Lithospheric velocity structure from the southern North China Craton to the Qinling orogen: Constraints from Puyang-Nanyang wide-angle reflection/refraction sounding profiles

Abstract As a key study area of inter-plate interactions, continental-continental collision orogeny, and crust-mantle deformation mechanisms, the Central and Southern part of North China spans the North China Craton and the northern margin of the Qinling-Dabie orogen. However, our understanding of the present tectonic framework and deep dynamic process in this region lacks the constraints and support of the deep geophysical fine detection results. The Seismological Bureau of Henan Province set up the Puyang-Nanyng seismic wide-angle reflection/refraction profile with a length of about 550km, and constructed a two-dimensional crust-mantle fine velocity structure spanning the main tectonic units. The detection results show: (1) The study area has a three-layer structure: the upper crust, middle crust and lower crust. The thickness of the crust ranges from 32.0 to 36.0 km. The thickest part is the northern margin of the South Qinling (about 36 km) and the Taikang Uplift-Kaifeng Sag (35.2km); (2) There are three large lithospheric discontinuities in the upper mantle, corresponding to the Shangdan suture, the Luanchuan-Minggang fault, and the Xinxiang-Shangqiu fault, respectively. The crust-mantle velocity structure and tectonic form on both sides of the three faults/ suture have significant heterogeneity in the vertical and lateral directions, and the overall features of lateral fragmentation and vertical decoupling are non-uniform. This feature is related to the tectonic evolution process since the Mesozoic, and the destruction and reconstruction of the North China Craton by tectonic evolution; (3) Low-velocity anomalies are relatively developed in the crust of the Northen North China Basin and the northern part of Southern North China Basin in Henan Province, and the combination of high and low velocity anomaliesis easy to induce earthquakes, which makes the study area have a deep seismogenic background for moderate and strong earthquakes.