Triassic age in t h e Quesnellia terrane (Nicola Group). No stratigraphic order is known, although the subterrane typically is not melange or broken formation (Trettin, 1980; Monger, 1981).
SENTINEL SUBTERRANE--The disrupted Senti- nel subterrane is dominated by bedded radio- l a r i w chert and argillite of Pennsylvanian and Permian ages and, in one place, of Mesozoic age (D.L. Jones, oral commun., 1982). In places, pillow basalt and diabase sills a re conformable with enclosing red chert. Elsewhere, extensive breccias com- prise blocks mainly of basalt, but locally of limestone. The limestone blocks a r e of Early Mississippian, mid- and la tes t Pennsylvanian, and Permian ages. In size, the blocks range from a few centimeters to I or 2 km in diameter. The breccias a r e commonly con- formable with bedding in the enclosing cher t and argillite and thus a r e believed to be olistostromes (Monger, 1975, 1977a), but in places they a r e tectonized and become foliated, with phacoidal blocks.
CK CHILLIWACK TERRANE--The coherent Chilliwack terrane includes the upper Paleozoic Chilliwack Group and the d~sconformably overlying Upper Triassic-Lower Jurassic Cultus Formation. These rocks a r e recum- bently folded and imbricated with the Nooksack terrane on east-dipping,
mid-Cretaceous thrust faults. Devonian s t ra ta have been reported from this terrane in northwestern Washington (Danner, 1965; Misch, 1966; Monger, 1970). In Canada, the stratigraphy appears to be coherent, with argillite, siltstone, Pennsylvanian limestone, and local plant-bearing conglomerate over- lain by Lower Permian limestone and dacitic and basaltic volcanic rocks. Disconformably above is Upper Triassic and Lower Jurassic argillite, siltstone, and volcanic sandstone. In one place, these rocks appear to be over- lain disconformably by Upper Jurassic (Oxfordian) black shales tha t a re possibly facies equivalent of the Nooksack Group. If so, t h e Nooksack and Chilliwack terranes can be linked by La te Jurassic t ime (loc. 5, table I). Chilliwack, Nooksack, and Shuksan terranes a r e brought together by mid- to Upper Cretaceous thrust faults.
Permian fusulinid faunas in the Chilliwack Group a r e similar to those in the Quesnellia terrane according to W.R. Danner (oral comrnun., 1980) and possibly also t o those of the Stikinia terrane (Monger and Ross, 1971).
CG CHUGACH TERRANE--The Chugach terrane, shown on the map a s a single unit, actually com- prises the following two distinctive tectono- stratigraphic assemblages (Plafker and others, 1977): (a) a strongly folded but coherent flysch assemblage of graywacke, argillite, and slate containing rare fossils of L a t e Cretaceous (Campanian to early Maestrichtian) age, and (b) a polymictic disrupted (melange) assemblage composed of blocks of rnafic volcanic rocks, chert , ultra- mafic rocks, limestone, and plutonic rocks in a matrix of cherty, tuffaceous argillite. Greenschist- to amphibolite-facies regional metamorphism locally overprints sporadic remnants of blueschist-facies metamorphism. Radiolarians in chert range in age from L a t e Jurassic to Early Cretaceous. These two assemblages a r e structurally interleaved in many places, but in general the disrupted assemblage tends to be structurally above the coherent flysch assemblage,
The Chugach terrane may have been floored by Upper Jurassic oceanic crust, because the blocks of radiolarian chert a r e associated with pillow basalt and minor serpentinite (Berg and others, 1978).
CR CRESCENT TERRANE--The Crescent terrane com- prises tholeiitic pillow basalt, amygdaloidal flows, aquagene tuff , and breccia with inter- calated volcanic sandstones containing early Eocene fossils. Dike complexes of basalt, diabase, and gabbro intrude the volcanic rocks (Muller, 198Ob).
GN GRAVINA-NUTZOTIN OVERLAP ASSEMBLAGE-- The Cravina-Nutzotin belt (Berg and others, 1972) comprises Upper Jurassic to mid- Cretaceous marine argillite and graywacke, minor nonmarine strata, interbedded andesi- tic to basaltic volcanic and volcaniclastic rocks, and subvolcanic plutons ranging from quartz diorite to dunite and peridotite (Berg and others, 1972, 1978). Preliminary paleo- magnetic studies show anomalously shallow inclinations with respect to stable North America (Panuska and Decker, 1982). The Gravina-Nutzotin belt lies depositionally on both the Alexander terrane (on Gravina,
Kupreanof, and Admiral ty Islands in the Alexander Archipelago) and t h e Wrangellia t e r r ane (near the Alaska-Y ukon boundary) and is thus a n over lap assemblage, linking t h e Alexander and Wrangellia t e r r anes in to a supe r t e r rane (locs. I and 2; table 1). T h e e a s t boundary of the b e l t with the Taku t e r r ane i s i n fe r red to be a zone of northeast- dipping thrust f au l t s (Berg and others , 1972, 1978). In places, however, t h e Taku t e r r ane con ta ins undated metagraywacke, argillite, and andesi t ic me ta tu f f t h a t may in p a r t co r re l a t e with Ju ras s i c or C r e t a c e o u s s t r a t a i n t h e Gravina-Nutzotin be l t (Berg, 1982, p. 13). If so, the b e l t may locally over lap the Taku t e r r ane , t h u s linking at l eas t p a r t of i t t o the Alexander-Wrangellia super terrane. T h e Dezadeash Format ion, a n Upper Jurassic-Lower Cre taceous sequence of flysch and subordinate volcaniclas t ic rocks nor theas t of the Denali f au l t in Yukon Terr i tory (Eisbacher, 1976; Eisbacher and Hopkins, 1977), is included in the Gravina-Nutzotin be l t on the basis of s imilar i t ies in lithology and s t r a t ig raph ic position. T h e eas t e rn side of t h e Dezadeash appea r s t o be involved in l a t e s t Cre taceous and ear ly Ter t i a ry s t ruc tu res and me tamor - phism associated with the C o a s t Plutonic Complex, and i t may be t h e protol i th of t h e Kluane t e r r ane (loc. 4, table 1).
