| Field mapping and thin section analysis provide the first detailed lithologic, petrologic, and structural data on Franciscan Complex rocks near Calaveras Reservoir. Coherent tracts of sandstone, similar to the Yolla Bolly terrane, and mélange comprise most of the study area. These units are juxtaposed along low-angle, bedding-parallel faults, and were deformed mainly by pressure solution. Detrital blueschist minerals in the sandstones imply Franciscan exhumation much earlier than previously documented. Detrital modes of coherent, mélange matrix, and mélange block sandstones suggest a common protolith, and a mélange matrix distinct from those studied elsewhere. A fault-bounded block in the northwestern part of the study area contains distinctive Franciscan rocks such as interbedded chert and sandstone, and a horse of Temblor Sandstone indicating a previously unmapped late Cenozoic fault zone. Franciscan map units and structures in the study area are not contiguous to the north, and a Mesozoic fault may separate the areas. |
