Supervisors: M.P. Searle (Oxford), J.M. Cottle (University of California,. Santa Barbara), D.J. Waters (Oxford) + collaboration with Professor Sun-Lin. Chung (NTU ...
Project EARTH-09-MPS1 Constraining continental extrusion: Determining the age of metamorphism, magmatism and shearing along strike-slip faults in Indochina (Red River, Gaoligong, Mae Ping and Sagaing faults). Supervisors: M.P. Searle (Oxford), J.M. Cottle (University of California, Santa Barbara), D.J. Waters (Oxford) + collaboration with Professor Sun-Lin Chung (NTU, Taiwan). One of major debates in continental tectonics of Asia is the role of large-scale strike-slip faults in the continental extrusion of crustal blocks of SE Asia away from the Indian indentor. The Red River fault (Yunnan, Vietnam), Jiale fault (SE Tibet), Gaoligong (Yunnan), Mae Ping faults (Thailand) and the Sagaing fault (Burma) all show exhumed metamorphic rocks and granites, both mantle-derived syenites and crustal-derived leucogranites, along the fault. One school of thought regards the strike-slip faults as cutting through the entire crust into the mantle, resulting in shear-induced metamorphism and melting, with large geological offsets and high slip rates (eg: Tapponnier et al., 1990, 2001; Leloup et al., 1993, 1995, 2001). The other school of thought regards the strike-slip faults as purely crustal, exhuming earlier formed metamorphic rocks and mantle-derived granites, with lower slip rates (eg: Searle, 2006). Central to the debate are the following questions: 1) Do U-Pb zircon ages from amphibole + quartz monzonite - syenite intrusions constrain the age of initiation of strike-slip shear along the RRSZ, or are they prekinematic? 2) Is high-grade metamorphism along the RRSZ synchronous with strike-slip or pre-kinematic with respect to strike-slip shearing? 3) Are the deformed leucogranites along the RRSZ syn-kinematic with respect to strike-slip shearing or pre-kinematic? The key to answering these questions lies in detailed field mapping combined with metamorphic petrology, micro-structural analysis and accurate time constraints. The latter will be obtained by high-precision U-(Th)-Pb dating (TIMS and LA-ICP MS) on metamorphic and granitoid rocks from the shear zones. The Red River Shear Zone consists of four major metamorphic complexes, the Xuelong Shan, Diancang Shan and Ailao Shan in Yunnan and the DoiNuiConVoi (DNCV) complex in North Vietnam, each of which is bounded by late, steep normal + strike-slip faults which dip at high angles away from the massifs. We already have some samples from the Mae Ping fault in NW Thailand and the Sagaing fault in Burma. The student will have two field seasons mapping, carrying out microstructural analyses and collecting samples for geochronology and strain analysis on the Red River, Jiale and Gaoligong faults in China and Vietnam. This will be undertaken with M.P. Searle and in collaboration with Prof.
Sun-Lin Chung (National Taiwan University). The student will be based at Oxford University, where petrology, SEM and microstructural work will be carried out with D.J. Waters and M.P. Searle. U-Pb dating using TIMS and LA-ICP MS will be carried out in UC, Santa Barbara under the supervision of J.M. Cottle. References Leloup, P.H., Harrison, T.M., Ryerson, F.J., Chen Wenji, Li Qi, Tapponnier, P. & Lacassin, R. 1993. Structural, petrological and thermal evolution of a Tertiary ductile strike-slip shear zone, Diancang Shan, Yunnan. Journal of Geophysical Research, 98, 6715-43. Leloup, P.H., Lacassin, R., Tapponnier, P., Schärer, U., Dalai, Z., Xiaohan, L., Liangshang, Z., Shaocheng, J. & Trinh, P.T. 1995. The Ailao Shan- Red River shear zone (Yunnan, China), Tertiary transform boundary of Indochina. Tectonophysics, 251, 3-84. Leloup, P.H., Arnaud, N., Lacassin, R., Kienast, J.R., Harrison, T.M., Trong, T.P., Replumaz, A. & Tapponnier, P. 2001. New constraints on the structure, thermochronology, and timing of the Ailao Shan-Red River shear zone, SE Asia. Journal of Geophysical Research, 106, 6657-71. Morley, C.K. 2007. Variations in Late Cenozoic – Recent strike-slip and obliqueextensional geometries within Indichina: The influence of pre-existing fabrics. Journal of Structural Geology, 29, 36-58. Searle, M.P., 2006. Role of the Red River Shear Zone, Yunnan and Vietnam, in the continental extrusion of SE Asia. Journal of the Geological Society, London, 163, 1025-1036. Comment, Reply: Leloup, Tapponnier, Lacassin – Searle. J. Geol. Soc. London October 2007. Tapponnier, P. et al. 2001. Oblique stepwise rise and growth of the Tibet Plateau. Science, 294, 1671-7. Tapponnier, P., Lacassin, R., Leloup, P.H., Schärer, U., Dalai, Z., Haiwei, W., Xiaohan, L., Shaocheng, J., Lianshang, Z. & Jiayou, Z. 1990. The Ailao Shan/Red River metamorphic belt: Tertiary left-lateral shear between Indochina and South China. Nature, 343, 431- 7.
