Abstract

The Papoose Flat pluton (75 to 81 m.y. old) is one of several Mesozoic granitic bodies in the White-Inyo Range which are regarded as satellites of the Sierra Nevada batholith. The pluton, composed chiefly of quartz monzonite with K-feldspar megacrysts, crops out as an elongated east-trending dome, 16 km long and 8 km wide. It was emplaced within the southwest limb of the major southeast-plunging Inyo anticline, consisting of virtually unmetamorphosed late Precambrian and Cambrian sedimentary rocks.

Stratigraphic units around the western half of the pluton have a regionally metamorphosed aspect and are tectonically and concordantly thinned to as little as 10% of their regional thicknesses without loss of Stratigraphic identity or continuity. Around the discordant eastern contact, however, wall-rock textures are hornfelsic, and there is little or no attenuation of the stratigraphic succession. Foliation, lineation, and preferred orientation of minerals are well developed in the western half of the pluton and its wall rocks and, together with the boudinaged wall rocks, are consistent with the geometry of strain required for attenuation of the stratigraphic succession.

The structural evidence indicates that the granite penetrated discordantly through lower formations in the anticline and formed a “blister” in the fold limb beneath the stretched higher formations. Metamorphic mineral assemblages of the wall rocks suggest a maximum temperature of metamorphism of less than 600 °C and a pressure of less than 2.5 kb.

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