Geochemistry and U–Pb Zircon Geochronology of the Gabbroic Rocks in the South Delhi Fold Belt: Insights Into Rodinia-Age Tectonics in Northwest India

Abstract

The South Delhi Fold Belt (SDFB) in NW India is juxtaposed against the Marwar Craton along its western margin through the Phulad Shear Zone (PSZ). Within the SDFB, a substantial occurrence of gabbroic rocks extends in an NE–SW orientation, mirroring the alignment of PSZ. These gabbroic rocks are closely associated with ~1 Ga granites within the SDFB that are often correlated with the Rodinia supercontinent formation. However, no age of the gabbroic rocks has been reported so far. The origin of these gabbroic rocks, often considered part of the Phulad Ophiolite, has been a subject of intense debate. To gain insights into the source and tectonic setting of the gabbroic rocks, we conducted detailed fieldwork, petrography, geochemical and geochronological analyses. The granites and gabbroic rocks are regionally deformed with a regional orientation parallel to the SDFB regional trend. Detailed field studies reveal that the gabbro and the PSZ underwent synchronous deformation. The geochemical study of gabbroic rocks documents tholeiite affinity, suggesting that their source magma likely formed from a low-degree partial melting of the spinel peridotite zone of the lithospheric mantle at a shallow depth. This magma was subsequently modified by crustal contamination during magma ascent. U–Pb zircon dates of the gabbroic rocks confirm a magmatic Concordia age of 978.2 ± 8.7 Ma. Integrating field relations, petrography, geochemistry and geochronological data, we suggest that the gabbro and granite were generated in an extensional tectonic setting during ~1 Ga in NW India. This finding challenges the Rodinia-age collision model previously suggested for NW India.