From the roots to the roof of a granite: The Closepet Granite of south India

Abstract

The Dharwar craton exposes a natural cross-section of the continental crust. This crust has been intruded during the Late Archaean by a large volume of granites. One of these is the Closepet Granite, which outcrops at different structural levels from deep (corresponding to palaeopressures of 7-8 Kbar) to shallow (2-3 Kbar) crust. This cross-section allows the study of all components of this granite: the root zone, displaying strong crust-mantle interaction, resulting in highly heterogeneous, enclave-rich monzonitic to granitic magmas; the transfer zone, with inferred upward movement of these magmas; and a rheological interface in the shallow crust at which the ascent of the magmas was arrested. At this level, only the less viscous (differenciated and enclave-free) magmas were able to rise through a network of dykes and fill small pockets, forming typical, elliptic granitic intrusions (the "intrusion zone").