THE SENTINEL GRANODIORITE: CONTACT RELATIONSHIPS WITH ADJACENT PLUTONS AND THE CASE FOR INCLUSION IN THE TUOLUMNE INTRUSIVE SUITE, CENTRAL SIERRA NEVADA BATHOLITH, CALIFORNIA

Contact relationships of the ~94.5 Ma Sentinel Granodiorite (Ks) to adjacent magmatic bodies of the central Sierra Nevada batholith are poorly documented. The Ks is primarily exposed as an ~160 square km body extending ~15 km westward from the Kuna Crest Granodiorite (Kkc), considered by some workers to be the outermost unit of the normally zoned ~94 to 85 Ma Tuolumne Intrusive Suite (TIS). The Ks intrudes and contains m-scale xenoliths of granite from the ~103-100 Ma Yosemite Valley Intrusive Suite (YVIS) along sharp, stepped contacts. These features and a weakly developed structural aureole in the granites imply that stoping was a material transfer process aiding emplacement of the Ks. To the SW, the Ks has sharp to diffuse contacts with an undated tonalitic unit, suggesting the tonalite may be an early mafic phase of an asymmetrically zoned Ks. Strong, contact-parallel, magmatic to high-T solid-state foliation is developed in the tonalite near the contact. Discontinuous internal contacts, chaotic schlieren and foliation, and homogenous regions composing large portions of the Ks suggest that the granodiorite was constructed by numerous magmatic pulses closely spaced in time. To the north, the Ks has a sharp to broadly transitional contact with the undated Yosemite Creek Granodiorite (Ky). Zones of modal layering up to 100 m wide mark the southern and northern boundaries of this transitional zone. Age relations determined from trough truncations and grading of layers imply that the Ks is slightly older than the Ky. To the east, the Ks is in gradational contact with the Kkc. This transitional zone is deformed by meter-thick, contact-parallel, solid-state ductile shear zones, and high-T, solid-state foliations. The shear zones display dip-slip, Kkc-side-up motion, suggesting vertical ductile transport of the Ks accommodated Kkc emplacement. Contact relations of the Ks with the tonalite, Ky, and Kkc are interpreted to reflect that: 1) an eastward sequence of intrusion occurred within a relatively short time span; 2) the tonalite, main Ks, and Ky are outliers of the TIS; and 3) the presence of these outliers interrupts the pattern of progressively more mafic magmas outward in the western TIS.