FIELD AND PETROGRAPHIC OBSERVATIONS FROM THE CENTRAL BELT EXPOSED BENEATH THE SMARTVILLE COMPLEX, HIGGINS CORNER, SIERRA NEVADA, CALIFORNIA

The westernmost units of the Sierra Nevada metamorphic belts are the Smartville Complex and the Central Belt. The Smartville Complex is an eroded Jurassic volcanic island arc system consisting of an asymmetric anticline with volcanic rocks surrounding a mafic plutonic core. Directly east of the Smartville Complex lies the Triassic-Jurassic Central Belt, which consists of a complicated mix of sedimentary, volcanic, plutonic, and ultramafic rock with medium to low grades that has often been described as a melange. On the east side of the Smartville Complex, near Higgins Corner, Nevada County, is an exposure of chert and argillite in close proximity to serpentinized ultramafic rocks that is crosscut by gabbroic plutons. This exposure has been interpreted as a tectonic window into the underlying Central Belt and has been referred to as the Higgins Corner tectonic window.

This presentation will discuss new field and petrographic observations from the Higgins Corner window. This work was conducted by sampling from locations mapped as metasediments, ultramafic rock, and gabbro. Preliminary observations indicate the presence of a previously unmapped metavolcanic unit closely associated with both ultramafic rocks and chert. These metabasalt, along with the ultramafics and chert, may be part of the ophiolitic basement present in much of the Central Belt. Additional geochronology, not presented here, may help test this hypothesis.