A GEOLOGICAL TRANSECT ACROSS THE SON VALLEY SECTOR OF THE VINDHYAN BASIN, INDIA: U-PB AND HF ISOTOPIC CONSTRAINTS ON BASIN EVOLUTION

The Vindhyan Supergroup, located in central peninsular India, is one of the largest and thickest Precambrian sedimentary successions of the world, outcropping over an area of over 104,000 km². The Vindhyan is the largest of the so-called “Purana” basins in India. Split into the upper Vindhyan and the lower Vindhyan (or Semri Series), the age of the Upper Vindhyan sedimentary sequence is the subject of considerable controversy. This study seeks to determine if the Vindhyan Basin is much older (possibly Mesoproterozoic) in age rather than an assumed Late Neoproterozoic age. Malone et al. (2008) and Gregory et al. (2006) argued for an early Neoproterozoic to late Mesoproterozoic closure (~1050 Ma) of Upper Vindhyan sedimentation whereas Azmi et al. (2009) argue for an Ediacaran-Cambrian age. Some recent work supports the older age of basinal closure for the Upper Vindhyan and a much younger age for the previously correlated sediments in the Marwar Basin. Our work has expanded on the initial studies by Malone et al. (2008) to look at a broader cross-section of Upper Vindhyan (and Marwar) rocks to test the hypothesis that the two basins are not temporally correlated. Our more detailed analysis shows detrital zircon populations in the Marwar Supergroup that are as young as Late Neoproterozoic whereas all detrital zircon populations so far analyzed from the Rajasthan and Son Valley sectors of the Upper Vindhyan show no populations younger than 1000 Ma. In addition, preliminary paleomagnetic data from the Marwar Supergroup (see Davis et al., this meeting) shows that the directions are distinct between the Marwar and Upper Vindhyan sediments. We also examine Hf-isotopic signatures of the two basins to help us distinguish source regions for these important basinal sediments in India.