E-W Extension at 19 Ma in the Kung Co Area, S. Tibet: Evidence for Contemporaneous E–W and N–S Extension in the Himalayan Orogen

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Active faulting in southern Tibet consists of N–S trending extensional faults and linked strike-slip faults, which are an expression of regional E–W extension. A second type of extensional deformation associated with N–S movement is also recognized. This extension is expressed as a series of shear zones and normal faults in the High Himalayas – the Southern Tibetan Detachment System – and mid-crustal rocks exposed in metamorphic domes. Reported constraints on the timing of movements associated with these two phases of extension indicate that N–S extension predates the onset of E–W extension. However, only a few studies have provided clear constraints on the timing of E–W extension and the extent to which the two kinematically distinct domains of extension were contemporaneous is unclear.

The Kung Co fault in southern Tibet is a major N–S trending normal fault. The associated E–W extension is locally expressed as high-strain ductile deformation. Both field and microstructural observations show that this deformation occurred synchronously with granite intrusion. Previously reported U–Pb zircon dating shows granite crystallization took place at around 19 Ma, implying that ductile E–W extension in the Kung Co area was also active at around 19 Ma. This is the oldest documented example of E–W extension in Tibet and shows that E–W extension was at least locally contemporaneous with N–S extension to the south at shallower crustal levels. Simultaneous mid-crustal N–S extension and upper crustal E–W extension may be explained by southward flow of Tibetan crust with a divergent radial component.


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Earth and Planetary Science Letters


Copyright © 2012 Elsevier