New Insights Into Crustal and Mantle Flow Beneath the Red River Fault Zone and Adjacent Areas on the Southern Margin of the Tibetan Plateau Revealed by a 3‐D Magnetotelluric Study

Abstract

A number of geodynamic models have been proposed for the southeastern margin of the Tibetan plateau and include a range of deformation processes. One unresolved issue is whether crustal and mantle flow occurs, and if it does, how flow contributes to the mass balance of the India-Asia collision. To address this question, new magnetotelluric data were collected and used to derive a three-dimensional electrical resistivity model of the crust and upper mantle beneath the Red River Fault (RRF) zone and adjacent areas. The most prominent features of the model are (1) a resistor in the upper-middle crust directly beneath the trace of the RRF; (2) a major change in upper mantle resistivity across the RRF; and (3) a significant conductor in the upper mantle northeast of the RRF, which extends upward into the crust, and which requires a melt fraction of up to 3%. The model suggests that the lower crustal conductors may be due to melt/fluids derived from the mantle, rather than from outward flow from Tibet. The most likely source of fluids and melts could be upwelling mantle flow related to the Hainan mantle plume. The change in resistivity across the RRF implies a change in lithospheric strength may explain the present-day localization of deformation and uplift at this location. The resistivity model may also give insights into the distribution of ore deposits in Ailao Shan, since many mineral deposits are derived from magmatic fluids generated in the mantle at the edges of regions of thick lithosphere. Plain Language Summary Continent-continent collisions are an important tectonics process that have formed mountain ranges such as the Himalaya and features such as the Tibetan Plateau. Some recent models have proposed that deformation in such regions is partly accommodated by ductile deformation processes such as crustal flow. They proposed that flow occurs locally overs tens of kilometers beneath the Himalaya and are supported by geological and geophysical evidence. Much larger crustal flow systems have been proposed to occur beneath the eastern margin of the Tibetan Plateau, where the collision has extruded large regions of the crust with upper crustal deformation focused on a system of major transform faults. This study investigates these models by using geophysical data to image the properties of rocks beneath the Red River Fault area of southeastern Tibet. The magnetotelluric method was used to map the resistivity of the rocks, which is a parameter sensitive to the presence of fluids, which in turn control the strength. Regions of low resistivity were mapped and inferred to be due regions of partial melt. These appear to originate in the mantle, and not be connected to similar features to the North. This implies that large-scale crustal flow may not occur in this region.

北喜马拉雅错那洞穹窿深部三维电性结构及其构造意义

“…In this model, in conjunctioncombined with the concentrated denudation of the surface, the southward channel flow (or crustal flow) led to the development of the STDS and the NGHD as well as the exposure of granite in the Northern Himalayas. The widely distributed weak mid-to-lower crusts in the plateau and the outward crustal flow are supported by numerous dynamic simulations and geophysical data Unsworth et al, 2004Unsworth et al, , 2005Zhao et al, 2012;Wang et al, 2018;Pang et al, 2019;Yu et al, 2020;Sun et al, 2020;Xue et al, 2021). In additionMoreover, an increasing number of studies indicate that the NHGD may result from complex tectono-magmatic activities and different deformation processes rather than a single model (Lee et al, 2000(Lee et al, , 2006Zhang, 2007;Zhang et al, 2012;.…”

“…Therefore, the magnetotelluric (MT) method is utilizedused to study structures beneath the Cuonadong dome in the Northern Himalayas, which is sensitive to fluids (saline fluids, partial melting, etc.) and is popularly used to explorestudy the resistivity structures of cratons and Tibetan Plateau where there a weak mid-to-lower crust is present (Unsworth et al, 2004(Unsworth et al, , 2005Wang et al, 2018;Ye et al, 2018;Jin et al, 2010;Xu et al, 2019;Chen et al, 2019;Hu et al, 2020;Yu et al, 2020;Xue et al, 2019Xue et al, , 2021. The Cuonadong dome is a newly discovered dome with rare-metal mineralization of beryllium (Be), polymetallic mineralization (lead-zinc (Pb-Zn), and gold-antimony (Au-Sb)), showing significant metallogenic potential Zhang et al, 2018;Xia et al, 2019;Liang et al, 2019Liang et al, , 2020.…”

“…The 3D MT inversion code ModEM ) based on finite difference numerical simulation and non-linear conjugate gradient method was employed for 3D inversion of the MT data collected in the Cuonadong dome. The algorithm has been extensively applied for forward and inverse simulation of MT data (Meqbel et al, 2014(Meqbel et al, , 2016Zhang et al, 2016;Yin et al, 2020;Sun et al, 2020;Yu et al, 2020;Xue et al, 2019Xue et al, , 2021. In the 3D MT inversion, the full impedance tensors (Z) at 22 periods with an interval on a logarithmic scale in the range of 0.003~1000 s form the input data.…”

“…When the subsurface fluids form a well-connected network and significantly increase the conductivity, the content of deep fluids can be quantitatively estimated (Unsworth et al, 2005;Hill et al, 2015;Sun et al, 2020;Yu et al, 2020;Xue et al, 2019Xue et al, , 2021). Archie's formula is utilised used to quantitatively estimate the content of deep fluids and the formula is shown as follows Unsworth et al, 2005;Xue et al, 2019Xue et al, , 2021:…”

The Influence of the Ailaoshan‐Red River Shear Zone on the Mineralization of the Beiya Deposit on the Southeastern Margin of the Tibetan Plateau Revealed by a 3‐D Magnetotelluric Survey

“…Finally, low‐resistivity anomalies in the crust have been widely imaged in Tibet and other active orogens and were explained by the presence of brine or melts (Bai et al., 2010; Comeau et al., 2020; Türkoğlu et al., 2008; Unsworth et al., 2005; Yu et al., 2020). It has been debated that if free fluids could exist for geological timescales in the lower crust (Hyndman et al., 1993; Wannamaker, 2000; Yardley & Valley, 1997).…”