Analysis of Remote Sensing Data for Geologic Mapping -
Ultrahigh Pressure Metamorphic Belt and Collisional Tectonics of
The Dabieshan Orogenic Belt, Central Eastern China*
Tectonic belts of the Dabieshan
Dabieshan is a part of the salient Kunlun-Qinling-Dabie-sulu (Shandonog-Jiangsu) orogenic belt in central China running over 5000 km east-west. In eastern China the Qinling-Tongbai-Dabie-Sulu orogenic belt separates the Sino-Koean plate in the north from the Yangtze plate in the south. Dabieshan is structurally bounded on the east by Tanchang-Lujiang fault (T-L-F.), on the west by Shangcheng-Macheng Fault (S-M F.) (Fig. 2). To the north of Dabieshan is Hefei Basin, a Mesozoic and Cenozoic sedimentary basin. To the south is foreland fold and thrust belt of the Yangtze plate. The Dabieshan may be characterized by four E-W trending tectonic belts, the northern Huaiyang belt, the Northern Dabie magmatic arc complex, the Southern Dabie UHP metamorphic belt and the Susong Metamorphic belt (Fig. 2). Each of the belts is separated from the others by major faults.
Figure 2. Sketched tectonic map of the Dabieshan Mountains (Simplified from Cong, 1996).
Legend
faults
L-D F. Lushan-Dawu fault, W-Sh F. Wuhe-Shuihou fault, T-L F. Tanchang-Lujiang fault, M. T. F. Majiao-Taihu fault, S-M F. Shangcheng -Macheng fault, M-H F. Maoji-Hefei fault, X-G F. Xiangfan-Guangji fault, X-MF. Xiantian-Mozitan fault.
Pz:Paleozoic group,
Mz :Mesozoic group
tectonic belts:
1. North Huiyang Backarc Flysch belt,
2. North Dabieshan Arc Complex belt,
3. South Dabieshan Collision Complex belt,
4 Susong Metamorphic Complex belt.
1. The Northern Huaiyang belt
The Northern Huaiyang is an E-W trending liner belt to the north of Xiaotian-Mozitan Fault (X-M F.) and is partly covered by Mesozoic and Cenozoic none-marine clastic sediments and volcanic of the Hefei Basin on the north.
2. The Northern Dabie magmatic arc complex belt
The Northern Dabie complex is separated from the Northern Huaiyang by the X-M F. on the north and from the UHP belt by a duclite shear zone on the south. It is characterized by polyphase igneous intrusion, migmatite and amphibole to granulite faces metamorphic rocks.
3. The Southern Dabie ultrahigh pressure metamorphic belt
Coesite-and diamond-bearing ultrahigh pressure metamorphic rocks found in a belt of about 30 by 50 km to the south of the Northern Dabieshan complex. They occur in three modes: coesite eclogite lenses in marble; elclogite lenses and layers in gneisses and eclogite associated with garnet peridotite.
4. The Susong Metamorphic Complex belt
To the south of the UHP belt in 80 km wide belt composed of a thick sequence of metasediments and metavolcanics named Susong Group (Bureau of Geology and Mineral Resources of Anhui Province, 1987). The Susong Group consists of two lithological units: cold eclogite unit and greenschist unit.
Data structures from magnetotelluric survey
Magnetotelluric survey across the Dabieshan was done by the Anhui Geophysical Survey. One of the major features revealed by the survey is a major low resistivity layer (MLRL) of 5-30 ohm-meters (Wm). Above the MLRL the Dabieshan is clearly composed of several thrust sheets of contrasting resistivity. The structurally highest sheet has a resistivity of 25600-110000(Wm). The second sheet lies below the first, has a resistivity of 8000-15000(Wm). This sheet crops out as an arrow belt is probably equivalent ot the UHP belt. The third thrust sheet lying below the UHP sheet has a resistivity of about 15000-35000 (Wm). The lowest thrust sheed extends 100 km as Sinian sedimentary rocks of the Yangtze plate. These geophysical observations are record deep structures which might not be constant with the surface geological configuration.
