The timing, duration and conditions of uht metamorphism in remnants of the former eastern gondwana

Abstract

Early Palaeozoic ultrahigh-Temperature (UHT) metamorphism in eastern Gondwana was an event that started with Gondwana amalgamation at c. 580Ma and lasted at least 50 Myr. Sapphirine quartz, Mg Al granulites preserve a record of the timing and duration of the event along the metamorphic belt. U Th Pb dating of zircon and monazite shows that metamorphism peaked almost simultaneously in Antarctica (554.064.7 Ma), Sri Lanka (555.564.6 Ma), southern India (548.168.1 Ma) and Madagascar (550.666.0 Ma), and ended in all locations at the same time, 530 520 Ma. Rare earth element (REE) compositions of the metamorphic zircon zones can be matched to the REE zoning in the associated garnet. Phase-diagram modelling indicates that the peak UHT P T conditions in Antarctica, Sri Lanka, and India were very similar, 1020 1040 _C at 0.8 GPa. Peak conditions in Madagascar were at higher T and similar P: 1090 _C and 0.8 GPa. The East African Orogeny before 600Ma preconditioned the crust of the eastern Gondwanan terranes by thickening it and harbouring heat-producing elements, heating the crust over c. 60 Myr; such that UHT conditions were reached when East and West Gondwana collided.