郯庐断裂带南段大地电磁主轴方位统计分析及其意义

本文利用多测点-多频点阻抗张量统计成像技术统计分析了三条横跨郯庐断裂带南段的大地电磁剖面上的电性主轴分布特征,从电性主轴的角度描绘了大别郯庐构造区不同构造的特征及构造间的几何关系.统计结果显示:郯庐断裂带南段在断裂带浅部的电性主轴方位及二维有效因子中有明显的显示,同时郯庐断裂带南段可能未影响断裂深部介质;扬子板块及大别块体东南部地区浅部和深部的主轴方位明显不一致,表明浅部和深部之间存在结构不整合,主轴方位表明不同深度的介质受不同方向构造力的作用;大别造山带南部及以南地区深部介质中EW向电性主轴可能是板块汇聚时期扬子板块深部韧性层受NS向挤压应力作用的结果,郯庐断裂带以东地区深部韧性层中NWW向的电性主轴则是扬子板块沿郯庐带向NNE方向运动形成的;北大别块体深浅一致的电性主轴分布特征符合中生代穹隆抬升、增厚的演化过程.对该地区电性主轴的统计结果为认识该地区的深部结构及地下介质的运动极性提供了重要的依据,也为认识大别郯庐构造区的演化过程提供了新的证据.

Statistical analysis of geo-electrical strike beneath the southern section of Tanlu fault zone and its significance

In this study,we applied the conjugate impedance transformation to decomposite the magnetotelluric impedance tensor of three profiles stretching across Tanlu fault zone,and obtained the structural dimensionality,geo-electrical strike and other parameters.The magnetotelluric impedance tensor imaging technique is used to analyze the distribution of geo-electrical strikes at different sites and frequencies.Distribution characteristics of geo-electrical strike reflect the distribution and contact relationship of different tectonic unit.Statistical results show the Tanlu fault zone is obviously displayed by the orientation of geo-electrical strike and the two-dimensional effective factor in the upper part,but it may not extend to the lower part.In Yangtze plate and southeast of Dabie block,geo-electrical strike orientations in the upper part is inconsistent with those in lower part.It reveals the structural unconformable contact between upper layer and lower layer,and indicates tectonic forces with different directions affected lower and upper media respectively.During the period of plate convergence,the north-south compressive stress influenced the lower ductile layer in the south of Dabie orogen and its south adjoining region,forming the east-west trending geo-electrical strike.Meanwhile,the Yangtze plate on the east of Tanlu fault zone moved along the north-north-east Tanlu fault zone,the lower ductile layer formed north-west-west geo-electrical strike.Uniformity geo-electrical strike of the upper and the lower in North Dabie unit conforms to the evolution process of the upraising and thickening of the orogen in Mesozoic.Statistical results of geo-electrical strike in this area provide an important basis for understanding the deep structure and the movement polarity of underground media in this area and new evidences for understanding the evolution process Dabie-Tanlu tectonic zone.