Magnetotelluric imaging of cold, dry lithospheric drips within a hot and volatile-rich asthenospheric mantle

Lithospheric foundering, through mechanical delamination or convective dripping, has been invoked to elucidate various perplexing geological phenomena, including near-surface deformation, sedimentation, and volcanism. Compared to delamination, direct evidence for the existence of modern lithospheric drips has been challenging to acquire because of their small-scale and transient nature. Here we present an image of the crustal and upper mantle electrical resistivity derived from high-quality, long-period magnetotelluric array data that extend from the southwest Songliao Basin (SLB), crossing the Great Khingan Range and onto the eastern Mongolia Plateau. The model reveals widespread layers of low resistivity in the deep crust and uppermost mantle beneath the mountainous regions surrounding the largely resistive SLB, where intense volcanism has occurred episodically during the Late Cenozoic. In the deep upper mantle, the model consistently reveals a set of elongated columns exhibiting high resistivity, interspersed with sub-vertical conductive anomalies. By incorporating additional petrologic, geochemical and experimental constraints, these drip-shaped resistive anomalies were interpreted as cold and dry lithospheric drips within a relatively hot and volatile-rich asthenospheric mantle. In light of the geological background, the dripping process may be linked to the edge-driven flow induced by the lithosphere thickness step between the rifted SLB and the adjacent mountainous areas. These results indicate that lithospheric dripping and induced asthenospheric upwelling may be significant factors in driving intraplate volcanism.