Huiru Xu, Joseph G Meert , Manoj K Pandit

We report a summary of geochronological data derived from detrital zircons in the Marwar Supergroup, Rajasthan, India. Although the age of deposition for the Marwar sequence was inferred to be post-Cryogenian, there is a lack of any direct age data. Two recent papers reached different conclusions based on geochronological data. A Rb-Sr age on a felsic flow within the Sonia sandstone yielded a whole-rock isochron age of 700 Ma. That age seemed consistent with geochronological data from the underlying Malani rhyolites and hinted that initiation of Marwar basin subsidence occurred concurrently with the waning phases of Malani volcanism. If correct, then the Marwar Supergroup sedimentation last from ~700-Cambrian. This conclusion was challenged by the discovery of detrital zircons within the Sonia sandstone with ages ~622 Ma which is consistent with earlier conjectures of a post-Cryogenian age. In this contribution, we detail our attempts to date the felsic volcanics at Chhoti Khatu. Although we did not obtain a crystallization age, the youngest zircon retrieved is 651 Ma. A total of 68 zircon analyses yielded a similar spectra compared to previous results and we conclude that the Marwar basin initiation was post-Cryogenian and the hiatus between Malani volcanism and sedimentation is on the order of 125 Ma.