Crustal thickening in the early Mesoarchaean? Insight from ancient high-pressure metamorphism in SW India

This item is only available electronically.Eoarchaean–Mesoarchaean crust typically registers uniformly high T/P metamorphism, thought to reflect a stagnant lid tectonic regime in the primitive Earth. However, we report evidence for high-pressure granulite metamorphism from the early Mesoarchaean in south-west India. Garnet-kyanite-rutile-bearing assemblages in felsic granulites record minimum peak metamorphic conditions of 13.1 kbar and 940oC. LA–ICP–MS analysis of zircon and monazite U–Pb isotopes and trace elements indicate high-pressure granulite facies metamorphism took place at ca. 3.15 Ga. Apparent thermal gradients of 72°C/kbar correspond to burial beneath ~45km of continental crust. The preservation of crust under these conditions is not expected this early in the Earth’s history under the conditions proposed for the stagnant lid regime. This implies that the transition toward a more modern style tectonic regime may have taken place earlier than what is currently recognised.Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 201