Features of the Faults in Center and North Tibetan Plateau: Based on Results of INDEPTH (Ⅲ)-MT
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摘要: 根据1998年和1999年INDEPTH (Ⅲ) MT在西藏中、北部所完成的德庆-龙尾错(500线)和那曲-格尔木(600线) 超宽频带大地电磁深探测剖面数据研究西藏高原中北部断裂构造特征, 有助于推进印度板块与亚洲板块碰撞、俯冲构造模式的研究.研究结果表明, 区内发育有F1~F10一系列深断裂.其中, F2向北倾斜是早期的主断裂, F1则是后期主逆冲断裂, 它们共同构成空间结构复杂的嘉黎深断裂带.班公-怒江缝合带的主断裂系由略微向南陡倾的F3、F4和F5三组超壳深断裂构成; 由于受后期构造运动强烈的改造, 缝合带内发育多条延深不大的上地壳断层.唐古拉断裂带由F6、F7两组主断裂和一系列次级断裂构成; 主断裂产状上陡、下缓, 总体向南倾斜, 向下延深达下地壳.而金沙江缝合带是由F8 (金沙江断裂)和F9 (可可西里断裂), 以及它们之间存在的一系列上地壳次级断层共同组成的, 是一组很宽的地块碰撞缝合带.F10即昆中断裂是产状陡立的超壳深断裂, 是昆仑山断裂带的主体构造, 它构成松潘-甘孜-可可西里地块的北部边界.从剖面电性结构特征分析, 昆中断裂以南属于西藏高原主体; 而以北地区是否还归属西藏高原?这有待更深入的讨论.值得特别关注的事实是, 研究区内2组缝合带之下都存在向上地幔延伸的壳内高导体, 它们可能反映区内壳幔热交换过程的痕迹.
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关键词:
- INDEPTH-MT /
- 大地电磁测深 /
- 断裂特征 /
- 壳幔热交换.
Abstract: The features of the faults in the center and north of the Tibetan plateau are discussed, based on two super-wide band magnetotulleric (MT) sounding profiles which belong to INDEPTH (Ⅲ) -MT and were finished between 1998 and 1999: one is from Deqing to Longweicuo (named line 500), the other is from Naqu to Golmud (named line 600). This work assists research on the collision and subduction mode between the India and Asia plates. The MT result shows that there are series of deep faults, F1 to F10, in the center and north Tibetan plateau. Of these faults, F2 is an earlier main fault which leans to the north, and F1 is a later main overriding fault. Jiali deep fault zone, which has a very complex space structure, is composed of these two faults. F3, F4 and F5 are super-deep faults. They are high angle faults and lean a little to the south. The main fault zone of Bangong-Nujiang suture is composed of these three faults. Because of later activity in the structure, several shallow faults formed in the upper crust within the Bangong-Nujiang suture. Tanggula fault zone is composed of two main faults, F6 and F7, and a series of sub-faults. The shallow segments of the main faults are in high angle and the deep segments of main faults are in low angle. These two faults lean to the south generally and extend into the lower crust. Jinshajiang suture is composed of Jinshajiang fault (F8) and Kekexili fault (F9), and there is a series of sub-faults in the upper crust between these two faults. Jinshajiang suture is a very wide suture caused by continent-continent collision. The Middle-Kunlun fault (F10), which is the main structure of Kunlun fault zone, is a high angle, super-deep fault. It is the north boundary of Songpan-Ganzi-Kekexili block. Based on the conductive structure of the profile, the south of the Middle-Kunlun fault belongs to the Tibetan plateau, but it is not certain whether the north of Middle-Kunlun fault also belongs to the Tibetan plateau. There are conductive bodies stretched from the crust into the upper mantle below Bangong-Nujiang suture and Jinshajiang suture. This may suggest heat exchange between crust and mantle. -
图 1 INDEPTH-MT测线布置(底图尹安, 2001)
Ⅰ.北祁连缝合带; Ⅱ.木里—拉脊山缝合带; Ⅲ.柴达木北缘缝合带; Ⅳ.玛沁缝合带; Ⅴ.金沙江—哀劳山缝合带; Ⅵ.龙木错—双湖—澜沧江缝合带; Ⅶ.班公错—怒江缝合带; Ⅷ.印度河—雅鲁藏布江缝合带; Ⅸ.甘孜—理塘缝合带
Fig. 1. INDEPTH-MT profile position
图 2 Tbt-628号点超宽频带大地电磁测深曲线(MT-24 & LIMS)
Fig. 2. Super wide-band MT sounding curve of site Tbt-628
图 3 500线(a)和600线(b) 大地电磁测深二维反演模型
Fig. 3. Line 500 (a) and line 600 (b) resistivity model from 2D MT inversion
图 4 500线(a)和600线(b) MT理论与实测MT响应拟断面的比较
Fig. 4. Observed and calculated MT pseudo-section of line 500 (a) and line 600 (b)
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