Abstract

Mesozoic metavolcanic and metasedimentary rocks in the northern White Mountains, eastern California and western Nevada, are separated from lower Paleozoic and Precambrian rocks by Jurassic and Cretaceous plutons. The large stratigraphic hiatus across the plutons is called the Barcroft structural break. Recent mapping and new U/Pb zircon ages of 154 +3/−1 Ma and 137 ±1 Ma. from an ash-flow tuff and a hypabyssal intrusion, respectively, indicate that part of the Mesozoic section and the Barcroft structural break are younger than the 160–165 Ma Barcroft Granodiorite, in contrast to previous interpretations. The Barcroft Granodiorite has been thrust westward over most of the Mesozoic section. It is everywhere in fault contact with overturned metasedimentary rocks on the west side of the range, rocks which were previously thought to be upright and the oldest part of the Mesozoic section. The McAfee Creek Granite, which has a 100 ±1 Ma U/Pb zircon age, postdates thrusting; therefore, the Barcroft structural break is primarily Early Cretaceous in age.

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