Geochemistry of ~1Ga granite and associated mafic rocks from the South Delhi Fold Belt, NW India, and its tectonic significance

Abstract

The South Delhi Fold Belt (SDFB) within the northwestern Indian Shield is a Proterozoic NE-SW trending fold belt. The western boundary of the SDFB is defined by the Phulad Shear Zone, formed during a transpression regime around 820-810Ma. Granite rocks of ~1Ga have been documented from the western part of the fold belt and are linked with the formation of the Rodinia Supercontinent. These granites are closely associated with gabbroic rocks. The present study focuses on the geochemistry of these granites and the mafic rocks, as well as their field structure and petrography. The granites and the mafic rocks are confined to a narrow linear belt along the western part of the fold belt. Detailed field studies reveal that the foliations in the granites, mafic and mylonites within PSZ share a common stress regime and are broadly synchronous. Geochemically these granites are ferroan, calc-alkalic, metaluminous to weakly peraluminous and their classification in granite discrimination diagrams confirms A-type and within plate granite. The mafic rocks exhibit a compositional range from tholeiitic to calc-alkaline, with a trace element ratio resembling enriched mid-oceanic ridge basalt (E-MORB) type magma. The tectonic discrimination diagram suggests rift-related magmatism. Geochemical analysis of these bimodal magmatic compositions in the SDFB, encompassing both mafic rocks and A-type granites are typically associated with areas experiencing extensional tectonics, particularly rift-related magmatism. Integrating field structures, petrography and geochemistry of these granite and the mafic rocks suggests that the ~1Ga granite and the associated mafic rocks formed in an extensional regime and are not directly linked to the collisional assembly of the Rodinia Supercontinent.  Keywords: South Delhi Fold Belt, Granite, Phulad Shear Zone, Rodinia supercontinent, Extensional regime