Petrogenesis of the protolith for the Tirodi gneiss by A-type granite magmatism: The geochemical evidence

摘要

In the Central Indian region, the Tirode gneisses occur intimately associated with the Sausar Group metasediments. The protoliths for these gneisses might have originated by rift-related intracontinental felsic A-type (anorogenic) magmatism. The geochemical signatures in them like high Zr + Nb + Y + Ce, Ga/Al, Zr/Ni, Rb/Sr and Y/Sc, are quite similar to the A-type granite characteristics and point to the derivation of the protoliths by the melting of lower crustal dehydrated assemblages at high temperatures attained as a result of possible ponding of basaltic magma/magma underplating. The occurrence of mafic rocks related to subduction zone magmatism and back-arc environment in the vicinity of these gneisses in the Central Indian region attest to such an origin for the protoliths of the Tirodi gneisses.