HR: 0800h
AN: T41A-1267    [Abstracts]
TI: A Thinned Lithospheric Image beneath the Tanlu Fault Zone, Northeastern China: Constructed from Wave Equation Based Receiver Function Migration
AU: * Chen, L
EM: lchen@mail.igcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Deshengmenwai, Qijiahuozi, P.O.BOX 9825 Chaoyang District, Beijing, 100029 China
AU: Zheng, T
EM: tyzheng@mail.igcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Deshengmenwai, Qijiahuozi, P.O.BOX 9825 Chaoyang District, Beijing, 100029 China
AU: Xu, W
EM: wwxu@mail.iggcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Deshengmenwai, Qijiahuozi, P.O.BOX 9825 Chaoyang District, Beijing, 100029 China
AB: Lithospheric reactivation and thinning have long been proposed as a dominant process occurred in the cratonic Northeastern China continent during late Mesozoic and Cenozoic, yet direct seismic observations of fine-scale lithospheric structure have been scarce. We apply the newly proposed wave equation-based receiver function poststack migration method to the NCISP broadband data to image the lithospheric structure of the Tanlu Fault Zone area in Northeastern China. Our migration result reveals a 60-to-80-km-thick present-day lithosphere beneath the study region, significant thinned from the Paleozoic lithosphere of > 180 km. The lithosphere-asthenosphere boundary (LAB) is coherently imaged along an about 300-km east-west profile, with its apex roughly coincident with the transverse location of the Tanlu Fault Zone at the surface. An obvious uplift from around 36 km to around 32 km of the Moho is also clearly detected right below this fault zone. The coincidence of the imaged Moho uplift and the LAB apex with the surface location of the Tanlu Fault Zone provides seismological evidence for the steep geometry and deep penetration of the fault system, and indicates that the Tanlu Fault Zone might have facilitated anthenosphere upwelling during the Mesozoic-Cenozoic continental extension and lithospheric thinning. Frequency analysis and synthetic modeling suggest that both the Moho and the LAB are sharp and strong. The latter, in particular, is constrained to be within a less-than-10 km depth interval with a shear-wave velocity reduction of at least 4%. The revealed structural feature of the LAB is unlikely to be fully explained by the upper mantle thermal structure of the study region. Our lithospheric image suggests that the uppermost portion of the Archean lithospheric mantle beneath the Tanlu Fault Zone area might have survived the lithospheric reactivation and thinning occurred during the late Mesozoic and Cenozoic time. The compositional contrast between the preserved cold cratonic lithospheric mantle veneer and the uplifted hot asthenospheric materials may partially account for the sharp seismic velocity gradient at the base of the lithosphere.
DE: 7203 Body waves
DE: 7218 Lithosphere (1236)
DE: 8103 Continental cratons
DE: 8110 Continental tectonics: general (0905)
SC: Tectonophysics [T]
MN: Fall Meeting 2005