Geologic and radiometric evidence demonstrates that the Pinchi Lake blueschists underwent an early deformation, blueschist metamorphism, uplift, cooling, and a second deformation during the Triassic Tahltanian orogeny. Potassium–argon dates on phengitic muscovites from the blueschists (211, 214, 216, 218 ± 7 my) are considered to mark the close of the second deformation which was contemporaneous with or immediately after uplift and cooling of the blueschists during the Late Triassic.

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