HZ HOZAMEEN TERRANE--The Hozameen t e r r ane comprises bedded che r t , argillite, basal t , minor ca rbona te rocks, and alpine-type u l t r amaf ic rocks, and i t has undergone metamorphism t h a t ranges f rom subgreen- schis t t o greenschis t facies. The lowest g rade rocks typically a r e disrupted. Radiolarian faunas ranging in age f rom Permian t o Middle Jurass ic have been re- cove red f rom this assemblage (Tennyson and others , 1982; R.A. Haugerud, wr i t t en com- mun., 1983). The Hozameen terraf ie i s thus similar in mos t respects t o t h e Bridge R ive r t e r r ane but i s separated f rom i t by the Fraser-Stra ight Creek dextra l f au l t system of Te r t i a ry age.
KA KANDlK RIVER TERRANE--Exposures of th is terrane along t h e internat ional border in Canada a r e cont inuous in to Alaska where KA i s described by Churkin and o the r s (1982) a s a thick sequence of flyschoid pel i t ic rocks and sandstone t h a t is mainly of Ea r ly Cre taceous a g e and generally f a u l t bounded against neighboring older rocks. T h e t e r r ane includes the upper p a r t of the Glenn Sha le and higher pa r t s of t h e Kandik Group which a r e isoclinally folded and a f f e c t e d by low- g rade metamorphism.
KL KLUANE TERRANE--The Kluane me tamorph ic t e r r ane is composed of quar tz-biot i te schis t (Kluane schist) (Kindle, 1953; Muller, 1967; Tempelman-Kluit, 1974, Eisbacher , 1976) t h a t apparent ly f ormed in L a t e Cre taceous time. I t s premetarnorphic age and correla- tion a r e uncer ta in , and i t i s distinguished herein a s a sepa ra te terrane. Eisbacher (1976) suggests t h a t i t i s the metamorphosed equivalent of Jurass ic-Cretaceous c l a s t i c sedimentary rocks (Gravina-Nutzotin belt), whereas Jones and o the r s (1981) include i t within the Taku t e r r ane , which i s known t o contain older s t r a t a .
KO KOOTENA Y TERRANE--The highly deformed,
locally strongly metamorphosed but s t ra t i - graphically coheren t Kootenay t e r r a n e mainly l ies e a s t of the Monashee t e r r ane , but rocks tentat ively co r re l a t ed with KO Ile t o the wes t of the Monashee t e r r ane as wcll. In t h e Kootenay A r c t o t h e e a s t and south, lower Pa leozo ic shale, qua r t z gr i t , maf i c volcanic rocks, and l imestone of t h e Lardeau Group over l ie l imestone of the Lower Cambrian Badshot Format ion (Read, 1977). The re la t ion between rhe Lardeau Group and t h e Badshot i s one of appa ren t stratigraphic conformity , but regional relations may re f l ec t a s t ruc tu ra l d iscordance (3.0. Wheeler, oral commun., 1982). In the inter- val f rom Early Ordovician t o Ea r ly Mississippian (probably in L a t e Devonian) t ime, p lu ton~sm, intense deformst lon, and low-grade metamorphism of the Lardeau Group preceded deposition of basal con- glomerate , l imestone, shale, Lrnpure q u a r t z sandstone, and local volcanics of t h e Milford Group of Ear ly Mississippian t o Pe rmian age. Rocks of t h e Kootecay t e r r ane a r e folded with rocks representat ive of c ra ton ic North America . T h e a g e of t h e par t icular fold a t local i ty 20 ( t ab le 1) i s uncertain. This fold appea r s t o belong to t h e ea r l i e s t phase of deformat ion and thus may be rnid- Paleozoic, which implies t h a t t he Kootenay t e r r ane was juxtaposed with North American rocks by t h a t time. Al ternat ively , t h i s fold could be a Jurass ic s t ruc tu re fo rmed during t h e major deformat ion in this a r e a (Brown and Read , 1983). The Kootenay t e r r ane resembles coeval rocks t o t h e eas t , which were deposited o n o r cont iguous t o c ra ton ic North Amer ica but which appea r t o have no record of mid-Paleozoic deformat ional events ; t h e Kootenay may well be a highly te lescoped f a c i e s equivalent of the North American s t r a t a . According t o Klepacki (19831, volcanic rocks in t h e Milford Croup may b e f ac ie s equivalents of rocks in t h e Slide Mountain t e r r ane t o t h e west , linking t h e t w o in l a t e Paleozoic t ime (loc. 19, t ab le 1). T o the wes t of the Monashee t e r r ane , shale, l imestone, fe ls ic and maf ic volcanic rocks, gr i t , and impure qua r t z i t e compose t h e Eagle Bay Format ion, which 1s of uncer- ta in s t ra t igraphic order and facing (V.A.G. P re to , in Brown and others , 1981). Zircons f rom fels ic volcanic rocks yield a n age of 387 Ma (Pre to and Sch ia r i t za , 1982), which suggests t h a t th is Intensely deformed and weakly metamorphosed fo rma t ion includes Lower Devonian rocks. Weakly de fo rmed Lower and Upper Mississippian shale, sand- stone, and l imestone, possibly correla t ive with t h e Milford Group, l ie in uncer ta in re la t ion t o the Eagle Bay Format ion.
