Evolution of the Chilka Lake granulite complex, northern Eastern Ghats Belt, India: First evidence of ~ 780 Ma decompression of the deep crust and its implication on the India–Antarctica correlation

Abstract

High-grade para- and orthogneissic rocks near the Chilka Lake granulite complex, northern part of the Eastern Ghats Belt show complex structural and petrological history. Based on field and petrographic characters, five (M1–M5) metamorphic events could be identified. The earliest metamorphic event (M1) produced amphibolite grade mineral assemblage which produced the peak granulite (M2) assemblages at 900–950°C, 8.5–9.0kbar. The third metamorphic event caused decompression of the deeper crust up to 700–800°C, 6.0–6.5kbar. This was followed by cooling (M4) and subsequent thermal overprinting (M5). Fluid-composition during M3 was dominated by high-density CO2 and changed to low-density mixed CO2–H2O during the M3. Zircon U–Pb SHRIMP data suggest 781±9Ma age for M3 event. Texturally constrained monazite U–Th–Pb EPMA data, on the other hand, yield a group age of 988±23Ma from grain interior, which can signifies the age of M2 event. Few spots with younger dates in the range of 550–500Ma are also noted. This interpretation changes the existing tectonothermal history of northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories. While the central Domain 2 evolved through early anticlockwise P–T path culminating in ultrahigh temperature, the northern Domain 3 evolved through a clockwise P–T path. It appears that the Domain 3 was contiguous to East Antarctica and became part of the Eastern Ghats Belt during the assembly of Gondwana. The ca. 780Ma decompression event in the northern Eastern Ghats Belt opens up new possibilities for interpreting the breakup of Rodinia.