Stenian sediments (

Abstract

The Meso- to Neoproterozoic tectonic evolution of the Aravalli orogen in northwestern India is poorly understood because of limited combined isotopic-geochemical constraints on magmatic and sedimentary rocks. In this study, we present new zircon U-Pb-Hf isotope and whole-rock geochemical data for the Sendra Granitoid Suite and associated host quartzite of the Sendra Formation (Kumbhalgarh Group of the South Delhi Supergroup). Detrital zircon grains reveal a maximum age of deposition during the Stenian at 1065 Ma, and two major sources in the hinterland: (1) a Neoarchean to Paleoproterozoic basement (HfTDM = 2.7 – 2.0 Ga) affected by crustal reworking at 1.8–1.6 Ga, and (2) a juvenile terrain derived from the depleted mantle at ca. 1.6 Ga, and periodically reworked until 1.06 Ga in the Aravalli hinterland. Sediment deposition occurred in a passive margin setting. The post-collisional Sendra granitoids intruded during the Tonian between 1000 and 970 Ma from multiple sources. The highly superchondritic I-type granitoids (εHft = +10.8 to +12.1; HfTDM = 1.22 Ga) were formed from the fractional crystallisation of calc-alkaline mafic magma generated from partial melting of a mantle wedge. In contrast, the A-type granitoids originated either from melting of (1) relatively young, arc-related juvenile basaltic crust (εHf1.0 Ga = +10.3 to +15.3), (2) ancient felsic crust of the Aravalli continental margin (εHf1.0 Ga = -4.4 to −6.4; TDM = 2.08 Ga), and/or (3) by mixing of melts derived from different crust and mantle sources (εHf0.98 Ga = +0.8 to +3.1). All together, the new results provide evidence that NW India underwent transformation from a passive margin to an accretionary orogenic terrane between 1065 and 1000 Ma, followed by post-collisional magmatism and extension until 970 Ma.