Appendix B: Summary Descriptions of Northern Cordilleran Terranes
Accreted Terranes
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46 NORTH AMERICA/Northern Cordillera and multiply deformed in Palaeozoic (?), Mesozoic, and Palaeogene times Dillinger (DL), Mystic (MY), and Nixon Fork (NX): small terranes in Intermontane Alaska whose stratigraphy and Early and Middle Palaeozoic faunas resemble those of the Siberian (or North Asian) craton margin Accreted Terranes Arc terranes terminally accreted in the Jurassic Quesnel (QN) and Stikine (ST): Devonian to Permian clastic rock and carbonate, arc-related volcanic, and plutonic rocks; local Palaeozoic ultramafic rocks, basalt, chert, pelite, and carbonate formed in marginal basins or ocean floor (¼SM?); overlying Late Triassic and Early Jurassic arc-related magmatic and clastic rock and minor carbonate Permian, Triassic, and Early Jurassic faunas most similar to those further south in the western conterminous USA and north-western Mexico; contrarily, palaeomagnetic data suggest little or no northward displacements ST apparently duplicated QN in the Early Mesozoic by oroclinal bending or left-lateral strike-slip faulting and enclosed the associated accretionary complex (CC) Arc terranes terminally accreted in the Cretaceous Alexander Terrane (AX): latest Proterozoic and Early Palaeozoic magmatic arc and associated clastic rock and carbonate, and Late Palaeozoic and Early Mesozoic rift-related clastic and volcanic rock and carbonate AX and WR apparently linked by Carboniferous plutons and overlapped by Middle Jurassic–Early Cretaceous arc rocks Palaeomagnetic data suggest an Early Palaeozoic palaeogeographical location either near eastern Australia or the Barents Sea; Silurian and Devonian faunas favour the latter location; Triassic palaeolatitudes of AX comparable with those of Alaskan WR Cadwallader (CD) and Methow (MT): Upper Triassic magmatic arc rocks and associated sedimentary rock overlying Permian ocean floor rocks; unconformably overlain by Early Jurassic to Early Cretaceous marine arc-derived clastic and local volcanic rocks; overlying Late Cretaceous continental arc volcanics carry palaeomagnetic signatures indicating $35 of northward displacement Chilliwack (CK): Devonian to Early Jurassic arcrelated volcanic and clastic rocks and carbonate; in general, stratigraphy and faunas resemble ST and QN; possibly a fragment of ST, sliced off and translated southwards by sinistral strike-slip faults in the Early Cretaceous Koyukuk (KY), Nyac (NY), and Togiak (TG): Late Jurassic–Early Cretaceous arc rocks in western Alaska associated with the subduction of AG and GN oceanic terranes Wrangellia (WR): Devonian to Middle Jurassic magmatic arc rocks, with associated clastic rock and carbonate, and conspicuous Upper Triassic plumerelated (?) tholeiitic basalt overlain by carbonate; Permian faunas comparable with some in Canadian Arctic and Urals; Early Jurassic faunas comparable with those elsewhere in the western Cordillera; palaeomagnetic data from Triassic strata on Vancouver Island indicate little or no latitudinal displacement, whereas those from southern Alaska indicate about 20 northward translation; interpreted as due to Tertiary separation of the two regions; WR linked to AX by Middle Jurassic and possibly Carboniferous Accretionary complex and back-arc basin terranes; ordered from continental interior to ocean Unless noted otherwise, all are characteristically highly disrupted and most contain melanges; pillow basalts, local alpine-type ultramafic rocks, and rare blueschists, in places associated with eclogite Pre-Late Jurassic accretionary complexes in the Cordillera typically contain abundant radiolarian chert, whereas younger ones contain abundant clastic rocks including sandstone Angayucham (AG), Goodnews (GN), and Slide Mountain (SM): remnants of oceanic and marginal basins SM is Carbonifereous to Triassic; AG and GN range in age from Devonian to Late Jurassic and appear to be accretionary complexes related to KY, NY, and TG arc terranes in western Alaska; SM in Yukon is associated with a Late Palaeozoic arc in YT and contains blueschist; further south, SM appears to be a back-arc basin, lacking melanges, eclogites, and blueschists, and separating QN from the former continental margin The late Palaeozoic palaeomagnetic record of SM suggests northward displacement of $20 with respect to the craton, in accord with displacements indicated by its Middle Permian fauna, which is similar to that in the south-western USA and north-western Mexico Cache Creek (CC) and Bridge River (BR): CC is Early Carboniferous to Early Jurassic and contains distinctive large masses of Late Carboniferous to Late Triassic shallow-water carbonate that probably formed as atolls capping seamounts, as several similar complexes of this age in the circum-Pacific region Middle Permian to Middle Triassic faunas