Joint inversion of ambient noise and earthquake data in the Trans-North China Orogen: On-going lithospheric modification and its impact on the Cenozoic continental rifting

Abstract

Situated in a transition zone between the Ordos basin and the Huabei basin, the Trans-North China Orogen (TNCO), or the central North China Craton, evolved as an extensional orogen during the late Mesozoic to Cenozoic, with Fenhe-Weihe Rift (FWR) developing in it in the Cenozoic. In this study, we construct a high resolution lithospheric model of TNCO by jointly interpreting the broadband surface wave dispersions derived from ambient noise and teleseismic surface wave data. The most significant features of the lithospheric mantle are the two separated low velocity anomalies beneath the northern and southern TNCO respectively. Considering that the Pacific slab subducted to the mantle transition zone with a gap under the Datong volcanic zone, and large-scale low-velocity mantle materials are ascending from the lower mantle through the slab gap, which is evidenced by teleseismic P wave tomography, we propose here that the northern TNCO was affected by the mantle upwelling from the lower mantle. On the contrary, the south TNCO was mainly modified from the dehydration reaction process of the stagnant Pacific slab. In the lower crust, we observe significant low velocities beneath the Datong volcanic field, which are interpreted as the recent magmatic underplating resulted from the ongoing mantle upwelling in the northern TNCO. In addition, the mantle upwelling has dominated the rifting process in the northern segment of the FWR. Although the passive rifting of the FWR propagated from south to north, the north FWR is under an active lithosphere thinning regime now.