Deep electrical structures of the eastern margin of the Songnen massif and the western margin of the Jiamusi massif

The Songnen and Jiamusi massifs are two important tectonic units in the east part of Northeast China. A 210 km-long magnetotelluric (MT) sounding profile with 40 broadband MT sites across the eastern margin of the Songnen massif and the western margin of the Jiamusi massif has been measured. Data processing and analysis include calculation of the 2D skewness and electric strike of the MT profile, and NLCG 2D inversion for apparent resistivity and phase data of TM mode. An electrical structure model of crust and upper mantle was established, which can be divided into three tectonic units the eastern margin of the Songnen massif, the collision belt and the western margin of the Jiamusi massif, which is consistent with the regional geology.The research shows that: (1) The upper crust of the study area may be volcanic rocks and granites representing multi-periodic magmatic activities, and the conductive bodies in the middle lower crust connected with the below conductive bodies may indicate the upwelling material channel of the mantle. (2) The west-dipping conductive body may be tectonic traces resulting from the subduction of the Jiamusi massif to the Songnen massif. (3) The study area may have undergone delamination, and the concomitant uplift of the mantle material is the major impetus of the extension.