摘要
A broadband seismic array of 7 stations was set up in the western Dabie Mountains (31°20′-31°50′N, 114°30′-115°E). Teleseismic events from May 2001 to November 2001 were collected and analyzed by radial receiver function to determine the S-wave velocity structure of the crust and uppermost mantle. The crustal thickness is 32-38 km beneath the array. The crust-mantle boundary appears as a gently north-dipping velocity discontinuity, but turns to be a velocity gradient beneath a station near the Qiliping shear zone in the south of the array. In the north of the array, a large offset of 4-6 km exists in the Moho along the Tongbai-Tongcheng shear zone, suggesting a suture zone formed by the northward subduction of the Yangtze plate beneath the North China plate. Along the Tongbai-Tongcheng shear zone, a north-dipping, EW-striking low-velocity zone was observed in the upper mantle, which may be related to the collision boundary between the Yangtze and the North China plates in the Triassic. Therefore the Tongbai-Tongcheng shear zone is the southern boundary of suture zone between the Yangtze and the North China plates. In the south of the array, a high-velocity body in the lower crust near the Qiliping shear zone probably results from the underplate of mafic magma into the lower crust, which is generally associated with large-scale extension triggered by delamination of the thickened crust.
A broadband seismic array of 7 stations was set up in the western Dabie Mountains (31°20′–31°50′N, 114°30′–115°E). Teleseismic events from May 2001 to November 2001 were collected and analyzed by radial receiver function to determine the S-wave velocity structure of the crust and uppermost mantle. The crustal thickness is 32–38 km beneath the array. The crust-mantle boundary appears as a gently north-dipping velocity discontinuity, but turns to be a velocity gradient beneath a station near the Qiliping shear zone in the south of the array. In the north of the array, a large offset of 4–6 km exists in the Moho along the Tongbai-Tongcheng shear zone, suggesting a suture zone formed by the northward subduction of the Yangtze plate beneath the North China plate. Along the Tongbai-Tongcheng shear zone, a north-dipping, EW-striking low-velocity zone was observed in the upper mantle, which may be related to the collision boundary between the Yangtze and the North China plates in the Triassic. Therefore the Tongbai-Tongcheng shear zone is the southern boundary of suture zone between the Yangtze and the North China plates. In the south of the array, a high-velocity body in the lower crust near the Qiliping shear zone probably results from the underplate of mafic magma into the lower crust, which is generally associated with large-scale extension triggered by delamination of the thickened crust.
基金
Supported by National Basic Research Program of China (Grant No. TG1999075505)
National Science Foundation of China (Grant No. 40634021)