MD McLEOD TERRANE--The McLeod me tamorph ic t e r r ane comprises poorly exposed hetero- genous me tamorph ic rocks including mica- c e o u s ga rne t and chlor i te schists, minor qua r t z i t e , and granitoid rocks (Armstrong and o the r s , 1969). These rocks a r e of uncer- ta in prernetamorphic a g e and correla t ion, bu t their general composition and s t ructural position ind ica te they may be equivalents of t h e Barkerville, Kootenay, and Yukon-Tanana terranes .
MT METHOW-TYAUCHTON TERRANE--The Methow- Tyaughton coheren t t e r r ane comprises Upper Triass ic t o Cre taceous , mainly mar ine c l a s t i c sedimentary s t r a t a t h a t con ta in local ca r -
bonate and volcanic rocks (Tozer, 1967: Jeletzky and Tipper, 1968; Coates, 1974; Tennyson and Cole, 1978). The oldest rocks are commonly fine-grained, distal turbidites that locally contain intercalated volcanic, carbonate, and coarse clast ic rocks. Younger rocks a r e mainly volcanic sandstones which by la tes t Early Cretaceous t ime were deposited a s a western sedimentary facies of the continental volcanic rocks of the Qwsnellia terrane (loc. 14, table I). A cher t PC and metamorphic source terrane to t h e west is reflected in lower Upper Cretaceous strata. No base to the terrane is known; speculatively i t could be the partly coeval oceanic Bridge River and Hozameen ter- ranes. Possibly the Methow-Tyaughton terrane, structurally imbricated with Bridge River and Hozameen terranes and then metamorphosed, forms part of the Skagit metamorphic terrane.
QN MO MONASHEE TERRANE-The Monashee metamorphic
terrane (Monashee Complex of Read and Brown, 1981) is a sequence of high-grade metamorphosed rocks older than 2.0 b.y. The stratigraphy and age of this terrane is apparently unique in the Canadian Cordillera. Cores of gneiss composed of hornblende or hornblende-biotite paragneiss and intermediate orthogneiss a s old a s 2.5 b.y. underlie a mantling sequence of basal quartzite, semipelitic, psammitic, and calc- silicate gneisses, and higher thin marble and quartzi tes which a r e of known stratigraphic facing and a r e c u t by orthogneiss intrusions a t least 2.0 b.y. in age. The highest gneisses a r e semi-pelitic and psarnmitic and a re intruded by abundant pegmatite. Intense Jurassic deformation and metamorphism formed complex nappes, which may have been preceded by phases of deformation and metamorphism so far unrecognized. The fau l t between this terrane and the Kootenay terrane apparently is cut by a mid-Jurassic pluton (kc. 21, table 1, Read and Brown, 1981). Because of differences in age between these rocks and Hudsonian conti- nental basement (about 1.7 b.y.1 to the eas t , and the presence in MO of a lower Proterozoic sedimentary sequence which is unknown to the east , the Monashee terrane is suspect.
NK NOOKSACK TE RRANE--The Nooksack coherent terrane, in part imbricated with the Chilliwack terrane on eastward-dipping mid-Cretaceous thrusts, comprises an orderly, although partly metamorphosed, succession of Triassic(?) conglomerate, sandstone, and argillite overlain by Middle Jurassic volca~iics (keratophy res and quartz- keratophyres; Harrison Lake, Wells Creek Formations), then Upper Jurassic and Lower Cretaceous marine, mainly green volcanic sandstone, conglomerate, and argillite of the Nooksack Formation and equivalent units (Misch, 1966; Monger, 1970). I t is possible, but not certain, that these rocks stratigraph- ically overlie the Chilliwack terrane (loc. 5, table 1).
