Proterozoic High-Temperature–Low-Pressure Metamorphism in the Mahakoshal Belt, Central Indian Tectonic Zone (India): Structure, Metamorphism, U-Th-Pb Monazite Geochronology, and Tectonic Implications

Abstract

To understand the protracted accretionary evolution along the Central Indian Tectonic Zone (CITZ), we investigated garnet-staurolite schists and associated lithologies from the central Mahakoshal Belt (MB). Mesoscale structures, porphyroblast growth, garnet zoning, and pseudosection modeling were coupled with U-Th-Pb monazite dating to reconstruct a clockwise pressure-temperature-time (P-T-t) path for the garnet- and staurolite-bearing schists. The prograde path is characterized by near isobaric heating conditions, which initiates at pressure-temperature (P-T) conditions of 4.5–5.0 kbar and 550°–560°C and attains peak metamorphism at 5.5–6.0 kbar and 610°–620°C. The peak metamorphism was contemporaneous with the emplacement of southern-margin granitoids at ~1.70 Ga, resulting in the perturbation of geotherms in the collision setting. The retrograde arm (MR) of the P-T path passes through isobaric cooling at ~5.0 kbar and ~500°C. This late Paleoproterozoic P-T-t path is overprinted by hitherto uncharacterized tectonism that coincides with the Sausar orogeny and provides evidence for the northward extension of 0.95–0.85 Ga orogenic activity within the CITZ. The 1.80–1.55 and 0.95–0.85 Ga tectonothermal events identified in this study support that crustal evolution in the CITZ involved a mosaic of domains that were accreted together in the Neoproterozoic time.