Crustal azimuthal anisotropy in the trans-North China orogen and adjacent regions from receiver functions

Abstract

The North China Craton (NCC) is an important part of eastern China. Recent studies have shown that the eastern NCC (ENCC) has undergone significant lithospheric thinning and destruction since the late Mesozoic. Destruction of the cratonic lithosphere is necessarily accompanied by crustal deformation. Therefore, a detailed crustal deformation model can provide basic observational constraints for understanding the process and mechanisms of the destruction of the NCC. In this study, we estimated the crustal azimuthal anisotropy beneath 198 broadband stations in the NCC with a joint analysis of Ps waves converted at the Moho from radial and transverse receiver function data. We also performed a harmonic analysis to test the reliability of the measured anisotropy. We obtained robust crustal azimuthal anisotropy beneath 23 stations that are mostly located on the western margin of the Bohai Bay Basin, Yin-Yan orogenic belt, and Taihang Mountains, which reflects the crustal deformation characteristics in those regions. The crustal shear wave splitting time was found to range from 0.05 s to 0.68 s, with an average value of 0.23 s, which reveals a distinct crustal anisotropy in the Trans-North China Orogen (TNCO) and its adjacent areas. Our analysis of the results suggests that the strong NW-SE tectonic extension in the late Mesozoic and Cenozoic played an important role in crustal anisotropy in this region. In addition, the E-W trending crustal anisotropy on the margin of the Bohai Bay Basin indicates an effect of the ENE-WSW trending horizontal principal compressive stress. The crustal anisotropy in the Yin-Yan orogenic belt may be an imprint of the multiple-phase shortening of a dominant N-S direction from the early-to-middle Jurassic to the Early Cretaceous. Stations in the Taihang Mountains show large splitting times and well-aligned NW-SE fast directions that correlate with those measured from SKS splitting and that are possibly related to the lithospheric modification and magmatic underplating from the Late Mesozoic to Cenozoic in this area.