Initiation of the intra-cratonic Cuddapah basin: Evidence from Paleoproterozoic (1995 Ma) anorogenic porphyritic granite in Eastern Dharwar Craton basement

• Alkaline granite dated at 1995 ± 11 Ma within basement to intracratonic Cuddapah basin rocks.
• Anorogenic granite linked to initiation of the riftogenic basin by asthenospheric upwelling.
• Petrogenesis by partial melting of mid- to lower crustal rocks due to underplated basalt.
• Attenuation in lithopsheric thickness at ∼1.9–2.0 Ga due to thermal erosion during rifting.

Initiation of large intra-cratonic sedimentary basins has been constrained by dating the magmatic rocks intercalated in the sedimentary sequence; one such major basin in southeastern India is the Paleoproterozoic Cuddapah Basin. Near-basal Cuddapah sediments, deposited over the Eastern Dharwar Craton basement, are interlayered with mafic lavas and intruded mafic–ultramafic sills (1885 ± 3 Ma) being evidence for mantle melting. One of the expected major consequences of the asthenospheric upwelling on the lithosphere, apart from crustal doming, would have been partial melting of the cratonic tonalite–granodiorite crust and generation of granitic melts with anorogenic geochemical characteristics, the precise dating of which would constrain the timing of the basin initiation.From the southeastern part of the eroded basin, being the only exposed part into the basement below the sediment cover, we report presence of exactly such intrusive porphyritic granite. Petrological and geochemical characteristics of these anorogenic metaluminous granites strongly support partial melting (∼10–12%) of the cratonic tonalite–diorite crust most likely due to basaltic underplating. The crystallization time of this granite, sampled from SE of SriKalahasti, was determined on magmatic zircons and yielded a precise 207Pb/206Pb weighted mean age of 1995 ± 11 Ma. As the felsic crustal melting phase significantly predated the 1885 ± 3 Ma-aged mafic sills emplacement, early events include significant erosion of the previously uplifted basement followed by sedimentation (>1500 m) before mafic volcanism and sill emplacement. This history broadly suggests active rift basin evolution from a non-extensional setting progressing to passive extension.