Implication of deformation fabrics of schist-migmatite-gneiss and granite in understanding regional tectonics: Eastern Dharwar Craton (EDC), India

Abstract

Structural fabrics of schist belt, gneiss, migmatites and younger granitoids are different. Various morphology of migmatites is recognized for the first time in the southern part of EDC along with gneiss. The younger granite plutons are examined from northern through central to southern part of EDC. The paleosome-dominated portions of migmatite were possibly formed from low degree partial melting of older rocks and identified as metatexites. Whereas, the neosome dominated parts were developed by complete melting and marked as diatexites. There is a link between diatexite and granite in the southern part, which is chracterized as catazone segment. The four sub-types of metatexites are observed (viz, patch, dilatant, net and stromatic). The diatexites are dominated by two major structures (viz, schollen or raft and schlieren). Gneisses show lit-per-lit as well as fold and leucocratic material flow features. The litho-structural variation from north to south connotes systematic changes from epizone through mesozone to catazone. The qualitative study of mineral content and textural aspects from rocks at different localities suggest preserved portions of different parts of a pressure–temperature path. However, exact quantification should be possible after thermo-barometry and pseudo section study. The present contribution focuses on documentation of classic representative outcrops and petrographic features of gneissic and migmatitic rocks of EDC. It is observed that the six (6) major ductile deformation stages of Kenoran orogeny implies ductile signature before granite plutonism. Subsequently post granite emplacement deformation phenomenon indicates a transition from ductile to brittle regime and entrance into Hudsonian orogeny.