Geoelectric Structure of Lithosphere Beneath Eastern North China: Features of Thinned Lithosphere from Magnetotelluric Soundings

Abstract

It is widely accepted that disassembly of the North China ancient craton and the thinning process of lithosphere at depth are essential for the dynamic evolution model of the China mainland since Mesozoic and Cenozoic times. To address these issues, the deep structure of the lithosphere beneath North China should be well delineated, which relies on a new generation of geophysical technology including ultra-broadband high-precision magnetotelluric (MT) sounding. In 2001 and 2005, MT survey was carried out along the Yingxian–Shanghe (HB-MT01) and Wenshui–Rizhao (HB-MT02) profiles in eastern North China, respectively. The results show that the crust and upper mantle along the profiles can be divided into four electric sections, and high-conductivity zones and high-conductivity layers exist in the lower crust and upper mantle, respectively. It is inferred that decoupling between crust and mantle is present beneath eastern North China which is associated with large-scale tectonic movements. The thickness of the lithosphere in eastern North China is estimated to be 50–80 km, which has apparently thinned with respect to usual continental cratonic regions. It involves the northern Taihangshan uplift, northern North China rifted basin and Luxi (western Shandong) fault-bounded uplift, which is different from the previous claim that the lithospheric thinning is confined to east of the Taihangshan gravity gradient zone. This study also demonstrates the importance of the modern high-precision MT sounding and combination of geophysics, geology, and geochemistry in the research of continental dynamics.