P R PACIFIC RIM TERRANE--The disrupted Pacific Rim terrane comprises grey wacke, argilli te, chert , and metabasal t of mainly L a t e Jurassic (late Kimmeridgian to early Tithonian) to Early Cretaceous (mid- Valanginian) ages (Muller, 1977). I t includes
the Leech River complex. Ammonites and conodonts of L a t e Triassic age have been found in this terrane (M.T. Brandon, H.W. Tipper, M J . Orchard, oral commun., 1983). The terrane appears to be tectonically anal- ogous to and stratigraphically correlative with parts of the Franciscan terrane of California and the Chugach terrane of southern Alaska (Muller, 1973; Cowan 1982).
PORCUPINE TERRANE--Within Canada this terrane comprises Precambrian(?) phyllite, slate, quartzite, and carbonate rocks, overlain by a structurally and stratigraphically complex assemblage of shallow-water marine carbon- a t e and fine-grained clast ic rocks ranging from Cambrian(?) t o L a t e Devonian in age. I t is continuous into a larger outcrop a rea in Alaska where P C also includes upper Paleozoic and Jurassic strata.
QUESNELLIA TERRANE--The undifferentiated par t of Quesnellia consists predominantly of coherent Upper Triassic and Lower Jurassic (upper Karnian t o Sinemurian) s trata. These a r e mainly marine, calc-alkaline to alkaline volcanic rocks (Nicola and Rossland Groups, part of t h e Takla and Quesnei River Groups, and Nazcha and Shonektaw Formations), comagmatic intrusions, and intercalated argillite, volcanic sandstone, and local lime- stone. Locally upper Paleozoic carbonate rocks a r e present. The volcanic s t ra ta interdigitate eastward with sedimentary rocks (Slocan "black phyllite"). Discon- formably and locally unconformably above these s t ra ta a r e Lower and Middle Jurassic shale, sandstone, and conglomerate (Ashcroft, Hall Formations), Below undif- ferentiated Quesnellia s t ra ta a r e two subter- ranes, Okanagan (QNO) and Harper Ranch (QNH) (Okulitch and Peatfield, 1977).
Probable stratigraphic linkages can be made between Quesnellia and rerranes to the e a s t and west. The Mesozoic rocks of undif- ferentiated Quesnellia overlap the Okanagan and Harper Ranch subterranes of the Quesnellia terrane and lie stratigraphically on the Slide Mountain terrane on the eas t (loc. 15, 16, 17, table I). To the west, blocks of volcanic rocks identical in lithology to those of t h e Nicola Group a r e found in melange within the Bonaparte subterrrane of the Cache Creek terrane, and clasts of Middle Triassic chert, a s well as basalt and ultramafic rocks, presumably derived from the Cache Creek terrane, a r e in Upper ,
Triassic (Norian) Nicola rocks, suggesting that QN was amalgamated with the Cache Creek terrane by L a t e Triassic time (loc. 13, table 1). Earliest Jurassic plutons appear to stitch the Quesnellia, Cache Creek, and Stikine terranes together (localities num- bered 11 on table 1). Lower Jurassic (Pliens- bachian) sandstone and conglomerate, apparently similar to t h a t in QN (Ashcroft Formation), lie on the Cache Creek terrane (Tipper, 1978, Tipper and others, 1981), suggesting tha t by Early Jurassic t ime the Quesnellia, Cache Creek, Stikinia, and Slide Mountain terranes were amalgamated (loc. 12, table 1). Triassic and some Early Jurassic (Pliensbachian) faunas have simi- larities with those in the Western conter- minous United States, but they a r e dissimilar from coeval faunas a t the same latitude on the craton (Tipper, 1981; Tozer, 1982).
QN H HARPER RANCH SUBTERRANE--The predom- inantly upper Paleozoic Harpe r Ranch sub- t e r r ane includes the Harper Ranch Group and Mount . Rober t s Format ion in British Columbia and the Anarchis t Group and Misdon Argillite (Mills and Davis, 1962) in Washington. I t includes argillite, volcanic- and cher t -detr i tus sandstone and conglom- e r a t e , basal t , andesi te and dac i t e and their pyroclas t ic equivalents, and l imestone bodies as long as a few ki lometers , a t l eas t some of which a r e olistoliths. T h e m a t r i x is " l a t e Paleozoic" and Triassic, and the l imestones range f rom l a t e s t Devonian t o Pe rmian i n age (Cockfield, 1948; Mills and Davis, 1962; Rinehar t and Fox, 1972; Sada and Danner, 1974; Monger, 1977a, b; W.R. Danner , oral commun., 1981; M.J. Orchard, oral commun., 1982). Although ol is tos t romal and s t ruc- tural ly complex, QNH does not appea r t o con ta in "broken formation" or t ec ton ic melange. This succession is unconformably overlain by Nicola Group rocks of the undif- f e ren t i a t ed Quesnellia t e r r ane e a s t of Kamloops (Read and Okulitch, 1977; loc. 15, t ab le I). Pe rmian f aunas of QNH have s imil iar i t ies with faunas in the Chilliwack t e r r ane (W.R. Danner, oral commun,, 1977; Ross and Ross, 1983) and those on the c ra ton in t h e southwestern United S ta t e s , but they a r e dissimilar f rom coeval faunas in the C a c h e Creek t e r r anes and on t h e c ra ton a t t he s a m e la t i tude.
