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首页> 外文期刊>Contributions to Mineralogy and Petrology >Fluid-induced mineral composition adjustments during exhumation: the case of Alpine stilbite
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Fluid-induced mineral composition adjustments during exhumation: the case of Alpine stilbite

机译：掘尸过程中流体引起的矿物质成分调整：高山闪石

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摘要

Stilbite is locally present as a very late mineral on fractures and fissures of granitic basement in the Central Swiss Alps. Stilbite samples from the Gotthard rail base tunnel provide evidence that they originally formed as a K-absent variety at depth. However, all stilbite samples from surface outcrops above the tunnel display significant potassium concentrations. Interestingly, water from fractures in the tunnel (at 50 °C) is oversaturated with respect to stilbite and essentially potassium-free whereas waters from high-Alpine brooks above the tunnel (and at other high-Alpine areas) have unusually high K/Na ratios. The data suggest that stilbite that may actively form on fissures at tunnel level as a K-absent variety by precipitation from water. Older stilbite that originally formed as coatings on fracture walls was gradually exhumed and uplifted and finally reached the today’s erosion surface about 2,000 m above the tunnel. However, the stilbite reaches the erosion surface as a K-rich variety as a result of interaction of the original low-K stilbite with surface water and near-surface groundwater. This leads to the conclusion that minerals once formed at depth may significantly change their composition once they reach the ground water zone on their way to the erosion surface. In the case of the stilbite, if surface outcrops would have been the only source of samples and data, the K-rich composition could have been mistaken for the composition of the mineral when it formed, which is not the case. Late-stage compositional readjustments may be difficult to discern in samples from surface outcrops. The provided data show that original mineral compositions may be adjusted by late-stage water–rock interaction in a highly selective way.
机译：在瑞士中部阿尔卑斯山的花岗岩基底的裂缝和裂隙中，史迪比特在当地作为晚期矿物存在。来自Gotthard铁路基础隧道的Stilbite样品提供了证据，表明它们最初在深度处是缺钾品种。但是，从隧道上方地面露头出来的所有闪锌矿样品都显示出明显的钾浓度。有趣的是，在隧道中（50°C）裂缝产生的水相对于闪锌矿而言过饱和，基本不含钾，而在隧道上方（以及其他高高山地区）高高山溪流中的水具有异常高的K / Na比率。数据表明，在水平面的裂缝中，由于水的沉淀而缺少钾的形式，可能会形成积极的链闪石。最初作为裂缝壁上的涂层形成的较老的方英石逐渐被挖掘并隆起，最终到达了今天的侵蚀面，距隧道约2,000 m。然而，由于原始的低钾闪石与地表水和近地表地下水的相互作用，使闪锌矿以富含钾的形式到达侵蚀表面。这得出的结论是，一旦在深处形成矿物质，在到达侵蚀面的途中到达地下水带后，它们的组成可能会发生重大变化。就闪锌矿而言，如果表面露头将是唯一的样品和数据来源，那么富含钾的成分可能会误认为矿物形成时的成分，事实并非如此。从地面露头的样品中可能很难分辨后期成分的调整。提供的数据表明，可以通过后期水-岩相互作用以高度选择性的方式来调整原始矿物成分。

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