Abstract

U-Pb zircon ages combined with stratigraphic and structural data indicate that ca. 160 Ma are rocks of the Smartville Complex were constructed across ca. 200 Ma arc rocks of the Slate Creek Complex, which were already juxtaposed against more easterly units in the northern Sierra Nevada. The Slate Creek Complex, an ophiolitic thrust sheet east of the Smartville Complex, is 200-210 Ma, which precludes previous correlations with ca. 160 Ma rocks of the Smartville Complex. The Slate Creek Complex tectonically overlies chert-rich Paleozoic-early Mesozoic units along a low-angle fault that is cut by 163-168 Ma and 158-161 Ma plutons. Seven new ages of 160-163 Ma for plutonic rocks in the Smartville Complex agree with previous ages from Smartville volcanic rocks, sheeted dikes, and other plutons. In addition, one tonalite is 198 Ma and is cut by a 163 Ma dike, thus providing the first evidence of the basement of the ca. 160 Ma rocks. The 198 Ma tonalitic basement is probably correlative with the Slate Creek Complex, which contains the only other ca. 200 Ma tonalite in the northern Sierra Nevada. Thrust emplacement of the Slate Creek Complex between 200 and 163 Ma was followed by locally extensional arc magmatism in the Smartville Complex at about 160 Ma, then by Nevadan contractional deformation, a sequence of Jurassic deformation similar to that in the Klamath Mountains. Nevadan deformation could be part of a noncollisional deformation or a long-lived arc (Slate Creek Complex) collision.

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