New radiometric dating constrains the time for initiation of the Karakorum fault zone (KFZ), SW Tibet
| 作者: |
Wang, S.F., et al. |
| 期刊名称: |
Tectonophysics |
| 发表年度: |
2009 |
| 卷: |
475 |
| 期: |
3-4 |
| 联系作者: |
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| 页码: |
503-513 |
| 摘要: |
The Karakorum fault zone (KFZ), composed of strike-slip faults, has played an important role in intra-continental deformation during the Cenozoic convergence between the Indian and Eurasian plates. However, the spatial and temporal evolution of the KFZ remains under debate. This paper reports new zircon U-Pb Sensitive High Resolution Ion MicroProbe (SHRIMP) and biotite Ar-40/Ar-39 ages for samples from the fault zone to clarify the timing of events. The ages of Zircon U-Pb fall mainly around 47-50 Ma, which corresponds to a period of important magmatic activity of the Gangdese granitic belt (also known as the Trans-Himalayan magmatic belt). A metamorphic event followed in the period around 32 Ma, and that was then followed by a medium temperature cooling event between about 12 and 7.7 Ma. Biotite Ar-40/Ar-39 ages provide evidence that the 12-7.7 Ma cooling event coincides with the initiation of the KFZ cutting through the Ayilari granite. The Ayilari granite pluton does not seem to have experienced the separate 25-23 Ma cooling event, as shown in previous studies 60-80 km west of the current study area [Lacassin, R., Valli, F., Arnaud, N., Leloup, PH., Paquette, J.L, Li, H, Tapponnier, R, Chevalier, M.L. Guillot. S.. Maheo, G., Xu, Z., 2004. Large-scale geometry, offset and kinematic evolution of the Karakorum fault Tibet. Earth and Planetary Science Letters 219 (3-4), 255-269.; Valli, F., Arnaud, N., Leloup, H.P., Sobel, E.R., Maheo, G., Lacassin, R., Guillot, S., Li, H., Tapponnier, P., Xu, Z., 2007. Twenty million years of continuous deformation along the Karakorum fault western Tibet: a thermochronological analysis. Tectonics 26, doi: 10.1029/2005TC001913.: Valli, F., Leloup, P., Paquette, J., Arnaud, N., L!, H., Tapponnier, P., Lacassin, R., Guillot, S., Liu, D., Deloule, E., Xu, Z., Mahe'o, G., 2008. New U-Th/Pb constraints on timing of shearing and long-term slip-rate on the Karakorum fault. Tectonics 27, doi:10.1029/200TrC002184.]. We conclude that the 25-23 Ma cooling event bears no relationship to the activity of the KFZ, but resulted from a local metamorphic event caused either by a regional tectonic event (such as activity of the south Kailas thrust fault) or by magmatism around Shiquanhe (also known as Gar). The study of the KFZ around Namru supports the opinion that the KFZ propagated along the fault strike to the Gar-Menshi area around 12 Ma. (C) 2009 Elsevier B.V. All rights reserved.
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