Collaborative Research: Geological Investigations of Non-Andersonian Conjugate Strike-slip Faults in Central Tibet

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).A foundation of Earth Sciences is the ability to relate spatial arrangements of geologic features such as tectonic plate boundaries, earthquake-related ruptures, mountain uplifts and fault patterns in general to their causative forces. In this regard, geoscientists have long used the experimentally established Coulomb fracture criterion, which predicts certain angular relationships between faults, to explain the dynamic causes of fault formation. This approach has faced increasing difficulties as more and systematic observations show that many natural faults defy these angular relationships. This research will involve the use of a new experimental apparatus to simulate natural faulting, as well as an examination of the geometric evolution of large fault systems in central Tibet, to determine if a mechanical principle different to the Coulomb criterion is needed to explain the geometry of natural faults. Our ability to interpret lithospheric deformation, and perhaps more importantly the coupling between the flowing middle and fracturing upper crust, depends critically on the knowledge that relates observed fault geometries to causative dynamic conditions. The most commonly used relationship in this regard is the Coulomb fracture criterion that predicts X-shaped conjugate faults oriented at ~30° from the maximum compressive-stress direction. In nature, X-shaped conjugate fault geometries in strike-slip systems are rarely observed, and while fault geometries can be complex and difficult to interpret due to post-faulting deformation, V-shaped geometries with faults orientated at 60-75º from sigma one have been essentially overlooked. These V-shaped fault systems are common in nature with prominent large-scale examples in the Alpine-Himalayan collision zone. These investigators will test whether V-shaped conjugate faults in central Tibet were created by vertical-axis rotation or paired-general-shear flow by performing structural mapping and paleomagnetic analysis. The results and associated models should have important implications for whether the large-scale deformation of continents is fundamentally plate-like or fluid-like over geologic timescales.