Comeau Matthew J, Becken Michael, Kuvshinov Alexey V, Demberel Sodnomsambuu
Institut für Geophysik, Universität Münster, Corrensstrasse 24, 48149 Münster, Germany.
Institute of Geophysics, Swiss Federal Institute of Technology (ETH), Sonneggstrasse 5, 8092 Zürich, Switzerland.
Earth Planets Space. 2021;73(1):82. doi: 10.1186/s40623-021-01400-9. Epub 2021 Apr 1.
Crustal architecture strongly influences the development and emplacement of mineral zones. In this study, we image the crustal structure beneath a metallogenic belt and its surroundings in the Bayankhongor area of central Mongolia. In this region, an ophiolite belt marks the location of an ancient suture zone, which is presently associated with a reactivated fault system. Nearby, metamorphic and volcanic belts host important mineralization zones and constitute a significant metallogenic belt that includes sources of copper and gold. However, the crustal structure of these features, and their relationships, are poorly studied. We analyze magnetotelluric data acquired across this region and generate three-dimensional electrical resistivity models of the crustal structure, which is found to be locally highly heterogeneous. Because the upper crust (< 25 km) is found to be generally highly resistive (> 1000 Ωm), low-resistivity (< 50 Ωm) features are conspicuous. Anomalous low-resistivity zones are congruent with the suture zone, and ophiolite belt, which is revealed to be a major crustal-scale feature. Furthermore, broadening low-resistivity zones located down-dip from the suture zone suggest that the narrow deformation zone observed at the surface transforms to a wide area in the deeper crust. Other low-resistivity anomalies are spatially associated with the surface expressions of known mineralization zones; thus, their links to deeper crustal structures are imaged. Considering the available evidence, we determine that, in both cases, the low resistivity can be explained by hydrothermal alteration along fossil fluid pathways. This illustrates the pivotal role that crustal fluids play in diverse geological processes, and highlights their inherent link in a unified system, which has implications for models of mineral genesis and emplacement. The results demonstrate that the crustal architecture-including the major crustal boundary-acts as a first-order control on the location of the metallogenic belt.
The online version contains supplementary material available at 10.1186/s40623-021-01400-9.
地壳结构对矿带的发育和就位有强烈影响。在本研究中，我们对蒙古中部巴彦洪戈尔地区一个成矿带及其周边的地壳结构进行成像。在该地区，一条蛇绿岩带标志着一个古老缝合带的位置，该缝合带目前与一个重新活动的断层系统相关。附近，变质带和火山带拥有重要的矿化区，并构成一个重要的成矿带，其中包括铜和金的矿源。然而，这些特征的地壳结构及其相互关系研究较少。我们分析了在该地区采集的大地电磁数据，并生成了地壳结构的三维电阻率模型，发现该模型在局部具有高度非均质性。由于上地壳（<25千米）通常具有高电阻（>1000Ωm），低电阻率（<50Ωm）特征很明显。异常低电阻率区与缝合带和蛇绿岩带一致，蛇绿岩带被揭示为一个主要的地壳尺度特征。此外，从缝合带向下倾伏方向变宽的低电阻率带表明，在地表观察到的狭窄变形带在更深的地壳中转变为一个广阔区域。其他低电阻率异常在空间上与已知矿化区的地表表现相关；因此，它们与更深地壳结构的联系得以成像。考虑到现有证据，我们确定，在这两种情况下，低电阻率都可以通过沿古流体通道的热液蚀变来解释。这说明了地壳流体在各种地质过程中所起的关键作用，并突出了它们在一个统一系统中的内在联系，这对矿物成因和就位模型具有重要意义。结果表明，包括主要地壳边界在内的地壳结构对成矿带的位置起着一级控制作用。
在线版本包含可在10.1186/s40623-021-01400-9获取的补充材料。
