Footwall Refrigeration Along a Detachment Fault: Implications for the Thermal Evolution of Core Complexes

Abstract

Oxygen isotope compositions of epidote and quartz from chloritic breccias that underlie the detachment fault in the metamorphic core complex of the Whipple Mountains yielded quartz-epidote fractionations that range from 4.1 to 6.4 per mil and increase systematically toward the fault. These fractionations give mean temperatures that decrease from ∼432°C at 50 meters below the fault to ∼350°C at 12 meters below the fault. This extreme thermal gradient of 82°C over 38 meters (2160°C per kilometer) is best explained by advective heat extraction by means of circulating surface-derived fluids. Models of lithospheric extension consider only conductive cooling resulting from tectonic denudation and thus require revision to include fluid-induced fault-zone refrigeration.