【摘要】 通过对汶川地震前观测的碌曲—若尔盖—北川—中江大地电磁剖面的数据处理和反演解释,揭示了沿剖面的松潘—甘孜地块、川西前陆盆地、龙门山构造带及秦岭构造带50 km深度的电性结构特征及相互关系,表明青藏高原东缘向东挤压,迫使向东流动的地壳物质沿高原东缘堆积,并向扬子陆块逆冲推覆.龙门山恰好位于松潘—甘孜地块与扬子陆块对挤部位,主要受松潘—甘孜地块壳内高导层滑脱和四川盆地基底高阻体阻挡的约束,地壳深部存在着西倾且连续展布的壳内低阻层,表明龙门山深部确实存在着逆冲推覆构造,其逆冲断裂系中的三条断裂不仅以不同的倾角向西北倾斜,并且向深部逐渐汇集,但茂县—汶川断裂可能在深部与北川—映秀断裂是分离的.龙门山两翼的四川盆地和松潘甘孜褶皱带的电性结构既具有明显差异性,又具有一定的相关性.四川盆地显示巨厚的低阻沉积盖层和连续稳定的高阻基底的二元电性结构,而松潘—甘孜地块则表现为反向二元结构,即上部大套高阻褶皱带,下部整体为低阻的变化带,龙门山逆冲构造带本身又表现为松潘地块逆冲上覆在四川盆地之上,构成上部高阻褶皱带、中部低阻逆冲断裂带和底部盆地高阻基底的三层电性结构.对比龙门山逆冲构造断裂带的西倾延伸上下盘两侧的两个反对称的二元电性结构,松潘区块深部推断的结晶基底与龙门山断裂带下盘推断的下伏盆地结晶基底又存在某种内在对应关系,推断可能存在一个西延至若尔盖地块的泛扬子陆块.因此,龙门山构造带地壳电性结构研究对于揭示青藏高原东缘陆内造山动力过程,探索汶川大地震的深部生成机理都具有重要意义.更多还原

【Abstract】 By processing, interpreting and inverting the magnetotelluric observation data obtained before the Wenchuan earthquake along the Luqu-Zhongjiang profile passing through Qinling Tectonic Zone, Songpan-Garze block and Longmen Shan Mountains, as well as Sichaun Basin, this paper reveals the crust architecture above 50 km depth of the Eastern Qinghai-Tibet Plateau and Western Sichuan foreland basin and the relationship between them. The eastward pressing of Qinghai-Tibet Plateau forces the Songpan-Garze block thrusting upon the Yangzi block, which obstructs the eastward movement of Qinghai-Tibet Plateau. The Longmen Shan is located at the joint of two blocks and it is found that there is a west-inclined low-conductivity layer in the crust at 10-20 km depth beneath the Longmen Shan Mountain, it is deduced as the deep conductivity characteristics of thrust belt structure in Longmen Shan tectonic zone. The three main faults of Maoxian-Wenchaun, Beichuan-Yingxiu and Peng-Guan of Longmen Shan fault belt dip to NW with different dip angles. The two faults of Beichuan-Yingxiu and Peng-Guan seem to converge together in the deep but they are probably separated with the Maoxian-Wenchaun fault. There are different characters between the Sichuan basin and Songpan-Garze fold belt located at the two sides of Longmen Shan. The Sichuan basin has a thick low-resistance sedimentary layer on a stable high-resistance basement, while Songpan-Garze block has high resisitivity cover of upper crust with continuous low resistance bed of the crust. Resulted from Songpan-Garze block thrusting onto the Sichuan Basin stable block, Longmen Shan tectonic zone formed a three-layer geoelectrical structure with high resistance in the upper and lower part and low resistance thrust fault zone in the middle. So the research on the MT profile is important for both continent dynamics in the orogenic zone and deep mechanism of Wenchuan earthquake at Longmeshan fault zone in the east of Qinghai-Tibet plateau.更多还原