Palaeoproterozoic (∼1.9 Ga) extension and breakup along the eastern margin of the Eastern Dharwar Craton, SE India: New Sm–Nd isochron age constraints from anorogenic mafic magmatism in the Neoarchean Nellore greenstone belt

The Neoarchean Nellore greenstone belt, located along the eastern margin of the Eastern Dharwar Craton, was the site for younger igneous activity. The timing of this magmatism and the host metabasalt, critical for constraining extensional events along the deformed southeast margin of the Eastern Dharwar Craton, was conducted by the Sm–Nd method.Samples from the large differentiated gabbroic Kandra igneous complex, a subset Kandra group a, define an isochron age of 1926 ± 110 Ma, Ndi = 0.51006 ± 12, MSWD = 0.98 (n = 5), εNd = −1.7, and the Kandra group b subset yielded a Model 3 isochron age of 1882 ± 120 Ma, Ndi = 0.50994 ± 14, MSWD = 1.8 (n = 4), εNd = −5.1. Whereas the three samples from north Pamuru gabbro-anorthosite yielded an isochron age of 1882 ± 160, Ndi = 0.51012 ± 18, MSWD = 0.064, εNd = −1.7, the Kandra group a and north Pamuru samples regressed together yielded a preferred isochron age of 1911 ± 88 Ma, Ndi = 0.51008 ± 10, MSWD = 0.62 (n = 8), εNd = −1.6, for the emplacement of gabbros. In contrast host greenstone belt metabasalt from Chundi yielded a Sm–Nd isochron age of 2693 ± 94 Ma, Ndi = 0.50920 ± 8, MSWD = 1.4 (n = 4), εNd = +1.2, whereas regressing the Chaganam and Chundi samples yielded an isochron age of 2654 ± 100 Ma, Ndi = 0.50923 ± 9, MSWD = 1.5 (n = 11), εNd = +0.7. Basal metapelite, underlying the metabasalt yields old Nd model ages between 2888 and 3054 Ma.The results of this study show that the ∼2.7 Ga Nellore greenstone belt was intruded by enriched MORB-type gabbros at ∼1911 Ma. It is proposed that this Palaeoproterozoic magmatism formed in response to a major extensional event along the Eastern Dharwar Craton margin that likely initiated breakup from the southeastern margin of the North China Craton. This exposed craton margin later evolved as the site for collisional events during the Late Palaeoproterozoic to Early Mesoproterozoic.