Was there a pre-Nunan India ،V Antarctica connection? Evidence from SHRIMP U-Pb Zircon Data
|Location||International Geological Congress,oslo 2008|
|Author||Reddy, Steven۱; Clark, Chris۱; Mazumder, Rajat۲|
|Holding Date||08 October 2008|
The Singhbhum Crustal Province (SCP), eastern India, is among one of the few Precambrian terrains in the world that records sedimentation and volcanism in varying tectonic regimes from the Mesoarchaean to Neoproterozoic eras. However a lack of precise age data from the SCP, particularly U-Pb, is a major impediment for regional and intercontinental correlation. 45 new SHRIMP II U-Pb zircon analyses from the Singhbhum Granite Phase III, the youngest basement on which younger supracrustal successions are deposited, are variably discordant and define a single trend with upper and lower age intercepts of 893 ،س 43 Ma and 3302 ،س 13 Ma, respectively. A subset of 11 analyses of <5% discordant analyses give a 207Pb/206Pb age of 3288 ،س 8 (2ƒم) Ma. The youngest Proterozoic alkaline rock bodies in the SCP succession (Sushina nepheline syenite) yields an age of 922.4 ،س 10.4 Ma (2ƒم) that is within error of the lower intercept from the Singhbhum Granite Phase III isotopic distribution. Our internally consistent data record part of both the original basement history during the Mesoarchaean as well as that of the youngest Neoproterozoic alkaline magmatism in the SCP. These two ages pin the stratigraphic evolution of the SCP. Additional age constraints from volcanic deposits and detrital zircon populations from the SCP provide further constraints temporal constraints that provide a framework for palaeogeographic correlation.
In a reconstructed Gondwana, the Singhbhum Carton is inferred to lie adjacent to the Vestfold Hills in East Antarctica and along the northern margin of a wide region of Neoproterozic orogenesis that marks one of the major Gondwana forming collision zones. The correlation is based primarily on the similarities between the Eastern Ghats in India and the Ruker Terrain in East Antarctica and the assumption that the relationships of the terranes within India and Antarctica today are unchanged. However prior to the amalgamation of Gondwana the relative position of the Singhbhum Craton relative to the East Antactic terranes is poorly constrained. Recent detrital zircon studies of the Vestfold Hills indicate that during deposition of the Chelnok Supracrustals, zircons were being sourced from regions with ages of 3.7, 3.2 and 2.8 Ga. Two of these ages (3.2 and 2.8 Ga) are ages of volcanism and granite emplacement suggesting that the Vestfold Hills may have sourced material from the Singhbhum craton and was therefore proximal to India for a long period of time prior to the amalgamation of Gondwana. Whether the Singhbhum Craton was part of proto-Antarctica or vice-versa needs further detailed geochronological investigation.