Paper No. 6
Presentation Time: 10:15 AM


PETSCHE, Joseph1, JOHNSON, Brendon2, VAN DYNE, Ashley1 and MILLER, Robert B.3, (1)Department of Geology, San Jose State University, San Jose, CA 95192-0102, (2)Geology, San Jose State University, 100 Washington Square, San Jose, CA 95192, (3)Department of Geology, San José State University, One Washington Square, San Jose, CA 95192-0102,

Three students from the Department of Geology, San Jose State University, have recently developed 1:24,000 structural geologic maps of areas within Yosemite National Park as part of their thesis research, as well as to fulfill EdMAP Grant requirements. The proximity of these field areas have provided us with the opportunity to compile and create a more comprehensive 1:24,000 digital map of our data, which provides a larger view of unit contacts and orientations of solid-state and magmatic fabrics. These studies have focused on the ~103-99 Ma Yosemite Valley Intrusive Suite (YVIS), ~97 Ma Yosemite Creek Granodiorite, and ~ 94.5 Ma Sentinel Granodiorite.

The YVIS formed prior to the emplacement of large zoned granodioritic suites of the Sierra Nevada batholith during a period of voluminous silicic (leucogranite to granodiorite) magmatism. The YVIS consists of older, generally higher-color-index, and coarser-grained rocks of the El Capitan Granite and similar units, the younger Taft Granite, and comagmatic diorites that are more ubiquitous within the southern part of the suite. Steep magmatic foliation in the suite is commonly margin-parallel, but in some >10 km2 domains, N- and NW-striking foliations are at high angles to contacts with host rocks and are interpreted to record regional NE-SW shortening.

The Yosemite Creek Granodiorite and Sentinel Granodiorite are smaller intrusions that are heterogeneous in composition and intrusive style and are in direct contact with the ~93-85 Ma Tuolumne Intrusive Suite (TIS). The rheology of the YVIS likely influenced the geometry and emplacement style of the younger intrusions. The western portion of the TIS, for example, does not penetrate far into the YVIS. Thin (<10 m wide) metasedimentary screens to km-wide pendants separate the YVIS and younger plutons along the eastern and northern margins of the suite-antecedent? Although the dominant fabrics in the Yosemite Creek and Sentinel Granodiorites are margin-parallel, a second, pervasive, regional NW-striking foliation in the Sentinel and Yosemite Creek granodiorites as well as in the YVIS is consistent with the overall Sierran strain field, but contrasts with that of the E-W-striking regional foliation in the younger TIS.