Ongoing Asthenospheric Upwelling and Delamination‐Style Down‐Welling Beneath Northeast China: Evidence From High‐Resolution Magnetotelluric Profiles

Northeast China was formed during the progressive closure of the Paleo-Asian Ocean before the Early Mesozoic, and was then later affected by the westward subduction of the Paleo-Pacific Plate and the west-to-east closure of the Mongolia-Okhotsk Ocean. Huge volumes of granites were emplaced across this region during the Mesozoic, and widespread Cenozoic volcanism is still active in the Quaternary. To study past and present magmatic processes in this region, two parallel high-resolution magnetotelluric profiles were collected to produce lithospheric resistivity models. Northwest of the Greater Xing'an Range, the lithosphere has a relatively low resistivity. The resistivity of the upper mantle low-resistivity anomaly (C2) is consistent with the presence of a few percent of basaltic melt. This feature connects with a shallower low-resistivity zone (C1) that extends into the crust. Its properties are consistent with 5-10% shoshonitic melt. The lithosphere in the southeast part is highly resistive. The upper mantle high-resistivity zones (R1 and R2) are interpreted as regions of thickened lithosphere that may be undergoing delamination. The lower crust exhibits localized low-resistivity zones (C3, C4, and C5), and they are interpreted as partial melt which may have originated in the ongoing upwelling. The overall pattern of magmatism appears to be driven by asthenosphere upwelling which might have been triggered by the Paleo-Pacific Plate retreat, but the upper mantle low-resistivity zone originates and rises from the northwest. Down-welling in the southeast might be the combined effect of the subduction and retreat of the Paleo-Pacific Plate and the instability of thickened lithosphere.