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• Significant resistivity contrast is revealed in NE Tibet. • Upper crustal deformation is responsible for the uplift of the Longmenshan belt. • Ductile deformation of lower crust play key role in crust thickening of west Qinling. The northeastern margin of Tibet is the youngest risen part and key area for understanding the growth mechanism of the Tibetan Plateau. New broadband magnetotelluric (MT) data are conducted at the conjunction of the Longmenshan and West Qinling orogenic belts in NE Tibet. The preferred resistivity model obtained using 3-D inversion method shows a dramatic resistivity contrast from the Sichuan Basin (SB) to the West Qinling Orogenic Belt (WQOB). Beneath the SB and Longmenshan Orogenic Belt (LMSOB), several low-resistivity zones are distributed in the upper crust underlain by an intact resistive lower crust, indicating the upper crustal deformation is responsible for the uplift of the LMSOB. While to the north, a prominently conductive lower crust is observed, favoring the ductile deformation of the weak lower crust plays a significant role in the crustal thickening of the WQOB. Therefore, we suggest contrasting crustal deformation mechanisms work in the LMSOB and WQOB, and diversified crustal deformations together contribute to the marginal growth of the plateau. Moreover, combining with other studies, we propose the deep conductive bodies beneath the WQOB would be induced by the hot upwelling related to the asthenospheric flow from the plateau. [ABSTRACT FROM AUTHOR]

As one of the most prominent deformation features on Tibetan plateau, a series of N-S systematic rifts and V-shaped conjugate strike-slip faults are well developed in central-southern Tibet. However the mechanism for the formation of the rifts and conjugate strike-slip faults is still controversial. An east-west trending magnetotelluric (MT) array has been operated across the Gyaring Co Fault (GCF) at the northern end of the Xainza-Dingjye Rift (XDR) in Lhasa block. Three-dimensional (3-D) inversions are employed to image lithospheric resistivity structure. Combined with the previous north-south MT 3-D inversion result, electrical resistivity models reveal obvious conductive layer in the mid-to-lower crust beneath the XDR and apparent resistivity change in the vicinity of the GCF. The calculated depth-integrated conductivity shows that the weak mid-to-lower crust (~30 km- ~ 60 km) characterized by high conductance (≥ ~10,000 S) and melt fraction of ~5–13%, is mainly distributed between the Indus-Yarlung suture (IYS) and the GCF, whereas the relatively rigid crust characterized by low conductance (≤ ~2000 S) and melt fraction of ~2–4% appears to the northeast of the GCF. The weak mid-to-lower crust in southern Tibet and the abrupt difference in the resistivity characteristics of the mid-to-lower crust in the vicinity of the GCF, suggest the formation of the rifts in Lhasa block is closely associated with the weak mid-to-lower crust. Taken together with the upper mantle seismic features, the weak mid-to-lower crust is believed to be attributed to the underplated Indian plate. An alternative geodynamic model is presented to respond to the eastward extrusion during the ongoing N-S convergence between the Indian and Eurasian plates, that the rigid crust in central Tibet is sandwiched by the weak mid-to-lower crust in southern and northern Tibet, and the rifts form above the weak mid-to-lower crust, whereas the conjugate strike-slip faults develop on the rigid crust in central Tibet. [Display omitted] • 3-D inversion resistivity models are obtained from the orthogonal MT arrays in Lhasa terrane. • Apparent resistivity variation in the mid-to-lower crust is revealed beneath the vicinity of the strike-slip faulting. • The rifts form above the weak crust, whereas the conjugate strike-slip faults develop on the rigid crust in central Tibet. [ABSTRACT FROM AUTHOR]

The Qinling Orogenic Belt is located at the central part of the China Central Orogenic Belt and links the Qilian and Kunlun Orogenic Belts to the west with the Dabie-Sulu Orogenic Belt to the east, which is sandwiched between the South China Block and North China Block. There have been several geodynamic models developed to explain the evolution process of the Qinling Orogenic Belt, but they remain controversial. The magnetotelluric (MT) method can study subsurface electrical structures. In order to have a better understanding of the tectonic evolution of the Qinling Orogenic Belt, a study of broadband and long period MT profile across the middle Qinling Orogenic Belt is carried out. The MT profile starts from the northeastern margin of the Sichuan basin, crosses the Qinling, and finally reaches the Weihe basin at about 108.5°E. Based on data analysis results, we have finally obtained a lithospheric electrical resistivity model of the middle Qinling Orogenic Belt through three-dimensional (3-D) inversion of magnetotelluric data. The MT result reveals that the Sichuan and Weihe basins may have remnants of the ancient craton basement in our study area. The electrical structure characteristics of the South Qinling Belt and North Qinling Belt are obviously different, the South Qinling Belt is relatively low resistivity, while the North Qinling Belt is relatively high resistivity. This may indicate that the Southern Qinling Belt is affected by the later strike slip extrusion and the Northern Qinling Belt is a relatively stable block. The lithospheric mantle of middle Qinling Orogenic Belt is characterized by overall high resistivity, which may indicate that the lateral extrusion effect of the Tibetan Plateau material is negligible in this region. • Lithospheric electrical structure of the middle Qinling Orogenic Belt was obtained from 3-D inversion of MT data. • The Southern Qinling is affected by the strike-slip fault and the Northern Qinling is a relatively stable block. • Lithospheric mantle is not greatly affected by the eastward extrusion of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• Magnetotelluric images were obtained across the Xiaojiang fault system (XJFS). • Fluid-based fault zone conductors divide the resistive upper crust into fault-parallel blocks. • Lower crustal conductors may be associated with shear-enhanced partial melting. • A dynamic model is proposed for understanding the deformation mechanism of the XJFS. It is widely accepted that large-scale strike-slip faults play an important role in accommodating the India‐Eurasia convergence, but the relationships between surface displacements and deep deformation along the faults remain largely uncertain. To address this issue, new magnetotelluric (MT) images were obtained along two profiles across the Xiaojiang strike-slip fault system (XJFS), one of the most tectonically active areas in southwest China. Although different in details, these two profiles show similar overall crustal structures. The upper crust is generally resistive but separated by several narrow, subvertical conductors that broadly coincide with the surface traces of the XJFS. These fault zone conductors (FZCs) are interpreted to represent fault damage zones that formed by strike-slip faulting/shearing along the faults and filled with deeply-sourced magmatic and/or metamorphic fluids. The lower crust is broadly characterized by enhanced conductivity and likely associated with partial melting at high temperatures. These observations are consistent with other geophysical measurements in this area and in favor of the development of ductile flow along the XJFS, although the pattern of flow is more complex than previously suggested. Based on these observations, we propose that active deformation along the XJFS can be better described, in the brittle upper crust, by strike-slip motion along the fluid-weakened faults, and by shear-enhanced ductile flow in the partially molten lower crust. These two mechanisms are not mutually exclusive but rather can be complementary to each other. [ABSTRACT FROM AUTHOR]