THE SENTINEL GRANODIORITE: STRUCTURE, EMPLACEMENT, AND RELATION TO THE TUOLUMNE INTRUSIVE SUITE, CENTRAL SIERRA NEVADA BATHOLITH, CALIFORNIA

The ~94.5 Ma Sentinel Granodiorite (Ks), one of the least studied plutons in the central Sierra Nevada batholith, is an ~160 sq. km body that is primarily exposed as a lobe extending ~15 km westward from the N-S trending, normally zoned 94 to 85 Ma Tuolumne Intrusive Suite (TIS), and as a narrow body conforming to the SW margin of the TIS. Previous workers have disagreed on whether the Ks and adjacent Yosemite Creek Granodiorite (Ky) are part of the TIS, leading to conflicting interpretations of the initiation of the TIS. Age data for the Ks comply with the increasing ages from the core of the TIS outwards, but the outcrop pattern of the Ks seems inconsistent with the nested pattern of the TIS. The Ks is cut by widespread, primarily N-NW striking pegmatite and aplite dikes, and exhibits steep magmatic foliations that lie both parallel and discordant to abundant schlieren. The Ks and Ky display a dominant N-NW striking and weaker E-W striking magmatic foliation; the latter is concordant to the foliation in the TIS considered to result from regional tectonic strain. To the SW and NE, the Ks intrudes and contains m-scale xenoliths of the El Capitan and Taft Granites of the Yosemite Valley Intrusive Suite, and locally metasedimentary rocks. Contacts with the suite are sharp and stepped, and the Ks truncates magmatic foliation in the El Capitan and Taft (i.e., no structural aureole). These contact relationships and the presence of xenoliths suggest that stoping was an important material transfer process during intrusion of the Ks. To the north, the Ks intrudes the undated Ky, which is typified by schlieren and stretched enclaves parallel to and near its contact with the Ks, suggesting that the Ky was near its solidus during intrusion of the Ks. To the east, the Ks is intruded by the Kuna Crest Granodiorite, the outermost unit of the TIS, and xenoliths of the El Capitan Granite lie along the contact. Meter thick, contact-parallel, solid-state ductile shear zones formed on either side of the contact. These dip-slip shear zones display Kuna Crest-side-up kinematics, suggesting vertical ductile transport of the Ks was, at least locally, a mechanism for accommodating Kuna Crest emplacement. The Ks-Kuna Crest contact shows a greater rheological contrast than the Ks-Ky contact, implying a longer temporal hiatus between the Ks and Kuna Crest Granodiorite.