Duration of high-pressure metamorphism and cooling during the intraplate Petermann Orogeny

Abstract

The Ediacaran-Cambrian Petermann Orogeny, central Australia, is an exceptional example of intraplate orogenesis. It involved sub-eclogite facies metamorphism and extreme basin inversion during the exhumation of Musgrave Province basement from beneath the formerly contiguous Centralian Superbasin. Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb geochronology of zircon, titanite and rutile, along with Ti-in-zircon thermometry from meta-igneous samples, have been used to determine the timing and duration of high-pressure metamorphism and subsequent cooling associated with this orogenic event. Peak metamorphic temperatures of 720-760°C were attained at 544±7Ma (U-Pb zircon). Subsequent cooling to 600-660°C by ~521Ma occurred at a rate of ~2.6-7.0°CMyr-1, as recorded by the closure of Pb diffusion in titanite. Further cooling to 585-560°C by 498-472Ma occurred at a rate of 0.9-4.8°CMyr-1, as recorded by Pb closure in rutile. The duration of tectonism was long-lived (>40Myr) across the central and western parts of the orogenic system, and deformation occurred in a comparatively warm and weak portion of crust, characterised by regional thermal gradients of 17-26°Ckm-1. This proposed duration of tectonism is much longer than that permitted by a shear heating mechanism, which requires an exceptionally short duration of tectonism, and additionally, an overall cold lithosphere characterised by geothermal gradients of ~9°Ckm-1. © 2012 International Association for Gondwana Research.