Lithospheric structure in the North China craton constrained from Gravity Field Model (EGM 2008)

Abstract

A detailed knowledge of the thickness of the lithosphere in the North China craton (NCC) is important for understanding the significant tectonic reactivation of the craton in Mesozoic and Cenozoic. We achieve this goal by applying the newly proposed continuous wavelet transform theory to the Gravity Field Model (EGM 2008) data in the region. Distinct structural variations are identified in the scalogram image of profile Alxa-Datong (大同)-Qingdao (青岛)-Yellow Sea (profile ABC), transversing the main units of NCC, which we interpret as mainly representing the Moho and lithosphereasthenosphere boundary (LAB) undulations. The imaged LAB is as shallow as 60-70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior. A rapid change of about 30 km in the LAB depth was detected at around the boundary between the Bohai (渤海) Bay basin (BBB) and the Taihang (太行) Mountains (TM), roughly coincident with the distinct gravity decrease of more than 100 mGal that marks the North-South Gravity Lineament (NSGL) in the region. At last we present the gravity modeling work based on the spectral analysis results, incorporating with the observations on high-resolution seismic images and surface topography. The observed structural differences between the eastern and western NCC are likely associated with different lithospheric tectonics across the NSGL. Combined with seismic tomography results and geochemical and petrological data, this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton.