TRANSITION FROM SUB GRAIN ROTATION TO GRAIN BOUNDARY MIGRATION IN A QUARTZITE. AN EXAMPLE FROM THE AUREOLE SURROUNDING THE EUREKA-JOSHUA FLAT-BEER CREEK PLUTON OF EASTERN CALIFORNIA

The Eureka - Joshua Flat - Beer Creek pluton of eastern California is surrounded by approximately 1.3 km of intensely deformed metasedimentary rocks. The Harkless quartzite can be tracked from where it first appears near the pluton (450 m from the contact), and is intensely deformed, to a distance where deformation has not occurred (2300 m). We collected a suite of rocks within the Harkless, from more deformed to less deformed rock. Skolithos tubes are evident 950 m from the pluton and ripple marks are observed at 2300 m. The rocks exhibits sub grain rotation recrystallization (SGR) and grain boundary migration (GBM). SGR decreases in abundance as the pluton is approached and GBM increases in abundance. Within 800 m from the pluton, GBM is the only recrystallization mechanism. CL images show the progression from original sedimentary grain structure through mobilization of Titanium during GBM as the pluton is approached. Undeformed Harkless sandstone cement is well preserved and contrasts with the luminescence of the original sand grains. Incorporation of cements into new grains during recrystallization occurs distally in the transect and grains appear more welded together than cemented. Closer to the pluton, CL images reveal undulating light and dark bands which may represent growth bands during GBM. The crystallographic preferred orientation of c-axes begins to occur where GBM begins to dominate.