QNO OKANAGAN SUBTERRANE--The disrupted Okanagan sub te r rane includes the Chapperon, Anarchis t , and Kobau Groups and Blind Creek, Independence, Showmaker , and Old Tom Format ions in British Columbia and Kobau Format ion in Washington. These rocks consist of low-grade metamorphosed and disrupted radiolarian che r t , argillite, basal t , local l imestone blocks, and u l t r amaf ic rocks, a l l associated with broken format ion and melange, and higher g rade metamorphosed siliceous schis t , chlor i te schis t , amphibolite, and marble. Ages appea r t o be mainly Carboniferous (P.B. Read, oral commun., 1979; D.L. Jones , oral commun.,l981). These rocks a r e unconformably over la in by Upper Triass ic s t r a t a of Q N (Read and Okulitch, 1977; loc. 16, t ab le 1).
SE SAINT ELIAS TERRANE--The Sa in t El ias t e r r ane is a fault-bounded block of metamorphosed volcanic and sedimentary rocks of amphib- o l i t e f ac i e s whose protol i ths a r e of probable l a t e Mesozoic age. T h e t e r r ane may b e a higher grade but s t ructural ly disconnected equivalent of t h e Chugach t e r r ane (Jones and others , 1981).
SH SHUKSAN TERRANE--The Shuksan t e r r ane com- prises act inol i t ic greenschis t , glaucophane schis t , phyllite, and phyllitic qua r t z g r i t (Misch, 1966). R e c e n t isotopic s tudies (Armstrong, 1980) ind ica te L a t e Jurassic- Ear ly Cre taceous blueschist metamorphism of a possible Ju ras s i c protalith.
SK SKAGIT TERRANE--The Skagi t t e r r ane comprises greenschist- t o amphibolite-facies rocks, including migmati tes , t h a t were derived f r o m a predominantly e l a s t i c sequence containing subordinate volcanic rocks and from a va r i e ty of metamorphosed intrusive rocks including u l t r ama t i c rocks (Misch, 1966). In
pa r t t h e protol i th may be imbricated equiv- a l en t s of t h e Hozameen, Bridge River , and Methow-Tyaughton t e r r anes (see McTaggart and Thompson, 1967), but older Paleozoic rocks appear t o be p resen t as well, T h e ma in metamorphism appea r s t o be of middle o r L a t e Cre taceous age. Mid-Cretaceous plutonic rocks i n t r u d ~ n g this t e r r ane have anomalously low paleomagnet ic inclinations with r e spec t t o s t ab le North America .
SM SLIDE MOUNTAIN TERRANE--The Slide Mountain t e r r ane (generally equivalent t o t h e "Eastern assemblage" of Monger, 1977a) consis ts of a number of isola ted ou tc rop a r e a s t h a t con- ta in similar rocks and have common s t ruc- tu ra l s e t t ings in t h e Canadian Cordillera. Each ou tc rop a r e a has received a dif ferent s t ra t igraphic name. F r o m north t o south, t hese are: Anvil Range ( la t 62'1, Sylvester ( la t 59O), Nina Creek ( la t 5 ~ ' ) ~ Slide Mountain ( la t 53'1, Fennel1 ( la t 51 1, and KaslolMilford ( la t 50'). Rocks in a l l t hese a r e a s appear t o have a s imilar gross s t ra t ig- raphy, and t o emphasize this we have no t sepa ra ted them into subterranes . A lower sedimentary sequence, comprising che r t , argi l l i te , sandstone, conglomerate , and minor ca rbona te rocks, with local maf i c sills, dikes, and flows, i s overlain by basal t , Local alpine- type u l t r amaf ic rocks, che r t , argillite, and conglomerate . The upper and lower sequences a r e commonly In s t ra t igraphic continuity, with major breaks, typically del ineated by serpent ini te , e i the r within t h e volcanic sequence o r e lse a r the base of the sedimentary sequence. However , in south- eas t e rn British Columbia, rocks probably co r re l a t ive with t h e sedimentary sequence e lsewhere , known a s the Milford Group, lie unconformably on t h e Lardeau Croup (loc. 19, table I) which fo rms par t of the Kootenay terrane. Although rocks of t h e Slide Mountain t e r r ane a r e commonly highly deformed, internally imbricated, and locally metamorphosed t o high grades , they rarely display t h e type of t ec ton ic melange o r broken format ion cha rac te r i s t i c of the Bridge River , C a c h e Creek , Chugach, or Pac i f i c Rim terranes . Age of the t e r r ane ranges f rom Ear ly Mississippian t o L a t e Permian, (Gabrielse, 1963; Monger, 1977a, b; Tempelman-Kluit, 1979; Struik , 1981; Gordey and others , 1982). In places, SM is overlain with apparen t disconformity by Upper Triass ic s t r a t a belonging t o the Quesncllla terrane. In places, SM lies with known o r assumed th rus t c o n t a c t on older rocks, a s shown by superposed Pe rmian on Upper Triass ic s t r a t a in t h e Yukon Ter r i to ry and by Mississippian on Pe rmian s t r a t a In cen t ra l British columbia. Evidence for considerable la t i tudinal displacement c o m e s f rom northern British Columbia where SM contains Upper Pe rmian fusulinids similar t o fo rms in the southwestern United S t a t e s and Mexico; n o Pe rmian fusulinids a r e known from coeval rocks a t t he s a m e la t i tude on t h e craton. According t o Klepacki (1983) volcanic rocks in t h e Milford Group of the Kootenay t e r r ane may be f ac ie s e q u ~ v a l e n t s of those in t h e Slide Mountain terrane.
