Geophysical transect across the North China Craton: A perspective on the interaction between Tibetan eastward escape and Pacific westward flow

Abstract

The North China Craton (NCC) is composed of the Eastern and Western Blocks amalgamated along the Central Orogenic Belt (Trans-North China Orogen, TNCO). Geological, geochemical, geochronological and geophysical studies have confirmed that the lithosphere beneath the Eastern Block has undergone significant destruction and modification during the Mesozoic, whereas the Western Block preserves the Archean lithosphere. The mechanisms and crustal response to the lithospheric disruption remain unclear. Here we construct a lithosphere-scale transect across the Western and Eastern Blocks and the intervening TNCO at the southern margin of the NCC. We interpret the lithosphere thickness, crustal P-wave velocity, density and thermal structure, and also seismic activity. Our results show that: (1) crustal thinning is consistent with lithospheric thinning from west to east of this transect; (2) the seismogenic structure is distinctly different among the Western Block, the TNCO and the Eastern Block; (3) a marked increase in crustal density and average P-wave velocity exists at the contacts between the Western Block and TNCO, and the TNCO and Eastern Block, as well as beneath the Tanlu fault at the eastern margin of the Eastern Block; and (4) a positive correlation is displayed between increasing P-wave velocity (density, temperature) and the occurrence of Mesozoic basalts and high-Mg andesites. Under the tectonic background of the amalgamation pattern between the Eastern and Western Blocks within the NCC, we attribute the lateral variation of crustal geophysical features to the lateral variation of crustal composition or the interaction of mantle flow from the eastward escape from Tibetan collision, and the westward mantle flow beneath the eastern NCC, without excluding the west–east variation of crustal response to lithospheric disruption.