松嫩地块东缘和佳木斯地块西缘电性结构

横过松嫩地块东缘和佳木斯地块西缘的大地电磁测深剖面揭示了两块体结合带附近的深部电性结构.本文对剖面测点做了标准化数据处理,并对二维偏离度、构造走向进行了计算和分析,采用非线性共轭梯度(NLCG)二维反演方法对TM模式的数据进行了反演,获得了该剖面的地壳、上地幔电性结构模型,划分出三个典型构造单元:松嫩地块东缘、碰撞拼合带和佳木斯地块西缘.研究结果表明,研究区上地壳基本呈高阻特征,可能为岩浆岩,代表其经历了多期次岩浆作用,而松嫩地块东缘和佳木斯地块西缘的中下地壳的高导体可能与地幔物质的上涌有关;拼合带下方存在西倾的高导体和高阻体,可能是佳木斯地块向西俯冲到松嫩地块下方的构造遗迹;研究区可能发生了拆沉作用,与之伴随的地幔物质上涌可能是后期伸展作用的一个动力.

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.