Publication 176
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
Zhang, L. M.J. Unsworth,, S. Jin, W. Wei, G. Ye, A.G. Jones, J. Jing, H. Dong, C. Xie, F. Le Pape, and J. Vozar
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.
Source
Earth and Planetary Science Letters, 415, 67-79, doi:10.1016/j.epsl.2015.01.025. [PDF]
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