GSA Connects 2021 in Portland, Oregon

Paper No. 53-5
Presentation Time: 2:30 PM-6:30 PM


ZHANG, Hanlin1, KLEIN, S.P.1, TOWER Jr., John1 and ROUGVIE, James2, (1)Department of Geology, Beloit College, 700 College Street, Beloit, WI 53511, (2)Department of Geology, Beloit College, 700 College St, Beloit, WI 53511-5509

The White Mountain Peak metavolcanic complex, located in the northern White-Inyo range of east-central California, formed in the Mesozoic Cordilleran continental arc to the east of the present day Sierra Nevada. These Jurassic rocks were intruded by the Barcroft pluton during the Jurassic and by the albitized Pellisier Flats Granite in the Late Cretaceous. The metavolcanic complex has undergone a complicated history of metamorphism and alteration.

Cathodoluminescence, PLM and SEM petrography show preservation of igneous textures whereas igneous feldspars are now near-endmember orthoclase or albite. Orthoclase displays mostly brown and minor blue CL. Fine-grained groundmass K feldspar exhibit transient blue luminescence. Brown CL is typical of low-T K feldspar. Albite displays red to dark-brown luminescence and locally replaces phenocrysts and most groundmass. The CL textures are similar to those from the Inyo Mountains volcanic complex and distinct from locations with higher-T overprints such as the Ritter Range and Alabama Hills which are dominated by blue CL K feldspar. Some, but not all, albite replacements display chessboard textures that are geographically widespread. The extent of replacement varies geographically which indicates intensity of albitization varies. Albite replacements contain microscale porosity and are consistent with interface-coupled dissolution-precipitation mechanisms. Whole rock alkali concentrations are disturbed. Both K and Na have undergone local gain or loss consistent with heterogeneity of alteration seen petrographically. Ca is variably depleted. K contents are not correlated with distance from intrusive rocks. Typically immobile elements like Ti and Al display trends similar to those from unaltered arc rocks.

Volcanic rocks in arc settings often undergo pre-plutonic alkali and alkaline-earth element alteration. In some localities these early events are masked by contact-metamorphism and alteration related to later plutons.