Effects of shock-induced incongruent melting within Earth's crust: The case of biotite melting
Biotite is an abundant hydrous silicate in the Earth's crust and plays a critical role in the formation of felsic magmas via incongruent melting. Although biotite incongruent melting reactions have been described for various contact and regional metamorphic environments, the effects of impact-induced melting of biotite remain poorly understood. Our observations from the 40-km-wide Araguainha impact structure indicate that biotite can undergo incongruent melting during impact processes, producing aluminous melts that can accumulate as pockets or fracture networks in crystalline target rocks. We observed that as much as 9% of the crystalline target at Araguainha is a crystallization product after biotite breakdown. Given the relatively low shock pressures recorded in the Araguainha central uplift (20-25GPa), our results imply that impacts in the size of Araguainha or larger are capable of generating substantial volumes of incongruent aluminous melts in crystalline crust underlying large (>40km diameter) impact structures. © 2011 Blackwell Publishing Ltd.