The anatomy of a deep intracontinental orogen

Abstract

The crustal architecture of central Australia has been profoundly affected by protracted periods of intracontinental deformation. In the northwestern Musgrave Block, the Ediacaran–Cambrian (600–530 Ma) Petermann Orogeny resulted in pervasive mylonitic reworking of Mesoproterozoic granites and granitic gneisses at deep crustal levels (P = 10–14 kbar and T = 700–800°C). SHRIMP and LA-ICPMS dating of zircon indicate that peak metamorphic conditions were attained at circa 570 Ma, followed by slow cooling to ∼600–660°C at circa 540 Ma driven by exhumation along the Woodroffe Thrust. Strong links between regional kinematic partitioning, pervasive high shear strains and partial melting in the orogenic core, and an anomalous lobate thrust trace geometry suggest that north vergent shortening was accompanied by the gravitational collapse and lateral escape of a broad thrust sheet. Like the present-day Himalayan-Tibetan system, the macroscopic structural, metamorphic, and kinematic architecture of the Petermann Orogen appears to be dominantly shaped by large-scale ductile flow of lower crustal material. We thus argue that the anatomy of this deep intracontinental orogen is comparable to collisional orogens, suggesting that the deformational response of continental crust is remarkably similar in different tectonic settings.