Uppermost mantle velocity and anisotropy structure beneath the North China Craton and its adjacent regions

Abstract

The North China Craton has experienced significant tectonic reactivation and destruction, and it is a natural place to study structural heterogeneities and their influences on the lithospheric evolution. In order to have a better understanding of the lithosphere modification of the North China Craton, we collected as many as possible bulletin and exceptionally high-quality handpicked Pn arrival times, yielding a well-distributed dataset with high lateral resolution, to conduct a new uppermost mantle velocity model of the North China Craton. The present tomographic results show distinct lateral heterogeneities in both velocity and anisotropy, which are well correlated with the major active tectonic units. Obvious high Pn velocity anomalies with E-W fast directions are imaged beneath the Ordos Block, suggesting the Ordos Block lithosphere may remain a strong Archean craton. The high-velocity North China Basin may indicate a thick detached lithospheric structure, which could have been preserved during multiple tectonic episodes. Prominent low Pn velocity anomalies are observed beneath the central North China Craton and along the Tanlu fault. These low velocity anomalies suggest complex lithospheric deformation due to the upwelling of hot material triggered by the northwestward subduction of the Pacific plate. The Pn fast directions beneath the central North China Craton are generally parallel to the strike of mountains, suggesting that the mountains may be formed in response to the deformation of the uppermost mantle velocity structure. The distribution of large earthquakes and the pattern of velocity anomalies may imply that the uppermost mantle velocity structure could increase seismicity and impact the corresponding active tectonic faults beneath the North China Craton. These observations provide new geophysical insights on the lithospheric deformation and mantle dynamic processes of the North China Craton.