Seismic anisotropy in and around the region of the Middle and Lower Reaches of the Yangtze River and its insight into the regional tectonics
The region lying on the eastern margin of the Dabie Mountains and the Middle and Lower Reaches of the Yangtze River Belt(MLYB)constitute one of the most structurally complex areas in eastern China.To profoundly understand the tectonic evolution and deformation characteristics of the crust and upper mantle of this region,we calculate the seismic anisotropy by fitting the Pms delay time in teleseismic P-wave receiver functions recorded by a dense portable seismic array across the MLYB.We further elucidate the distinct characteristics and origin of the crustal and upper mantle seismic anisotropy by integrating previous similar studies in and around MLYB.Our research reveals obvious lateral zoning in crustal anisotropy in MLYB and its surrounding North China Block(NCB)and South China Block(SCB).The southeastern part of the NCB predominantly displays crustal anisotropy in nearly NWW directions,while the MLYB and the northeastern part of SCB show a predominance in the NE direction.Vertically,there is a conspicuous disparity in anisotropic directions in the crust and upper mantle of this region.The fast wave directions of Pms anisotropy exhibit a general difference of about 30° to 60° from the XKS(PKS,SKS,SKKS)fast wave polarization directions,delineating a"flyover"style structure of crust-mantle anisotropy in this region.This study suggests that the differences in the rheological strength between NCB and SCB and in regional tectonic evolution during the Indosinian and Yanshanian periods play a crucial role in creating this"flyover"style anisotropy.The Pms anisotropy characteristics in NCB reflect the deformation traces of the middle and lower crust formed during the Indosinian continental collision between NCB and SCB,while that in the northeastern part of SCB are dominantly controlled by the intraplate compression formed during the northwestward subduction of the Paleo-Pacific plate.The subduction of the Paleo-Pacific Plate in the Yanshanian period caused not only the asthenospheric flow along NW or W direction and the lattice-preferred orientation of mineral alignment,but also intraplate compression in the crust and lithosphere and culminated the observed deformation and seismic anisotropy features of the middle and lower crust in and around the MLYB.
Middle and Lower Reaches of the Yangtze RiverSeismic anisotropyReceiver functionRegional tectonic evolution
万方数据
维普
