Abstract

Significant contractional structures that deform Permian rocks but predate an Early Triassic overlap sequence are recognized within the Cordilleran orogen, western United States. Thrusting in the Death Valley region of the orogen, however, has been regarded as Middle Triassic or younger and thus kinematically distinct. We present new isotopic age limits on two posttectonic stocks that intrude major structures of the Death Valley thrust belt. The stocks are no younger than Middle Triassic, but are likely Late Permian in age, consistent with stratigraphic and structural data suggesting that thrusting predates the overlap sequence. We hypothesize that Permian shortening may have affected more than 700 km of the Cordilleran orogen at the same time arc activity began within cratonic North America but prior to Early Triassic emplacement of the structurally higher Sonomian arc terrane.

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