Day 3: Lamarck Pluton at Long Lake
Published:January 01, 2005
2005. "Day 3: Lamarck Pluton at Long Lake", Incremental assembly and emplacement of Mesozoic plutons in the Sierra Nevada and White and Inyo ranges, California, Drew S. Coleman, John M. Bartley, Allen F. Glazner, Richard D. Law
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There is only one long traverse today, with a long approach. We will examine field relations of an accessible portion of the 90–94 Ma Lamarck Granodiorite (Coleman et al., 1995; Wenner, Gracely, and Coleman, work in progress). Examples of similar (and, in some cases, more spectacular) features are found in other plutons exposed in the high Sierra Nevada, but this is the only example we are aware of that can be examined on a day hike.
The Lamarck Granodiorite is a long, narrow map unit that extends more than 60 km along strike, but it typically is less than 5 km wide and only locally reaches its maximum width of 10 km (Fig. 21). Thus, in sharp contrast to the TIS visited on Days 1 and 2, the Lamarck is dike-like in map view. The Lamarck pluton is composed of a diverse group of intrusive rocks that range in composition from diorite to granite and have been interpreted to be related by magma mixing (Bateman and Moore, 1965; Frost and Mahood, 1987; Coleman et al., 1992).
Hathaway (2002) mapped the south-central part of the Lamarck pluton in significant detail and subdivided it into ten map units (Fig. 22). He interpreted the units to be dike-fed and, at least in part, to have been intruded along faults including the Long Lake shear zone which we will see today. The main focus of today's traverse is the Treasure Lakes mass of Hathaway (2002), a very early—perhaps the earliest—phase of the Lamarck.
Figures & Tables
Incremental assembly and emplacement of Mesozoic plutons in the Sierra Nevada and White and Inyo ranges, California
This field guide was created in coordination with the Geological Society of America Field Forum “Rethinking the Assembly and Evolution of Plutons: Field Tests and Perspectives,” held 7-14 October 2005 in the Sierra Nevada and White and Inyo ranges, California. The goal of this five-day field trip was to examine field relations and characteristics of plutons in the central Sierra Nevada and in the White and Inyo ranges as they relate to processes of pluton growth and emplacement and, more particularly, as they relate to the hypothesis that plutons are assembled slowly and incrementally.