6 Mysteries of the Sierra Nevada (Posters)

Wednesday, 2 April 2025
8:00 AM - 5:30 PM
Sierra Ballroom

POSSIBLE NORTHERN EXTENSION OF THE TRIASSIC-JURASSIC TUOLUMNE OPHIOLITE AND OVERLYING ARC ROCKS NEAR PARDEE RESERVOIR, CALIFORNIA

Paper number: 6-7
Program: Theme Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The Tuolumne Ophiolite of the Triassic-Jurassic Sierra Nevada Central Belt consists of a large ultramafic body, overlain by Jasper Point Formation consisting of metabasalt, metachert, and metapelite. The Jasper Point is in turn overlain by the Peñon Blanco Formation's basaltic metatuff and volcaniclastic rocks. The Jasper Point Formation ranges from late Triassic to early Jurassic based on fossils. The Peñon Blanco Formation is older than 200 Ma, based on U-Pb geochronology of the cross-cutting of the Don Pedro intrusive suite. Together, the Jasper Point and Peñon Blanco Formations have been interpreted as an arc overlying an ultramafic body. While the Tuolumne Ophiolite and overlying arc rocks have been extensively studied in the Red Hills, near Lake Don Pedro, the continuation of the units to the north is poorly understood.

In this poster, we present petrography and field relationship from exposures of a steeply dipping strip of ultramafic and volcanic rocks around Pardee Reservoir, near the town of Jackson, California, that may represent a northern continuation of the Tuolumne Ophiolite. The rocks consist of serpentinite overlain by greenstone and interbedded chert. Both the serpentinite and greenstone are intruded by a diabase unit. These units are then overlain by mixed volcanic and sedimentary units consisting of tuff with interbedded shale and greywacke, followed by volcanic breccia.

We suggest that the serpentinite may be equivalent to the Tuolumne ultramafic body, and the volcanic rocks may be equivalent to the Jasper Point and/or Peñon Blanco volcanics. In that case, this exposure may be lateral equivalents of the Tuolumne Ophiolite and overlying arc rocks exposed in the Red Hills. It is not clear how far north similar rocks are exposed in the Central Belt.

Geological Society of America Abstracts with Programs. Vol. 57, No. 4

doi: 10.1130/abs/2025CD-410196

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