LAUSR

Abstract Sri Lanka is composed of four major tectonic units known as the Wanni, Highland, Kadugannawa and Vijayan complexes, and preserves important records of the history of the Gondwana supercontinent. The Highland Complex records Neoproterozoic–Cambrian metamorphism associated with the assembly of the supercontinent Gondwana. We combine phase equilibria modelling with isotopic and trace element geochemistry to provide a time-integrated P–T evolution using representative garnet-bearing mafic granulites from the Highland Complex. New zircon U–Pb geochronology and garnet trace element data from one locality in the EHC, together with a dataset compiled from published results, indicate garnet and zircon existed in equilibrium during long-lived high temperature metamorphism for possibly longer than 100 Ma (ca. 660–520 Ma). Calculated pseudosections imply high-temperature to potentially ultrahigh temperature (>850 °C) conditions for peak metamorphism. The Highland Complex is characterised by a small decrease in pressure and temperature following peak conditions. This was followed by an accelerated rate of exhumation, leading to the partial replacement of garnet-bearing assemblages by lower pressure parageneses. Although the post-peak cooling/modest pressure decrease is a comparatively minor part of the P–T evolution, compiled zircon U–Pb data suggest it was the temporally dominant part of the thermobarometric history, comprising >100 Myr. The long-lived high post-peak temperatures require a stable in-situ heat source, which based on regional litho-tectonic correlations, was almost certainly elevated rates of crustal heat production. The minor cooling interval from P–T space is in fact is the temporally dominant part of the P–T evolution highlights that without time analysis, the P–T evolution does not convey the long-lived baric stability of the high-temperature history of the Highland Complex.