Combined U-Pb/Hf isotopic studies and phase equilibrium modelling of HT-UHT metapelites from Kambam Ultrahigh temperature Belt, South India: Constraints on tectonothermal history of the terrain

Abstract The Madurai Block which forms the central crustal block in the Precambrian Southern Granulite Terrain, south India preserves crustal evolution history with record of multiple magmatic and metamorphic episodes ranging from early Archaean to late Neoproterozoic. Documenting the precise chronology and tectonothermal evolution of these events are of paramount importance to correlate with other crustal blocks in Southern Granulite Terrain as well as to link with other continental fragments of East Gondwana. The present study focuses on hitherto unreported location within a key section of Madurai Block along the transcrustal Suruli Shear Zone known as Kambam Ultrahigh temperature Belt. This belt is noticeable for the proliferous occurrence of HT-UHT metapelites with an overall clockwise P-T trajectory. Samples of Garnet-Spinel granulite, Cordierite-Spinel granulite and associated Granite gneiss were subjected to detailed petrographic, thermobarometric and geochronologic analysis. Combined petrography, mineral reaction, geothermobarometry and pseudosection modelling of the granulite samples reveals HT-UHT metamorphic conditions with clockwise P-T path demonstrating significant decompression and cooling. LA-ICPMS U Pb dating of zircon, monazite and rutile phases within these samples constrain the timing of metamorphism as well as cooling. U Pb zircon ages of ~2500 Ma from the granulites points to new evidences for Paleoproterozoic high-grade metamorphism in the area where monazite U Pb ages at ~593 and ~ 557 Ma throw light into the imprints on ~36 Ma prolonged Neoproterozoic thermal event attributed to Pan African collisional orogeny. LA-MC-ICPMS Hf isotopic record from zircon cores point to the role of significant juvenile crustal melting/anatexis during Paleoproterozoic. In addition, numerous whispered metamorphic episodes are also identified evincing the polydeformed evolutionary history of these rocks. The ca. ~432 Ma cooling age record from rutile estimates an average cooling rate of ~3 °C/Ma over a time period of ~125 Ma, classifying Madurai block as a classic slow cooled granulite terrain with long lived UHT orogenic history. The results also bring to the fore the importance of Kambam Ultrahigh temperature belt and Suruli Shear zone which can be projected as a major terrain boundary within Southern Granulite Terrain.