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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• 作者：Mayumi Mitsuishi^a ; ^{mitsuishi.mayumi@nagoya-u.jp} ; ^{mitsuishi-mayumi@jogmec.go.jp} ; Simon R. Wallis^a ; Mutsuki Aoya^b ; Jeffrey Lee^c ; Yu Wang^d
• 关键词：southern Tibet ; normal faulting ; age of extension ; remote sensing
• 刊名：Earth and Planetary Science Letters
• 出版年：2012
• 期刊代码：18_0012821x
• 类别：ph
• 出版时间：1 April, 2012
• 卷：325-326
• 期：Complete
• 页码：10-20
• 文件大小：3212 K

摘要

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.