Grenvillian-age deep crustal thrusting, terrane juxtaposition and subduction polarity reversal from the Eastern Ghats Belt, India and its tectonic implications

Abstract

The Proterozoic Eastern Ghats Belt (EGB) represents an arcuate orogenic belt along the east coast of India. Its western boundary is marked by a thrust-cum subduction zone system along which granulite facies rocks of the EGB were thrust over the cratonic rocks while its northern margin with the craton is marked by several crustal-scale shear zones of unresolved kinematic status. The present study generates new structural, kinematic and age data from the Mahanadi Shear Zone (MSZ) of the EGB northern margin that unveils a hitherto undisclosed chronicle of deep crustal thrusting and terrane amalgamation. Correlation of our earlier reported (M₁) high-pressure metamorphism (ca. 980–960 Ma) and clockwise pressure-temperature path in the MSZ with the presently reported deep crustal thrusting (600–800 °C) at ca. 950–900 Ma led us to infer that the MSZ represents a Grenvillian-age oblique collisional zone signifying northerly underthrusting of the Phulbani domain below the Angul-Tikarpada domains at ca. 980–900 Ma. The proposed SW directed thrusting along MSZ is at variance with the earlier reported coeval NW directed thrusting along the EGB western margin. This new report thus warrants subduction polarity reversal along the two margins of the arcuate EGB orogenic front at the same time frame. The difference in displacement velocity vectors along the two margins was resolved via combined movements on the orogen sub-parallel dextral-slip Koraput Shear Zone and the orogen transverse sinistral-slip Nagavalli-Vamshadhara Shear Zone system. The proposed tectonic model visualises the arcuate shape of the EGB orogenic front as a primary structure inherited from the original craton margin configuration.