CHANGING QUARTZ MICROSTRUCTURES ASSOCIATED WITH PLUTON EMPLACEMENT ACROSS THE AUREOLE OF THE EJB PLUTON, WHITE INYO MOUNTAINS

The Jurassic Eureka Valley-Joshua Flat-Bear Creek (EJB) composite pluton intruded through a package of Neoproterozoic to Cambrian sediments in the White Inyo Mountains of Eastern California. Massive quartzite beds within the Lower Cambrian Harkless Formation have been folded and deformed within the pluton aureole and can be followed regionally outside the aureole. We present field structures, optical microstructures, and electron backscatter diffraction (EBSD) data along a transect following the Harkless Formation quartzites from within 500 m of the pluton’s southwest margin to several kilometers away from the margin. Structural measurements in the field reveal a large scale, moderately plunging fold that rotates Harkless Quartzite bedding from sub-horizontal to concordance at the nearly vertical pluton contact. Optical quartz microstructures of quartzites along the transect show a gradient from fine-grained primary sandstone grains to large, recrystallized quartz exhibiting evidence for grain boundary migration. Recrystallized grain size increases dramatically within the pluton-concordant limb of the large-scale fold. Quartz c-axis crystallographic preferred orientation (CPO) pole figures have predominantly y-max patterns close to the pluton margin and more cross-girdle type patterns away from the margin, though CPO patterns are relatively weak everywhere. These datasets are integrated to discuss the effect of physical emplacement and heat production of the EJB pluton on recrystallization processes within quartz.