近日，中国地质大学景建恩团队研究了青藏高原南部新扎-定野裂谷深部物质运移特征及地震孕育环境。相关论文于2025年7月21日发表在《中国科学：地球科学》杂志上。

新生代以来，青藏高原南部发育了一系列南北伸展的正断层和片麻岩-花岗岩穹丘，其形成机制具有重要的科学意义，并对青藏高原的构造动力学具有重要意义。其中最典型的是青藏高原中部新扎—谢通门—定野地区的新扎—定野裂谷和马卜加片麻岩穹丘。在该研究中，该地区的大地电磁测量以生成地下高分辨率三维电阻率模型为主题，并分析导电带的特征。中下部赤铁矿的大规模导电带可能是由水熔体部分熔融形成的，而中上部赤铁矿的小规模导电带可能是由含盐流体形成的，可能含有不同体积的熔体。

随后，基于电阻率模型，结合地质、地球化学和地球物理数据的时空耦合，研究组揭示了成矿物质的状态和迁移特征。结果表明，与印度岩石圈板块撕裂有关的地幔物质沿俯冲通道和板块窗上涌，导致拉萨地体中下嵴部分熔融。此外，特提斯—喜马拉雅地体中上地壳的部分熔融是由于拉萨地体中地壳物质的南移所致。这两种机制都能显著降低有效粘度。

研究组推测，受以弱流变为特征的大规模韧性层控制的脆性上嵴变形是裂谷演化的主要动力机制。与此同时，特提斯—喜马拉雅地体中上顶的变质作用和深熔作用与物质南移有关，促进了马布加片麻岩穹丘的演化。中新世中期，岩浆物质的南移可能受到了马布加片麻岩穹下冷却事件的影响，这可以解释马布加片麻岩穹下深部具有中-高电阻率的原因。

此外，该研究区域位于地中海-喜马拉雅地震带，主要包括浅源地震和中深地震。在北部，浅源地震主要受上覆地壳脆性层与中下地壳韧性层的应力积累控制。在南部，浅源地震（如定日MS6.8地震）主要发生在被导电带包围的刚性阻性块体中，这可能是因为这些阻性块体阻碍了流体的运移。中深地震主要受地下响应控制，这与印度岩石圈地幔与印度地幔的分离有关。

附：英文原文

Title: Characterizing the migration of deep materials beneath the Xainza-Dinggye rift and the seismogenic environment in the southern Tibetan Plateau: Insights from a 3-D electrical resistivity model

Author: Yue SHENG, Sheng JIN, Zengqian HOU, Matthew J. COMEAU, Michael BECKEN, Wenbo WEI, Gaofeng YE, Letian ZHANG, Hao DONG, Yaotian YIN, Chengliang XIE, Jian’en JING

Issue&Volume: 2025/07/21

Abstract: Since the Cenozoic, a series of extensional south-north normal faults and gneiss-granite domes evolved in the southern Tibetan Plateau, the formation mechanism of which is of scientific interest and which has implications for the tectonic dynamics of the plateau. Typical of such features are the Xainza-Dinggye rift and the Mabja gneiss dome, which are located in the Xainza-Xietongmen-Dinggye region in the central Tibetan Plateau. In this study, Magnetotelluric measurements across this region are used to generate a high-resolution 3-D electrical resistivity model of the subsurface and to analyze the cause of the conductive zones. The large-scale conductive zones identified in the middle-lower crust may result from aqueous melt partial melting, whereas the smaller-scale conductive zones in the upper-middle crust may result from saline fluids, possibly with varying minor volumes of melts. Subsequently, based on the electrical resistivity model and combined with the spatiotemporal coupling of the geological, geochemical, and geophysical data, the state and migration features of crustal materials are discussed. The results show that the upwelling of mantle materials along subduction channels and slab-windows related to the tearing of the Indian lithospheric plate contributed to the partial melting of the middle-lower crust in the Lhasa terrane. Furthermore, partial melting of the upper-middle crust in the Tethys-Himalaya terrane resulted from southern extrusion of crustal materials in the Lhasa terrane. These two mechanisms can significantly reduce the effective viscosity. We speculate that the deformation of the brittle upper crust that is controlled by large-scale ductile layers characterized by weak rheology is the main dynamic mechanism of rift evolution. Meanwhile, the metamorphism and anatexis in the upper-middle crust of the Tethys-Himalaya terrane related to the southern extrusion of materials contributed to the evolution of the Mabja gneiss dome. During the middle Miocene, the southern extrusion of crustal materials may have been influenced by the cooling events beneath the Mabja gneiss dome, which can explain why the deep areas beneath the Mabja gneiss dome have middle-high resistivity. In addition, our study region is located in the Mediterranean-Himalayan seismic belt, and mainly includes shallow-focus earthquakes and intermediate-depth earthquakes. In the north, shallow-focus earthquakes are mainly controlled by the accumulation of stress in the brittle layer of the overlying crust related to the ductile layer of the middle and lower crust. In the south, shallow-focus earthquakes (e.g., Dingri MS6.8 earthquake) mainly occur in the rigid, resistive block, which is surrounded by conductive zones, possibly because fluid migration may be hindered by these resistive blocks. The intermediate-depth earthquakes are mainly controlled by the response in the subsurface area, which is related to the detachment of the Indian lithospheric mantle from the Indian crust.

DOI: 10.1007/s11430-024-1609-2

Source: https://www.sciengine.com/10.1007/s11430-024-1609-2