The Neoproterozoic Malani magmatism of the northwestern Indian shield: implications for crust-building processes

Abstract

Malani is the largest event of anorogenic felsic magmatism (covering ∼50, 000 km2) in India. This magmatic activity took place at ∼750 Ma post-dating the Erinpura granite (850 Ma) and ended prior to Marwar Supergroup (680 Ma) sedimentation. Malani eruptions occurred mostly on land, but locally sub-aqueous conditions are shown by the presence of conglomerate, grits and pillow lava. The Malani rocks do not show any type of regional deformation effects. The Malanis are characterised by bimodal volcanism with a dominant felsic component, followed by granitic plutonism and a terminal dyke phase. An angular unconformity between Malani lavas and basement is observed, with the presence of conglomerate at Sindreth, Diri, and Kankani. This indicates that the crust was quite stable and peneplained prior to the Malani activity. Similarly, the absence of any thrust zone, tectonic mélange and tectonised contact of the Malanis with the basement goes against a plate subduction setting for their genesis. After the closure of orogenic cycles in the Aravalli craton of the northwestern shield, this anorogenic intraplate magmatic activity took place in a cratonic rift setting under an extensional tectonic regime.