A lower crustal origin for massif-type anorthosites

Abstract

The origin of batholith-sized masses of plagioclase-rich crustal rocks, mainly Proterozoic in age, has mostly been ascribed to aluminous magmas of mantle derivation. Here we propose that such masses are derived by partial melting of an aluminous lower continental crust, which has developed following extraction of a granitic upper crust by intra-crustal melting. This segregation of upper and lower crusts occurred principally in the late Archaean. As the lower crust was depleted in heat-producing elements during the initial melting to produce granites, an external source of heat is required to produce Proterozoic massif-type anorthosites. We speculate that this heat resulted from the continental crust moving over a mantle hotspot or line plume. Show more