A PETRO-CHRONOLOGICAL STUDY TO CHARACTERIZE PROTEROZOIC CRUSTAL REWORKING FROM THE ARAVALLI SUPERGROUP OF ROCKS, NW INDIA AND ITS IMPLICATIONS FOR PROTEROZOIC SUPERCONTINENT CYCLES

Abstract

The Aravalli Delhi Fold Belt (ADFB) in the north-western part of India preserve a rich record of Proterozoic orogenies that reflect global cycles of convergence and extension. A garnet-biotite migmatitic orthogneiss that occurs within the Agucha-Kekri Shear Zone at the northern margin of Bhilwara Belt, marking its contact with the North Delhi Fold Belt (NDFB) has two zircon populations yielding U-Pb ages of 1726 Ma and 938 Ma. The older age is correlated with the intrusion of the protolith of the migmatite, consistent with the partial melting event recorded in gneisses in the southern margin of Bhilwara Belt. The younger age population is interpreted as the age of partial melting and migmatisation. Petrographical observations and P-T pseudosection analyses indicate the breakdown of biotite and plagioclase, leading to the formation of garnet, potash feldspar, and melt under water-fluxed conditions. The peak conditions of ~ 9 kbar and ≥700ºC estimated for the partial melting are similar to those of coeval migmatisation recorded at the northwestern margin of the Bhilwara Belt but lower than those in the adjacent NDFB. This is interpreted to indicate the formation of a migmatitic front along the northwestern margin of the Bhilwara Belt while this was being under-thrusteded under the NDFB.