Features of the Faults in Center and North Tibetan Plateau: Based on Results of INDEPTH (Ⅲ)-MT

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.