Abstract

Metavolcanic and volcaniclastic rocks of the Sullivan Creek terrane in the Merced River region of the western Sierra Nevada metamorphic belt are the remnants of a submarine magmatic arc of Jurassic age. Metasedimentary assemblages consist predominantly of argillite but include chert-argillite, pebbly mudstone, sandstone, limestone blocks of Paleozoic and Mesozoic age, and volcanic debris. Sandstone framework modal clast compositions indicate a continental provenance. Rocks are characteristically highly deformed and contain a penetrative flattening foliation and a domainal crenulation cleavage. Locally undeformed rocks allow partial reconstruction of the stratigraphy. Crosscutting plutons constrain a minimum age of mid-Jurassic (pre-Callovian); its maximum age is probably Early to Middle Jurassic. Based upon the intermingling of volcanic and clastic detritus, we suggest that the magmatic arc formed near a continental margin. Nearby volcaniclastic and sedimentary rocks compose the Bullion Mountain sequence. In contrast to the Sullivan Creek terrane, the rocks of the Bullion Mountain sequence are largely undeformed. The Bullion Mountain sequence is part of a regionally extensive overlap sequence of Callovian-Oxfordian age emplaced across previously amalgamated pre-Late Jurassic terranes.

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