Evolution of fluid redox in a fault zone of the Pic de Port Vieux thrust in the Pyrenees Axial Zone (Spain)

IF 3.2 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Delphine Charpentier, Gaétan Milesi, Pierre Labaume, Ahmed Abd Elmola, Martine Buatier, Pierre Lanari, Manuel Muñoz
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Abstract

Abstract. In mountain ranges, crustal-scale faults localize multiple episodes of deformation. It is therefore common to observe current or past geothermal systems along these structures. Understanding the fluid circulation channelized in fault zones is essential to characterize the thermochemical evolution of associated hydrothermal systems. We present a study of a palaeo-system of the Pic de Port Vieux thrust fault. This fault is a second-order thrust associated with the Gavarnie thrust in the Axial Zone of the Pyrenees. The study focused on phyllosilicates which permit the constraint of the evolution of temperature and redox of fluids at the scale of the fault system. Combined X-ray absorption near-edge structure (XANES) spectroscopy and electron probe microanalysis (EPMA) on synkinematic chlorite, closely linked to microstructural observations, were performed in both the core and damage zones of the fault zone. Regardless of the microstructural position, chlorite from the damage zone contains iron and magnesium (Fetotal / (Fetotal + Mg) about 0.4), with Fe3+ accounting for about 30 % of the total iron. Chlorite in the core zone is enriched in total iron, but individual Fe3+/Fetotal ratios range from 15 % to 40 %, depending on the microstructural position of the grain. Homogeneous temperature conditions about 280–290 °C have been obtained by chlorite thermometry. A scenario is proposed for the evolution of fluid–rock interaction conditions at the scale of the fault zone. It involves the circulation of a single hydrothermal fluid with homogeneous temperature but several redox properties. A highly reducing fluid evolves due to redox reactions involving progressive dissolution of hematite, accompanied by crystallization of Fe2+-rich and Fe3+-rich chlorite in the core zone. This study shows the importance of determining the redox state of iron in chlorite to calculate their temperature of formations and to consider the fluid evolution at the scale of a fault.
比利牛斯轴心区(西班牙)维耶港推力断层带流体氧化还原作用的演变
摘要在山脉中,地壳尺度的断层会产生多次局部变形。因此,沿这些构造观察当前或过去的地热系统很常见。了解断层带中的流体循环通道对于确定相关热液系统的热化学演化特征至关重要。我们介绍了对维耶港断层(Pic de Port Vieux thrust fault)古系统的研究。该断层是与比利牛斯山脉轴心地带加瓦涅推力相关的二阶推力断层。研究的重点是植硅体,它可以在断层系统的尺度上对流体的温度和氧化还原作用的演化过程进行制约。研究人员在断层带的核心区和破坏区对合晶绿泥石进行了 X 射线吸收近缘结构(XANES)光谱和电子探针显微分析(EPMA)的综合研究,这些研究与微观结构观测密切相关。无论微观结构位置如何,破坏区的绿泥石都含有铁和镁(Fetotal / (Fetotal + Mg) 约 0.4),其中 Fe3+ 约占总铁量的 30%。核心区的绿泥石富含总铁,但根据晶粒的微观结构位置,单个 Fe3+/Fetotal 的比例从 15 % 到 40 % 不等。通过绿泥石测温法获得了约 280-290 °C 的均匀温度条件。针对断层带规模的流体-岩石相互作用条件的演变提出了一种方案。它涉及温度均匀但具有多种氧化还原特性的单一热液循环。由于氧化还原反应涉及赤铁矿的逐步溶解,并伴随着核心区富含 Fe2+ 和 Fe3+ 的绿泥石的结晶,高还原性流体不断演化。这项研究表明,确定绿泥石中铁的氧化还原状态对于计算地层温度和考虑断层尺度上的流体演化非常重要。
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来源期刊
Solid Earth
Solid Earth GEOCHEMISTRY & GEOPHYSICS-
CiteScore
6.90
自引率
8.80%
发文量
78
审稿时长
4.5 months
期刊介绍: Solid Earth (SE) is a not-for-profit journal that publishes multidisciplinary research on the composition, structure, dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. The journal invites contributions encompassing observational, experimental, and theoretical investigations in the form of short communications, research articles, method articles, review articles, and discussion and commentaries on all aspects of the solid Earth (for details see manuscript types). Being interdisciplinary in scope, SE covers the following disciplines: geochemistry, mineralogy, petrology, volcanology; geodesy and gravity; geodynamics: numerical and analogue modeling of geoprocesses; geoelectrics and electromagnetics; geomagnetism; geomorphology, morphotectonics, and paleoseismology; rock physics; seismics and seismology; critical zone science (Earth''s permeable near-surface layer); stratigraphy, sedimentology, and palaeontology; rock deformation, structural geology, and tectonics.
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