First Constraints on the Pressure-Temperature-Time Evolution of the Vijayan Complex, Sri Lanka: Implications for Its Position in Gondwana

Sri Lanka occupies a pivotal geological position within East Gondwana, featuring four prominent high-grade Precambrian lithotectonic units: the Highland Complex (HC), the Wanni Complex, the Vijayan Complex (VC) and the Kadugannawa Complex. Despite reasonable geochemical and geochronological investigations into rocks in the VC, a comprehensive understanding of their petrological characteristics, particularly their pressure-temperature-time evolution, remains limited, impeding accurate terrane correlations. In this study, a detailed analysis of mineral assemblages, reaction textures, and U-Pb zircon ages in samples collected from the eastern margin of the HC to the eastern coast, in the VC were conducted. Results indicate that the VC preserved textural evidence for prograde dehydration reactions indicating upper amphibolite to granulite facies transition. The peak metamorphism is followed by a stage of near isobaric cooling stage. Conventional geothermobarometric analysis coupled with phase equilibria modeling of VC gneisses reveal peak metamorphic P-T conditions of 790 degrees C-830 degrees C and 7-8 kbar. Retrograde metamorphism has occurred until the temperature decreased to 740 degrees C. The U-Pb zircon dates at ca. 1010-960 Ma suggest protolith ages of the VC coinciding with Rodinia amalgamation and dispersal, aligning metamorphic thermal peaks at ca. 575-545 Ma with the Kuunga orogeny during Gondwana amalgamation. Our data signifies connections between the VC and both the Lurio foreland in Mozambique and the Innhovde Suite and Yamato-Belgica Complex in East Antarctica, however, the differences in metamorphic conditions and geochronological signatures necessitate further investigation into its tectonic history and paleogeographic evolution.