The connection between hydrothermal fluids, mineralization, tectonics and magmatism in a continental rift setting: Fluorite Sm-Nd and hematite and carbonates U-Pb geochronology from the Rhinegraben in SW Germany
The connection between hydrothermal fluids, mineralization, tectonics and magmatism in a continental rift setting: Fluorite Sm-Nd and hematite and carbonates U-Pb geochronology from the Rhinegraben in SW Germany
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DOI：
10.1016/j.gca.2018.08.012
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发表时间：
2018-11
影响因子：
5
通讯作者：
B. Walter;A. Gerdes;I. Kleinhanns;I. Dunkl;H. Eynatten;S. Kreissl;G. Markl
中科院分区：
文献类型：
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作者：
B. Walter;A. Gerdes;I. Kleinhanns;I. Dunkl;H. Eynatten;S. Kreissl;G. Markl
了解构造事件的物理基础，相关的流体流动和成矿作用是现代地球科学面临的巨大挑战之一。本文利用德国西南部上莱茵地堑裂谷附近的黑森林中与不整合相关的脉型矿床中热液萤石的Sm-Nd年龄和碳酸盐和氧化铁的U-Pb年龄，区分热液流体活动的不同脉冲，并了解它们与大规模构造和岩浆活动的关系。萤石的年龄为早侏罗世至渐新世，碳酸盐岩（方解石、白云石、菱铁矿）和赤铁矿的U-Pb等时线年龄记录为二叠纪至第四纪，并在新近纪达到明显的高峰。这些新的年龄数据与萤石和碳酸盐岩中生长带原生流体包裹体的显微测温数据相结合，可用于确定流体特征的时间。这一贡献表明，年龄与流体性质的变化和/或在不断演变的大陆地壳的构造事件。与已发表的热年代学数据相比，与URG有关的火山岩的表观年龄和上莱茵地堑裂谷的构造-沉积演化表明热液成矿作用的强度（以及因此受束缚的流体流动的强度）与U-Pb碳酸盐年龄之间存在明显的相关性。中三叠世Muschelkalk钾长岩在低盐度、高温（1-6 wt.%）、高矿化度（1- 6 wt. %）和高矿化度（1-6 wt.%）条件下沉积后，流体性质发生了变化，成矿物质在沉积过程中表现出强烈的热液动力学特征，成矿物质在沉积过程中表现出强烈的热液动力学特征NaCleq，200-270 °C，冷却晚变质基底流体）到高盐度，中等温度（20-26重量% (NaCl+ CaCl 2），50-170 °C，改性盐卤盐水（“基底盐水”）与岩盐溶解盐水的混合物）。这一变化导致了大规模的矿石沉积（萤石-重晶石-石英与Pb-Zn-Cu、Bi-Co-Ni-Ag-U、Fe-Mn矿石）。早第三纪和晚第三纪期间，来自不同沉积单元的先前分离的含水层通过莱茵地堑裂谷期间流体源岩的并列而连接，这导致了不同盐度和温度的流体（1-26重量%）。%（NaCl + CaCl2），50-350 °C）。与此相关的典型矿化显示出含大量重晶石的贫瘠或铅锌铜矿脉。
Understanding the physical basics of tectonic events, related fluid flow and ore deposition represents one of the great challenges in modern geosciences. In this contribution, Sm-Nd ages of hydrothermal fluorites and U-Pb ages of carbonates and iron oxides from unconformity-related vein type deposits in the Schwarzwald next to the Upper Rhinegraben rift in SW Germany are used to distinguish different pulses of hydrothermal fluid activity and to understand their relation to large-scale tectonics and magmatism. While the fluorites are of Early Jurassic to Oligocene age, carbonate (calcite, dolomite, siderite) and hematite dated by U-Pb small-scale isochrons records formation from Permian to Quaternary with a clear culmination in the Neogene.These new age-data in combination with microthermometry data of primary fluid inclusions from growth zones in the fluorites and carbonates are used to constrain the timing of fluid signatures. This contribution shows that the ages are correlated with changes in fluid properties and/or tectonic events in the evolving continental crust. Comparison with published thermochronological data, apparent ages of URG-related volcanic rocks and the tectono-sedimentary evolution of the Upper Rhinegraben rift show clear correlations between the intensity of hydrothermal mineralization (and, hence, the intensity of fracture-bound fluid flow) with the U-Pb carbonate ages. This method accordingly provides an excellent tool to date rift-related processes like fluid flow, ore deposition and tectonic activation or reactivation of fractures.Fluid properties changed after the deposition of Middle Triassic Muschelkalk evaporites from low salinity, high temperature (1–6 wt.% NaCleq, 200–270 °C, cooling late-metamorphic basement fluids) to high salinity, moderate temperature (20–26 wt.% (NaCl + CaCl2), 50–170 °C, mixture of a modified bittern brine (“basement brine”) with halite dissolution brine). This change led to large scale ore deposition (fluorite-barite-quartz with Pb-Zn-Cu, Bi-Co-Ni-Ag-U, Fe-Mn ores). During the Paleogene and Neogene, previously separated aquifers from various sedimentary units were connected by juxtaposition of the fluid source rocks during Rhinegraben rifting, which resulted in variable salinity and temperature fluids (1–26 wt. % (NaCl + CaCl2), 50–350 °C) by a multi-component fluid mixing process. Typical mineralization related to this shows barren or Pb-Zn-Cu veins with large amounts of barite.