MELT TRANSFER AND GNEISS DOME EMPLACEMENT DURING OBLIQUE DILATION

The rapid transfer of partially molten crust and the formation of gneiss domes and metamorphic core complexes commonly take place by localization of normal or oblique extension in the upper crust. In Marie Byrd Land, Antarctica, a transition from wrench to oblique extension occurred during the development of the West Antarctic Rift System in mid-Cretaceous time. Migmatites within the Fosdick Mountains gneiss dome, Marie Byrd Land, Antarctica, exhibit early steep fabrics formed during wrenching that host steep granite networks. The granites have U Pb SHRIMP zircon crystallization ages of 117–115 Ma. The steep structures are overprinted by subhorizontal foliation and leucogranite sheets with crystallization ages of 109–102 Ma. The subhorizontal leucogranite sheets occupy sites at the NE and SW edges of the elongate migmatite-cored gneiss dome, suggesting melt migration into dilational sites during dextral transtension. These syntectonic granite sheets also intrude into the South Fosdick Detachment zone, the structure that bounds the domes on the south. The U Pb SHRIMP zircon ages for granites constrain the time of onset of detachment tectonics that led to rapid exhumation of the terrain; corroborated by 40Ar/39Ar ages of biotite and hornblende that are 100-98 Ma. This study has implications for understanding melt transport, magma accumulation, and the formation of detachments in an oblique tectonic setting.