Constrained potential field modeling of the crustal architecture of the Musgrave Province in central Australia: Evidence for lithospheric strengthening due to crust‐mantle boundary uplift

We image the crustal architecture of the Musgrave Province with petrophysically constrained forward models of new potential field data. These models image divergent shallow‐dipping crustal scale thrusts that, at depth, link with an axial zone defined by steeper, lithospheric scale transpressional shear zones. They also show that to permit a near‐surface density distribution that is consistent with petrophysical and geological observations, approximately 15–20 km of crust‐mantle boundary uplift is necessary beneath the axial zone. The long‐term preservation of this crust‐mantle boundary offset implies a change from relatively weak lithosphere to relatively strong lithosphere during the intraplate Petermann Orogeny. To explain this, we propose a model in which uplift of the axial zone of the orogen leads to local lithospheric strengthening as a result of the uplift of mantle rocks into the lower crust, coupled with long‐term lithospheric cooling due to the erosion of a radioactive upper crust. Brace‐Goetze lithospheric strength models suggest that these processes may have increased the integrated strength of the lithosphere by a factor of 1.4–2.8. Because of this strengthening, this system is self‐limiting, and activity will cease when lithospheric strength is sufficient to resist external forces and support isostatic imbalances. A simple force‐balance model demonstrates that the force required to uplift the axial zone is tectonically reasonable and that the system can subsequently withstand significant tensional forces. This example shows that crust‐mantle boundary uplift coupled with reduced crustal heat production can profoundly affect the long‐term strength of the continental lithosphere and may be a critical process in the tectonic stabilization of intraplate regions.