LINKING COMPLEX MICROSTRUCTURES IN GRANITES TO TECTONIC EVENTS

Petrographic, backscattered electron, secondary electron and cathodoluminescence (CL) imagery of two Miocene-age S-type peraluminous granites (Salihli and Turgutlu) that intrude a detachment fault in western Turkey document the rocks’ complicated tectono-metamorphic history. The granites are cut by the Alasehir detachment of the Menderes Massif, a large-scale metamorphic core complex. They are separated by an E-W distance of ~50 km and are thought to have been generated due to subduction in a volcanic arc setting, were subjected to phases of compression, and have been exhumed due to large-scale extension. Their geochemistry and mineralogy suggest different magma compositions, but their structural setting indicates syntectonic emplacement during extension and both have been subjected to greenschist facies conditions. To interpret their microstructures and nature of element migration facilitated by deformation, X-ray element mapping was employed. The goals are to link the deformation history of the granites to their microtectonic features and to examine the pathways of fluids along microcracks and their role in the granites’ alteration and reaction history. The rocks contain crack swarms, corroded plagioclase cores, transgranular and intragranular cracks, and grain boundary deformation. We consider them a physical library that records their generation under submagmatic conditions, migration through the crust, and fault-driven exhumation history. Microcracks in these granites are best seen in plagioclase grains, which display a range of zoning types (oscillatory, patchy) and many have complex corroded cores. Due to the difference in annealing temperatures between quartz and other minerals present in the rocks, transgranular microcracks can be identified and linked to lower temperature deformation. Using the imagery and X-ray element (Ca, Na, Fe, Al, Sr) mapping of plagioclase in the granites, the series of tectonic events which affected the rocks can be unraveled.