Abstract
Abstract. Geophysical evidence for lower continental crustal earthquakes in almost all collisional orogens is in conflict with the widely accepted notion that rocks, under high grade conditions, should flow rather than fracture. Pseudotachylytes are remnants of frictional melts generated during seismic slip and can therefore be used as an indicator of former seismogenic fault zones. The Fregon Subdomain in Central Australia was deformed under dry sub-eclogitic conditions of 600–700 °C and 1.0–1.2 GPa during the intracontinental Petermann Orogeny (ca. 550 Ma) and contains abundant pseudotachylyte. These pseudotachylytes are commonly foliated, recrystallized, and cross-cut by other pseudotachylytes, reflecting repeated generation during ongoing ductile deformation. This interplay is interpreted as evidence for repeated seismic brittle failure and post- to inter-seismic creep under dry lower-crustal conditions. Thermodynamic modelling of the pseudotachylyte bulk composition gives the same PT conditions of shearing as in surrounding mylonites. We conclude that pseudotachylytes in the Fregon Subdomain are a direct analogue of current seismicity in dry lower continental crust.
Highlights
Predicting the rheology of the Earth’s crust is crucial for all geodynamic models over the whole range of length and timescales from plate tectonics to seismic hazard estimation
The Fregon Subdomain in Central Australia was deformed under dry sub-eclogitic conditions of 600–700 ◦C and 1.0–1.2 GPa during the intracontinental Petermann Orogeny and contains abundant pseudotachylyte
We focus on the Fregon Subdomain in the eastern Musgrave Block, which represents the hanging wall of the Woodroffe Thrust (Camacho et al, 1997; Camacho and McDougall, 2000; Wex et al, 2017)
Summary
Predicting the rheology of the Earth’s crust is crucial for all geodynamic models over the whole range of length and timescales from plate tectonics to seismic hazard estimation. An alternative “crème brûlée” model considers a wet olivine rheology for the upper mantle, and limits all significant strength and seismicity to the upper crust (Burov and Watts, 2006; Jackson, 2002a). In contradiction to such models that limit brittle deformation exclusively to the upper crust, seismicity is recorded in the lower crust in almost all collisional settings, e.g. the Alps (Deichmann and Rybach, 1989; Singer et al, 2014), the Himalayas (Jackson, 2002b; Jackson et al, 2004), the Tien Shan (Xu et al, 2005), the Central Indian Shield (Rao et al, 2002), and the North Island of New Zealand (Reyners et al, 2007)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
