Proterozoic rifting in the Pranhita-Godavari Valley: Implication on India-Antarctica linkage

摘要

The Pranhita-Godavari (PG) Valley, a major lineament within the South Indian cratonic province, that preserves sediment dominated deposits spanning from Mesoproterozoic to Mesozoic, appears to be a key element in supercontinent reconstruction. The sedimentary basins of the Valley include a thick succession of Early Mesoproterozoic to Late Neoproterozoic rocks, the Godavari Supergroup, which is unconformably overlain by the Late Palaeozoic-Mesozoic Gondwana sequence. The Godavari Supergroup is internally punctuated by several regional and interregional unconformities into a number of unconformity-bound sequences having group level and subgroup level status. The lithostratigraphic attributes of the succession indicate multiple events of fault controlled sedimentation marked by transgression and regression, as well as uneven rates of uplift and subsidence of the basin floor in an extensional tectonic regime. The amplitude of translation of the unconformity surfaces across the base level attests to collective role of tectonic movement and sea level changes in building the stratigraphic framework of the Valley. The stratigraphic framework and depositional systems, such as fan and fan-deltas, together with local outburst of felsic volcanism further indicate repeated rifting of the craton.Geochronologic data indicate that the rift basin started to open in Early Mesoproterozoic, concomitantly with the breakup of the Mesoproterozoic supercontinent during which the India and East Gondwana fragments were separated. The spatial variation in the declivity of the unconformity surfaces, and the trend of thickness variation of the unconformity-bound sequences point that the basin deepened and opened towards southeast to join an ocean that developed between the South Indian craton and East Antarctica. The contractional deformation structures preserved in several lithounits were produced under NE-SW directed regional compression during Late Neoproterozoic basin inversion.