Authigenic quartz reveals the triple oxygen isotope composition and diagenetic temperature of saline brines

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Chemical Geology Pub Date : 2024-05-28 DOI:10.1016/j.chemgeo.2024.122193

Fabian Zahnow , Michael Tatzel , Jakub Surma , Andreas Pack

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Abstract

Triple oxygen isotope compositions of authigenic minerals are an emerging tool for the reconstruction of fluid temperatures and the fluid isotopic composition. In this study, we analyzed euhedral authigenic quartz crystals from a halite deposit of the Upper Permian Zechstein evaporitic basin for their triple oxygen isotope composition using laser fluorination isotope ratio mass spectrometry. In the triple oxygen isotope space, additional information, such as the triple oxygen isotope composition of the ambient water, provides insights into equilibrium conditions during quartz formation that cannot be identified from δ¹⁸O alone. The triple oxygen isotope composition of authigenic quartz shows, that single oxygen isotope (δ¹⁸O) thermometry is not applicable for samples from evaporitic environments, where the fluids' δ¹⁸O deviates from dynamic oxygen isotope equilibrium. By combining the Craig and Gordon evaporation model with H₂O – SiO₂ triple oxygen isotope equilibrium fractionation, we reconstruct the formation temperature of authigenic quartz and the triple oxygen isotope composition of the marine-derived saline brine pore fluid in equilibrium with the quartz. We obtain temperatures of 90 to 130 °C that is interpreted as crystallization temperatures of microcrystalline quartz in pore fluid of halite during burial diagenesis. The triple oxygen isotope composition of authigenic quartz from evaporitic environments is suited as a geochemical tracer for fluid oxygen isotope compositions and ancient fluid or diagenetic temperatures.

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成岩石英揭示了盐湖卤水的三重氧同位素组成和成岩温度

自生矿物的三重氧同位素组成是重建流体温度和流体同位素组成的新兴工具。在这项研究中，我们利用激光荧光同位素比质谱法分析了上二叠统泽希施泰因蒸发盆地一个海绿石矿床中的八面体自生石英晶体的三重氧同位素组成。在三重氧同位素空间中，环境水的三重氧同位素组成等附加信息可帮助人们深入了解石英形成过程中的平衡条件，而仅凭δ18O 是无法确定这些平衡条件的。自生石英的三重氧同位素组成表明，单一氧同位素（δ18O）温度测定法不适用于蒸发环境中的样本，因为在这种环境中，流体的δ18O偏离了动态氧同位素平衡。通过将克雷格和戈登蒸发模型与 H2O - SiO2 三重氧同位素平衡分馏法相结合，我们重建了自生石英的形成温度以及与石英平衡的海相盐卤孔隙流体的三重氧同位素组成。我们得到的温度为 90 至 130 °C，可解释为埋藏成因过程中卤水孔隙流体中微晶石英的结晶温度。蒸发环境中的自生石英的三重氧同位素组成适合作为流体氧同位素组成和古流体或成岩温度的地球化学示踪剂。

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来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.