Continental Growth Along Craton - Mobile Belt Interface: The Bastar Craton - Eastern Ghats Belt Scenario from Petrology, Geochemistry and Geochronology

Padmaja, J. (2025) Continental Growth Along Craton - Mobile Belt Interface: The Bastar Craton - Eastern Ghats Belt Scenario from Petrology, Geochemistry and Geochronology. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Padmaja J. (18RS101)) 18RS101.pdf - Submitted Version Restricted to Repository staff only Download (20MB)

Abstract

The Terrane Boundary Shear Zone (TBSZ), delineating the interface between the Archean Bastar Craton (BC) and the Proterozoic Eastern Ghats Province (EGP) in central India, encapsulates a complex tectonothermal history. The TBSZ serves as a key archive for understanding craton-mobile belt interactions, preserving signatures of ancient continental collisions and crustal growth. Petrological, geochemical, and geochronological analyses reveal that the TBSZ comprises lithologies from both BC and EGP, including mafic granulites, Grt-Opx bearing granitoids, Mg-Al granulites, khondalites, and Opx-bearing gneisses, each exhibiting distinct metamorphic and geochemical traits. Petrological and geochronological studies of mafic granulites reveal two distinct groups with contrasting origins and metamorphic histories. Group A mafic granulites and associated Grt-Opx granitoids, record Paleoarchean depleted mantle Nd model ages (3.3–3.1 Ga) and underwent high-pressure granulite facies metamorphism (~9.75 kbar, ~875°C) along clockwise P-T path, suggesting derivation from BC. In contrast, Group B mafic granulites, characterized by coronal garnet textures, yield younger Nd model ages (~2.2 Ga) and record lower peak metamorphic conditions (~9.25 kbar, ~825°C), indicating affinity with the EGP. The high-pressure granulite facies metamorphism of the cratonic rocks indicates further burial of BC during the final collision between BC and EGP, suggesting cratonic underthrusting as the collisional mechanism. Constraints on the tectonothermal evolution of the EGP-Bastar interface are provided by petrochronological studies of Mg-Al granulites and associated metapelites, which exhibit ultrahigh-temperature (UHT) metamorphism (>900°C, 8–8.5 kbar) along clockwise path and subsequent decompression and cooling to ~770°C, 5–6 kbar indicating exhumation along a retrograde path. Monazite geochronology reveals four key age populations (~1000 Ma, ~920 Ma, ~850 Ma, and ~500 Ma), with the ~920 Ma age corresponding to the UHT metamorphism during the EGP-Bastar collision and the ~500 Ma corresponding to widespread amphibolite-facies reworking, most probably due to far-field stress from the Kuunga orogeny. This Pan-African reactivation obliterated much of the earlier metamorphic signatures and highlights the prolonged tectonic history of the TBSZ. Geochemical, U-Pb zircon geochronological and petrogenetic analyses further substantiate the Bastar affinity of high-pressure granulite-facies rocks within the TBSZ. Comparative geochemical studies of Opx-bearing gneisses (zircon U-Pb age of ~2.7 Ga), Grt-Opx granitoids (zircon U-Pb age of ~2.5 Ga), and Group A mafic granulites of TBSZ with TTG gneisses, Hbl-Bt granites, and mafic dykes of BC confirm their cratonic derivation. Path-dependant open-system phase equilibria and trace element modelling suggest that the Neoarchean Hbl-Bt granites of BC formed via partial melting of TTG gneisses, with peritectic assemblage entrainment contributing to their compositional diversity. This forward modelling approach have broader implications for understanding Archean crustal differentiation and late-stage felsic magmatism in cratonic settings. Collectively, this study provides new evidence for the high-pressure metamorphism and underthrusting of the BC beneath the EGP, refining our understanding of the tectonic evolution of the India – Eastern Ghats Belt margin and its role in the assembly of Rodinia and Gondwana. Moreover, the reactivation of the TBSZ at ~500 Ma highlights the long-lived tectonic significance of suture zones in continental reworking.

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