Search

Mantle tectonics, such as asthenospheric upwelling and lithospheric decoupling, usually controls subsequent fluid formation and migration from deep to shallow levels in the lower lithosphere and promotes rock failure and deformation. Based on the concept whereby the fluid migration location defines the structural inheritance, we aim to relate crustal processes to mantle tectonics using fluids revealed by a new magnetotelluric (MT) array across the Ailao Shan-Red River belt. As imaged via a 3D resistivity model, two lower-lithospheric conductive anomalies are determined as consistent with the Dian-Qiong (DQ) suture and Song Da (SD) belt and interpreted to contain interconnected melt. Because potassic magmatism was enabled by partial melting in the lower lithosphere, we could infer that the DQ and SD have reworked as the major fluid migration channels. Fluid migration is considered to drive lithospheric decoupling at a low-viscosity conductive layer, which is inferred feeding by aqueous and melt fluids originating from the two channels and diffusing at depths from 15 to 20 km. Constrained by the geochronology results, this weak layer could have provided convenience to induce the entirely upper crustal translation-rotation within the time interval between potassic magmatism and strike-slip of the Red River fault. This translation-rotation process is inherited from the underlying mantle processes and may further be remotely affected by the upper crustal movement of the Tibetan Plateau, conforming with the crustal rotation observed to the north of our study region. This work provides a compelling example of the tectonic control of the mantle on inherited responses in the crust. Plain Language Summary Crustal deformation is usually controlled by mantle tectonic processes, especially the southeastern Tibetan Plateau. Some models have proposed that lithospheric shearing and lower-crustal flow have controlled the crustal deformation in the Cenozoic. However, crustal rotation models show less possibility of a channel flow and relate the crustal deformation to the remote effect of India-Asia collision. Our study investigates above hypotheses by imaging the electrical resistivity of rocks beneath the major Red River Fault area in southeastern Tibet, using magnetotelluric data with high quality in a dense array. The lithosphere of the study area is interpreted to have been divided into two horizontal systems by a fluid diffusion layer at the bottom of upper crust. Resistivity low in the lower lithosphere is inferred due to partial melting of deep lithosphere and reworking of the paleo sutures in the Late Cenozoic, which have spread at the bottom of upper crust. Rather than the channel flow, this fluid migration process sensitively reflected in our model relates the mantle tectonics to crustal rotation by providing rheological conditions. We, hence, propose an inherited structure model featured by lithospheric decoupling and upper-crustal translation-rotation that may occur before the major strike-slip event. [Display omitted] • A new 3D model reveals electrical structures on the southeastern Tibetan Plateau. • The Red River fault is discontinuous at a depth of ∼20 km and may move away from the palaeo-suture. • Palaeo-suture was reconstructed into two activated zones and reworked as channels for fluid migration. • Fluid migration has driven the lithospheric decoupling and upper crustal inheritance. • The upper crust experienced a translation-rotation process before the internal strike-slip event. [ABSTRACT FROM AUTHOR]

Dense array Magnetotelluric sounding (MT) was applied in the study of the emergence of massive gold deposits relating to the tectonic activity responsible for the creation of the North China Craton. This study focuses on understanding the shallow crustal electrical structure characteristics (>1.5 km) of Pb Zn and Au Ag deposits in the Qingchengzi orefield, through the analysis of shallow electrical resistivity distribution at depths less than 5 km, obtained by 3D inversion of full impedance at a frequency range of 320–0.107 Hz. The results showed that the electrical characteristics of Xiaotongjiapuzi and Taoyuan deposits in the 3D resistivity model are consistent with the known 2D resistivity model, and the Jianshanzi fault plays an important role in the gold mineralization, acting as a migration channel and precipitation zone for ore-forming materials. It is inferred that the fault extends at least 5 km deep with deep mineralization prospects. The strata of Liaohe Group in the north of the orefield, the intrusive granite in the south, and the NW-trending Jianshanzi and Yushanggou faults show distinguishable electrical properties, which are either high resistance, low resistance, or high and low resistance transition zone on the depth slice map. Furthermore, the Xinling rock mass has a NE trending extension, which confirms the inference that the Jianshanzi fault extends to a depth of 5 km into the crust. • Imaging shallow crustal electrical structures through 3D inversion of MT data. • Relationship of mineralization with the electrical structure, fault, and lithology. • Guide the deep prospecting direction of polymetallic deposits in the future. [ABSTRACT FROM AUTHOR]

