First evidence of ca. 1.77 Ga S-type magmatism, Aravalli orogen: Implications for the late Paleoproterozoic geodynamic evolution of NW India

Present models for the late Paleoproterozoic evolution of the Aravalli orogen (NW India) postulate the existence of a continental magmatic arc active between 1875 Ma and 1810 Ma, followed by a phase of post-collisional magmatism between 1730 Ma and 1700 Ma. However, the tectono-magmatic processes occurring between these two events remain cryptic. In this study, evidence for an intervening magmatic phase is revealed based on the investigation of granitoids exposed in the southern part of the Aravalli orogen. U-Pb zircon dating of these granitoids (granites to tonalites) yielded emplacement ages between 1770 Ma and 1760 Ma. Whole-rock geochemical data indicate a strongly peraluminous, S-type, high-K calc-alkaline character, with magnesian to ferroan signatures and a syn-collisional tectonic affinity. The REE patterns are predominantly highly fractionated, displaying depleted HREE profiles and moderate to weak negative Eu anomalies. The geochemical data further suggest derivation of the granitoids by partial melting of meta-greywackes at temperatures > 800 °C. Subchondritic eHf (t) values (−11.0 to −2.6) further indicate reworking of a heterogeneous crust. ... mehrThe results of this and previous studies collectively indicate that the Aravalli orogen evolved through three distinct late Paleoproterozoic tectono-magmatic phases:
(1) subduction-related magmatism at 1875 1810 Ma, (2) syn-collisional S-type plutonism at ca. 1770 Ma, and (3) post-collisional extension-related A-type magmatism at ca. 1720 Ma. Globally, Paleoproterozoic S-type granites were predominantly derived by anataxis of Archean crust. Additionally, the data suggest that the northern margin of proto-India collided with fragments of the Columbia supercontinent at ca. 1770 Ma, postdating Columbia’s maximum packing time (1900–1850 Ma).