Contrasted granite emplacement modes within an oblique crustal section: The Closepet Granite, South India

The Closepet Granite, in South India, is a large. syntectonic. Archaean gra nitic complex. Differential erosion has exposed it from the lower (25 km) t o upper crust. (5 km). Four main pal ts al e recognized from bottom to top: (i) A root zone where magmas formed, collected and rose within active shea r zones, leaving schlieren behind. The surrounding crust was highly: ductil e, leading to diffuse deformation. (ii) A transfer zone, where the magma wa s progressively enriched in K-feldspar phenocrysts during its ascent. In th is part, the granite rose as a mush moving as a whole within a less ductile crust, Slow cooling was responsible for a long magma. residence time under conditions favoring to fabric enhancement and strain partitioning, leading to horizontal and vertical melt migration. (iii) A " gap " (dyke complex t hat acted as a filter zone), were the ascent of the mush was stopped. proba bly due to high phenocryst load and high viscosity contrast with the wall r ocks, Only crystal-poor melts could continue their ascent through the dykes , (iu) X zone of shallow intrusions? where the liquids extracted from the m ush filled small, elliptical plutons, cooling quickly and developing only v ery weak fabrics. (C) 2001 Elsevier Science Ltd. All rights reserved.