Thermochemical structure of the North China Craton from multi-observable probabilistic inversion: Extent and causes of cratonic lithosphere modification

Abstract

We present a 3D thermochemical model of the North China Craton (NCC) from the surface down to 350km by jointly inverting surface wave phase velocity data, geoid height, surface heat flow and absolute elevation with a multi-observable probabilistic inversion method. Our model reveals a thin (~65–100km) and chemically fertile lithosphere (87<Mg#<90) beneath the Eastern NCC, consistent with independent results from mantle xenoliths, and supports the idea that the Eastern NCC experienced significant lithospheric destruction and refertilization during the Phanerozoic. In contrast, beneath the Trans-North China Orogen, Inner Mongolia Suture Zone and Yinshan belt, we observe a more heterogeneous (chemically and thermally) lithosphere, indicating that these areas have been partly involved in lithospheric modification and mechanical erosion at multiple scales. A cold and chemically refractory (Mg#>90) lithospheric mantle is imaged beneath the central TNCO and Ordos Block, reaching depths >260km. This lithospheric “keel” is surrounded to the east by a high-temperature sublithospheric anomaly that originates at depths >280km. The spatial distribution of this anomaly and its correlation with the location of recent volcanism in the region suggest that the anomaly represents a deep mantle upwelling being diverted by the cratonic keel and spreading onto regions of shallow lithosphere. Our results indicate that the present-day thermochemical structure beneath the NCC is the result of a complex interaction between a large-scale return flow associated with the subduction of the Pacific slab and the shallow lithospheric structure.