MICROSTRUCTURES AND DEFORMATION MECHANISMS ON THE WESTERN MARGIN OF THE EUREKA VALLEY-JOSHUA FLAT-BEER CREEK PLUTON, CALIFORNIA

1:5,000 scale mapping along the western margin of the Jurassic Eureka Valley-Joshua Flat-Beer Creek (EJB) composite pluton in the White-Inyo range of eastern California indicate intense strains of the surrounding sedimentary wall rocks associated with pluton emplacement. Emplacement is also accompanied by extensive partial melting in the surrounding pelitic layers. Longitudinal strains were calculated for three formations mapped in the aureole based on their change of unit thickness from published values taken from the unmetamorphosed part of the range. Strains vary between 0.75, 0.69, and 0.57. Observable deformation mechanisms in the partially molten aureole that accommodate the intense strains are: 1) Slip along low-angle extensional shear bands, 2) Ductile layer parallel extension marked by ubiquitous boudinage on the cm to km scale and strong development of crystallographic preferred orientations in quartz and marble layers, and 3) Grain boundary sliding documented by flow of grains around off-set contacts. In the partially molten pelitic unit at the contact, meter scale marble layers are boudinaged, indicating that marble was the higher viscosity layer. Chocolate-tablet boudinage of the intruded layers document how layers have been pulled apart vertically and horizontally as a result of pluton emplacement.