ST STIKINIA TERRANE--Stikinia is a cohe ren t t e r r a n e comprising s t ra t igraphical ly s t acked Mississippian, Permian, Tr iass ic , and Jurass ic marine and nonmarine volcanic and sedimen- t a ry s t r a t a and coeval intrusions (Souther,
1971, 1972; Tipper and Richards, 1976; Monger, 1977a, b). Upper Paleozoic carbonate rocks a r e well represented. Named units within the terrane include the Asitka Group of Permian age, Takla and Stuhini Groups and Sinwa Formation of Triassic age, and Hazelton Group of Jurassic age. Dated Pennsylvanian rocks a r e rare; deformation, metamorphism, and intrusion occurred in Early or Middle Triassic time, and there appears to be a terrane-wide earliest Jurassic hiatus. To the north and e a s t the terrane is limited by mid- to late Mesozoic thrust faults, on which the Cache Creek terrane is emplaced on ST, and detr i tus from the Cache Creek occurs in late Middle Jurassic s t ra ta of the Bowser basin, which lies entirely on ST (loc. S, 9; table I). Amalgamation of the Stikinia and Cache Creek terranes in latest Triassic t ime is suggested by interbedded chert and graywacke of Norian age in the Cache Creek terrane (kc . 7, table 1). The graywacke is lithologically identical with Norian graywacke in ST. Evidence for displacement of ST comes from Permian, Triassic, and Jurassic faunas that a r e dissimilar from coeval faunas a t t h e same present latitude on the craton (Monger and Ross, 1971; Tipper, 1981; Tozer, 1982), although the Permian faunas appear to be similar to those of the Quesnellia and Chilliwack terranes. Anomal- ous Triassic and Jurassic paleolatitudes derived from magnetic inclinations indicate northward displacement of about 13' with respect to the craton (Monger and Irving, 1980).
TUS, TAKU TERRANE--Taku terrane is an enigmatic, pos- TUN sibly polygenetic assemblage of multiply de- TUC formed and metamorphosed strata containing
sparse fossils of Permian and Middle and L a t e Triassic ages (Silberling and others, 1982). Key lithologies include: Permian crinoidal marble intercalated with pelitic phyllite and felsic metatuff; upper Paleozoic basaltic metatuff and agglomerate; Middle and Upper Triassic carbonaceous and concre- tionary limestone, slate, phyllite, and basal tic pillow breccia; undated meta flysch and metatuff lithologically similar to Jurassic or Cretaceous strata in the Gravina- Nutzotln belt; and undated quartzi te and subordinate felsic metatuff. Near the south end of the Taku terrane, locally conspicuous lenses of rnetaconglomerate contain promi- nent relict roundstone clasts of trondhjemite (leucocratic quartz diorite) and quartzi te and less-conspicuous clasts of fine-grain detrital rocks (Berg, 1982). Matrix of the metacon- glomerate is pelitic schist. The premeta- morphic age of the rnetaconglomerate is unkown. In places i t appears to grade into upper Paleozoic crinoidal marble; in other places i t is intercalated with pelitic and tuffaceous rocks lithically similar to those in the Cravina-Nuttotin belt, suggesting that metaconglomerate occurs a t least a t two stratigraphic levels.
The stratigraphic base of the Taku terrane is not known. The clasts of trond- hjemite in the metaconglomerate a r e litho- logically similar to trondhjemite in the Ordovician-Silurian volcanoplutonic complex in the Annette and Craig subterranes of the Alexander terrane, Which may have been their source, but there is no stratigraphic evidence of pre-upper Paleozoic crystalline
basement beneath the presently mapped extent of the Taku terrane. If the premeta- morphic age of the trondhjemite-clast- bearing metaconglomerate, which appears to grade into marble of late Paleozoic age, is also la te Paleozoic, and if the source of clasts is the Annette or Craig subterrane, then the metaconglomerate may record structural juxtaposition (amalgamat~on) of a t least the southern Alexander and Taku ter- ranes by la te Paleozoic t ime (Berg, 1982, p. 14).
