Abstract

Stratigraphy and structural styles vary greatly in two areas of the Coast Belt near Chilko Lake (Chilcotin Ranges in the east and Coast Mountains in the west). No definite continuity between the two belts has been established in the pre-mid-Cretaceous geology, but this area may be a long-lived, episodic magmatic arc and nearby arc-related basin. The stratigraphic contrasts may reflect inherent differences between an arc and related basinal sequence. Triassic volcanic-arc sequences are part of the Stikine (western belt) and Cadwallader (eastern belt) terranes, which may be part of the same arc. The Jurassic is represented by one dated pluton in the west compared with almost continuous deposition of volcanogenic clastic rocks in the east. Lower Cretaceous sequences in the west and east may represent a volcanic arc and back-arc basin. The Taylor Creek Group (Albian) is the first definitive link between the two belts and represents an arc and intra-arc or back-arc basin. The structural evolution of the two belts also differs significantly. The early Late Cretaceous Eastern Waddington thrust belt comprises all major structures in the west, but only has minor expression in the east. Most of the structures in the east are part of the latest Cretaceous(?) to early Tertiary dextral-strike-slip, Yalakom fault system. These differences were most likely caused by the Late Cretaceous change from nearly orthogonal subduction to a dextral-oblique convergent margin.

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