HR: 14:25h
AN: T53D-04 INVITED     [Abstracts]
TI: Comparison of Conductivity Structure of the Crust and Upper Mantle Between Continental Blocks and Their Boundary Belts in China Continent
AU: * Zhao, G
EM: zhaogz@ies.ac.cn
AF: Institute of Geology, China Earthquake Administration, China, Beijing, 100029 China
AU: Zhan, Y
T53D-04 AF: Institute of Geology, China Earthquake Administration, China, Beijing, 100029 China
AU: Tang, J
T53D-04 AF: Institute of Geology, China Earthquake Administration, China, Beijing, 100029 China
AU: Chen, X
T53D-04 AF: Institute of Geology, China Earthquake Administration, China, Beijing, 100029 China
AU: Jiang, Z
T53D-04 AF: Institute of Geology, China Earthquake Administration, China, Beijing, 100029 China
AB: Numerous MT surveys throughout China have produced electrical profiles that cross undeformed crustal blocks, e.g., Cenozoic/Mesozoic basin and relatively stable blocks and the highly deformed boundary belts between the blocks, such as orogenic zones and active seismotectonic belts. 2-D electrical structures obtained by using similar inversion techniques show similar characteristics among different profiles in different regions. A 950 km profile in the conjunction area of the Tibet Plate (TP) and North China plate (NC) in the northeastern margin of Qinghai-Tibet plateau extended in a northeasterly direction from the northeastern margin of the TP, crossing the North-South Seismotectonic Belt (NSSB) and ending at Jingbian in the Ordos plate of the NC. Four crustal blocks can be determined from southwest to northeast: Bayan Har (BH), Qin-Qi (QQ), Haiyuan (HY) or the North-South seismotectonic belt and Ordos block (OD). The BH, QQ and OD lithospheric blocks exhibit similar structure. The upper crust is highly resistive; the upper part of lower crust represents a low-resistivity layer, whose resistivity increases gradually with depth from the bottom-most crust into the upper mantle. This pattern is similar to that in complete blocks on the southern and eastern margins of the Qinghai-Tibet Plateau and Jungar basin in northwestern China and represents typical electrical layering of the crust in slightly deformed or undeformed intracontinental blocks. The crust in the HY block in the NSSB has been significantly deformed. The electrical layering was destroyed and the structure is complex, lacking a large region of low resistivity. This block recently has become tectonically active. Seismic reflection/refraction data along the same profile indicates that average crustal velocity in the HY block is lower than in other blocks along the profile, and the Moho has been faulted in the HY block. A similar electrical structure can be found in the Tianshan mountains in NW China, in the Himalayan mountains in southern Tibet and in the Xianshuihe-Longmenshan faults in eastern margin of Tibet. Crustal fluids are assumed to cause low resistivity zones in undeformed or slightly deformed blocks. Pore fluids in layers of mid-lower crust is are preserved and provide for larger zones of low resistivity. In highly deformed boundary belts, however, fluids -whether water or partial melt - may have escaped, eliminating the large zone of low resistivity.
DE: 8100 TECTONOPHYSICS
DE: 8109 Continental tectonics: extensional (0905)
DE: 8110 Continental tectonics: general (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005