New Insights into the Structure of the Northern Margin of the India-Asia Collision from Magnetotelluric Data across the Central Altyn Tagh Fault

Abstract:

The Altyn Tagh Fault (ATF) is a left-lateral, strike-slip fault that forms the northern margin of the Tibetan Plateau and plays a significant role in accommodating the convergence between the colliding Indian and Eurasian plates. As a part of the fourth phase of the INDEPTH project, magnetotelluric (MT) data were collected across the central segment of the ATF to determine the lithospheric-scale structure of the fault system. Dimensionality analyses demonstrated that the MT data can be interpreted using two-dimensional approaches, but some localized 3-D effects are seen. Consequently, both 2-D and 3-D inversions were carried out, and a joint interpretation was made on the basis of these two types of models. Inversion models revealed two major conductors beneath the Qaidam Basin (QB) and Altyn Tagh Range (ATR), respectively. The conductive region beneath the QB was interpreted as a ductile layer in the lower crust to upper mantle that might represent flow beneath the western margin of the QB, whereas the large scale south-dipping conductor beneath the ATR is interpreted as a region with high fluid content formed by metamorphism associated with the oblique underthrusting of the Tarim Block beneath the northern Tibetan Plateau. These fluids migrate upward through the fault system and have formed serpentinized zones in the crust. Combining these interpretations, a structural model compatible with diverse geophysical observations is proposed, in which we suggest the competing end-member rigid block model and continuum model are reconcilable with the continuum model locally dominant for the study region, as evidenced by a thickened crust.

* This work was funded by National Natural Science Foundation of China (41404060, 40974058, 40904025) and Fundamental Research Funds for the Central Universities (2652014016).

Reference:

Zhang, L., Unsworth, M., Jin, S., Wei, W., Ye, G., Jones, A.G., Jing, J., Dong, H., Xie, C., Le Pape, F., Vozar, J., 2015. Structure of the Central Altyn Tagh Fault revealed by magnetotelluric data: New insights into the structure of the northern margin of the India–Asia collision. Earth and Planetary Science Letters 415, 67-79. http://dx.doi.org/10.1016/j.epsl.2015.01.025.