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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 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]

• Melt-bearing conductive crust beneath southeastern Tibet can flow laterally. • High conductivities beneath Chuxiong basin require saline aqueous fluids. • Thick resistor underneath the Emeishan large igneous province (ELIP) reflects remnants of a plume-modified lithosphere. • Rigid core of the ELIP inhibits crustal flow from Tibet. • Crustal growth via two distinct but closely related mechanisms. Broadband and long-period magnetotelluric (MT) data were used to obtain a continuous image of the lithospheric electrical conductivity structure across the southeastern Tibetan Plateau margin, where long-wavelength crustal thickening and surface uplift have been attributed to the influx of weak crustal material from Tibet into the adjacent Yangtze Block. The resulting resistivity model reveals two major conductive features in the middle–lower crust beneath southeastern Tibet and the Chuxiong basin, both of which are consistent with the presence of fluids and likely enhanced by shear deformation along large faults. The horizontally extensive conductor beneath southeastern Tibet could be interpreted as a partially molten layer that represents topography-driven crustal flow from central Tibet, whereas the anomalously high conductivities observed beneath the Chuxiong basin require the addition of substantial amounts of saline aqueous fluids. These two conductors are separated by a lithospheric-scale, high-resistivity body that situated beneath the geologically inferred core of the Emeishan large igneous province (ELIP). Together with other geophysical and geological evidence, we interpret this anomaly as remnants of a plume-modified lithosphere that originally formed during the Permian Emeishan volcanism, and speculate it acts as an obstruction to the southeastward crustal flow from Tibet since Late Cenozoic. These results indicate that topography-driven crustal flow may contribute to crustal thickening and uplift in southeastern Tibet, but not in the adjacent foreland. Instead, magmatic underplating associated with the Permian plume activity could account for both the elevated topography and thickened crust of the adjacent Yangtze Block without the need for crustal flow. [ABSTRACT FROM AUTHOR]