The west boundary of the Taku ter- rane is a zone of mapped and inferred north- east-dipping thrust faults. The northeast boundary is the western contact of a persis- t en t northwest- to north-trending zone of foliated tonalite sills tha t also marks the southwestern boundary of the "Coast plutonic complexff (Brew and Ford, 19811, ' which probably was emplaced along a now-obliter- ated Mesozoic suture tha t bounded Taku and Tracy Arm terranes.
In a preliminary interpretation, the Taku terrane appears to comprise a t least three distinctive stratigraphic assemblages whose northwest-trending boundaries and internal lithologic trends obl~quely intersect the western and eastern boundaries of the terrane. The northern part of the terrane (TUN) is distinguished by upper Paleozoic basaltic volcanic and volcaniclastic rocks (Berg and others, 19781, and the southern part (TUS) by coeval, mostly pelitic clastic, carbonate, and felsic volcaniclastic rocks (Berg and others, 1978; Silberling and others, 1982). The central part of the Taku terrane (TUC) is distinguished by undated quartzi te o r quartzitic gneiss and subordinate felsic metatuff (H.C. Berg, D.L. Jones, and P.J. Coney, unpub. field data, 1981). The strati- graphic differences suggest tha t the Taku terrane comprises structurally juxtaposed and originally disjunct crustal blocks, and the truncation of their trends supports the inter- pretation t h a t the terrane is bounded by partly obliterated regional faults.
TA TRACY ARM TERRANE--The Tracy Arm metamor- phic terrane consists of pelitic and quartzo- feldspathic schist and paragneiss, amphibo- lite, marble, minor serpentinite, and other metamorphosed sedimentary and igneous rocks that form roof pendants, screens, and xenoliths in the Coast Plutonic Complex eas t of the zone of tonalite sills that forms the northeastern boundary of the Taku terrane. The premetamorphic stratigraphy of TA is unknown; some of the rocks may be of Mesozoic age, others much older. For ex- ample, quartz-muscovite and quartz-biotite schist, marble, and minor amphibolite in northwestern British Columbia predate Early Triassic intrusions and have a possible proto- lith age of l a te r Precambrian (ca. 900 Ma), on the basis of strontium isotope studies (loc. 10, table I; Werner, 1978, and oral commun., 1979). These rocks a r e overlain with unknown relations by Upper Triassic s t ra ta similar to those of the Stikinia terrane and a r e cu t by dikes of porphyry similar to feeders of adjacent Upper Triassic volcanic rocks of Stikinia, suggesting tha t a t least this par t of TA is basement to the Stikinia ter- rane or t h a t the two terranes were amalga- mated by Late Triassic t ime (loc. 10; table 1). The southern part of the Tracy Arm terrane may merely be higher grade rneta-
morphic equivalents of flanking terranes . Northeast of Ketchikan in southeastern Alaska, T racy Arm te r rane rocks a r e sepa ra ted f r o m Stikinia t e r r ane rocks by a northeast-dipping th rus t zone t h a t i s intruded by Eocene plutons (Berg, 1982, p. 15).
WM WINDY-MCKINLEY TERRANE--The Windy-McKinley t e r r ane is a composi te heterogenous assem- hlage t h a t includes notable amoun t s of u l t r amaf ic rocks, blocks o f Devonian lime- s tone, Pennsylvanian and Pe rmian che r t , and, locally, Triassic pillow basalt. This t e r r a n e i s poorly exposed in Canada bu t cont inues westward i n Alaska t o nea r t h e Denali f a u l t (Jones and Silberling, 1979; J o n e s and others , 1981).
WR WRANGELLIA TERRANE--Wrangellia is a coherent t e r r ane with remarkably uniform Triass ic s t ra t igraphy. The oldest rocks commonly a r e m a f i c to fe ls ic volcanic rocks, l imestones, pelites, and graywackes of l a t e Paleozoic (Pennsylvanian) a g e belonging t o t h e Sicker and Skolai Groups. Devonian U l P b a g e s f rom t h e Sicker Group have been reported on southern Vancouver Island (Muller, 1980a). Overlying t h e Paleozoic rocks a r e Middle(?) and L a t e Triass ic s t r a t a t h a t include thick (over 6,000 m on Vancouver Island) submarine t o subaer ia l tholei i t ic basal t (Karmutsen and Nicolai Formations), overlain in turn by shallow- t o deep-water ca rbona te and pel i t ic rocks (Quatsino, Parson Bay, Kunga, Chi t is tone, Nizina, and McCarthy Formations). Black argi l l i te locally underlies the Karmutsen and Nicolai Formations. In southern Alaska th i s sequence is overlain by Jurass ic deep-water sedimentary rocks, but o n Vancouver Island and Queen C h a r l o t t e Islands i t i s overlain by Lower Jurass ic calc-alkaline volcanic and volcaniclas t ic rocks (Bonanza Group; Maude and Yakoun Format ions) associated with cornagmatic intrusions. Pa leomagne t i c data f rom Triass ic (Symons, 1971; Irving and Yole, 1972; Hillhouse, 1977; Yole and Irving, 1980) and Jurass ic (Irving and Yole, 1983) rocks of Wrangellia a r e anomalous with r e spec t t o s t ab le North Amer ica and indicate der ivat ion f rom low paleolatitudes. Pos tacc re t ion rifting, in p a r t Neogene, has f ragmented th i s once-continuous t e r r ane (Yorath and Chase, 1981).
