IMPLICATIONS FOR THE TECTONIC SETTING OF LONG-LIVED GRENVILLIAN-AGED TECTONISM IN THE MUSGRAVE PROVINCE, CENTRAL AUSTRALIA, BASED ON CONSTRAINTS FROM LARGE-SCALE ISOTOPIC HOMOGENEITY AND THERMOBAROMETRY

The east-west trending Musgrave Province is a major Grenvillian-aged belt in central Australia. It covers an area of some 120000 km² (700 km E-W) and is the least studied, and thus least understood, Proterozoic province within central Australia. The Musgrave Province occurs at a ‘triple junction’ between three older and thicker cratonic blocks. The tectonic setting of Grenvillian tectonism in Australia is not well constrained. Understanding the tectonic (and temporal) evolution of the Musgrave Province is of importance for reconstruction models of Australia and for further understanding the global Grenvillian system.

Smithies et al. (2011, J Petrology, 52, 931-958) documents a long-lived (~100 M.y.), high temperature (≥1000 °C) and high geothermal gradient system (>>40 °C/km) for the west Musgrave Province over the period ca. 1220-1120 Ma. The tectonic setting was proposed as intracratonic and extensional based on the geochemistry of voluminous and comparatively juvenile 1220-1120 Ma ‘charnockite series’ felsic magmatic rocks coupled with thermobarometry. Extending to the less-studied far east of the Province, Grenvillian-aged felsic magmatic rocks occupy the same isotopic envelope (εNd, εHf) as in the west, indicating a homogeneous source region that extends laterally over at least 700 km.

Old fabrics in the Musgrave Province are dominated by a roughly north to northeasterly trend. Although the age of fabric is not everywhere known with certainty, it is possible that the Province was a roughly N-S trending belt during Grenvillian times. If true, this has important implications for large-scale Proterozoic reconstructions involving the Musgrave Province which typically depict the system as E-W trending. In addition, there are significant implications for the nature of the of the isotopically homogeneous source region given an across-strike extent of ≥700 km.

Based on the existing geochemical, isotopic and thermobarometric data for the Musgrave Province, we propose that the Province may preserve a cryptic record of an ancient, N-S trending Grenvillian belt involving a hot, thin, continental back-arc-type environment. This hypothesis is somewhat analogous to the modern-day Basin and Range Province.