Geochemistry and geochronology of A-type basement granitoids in the north-central Aravalli Craton:Implications on Paleoproterozoic geodynamics of NW Indian Block

The basement granite gneisses from the north-central Aravalli Craton in NW India were investigated for geochemistry and geochronology.In a peneplain terrain,the granite gneiss outcrops are scanty and samples were collected mainly from two small hills and several ground-level exposures in the Sakhun–Ladera region.Wellfoliated granite gneiss is the dominant lithology that also hosts dark,lenticular enclaves,and is in turn,intruded by mafic dykes.The granite gneiss has silica content ranging from 61.37 wt.% to 68.27 wt.% that marks a slight overlap with the enclaves(54.32 wt.% to 62.17 wt.%).Both groups have a high KO/NaO(～2 or higher) ratio.Geochemically,the granite gneiss classify as granite–granodiorite,and enclaves as granodiorite-diorite.The In-situ LA-ICP-MS zircon U–Pb geochronology of granite gneiss has yielded a statistically valid 1721 ± 9 Ma age that we interpret as the emplacement age for the granitic protolith.Geochemical characteristics of granite gneiss underline fractional crystallization of an I-type melt as the main process,and continuity of trends in enclaves underlines their mutual genetic link.The genetic association is further verified by a consistency in the trace element characteristics and REE patterns.The Nd-isotope signatures define a single grouping for both granite gneiss and enclaves,with εNd(t) values ranging from-6.38 to-6.61,further substantiating a common source.The geochemical tectonic discrimination schemes consistently point toward an extensional setting and A-type characteristics for granite gneiss and enclaves.These are analogous to the coeval(1.72–1.75 Ga),A-type granitoids from the Khetri and Alwar basin in the North Delhi Fold Belt,implying a much larger areal extent for the Paleoproterozoic anorogenic magmatism in the northern segment of the Aravalli Craton.The Paleoproterozoic age for the presumed ‘Archean’ basement in this region offers tacit evidence that the BGC–II is a stratigraphically younger terrane as compared to the Archean age,BGC–I.