HR: 14:25h
AN: T22C-04    [PDF]
TI: Gaoligong and Chong Shan Shear Zones, Yunnan, and Accommodation of the Northward Movement of India Relative to Indochina During the Mid-Cenozoic
AU: * Akciz, S O
EM: akciz@mit.edu
AF: EAPS, MIT, 77 Massachusetts Ave., Cambridge, MA 02139
AU: Burchfiel, C B
EM: bcburch@mit.edu
AF: EAPS, MIT, 77 Massachusetts Ave., Cambridge, MA 02139
AU: Crowley, J L
EM: jlcrowle@MIT.EDU
AF: EAPS, MIT, 77 Massachusetts Ave., Cambridge, MA 02139
AU: Jiyun, Y
EM: chenlzh@public.km.yn.cn
AF: Yunnan Institute of Geological Sciences, No. 131 Baita Road, Kunming, 111004 China
AU: Liangzhong, C
EM: chenlzh@public.km.yn.cn
AF: Yunnan Institute of Geological Sciences, No. 131 Baita Road, Kunming, 111004 China
AB: Since the collision between Eurasia and India at ca. 45 Ma, there has been 2000-3500 km of convergence between India and Asia. How and where the indentation was accommodated in the region east of the India indenter are still subject to speculation, due to lack of geological investigations carried out in the region. Our field studies show that a significant part of the post-collisional northward indentation of India into Asia has been absorbed by the previously undocumented Gaoligong Shan (GSSZ) and Chong Shan (CSSZ) shear zones, in addition to the left-lateral displacement along the better-known Ailao Shan shear zone that lies farther NE in Yunnan, China. Penetrative ductile deformation marked by steep foliation and subhorizontal lineation affects all rock types within both shear zones and kinematic indicators show right-lateral and left-lateral shear along the GSSZ and CSSZ, respectively. U/Pb ages on several monazite grains and grain fractions from mylonitic to non-mylonitic leucogranites within the shear zone range from ca. 80-18 Ma. The youngest ages come from undeformed leucogranites cross-cutting the foliation, which indicate that right-lateral movement ended before ca. 18 Ma, when right-lateral shear between India-Sibumasu switched to the Sagaing fault zone in Burma. High-temperature sinistral strike-slip shearing along the CSSZ was active at ca. 28 Ma and terminated before ca.17 Ma, based on U/Pb ages of monazite grains from deformed and foliation cross-cutting leucogranites. These new geochronological data suggest that both the GSSZ and CCSSZ are not belts of Precambrian metamorphic rocks as previously suggested, but are important Cenozoic shear zones that are contemporaneous with the left-lateral Ailao Shan shear zone. The documentation of these structures also indicate that crustal fragments in SE Asia did not extrude to the southeast as a single block, but rather extruded as at least two crustal fragments with considerable internal deformation, bounded by three large-scale intra-continental shear zones.
DE: 1208 Crustal movements--intraplate (8110)
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting