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首页> 外文期刊>Contributions to Mineralogy and Petrology >Microtextural constraints on the interplay between fluid-rock reactions and deformation
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Microtextural constraints on the interplay between fluid-rock reactions and deformation

机译：微观岩石对流体岩石反应与变形相互作用的约束

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Schists from two mylonitic localities in the footwall of a low-angle normal fault in the eastern Alps record different degrees of embrittlement during exhumation, depending on the extent to which fluid-rock reactions proceeded. At one site, graphitic schists preserve textural evidence for two metamorphic reactions that modified X_(CO_2) and/or fluid volume: (1) reaction between graphite and aqueous fluid that increased X_(CO_2) without changing the molar amount of fluid, and (2) replacement of titanite by rutile, calcite, and quartz. The latter reaction involved net consumption of increasingly CO_2-rich fluid. Areas where the first reaction proceeded are associated with abundant Mode I microcracks. Fluid inclusion arrays within the microcracks show that X_(CO_2) increased from approx 0.1 to 0.6 during decompression from 4.75 to 2 kbar at a reference temperature of 500°C. Titanite consumption is most pronounced within transgranular Mode I microcracks, but microcracks do not crosscut products of this reaction; fluid consumption during reaction was coeval with the end of microcracking, at least on a local scale. At the other site, graphitic schists lack small-scale Mode I cracks as well as evidence for graphite consumption during decompression. SEM imaging shows that graphite is anhedral and pitted at the first site, but occurs in clusters of euhedral grains at the second site. Mass balance calculations demonstrate that rocks with partially consumed graphite were infiltrated by an externally derived, H_2O-rich fluid that drove subsequent graphite-fluid reaction. Evidence for similar fluid infiltration is absent at the second site. Variations in the degree of reaction progress indicate that fluid pathways and deformation style were heterogeneous on the scale of millimeters to kilometers during exhumation from mid-crustal depths.
机译：来自阿尔卑斯山东部一个低角度正断层的下盘壁的两个条带化带片岩在发掘期间记录了不同程度的脆性，这取决于流体岩石反应的程度。在一个位置，石墨片岩保存了两个修饰X_（CO_2）和/或流体体积的变质反应的构造证据：（1）石墨与增加X_（CO_2）的水性流体之间的反应，而不会改变流体的摩尔量，以及2）用金红石，方解石和石英代替钛矿。后者反应涉及到越来越多的富含CO_2的流体的净消耗。进行第一反应的区域与大量的I型微裂纹有关。微裂纹内的流体包裹体阵列显示，在500°C的参考温度下，X_（CO_2）在从4.75降到2 kbar减压期间从约0.1增至0.6。在跨晶型I型微裂纹中，钛矿的消耗最为明显，但微裂纹不会影响该反应的产物。至少在局部规模上，反应期间的流体消耗与微裂纹的结束同时发生。在另一处，石墨片岩缺乏小规模的I型裂缝，也缺乏减压过程中石墨消耗的证据。 SEM图像显示，石墨在第一个位置呈反面和点蚀，但在第二个位置出现在整面晶粒簇中。质量平衡计算表明，具有部分消耗的石墨的岩石被外部衍生的富含H_2O的流体渗透，从而推动了随后的石墨流体反应。在第二部位没有类似的液体浸润的证据。反应进程程度的变化表明，在从地壳中部深度挖掘出的过程中，流体路径和变形方式在毫米到千米的范围内是异质的。

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