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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]

The Central Yunnan block (CYB) plays a key role in accommodating the crustal tectonic deformation of the southeastern Tibet, but its exact mechanism is poorly understood. Here we obtained a fine S-wave velocity structure of the upper crust across the Xiaojiang fault system in CYB, using the ambient noise tomography with a linear dense short-period array. The result shows a strong S-wave velocity variation along the profile, which is consistent with geomorphology and hypocenters occurred in this area. The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with the transition from surface erosion, to ductile basement and to rigid basement in the greater depth. Combining the upper crustal structure from our image with the location of hypocenters, we propose that most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the CYB. • Ambient noise tomography shows a fine S-wave velocity structure of the upper crust across Xiaojiang fault system. • The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with geomorphology and hypocenters occurred in this area. • Most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the Central Yunnan Block. [ABSTRACT FROM AUTHOR]

The Qilian Shan is located along the northeastern margin of the Tibetan Plateau, which is a key area for studying the growth and expansion of the Tibetan Plateau. There have been several geodynamic models developed to explain the deformation pattern of the Tibetan Plateau extending to the northeast, but they remain controversial. The magnetotelluric (MT) method can study subsurface electrical conductivity and rheological properties. A dense broadband and long period magnetotelluric (MT) profile across the middle Qilian Shan has been completed. The MT profile starts from the northeastern margin of the Qaidam Basin, crosses the Qilian Shan and Hexi Corridor, and finally reaches the southwestern margin of the Alashan Block. Based on data analysis results, a three-dimensional (3-D) resistivity model of the crust and upper mantle has finally been obtained. The MT results show that a relatively low resistivity zone exists at the bottom of the upper crust of the Qilian Shan, features as an intracrustal decollement, which indicates the decoupling deformation between the upper and lower crust. The isolated conductive bodies in the middle-lower crust of the Qilian Shan may have formed during the primary stage of plateau growth, suggesting that there may be no existence of the middle-lower crustal flow beneath the Qilian Shan. The Alashan Block lithospheric mantle may have partly underthrust southward the Northeastern Tibetan Plateau. The Tibetan Plateau may have grown and expanded northeastward across the Hexi Corridor to the Heli Shan Fault. • Lithospheric electrical structure along a profile across the Qilian Shan was obtained from 3-D inversion of MT data. • There may be no crustal flow. Alashan Block may have partly underthrust the Northeastern Tibetan Plateau. • Tibetan plateau may have extended northeastward across the Hexi Corridor to the Heli Shan Fault. [ABSTRACT FROM AUTHOR]

Broadband and long-period magnetotelluric (MT) soundings were collected along a 600-km-long EW-trending profile across the southwestern segment of the Jiangnan Orogenic Belt (JOB) to explore the possible remnants of ancient tectonic processes beneath the central South China Block (SCB). Beneath the JOB, the resistivity model reveals a west-dipping, trans-lithosphere conductor (<20 Ω ∙ m) embedded within the relatively thick (80–120 km) and highly resistive (>1000 Ω ∙ m) lithosphere, possibly associated with relics of the Neoproterozoic subduction zone between the Yangtze and Cathaysia blocks. The crustal portion of this conductor is interpreted as solid conducting materials (e.g., graphite, sulfide) that were emplaced into the crust during subduction and orogenesis, whereas its lithospheric mantle portion is more likely to be volatile-bearing minerals formed by subduction-related metasomatic processes. We attribute the greatly reduced asthenospheric resistivities (1~10 Ω ∙ m) below the JOB to low-degree melting of the early-formed metasomatized mantle. In contrast, the lithosphere of the Cathaysia Block is evidently thinned (60–100 km) and segmented by several subvertical, lithospheric-scale conductors (1~30 Ω ∙ m) that are likely associated with fossil fluid pathways along reactivated shear/fault zones. Notably, the thinnest lithosphere sits above a prominent low-resistivity (10 ~ 30 Ω ∙ m) anomaly in the asthenospheric mantle and is spatially coincident with the location of Late Jurassic basaltic outcrops. We interpret these features as signs of lithospheric extension and asthenospheric upwelling driven by roll-back of the Paleo-Pacific Plate during the Late Mesozoic. The results provide key constraints on subduction–accretion tectonics associated with the Neoproterozoic assembly of the SCB and the subsequent lithospheric evolution during the Phanerozoic. [Display omitted] • Dense magnetotelluric soundings reveal high-resolution lithospheric structure beneath central South China. • Relics of Neoproterozoic subduction preserved beneath the Jiangnan Orogenic Belt. • A notably thinned lithosphere is identified beneath the westernmost Cathaysia Block. [ABSTRACT FROM AUTHOR]