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Abstract

The 1200 km2 TIS is one of several large-volume zoned intrusive suites emplaced in the Sierra Nevada in the Late Cretaceous (Fig. 4). These suites all have mafic granodioritic outer phases that grade progressively inward to granodioritic or granitic cores (Bateman, 1992), and were intruded at pressures of 1–3 kbar (Ague and Brimhall, 1988). There is a significant mismatch between the wall rocks on the east and west sides of the TIS (Bateman, 1992): the eastern wall is dominated by Jurassic metavolcanic rocks and plutons, whereas the west is dominated by 103 Ma plutonic rocks of the ISYV (Ratajeski et al., 2001) intruded into pre-batholithic metasedimentary rocks. This mismatch may result from intrusion of the TIS into an intrabatholithic shear zone.

Geochronologic data indicate that the TIS was assembled over a period of at least 10 m.y. between 95 and 85 Ma and that the Half Dome Granodiorite 1 intruded over a period approaching 4 m.y. (Kistler and Fleck, 1994; Coleman and Glazner, 1997; Coleman et al., 2004; Matzel et al., 2005). Ages of the intrusive rocks decrease regularly from core to rim within the suite. The rocks include the Sentinel Granodiorite (95 Ma), the granodiorite of Kuna Crest and the tonalite of Glen Aulin (93.5-93.1 Ma; assumed to represent the eastern and western parts of the same intrusion; Bateman and Chappell, 1979), the Half Dome Granodiorite (92.8-88.8 Ma), the Cathedral Peak Granodiorite (88.1-86 Ma), and the Johnson Granite Porphyry (85 Ma; Fig. 4).

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