We conducted broadband Magnetotelluric survey to obtain 2D lithospheric electrical structures of Alxa block through two NE-SE trending profiles, which revealed the electrical evidence of bidirectional subduction of Paleo-Asian Ocean with spatial difference beneath Enger Us fault belt. [Display omitted] • Lithospheric electrical structures of the Alxa block were imaged through two NW-SE BMT profiles. • There was bidirectional subduction of the Paleo Asian Ocean beneath the Enger Us fault belt. • The low resistivity bodies of the middle and upper crust in the northwest are related to large-scale horizontal nappe tectonics. • The high conductivity bodies that extend deep in the southeast are attributed to the partial melting. The Alxa Block, situated between the Tarim and North China cratons, is essential to understand the tectonics of northwest China. It has undergone several tectonic cycles, including rifting from northern Gondwana in Neoproterozoic, subduction-accretion of the Paleo-Asian Ocean during Paleozoic, and intracontinental deformation in Mesozoic. Broadband magnetotelluric data covering a frequency range of 320 Hz to ∼ 10000 s was collected along two NW-SE trending lines across major tectonic units of the Alxa region to investigate the deep structures of the Alxa Block. By applying the nonlinear conjugate gradient (NLCG) inversion approach, two-dimensional (2D) electrical resistivity models were obtained at a 100 km depth. These findings indicate that the Zhusileng-Hangwula and Zongnaishan-Shalazhashan tectonic zones have high resistivity in their lower crust and upper mantle, with an overall layered high-low–high resistivity pattern. The upper crust of the Nuru-Langshan tectonic zone is primarily characterized by high resistivity values, whereas the lower crust and upper mantle contain a large-scale low-resistivity (or conductive) zone that is likely the result of partial melting. The large-scale Early–Middle Jurassic nappe structures may be connected to sub-horizontal low-resistivity anomalies in the shallow strata, which are located up to 20 km below the Yagan and Zhusileng–Hangwula tectonic zones. Below the Engger Us fault, two low-resistivity bands are interpreted as the product of bidirectional subduction and final closure of the Paleo-Asian Ocean. The Alxa Block may have subducted southwards beneath the Ordos Block, as suggested by a clear low-resistivity anomaly between the two blocks. Furthermore, partial melting may have happened for high-conductivity bodies in the upper mantle based on the modified Archie formula's evaluation of their melting degree. [ABSTRACT FROM AUTHOR]

• Three-dimensional electrical resistivity structure beneath Ganzi Basin, eastern margin of Tibetan Plateau was obtained. • 3D electrical model reveals the shallow and deep geothermal reservoirs in Ganzi geothermal system. • The Ganzi fault provides the pathway for transport heat and the circulation of geothermal fluids. The Ganzi geothermal system located in the eastern margin of Tibetan Plateau, is found to distribute the strongly active surface manifestations, such as boiling springs, and fumaroles. The resistivity structure of high-temperature hydrothermal system beneath Ganzi Basin has been obtained from the three-dimensional (3-D) magnetotelluric inversion of 103 broadband MT stations in period range from 320 Hz to 1000s. The MT stations have an average spacing of 500 m and completely cover the Ganzi Basin. The detailed 3-D resistivity structure which the authors found has been described characteristics of the shallow and deep geothermal reservoirs as well as to correlate with the structural features present in the Ganzi Basin. The shallow geothermal reservoir is mainly composed of the sedimentary layer, with a depth of 300−800 m, while the deep geothermal reservoir mainly consists of the fault fracture zone with a depth of 1−5 km. The porosity of the geothermal reservoirs is in the range 5–10 %, estimated based on the resistivity model. The Ganzi fault provides the pathway for transport heat and the circulation of geothermal fluids. The possible heat source for the Ganzi geothermal system has been attributed to tectonic deformation heating in the crust, radiogenic heat production derived from the decay of U, Th and K, and heat from the mantle. [ABSTRACT FROM AUTHOR]