Large, multilevel magmatic intrusions as an important carbon degassing source in a nonvolcanic setting

Magmatic intrusions in nonvolcanic areas are believed to cause extensive CO2 degassing and seismicity. However, the size, geometry, and spatial relationships of these hypothesized intrusive bodies remain unclear due to a lack of high-resolution geophysical data, especially in Northeast China sedimentary basins. Here, we present a three-dimensional electrical resistivity model based on magnetotelluric data from the Songliao Basin in Northeast China. The model shows a low-resistivity anomaly at the Moho depth vertically connecting to two shallower, sill-like anomalies in the crust. These anomalies are interpreted as multilevel basaltic intrusions, with the mid-crust sills estimated to contain up to 150 km3 of melt. The layering of the crust, as well as the level of neutral buoyancy, plays a critical role in controlling the geometry and depth of the intrusions in the basins. Seismicity, high heat flow, and CO2 degassing indicate that this huge magmatic system, although located in a nonvolcanic area, is still active.