Abstract

Quesnel Terrane, at Quesnel Lake, consists of two regional Triassic–Jurassic age-equivalent units, the Takla–Nicola and Slocan – King Salmon assemblages, as determined from conodonts and macrofossils. The upper mainly volcanic unit (Takla–Nicola) overlies the mainly pelitic unit (Slocan – King Salmon) and was probably emplaced by thrusting. The lower unit consists of dark grey pelite, siltite, limestone, and lesser amounts of fragmental basalt and greywacke. The upper unit consists of fragmental basalt, diorite, greywacke, and lesser amounts of dark grey siltite and pelite and limestone. The unit age and stacking order suggest that during the Jurassic, the volcanic-rich thrust sheet was transported northeastward over an eastern, more pelitic facies of the terrane. The northwesterly trending thrust trace is approximately 300 km long. The Triassic and Lower Jurassic subduction-generated volcanic unit may have been deposited on sediments and volcanics equivalent to the upper Paleozoic Harper Ranch Group; the eastern Triassic and Lower Jurassic pelite unit may have been deposited on the pillow basalt and ribbon chert of the upper Paleozoic Slide Mountain Group. The upper Paleozoic Harper Ranch and Slide Mountain group rocks may have rested on attenuated North American crust.

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