Crustal root of the Eastern Dharwar Craton: Zircon U–Pb age and Lu–Hf isotopic evolution of the East Salem Block, southeast India

Abstract

The Salem Block represents the northern part of the Southern Granulite Terrane in SE India, adjacent to the southern Dharwar Craton. New zircon U–Pb and Lu–Hf results on charnockites, granitoids and migmatites from the eastern Salem Block indicate that it mainly consists of bimodal juvenile Neoarchaean – early Palaeoproterozoic (∼2.75–2.65Ga and ∼2.55–2.48Ga) crust that underwent peak metamorphism at ∼2.53Ga. These U–Pb ages and Lu–Hf isotopic signatures characterize the Salem Block as part of the lower crust of the Eastern Dharwar Craton. The oldest (∼2.75–2.65Ga) granulites can be traced along important shear zones (Salem-Attur and Gangavalli Shear Zones), which may thus expose deeper levels of Eastern Dharwar lower crust, in a way similar to that proposed for the Nilgiri granulites. An additional (minor) contribution of recycled Western Dharwar Craton in the Salem Block is suggested by the presence of limited ∼3.65–3.35Ga recycled crust and ∼2.9–2.6Ga detritus.Younger intrusions within the Salem Block include the Cryogenian (∼820–800Ma) Yelagiri alkaline complex and the Ediacaran (559.1±3.5Ma) Sankari-Tiruchengode granitoid complex. These were sourced from recycled Neoarchaean protoliths of the Salem Block. Cryogenian-Tonian age magmatism is widespread within the Southern Granulite Terrane and is possibly related to initial subduction of the Mozambique Ocean. The Ediacaran A-type granitoids are thought to have formed during the Malagasy Orogeny that is related with the final consumption of the Mozambique Ocean and the collision of India with Azania-East Africa.