Isotopic Signature of Pan-African Rejuvenation in the Kerala Khondalite Belt, Southern India: Implications for East Gondwana Reassembly

Sm-Nd isotope systematics on mineral separates from sillimanite-and cordierite-bearing metapelite (khondalite), and garnet-and biotite-bearing gneiss (leptynite) from the Kerala Khondalite Belt (KKB), southern India, yielded mineral isochron ages (wr-feld-bio-gar) of 537 ± 27 Ma (MSWD = 0.9) and 534 ± 26 Ma (MSWD = 1.23) respectively. Rb-Sr systematics in the same samples gave wr-feld-bio mineral isochron ages of 437 ± 9 Ma (MSWD = 0.67) and 467 ± 9 Ma (MSWD = 0.76), These results provide the first mineral isochron ages for the regional metasedimentaries in the KKB. The ε (Nd T) values at 550 Ma for Khondalite and leptynite are -22.7 and -21.8 respectively. These results demonstrate a complete rejuvenation of the crust during Pan-African times. Coeval alkaline plutons emplaced along fault-lineaments in this area suggest an extensional tectonic regime. Geochronologic correlations with the Lutzow-Holm Bay Complexes in East Antarctica, and the Highland and Southwestern Complex of Sri Lanka show that a similar Pan-African tectonothermal event manifested in all the East Gondwana crustal fragments.