HR: 1340h
AN: T13E-1625    [Abstracts]
TI: Crustal and Uppermost Mantle Structure of the Yanshan Belt and Adjacent regions at the northeastern boundary of the North China Craton from Rayleigh Wave Dispersion Analysis and Inversion
AU: * Tang, Q
EM: tqsh@mail.iggcas.ac.cn
AF: Seismological Laboratory (SKL-LE), Institute of Geology and Geophysics, Chinese Academy of Sciences, NO. 19 Beituchengxilu, Deshengmenwai Qijiahuozi, Chaoyang District, Beijing, 100029, China
AU: Chen, L
EM: lchen@mail.iggcas.ac.cn
AF: Seismological Laboratory (SKL-LE), Institute of Geology and Geophysics, Chinese Academy of Sciences, NO. 19 Beituchengxilu, Deshengmenwai Qijiahuozi, Chaoyang District, Beijing, 100029, China
AU: He, Y
EM: ymhe@mail.iggcas.ac.cn
AF: Seismological Laboratory (SKL-LE), Institute of Geology and Geophysics, Chinese Academy of Sciences, NO. 19 Beituchengxilu, Deshengmenwai Qijiahuozi, Chaoyang District, Beijing, 100029, China
AB: We present a high resolution shear wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the North China Craton (NCC) by Rayleigh wave dispersion analysis and inversion. The data came from 46 broadband seismometers densely deployed along N-S direction in the region under a sub-project of the NCISP. Rayleigh wave phase velocities were measured at periods from 10 to 48 s, and were utilized in subsequent inversions to solve for the shear wave velocity structure from 15 km up to 120 km depth. The inverted lower crust and uppermost mantle velocities, about 3.75 km/s and 4.3 km/s on average, are apparently low compared with the global average. The Moho was constrained within the depth range of 30-40 km with an average of about 35 km, indicating a generally normal-in-thickness crust in the region. A thin lithosphere of no more than 100 km, however, was imaged under a large part of the profile with the thinnest of only ~60 km under the Inner Mongolian Axis (IMA) where an abnormally slow anomaly was observed below 60-km depth. The overall structural features resemble those of typical continental rift zones and are likely associated with the lithospheric reactivation and tectonic extension widespread in the eastern NCC during the Mesozoic-Cenozoic time. Distinctly, high velocities were found in both the crust and uppermost mantle immediately to the south of the IMA beneath the northern Yanshan Belt (YSB). In particular, the mantle anomaly reaches a deep extent of > 100 km and shows velocities as high as ~4.6 km/s, presumably representing the cratonic lithospheric lid of the region that may have not been affected by the Mesozoic-Cenozoic deformation process as strongly as other regions in the eastern NCC. Based on our shear wave velocity structural image in together with other geophysical observations, we proposed a possible lithosphere-asthenosphere interaction scenario at the northeastern boundary of the NCC. We speculate that significant undulations of the base of the lithosphere, which might have resulted from the uneven Mesozoic-Cenozoic lithospheric thinning, may induce mantle flows concentrating beneath the weak IMA and probably also under the southern edge of the YSB where it borders the Bohai Bay Basin to the south. The relatively thick lithospheric lid in the northern YSB likely serves as a tectonic barrier separating the on-craton and off-craton regions into different upper mantle convection systems at the present time.
DE: 7218 Lithosphere (1236)
DE: 7255 Surface waves and free oscillations
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting