Paleomagnetism and detrital zircon geochronology of the Upper Vindhyan sequence, Son Valley and Rajasthan, India: A ca. 1000 ma closure age for the Purana Basins?

The utility of paleomagnetic data gleaned from the Bhander and Rewa Groups of the Purana-aged Vindhyanchal Basin has been hampered by the poor age control associated with these units. Ages assigned to the Upper Vindhyan sequence range from Cambrian to the Mesoproterozoic and are derived from a variety of sources, including Sr-87/(86) Sr and delta C-13 correlations with the global curves and Ediacara-like fossil finds in the Lakheri-Bhander limestone. New analyses of the available paleomagnetic data collected from this study and previous work on the 1073 Ma Majhgawan kimberlite, as well as detrital zircon geochronology of the Upper Bhander sandstone and sandstones from the Marwar SuperGroup suggest that the Upper Vindhyan sequence may be up to 500 Ma older than is commonly thought. Paleomagnetic analysis generated from the Bhander and Rewa Groups yields a paleomagnetic pole at 44 degrees N, 214.0 degrees E (A95 = 4.3 degrees). This paleomagnetic pole closely resembles the VGP from the well-dated Majhgawan intrusion (36.8 degrees N, 212.5 degrees E, alpha(95) = 15.3 degrees). Detrital zircon analysis of the Upper Bhander sandstone identifies a youngest age population at similar to 1020 Ma. A comparison between the previously correlated Upper Bhander sandstone and the Marwar sandstone detrital suites shows virtually no similarities in the youngest detrital suite sampled. The main 840-920 Ma peak is absent in the Upper Bhander. This supports our assertion that the Upper Bhander is older than the 750-771 Ma Malani sequence, and is likely close to the age of the 1073 Ma Majhgawan kimberlite on the basis of the paleomagnetic similarities. By setting the age of the Upper Vindhyan at 1000-1070 Ma, several intriguing possibilities arise. The Bhander-Rewa paleomagnetic pole allows for a reconstruction of India at 1000-1070 Ma that overlaps with the 1073 +/- 13.7 Majhgawan kimberlite VCP. Comparisons between the composite UpperVindhyan pole (43.9 degrees N, 210.2 degrees E, alpha(95) = 12.2 degrees) and the Australian 1071 +/- 8 Ma Bangamall Basin sills and the similar to 1070 Ma Alcurra dykes suggest that Australia and India were not adjacent at this time period. (c) 2008 Elsevier B.V. All rights reserved.