Thermochemical State of the Upper Mantle Beneath South China From Multi-Observable Probabilistic Inversion

摘要

We present an upper mantle model of seismic velocities, temperature, density, and bulk composition for the South China Block (SCB) and adjacent areas by jointly inverting Rayleigh wave phase and group dispersion data, absolute elevation, geoid height, and surface heat flow using a probabilistic inversion method. The lithospheric structure of this region is dominated by a thick root (200-240 km) under the western Yangtze and thinner lithosphere (70-120 km) under the eastern SCB, in agreement with independent xenolith data. We reveal for the first time the extent of metasomatism/refertilization in the lithospheric mantle beneath the Yangtze Craton (YC). Our results show pervasive refertilization of the lithospheric mantle associated with the basaltic lavas of the Emeishan large igneous province. We also show that the refertilized mantle identified in the northern boundaries of the YC extends into the interior of the craton further than previously recognized, reaching at least parts of the Sichuan basin. The only region that preserve a depleted mantle signature is the central segment of the Yangtze craton. In contrast, the eastern SCB lithosphere is characterized by an alternating pattern of fast/slow seismic and depleted/fertile anomalies, supporting the hypothesis that the lithospheric mantle has been partly replaced/modified by deep mantle processes during the Phanerozoic. Also, we found no evidence for a linear plume track associated with the Hainan plume that can be used to independently constrain the plate motion history of the SCB.