Age and sedimentary provenance of the Southern Granulites, South India: U-Th-Pb SHRIMP secondary ion mass spectrometry

Southern India lies at a junction in the Gondwana-forming orogenic belts, between the East African Orogen and the Kuunga Orogen. It contains voluminous high-grade metasedimentary gneisses that make up an important component of the record of collision and amalgamation of Gondwana. Here we present U-Pb Secondary Ion Mass Spectrometry (SIMS) isotopic data from detrital zircon cores from throughout southern India that demonstrate dominant Neoarchaean to Palaeoproterozoic age components that are incompatible with the known ages of potential southern and central Indian source regions. The original sediments to the Trivandrum Block gneisses were deposited between ∼1900 and ∼515 Ma, whereas a sample from the Achancovil Unit, and possible also a sample from the Madurai Block, were deposited in Neoproterozoic times. We speculate that these rocks broadly correlate with southern and western Malagasy metasedimentary rocks (including the Itremo and Molo Groups) and formed an extensive basin (or basins) that lay on the west side (present orientation) of the Neoproterozoic continent Azania. In addition, metamorphic zircon from four samples yielded an age of 513 ± 6 Ma that is interpreted as dating high-grade metamorphism throughout much of the Southern Granulite Terrane.