YA YAKUTAT TERRANE--The Yaku t a t terrane, origi- nally cal led t h e Yaku ta t block by Plafker and o the r s (i980), contains upper Mcsozoic mar ine slate, graywacke, and melange simi- lar t o t h a t of Chugach t e r r ane f rom which i t d i f fers by a l so including a sequence of marine and cont inental Cenozoic rocks.
YT YUKON-TANANA TERRANE-Yukon-Tanana t e r r ane i s a heterogenous metamorphic terrane. I t contains t h r e e su i t e s of ductile-deformed me tamorph ic rocks t h a t r e s t on a basement of older gneiss. T h e older gneiss may b e Precambrian basement , locally mobilized in t h e Devonian. Above t h e gneiss is a sheared s l ice of Mesozoic sedimentary and intermediate-volcanic rocks. Nex t is a s l ice of Paleozoic greenstone and u l t r amaf ic rocks, possibly a dismembered ophiolite. T h e highest slice i s sheared Devonian grano- diorite. T h e th ree allochthonous s l ices a r e internally disrupted, and have well-developed f laser fabrics; their depositional re la t ions t o
o the r rocks a r e unknown. T h e s t r a in fabr ic , imposed ea r ly in t h e Jurass ic , i s subhori- zontal ac ross large a r e a s (Tempelrnan-Kluit, 1979, and o ra l commun., 1982).
Table 1.--Evidence f o r amalgamation between t e r r anes
[AL, Alaska; BC, British Columbia; WA, Washingto% YU, Yukon Terr i tory; NE, northeasr; NW, northwest; SW, south- west; SE, southeast; SC, south-central; C, centra l ; bdy, boundary I
Local i ty number General on m a p locat ion
Na tu re of linkage
1 AL-YU bdy Upper Jurass ic Gravina-Nutzotin s t r a t a on Wrangellia.
Upper Ju ras s i c Gravina-Nutzotin s t r a t a on Alexander terrane.
Pe rmian s t r a t a of t h e Cra ig sub te r rane of Alexander t e r r a n e contain c l a s t s f rom Admiral ty subterrane.
4 SW YU Jurass ic-Cretaceous Gravina-Nutzotin s t r a t a possibly me tamorphosed in l a t e s t Cretaceous- ea r ly Te r t i a ry t ime t o fo rm Kluane terrane.
5 SW BC - WA bdy Upper Jurass ic s t r a t a (Nooksack equivalent?) on Chilliwack terrane.
6 SW BC - WA bdy Nooksack, Shuksan, Chilliwack, Skagi t t e r r anes juxtaposed o n L a t e Cre taceous th rus t faul ts .
Graywacke, in ter- bedded with Norian c h e r t of C a c h e C r e e k t e r r ane , li thologically ident ical with Norian graywacke of Stikinia.
C a c h e Creek t e r r ane th rus t on Stikinia in middle t o L a t e Jurass ic time.
C a c h e Creek de t r i tu s in upper Middle Jurass ic c l a s t i c rocks of t h e Jurass ic- C r e t a c e o u s Dowser Basin, which l ies on S tikinia.
Metamorphic rocks of Tracy Arm te r rane c u t by dikes lithologically s imilar t o ad jacen t Tr iass ic volcanics of S tikinia.
Early Jurassic plutons c u t Quesnellia, Cache Creek, Stikinia terranes.
Similar Lower Jurassic (Pliensbachian) s t ra ta lie on Cache Creek and Quesnellia terranes.
Upper Triassic volcanic rocks from Quesnellia(?) in Cache Creek melange; Cache Creek detr i tus in Upper Triassic clast ic rocks of Quesnellia.
Upper Lower Cretaceous Quesnellia volcanic rocks interfinger with Methow-Tyaughton clast ic strata.
Upper Triassic Quesnellia volcanic rocks overlie Harper Ranch (QNH) subterrane.
Upper Triassic Quesnellia sedimentary rocks overlie Okanagan (QNO) subterrane.
Middle and Upper Triassic Quesnellia sedimentary rocks overlie Slide Mountain terrane.
Slide Mountain terrane structurally overlies Barkerville on post- Permian, pre-late Early Jurassic thrusts.
Slide Mountain terrane may be facies equivalent of volcanic rocks in upper part of Kootenay terrane; Slide Mountain lies structurally on Kootenay terrane.
North America- Kootenay terrane boundary def ormed by fold t h a t may be ei ther mid- Paleozoic or Jurassic.
Faul i separating Monashee terrane from Kootenay terrane c u t by mid-Jurassic pluton.
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