Crustal Growth by Magmatic Accretion Constrained by Metamorphic P-T Paths and Thermal Models of the Kohistan Arc, NW Himalayas

Abstract

Magmatic accretion is potentially an important mechanism in the growth of the continental crust and the formation of granulites. In this study, the thermal evolution of a magmatic arc in response to magmatic accretion is modeled using numerical solutions of the one-dimensional heat conduction equation. The initial and boundary conditions used in the model are constrained by geological observations made in the Kohistan area, NW Himalayas. Taking consideration of the preferred intrusion locations for basaltic magmas, we consider two plausible modes of magmatic accretion: the first involves the repeated intrusion of basalt at mid-crustal depths (‘intraplate model’), and the second evaluates the simultaneous intrusion of basalt and picrite at mid-crustal depths and the base of the crust respectively (‘double-plate model’). The results of the double-plate model account for both the inferred metamorphic P–T paths of the Kohistan mafic granulites and the continental geotherm determined from peak P–T conditions observed for granulite terranes. The double-plate model may be applicable as a key growth process for the production of thick mafic lower crust in magmatic arcs.