In situ Rb–Sr insights in the cooling history of the Petermann Orogeny, Central Australia

Abstract

The Ediacaran–Cambrian Petermann Orogen is a dextral transpressional orogen exposed in central Australia, which facilitated the exhumation of a high-pressure core and the deformation of the Neoproterozoic–Palaeozoic Amadeus Basin. Several studies have investigated the metamorphic and deformational evolution of the Petermann Orogen; however, the spatiotemporal variation of the deformation and cooling history is yet to be fully understood. In situ muscovite and biotite Rb–Sr geochronology, in combination with Ti-in-quartz thermometry is applied to map the spatiotemporal deformation and cooling patterns of the northern part of the Petermann Orogen. Interpreted muscovite Rb–Sr growth ages obtained from samples in the Petermann Nappe Complex (PNC), range between c. 598 Ma and 565 Ma, which correlate with the timing of deformation during the 600–520 Ma Petermann Orogeny. Interpreted muscovite and biotite cooling ages are younger in the east of the PNC (c. 556–541 Ma) and broadly correlate with the regional pattern of crustal heat production, suggesting that the geothermal gradient had a significant control on the timing and duration of cooling. Biotite Rb–Sr cooling ages between c. 555 Ma and 497 Ma for the orogenic core show no correlation with high heat production areas, however, differences in exhumed crustal levels across the Petermann Orogen are observed: high-P granulite facies rocks in the orogenic core vs middle-upper crustal rocks in the PNC, indicating that at least part of the spatiotemporal variation of cooling ages can be attributed to differential exhumation during the Petermann Orogeny. Hence, crustal heat production and differential exhumation were likely the main controlling factors on the duration and variation of cooling rates in the Petermann Orogen.