First Record of Circa 970 Ma Post-Collisional A-Type Magmatism in the Sendra Granitoid Suite, Central Aravalli Orogen, Northwest India

Abstract

This study provides the first record for the emplacement of post-collisional A-type granites in extensional regime during the late Grenvillian period in northwest India. The ca. 970 Ma granites of the Sendra Granitoid Suite (Chang pluton) intrude calc-silicate rocks of the South Delhi Supergroup in the central Aravalli orogen. The Chang pluton is composed of granite sensu stricto ; the granites are metaluminous, ferroan, calc-alkalic, and are characterized by high Ga/Al (>2.5), Nb + Y (>60 ppm), Ta + Yb (>6 ppm), REE, HFSE and zircon saturation temperatures, typical of A-type granites. The Y/Nb >1.2 further classified the rocks as A2-subtype, signifying their derivation from crustal sources in a post-collisional setting. The crustal source is also supported by their high LILE (Rb, K and Ba), and Pb, Th and REE. The geochronological data and tectonics of the region indicate that the granites were emplaced about 30 Myr after the Grenvillian collisional orogeny. This scenario likely resulted due to delamination of the lower part of the thickened orogenic lithosphere. These results are expected to have significant implications for the assembly tectonics of the Rodinia supercontinent.