Experimental metasomatic alteration of titanite in a series of metamorphic fluids at 700 °C and 200 MPa

IF 1.4 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Wiktoria Gmochowska, Daniel Harlov, Ewa Słaby, Petras Jokubauskas, Jiří Sláma, Marcin Łącki
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Abstract

Seven experiments exploring the reaction of titanite with various hydrothermal solutions have been carried out at 700 °C and 200 MPa for a run duration of 16 days. In experiments involving fluids consisting of NaCl+H2O, KCl+H2O, CaCl2+H2O, 2M NaOH, or 2M KOH, no reaction of the titanite with the fluid was observed other than a slight dissolution of the titanite. Experiments involving NaF+H2O and Ca(OH)2+H2O resulted in visible alteration of the titanite in texture and composition, coupled with the formation of perovskite. In the NaF+H2O experiment, perovskite, enriched with rare earth elements (REE), formed as euhedral to subhedral crystals on the surface of the recrystallized titanite. In the Ca(OH)2+H2O experiment perovskite took in minor amounts of REE, and formed as a reaction rim partially replacing the titanite via a coupled dissolution-reprecipitation reaction. Wollastonite, along with minor calcite, and grossular garnet, formed as an outer rim on the perovskite. In the NaF+H2O experiment major and trace elements were leached from the titanite, whereas in the Ca(OH)2+H2O experiment no leaching of major or trace elements was observed. Nb/Ta, Th/U, and Y/Ho were investigated as potential indicators of hydrothermal processes. While the Nb/Ta ratio was altered in the experimentally metasomatised titanite, the degree of alteration was the same for both fluids. In contrast, only small changes in the Th/U and Y/Ho ratios between the altered and original titanite were seen for either experiment. The formation of perovskite at the expense of titanite in NaF+H2O or Ca(OH)2+H2O fluids demonstrates how titanite reacts with these fluids in simple, low silica activity systems under mid to upper crustal P-T conditions.

Abstract Image

钛铁矿在一系列变质流体中在 700 °C 和 200 MPa 条件下的变质蚀变实验
在 700 °C 和 200 MPa 条件下进行了七次实验,探索钛铁矿与各种热液的反应,实验持续时间为 16 天。在涉及由 NaCl+H2O、KCl+H2O、CaCl2+H2O、2M NaOH 或 2M KOH 组成的流体的实验中,除了钛铁矿发生轻微溶解外,未观察到钛铁矿与流体发生任何反应。在 NaF+H2O 和 Ca(OH)2+H2O 的实验中,钛铁矿的质地和成分发生了明显的变化,并形成了透辉石。在 NaF+H2O 实验中,富含稀土元素 (REE) 的透辉石在重结晶钛铁矿的表面形成了斜方晶体到亚斜方晶体。在 Ca(OH)2+H2O 实验中,透辉石吸收了少量的稀土元素,并通过溶解-重沉淀耦合反应形成了部分取代榍石的反应边缘。硅灰石以及少量方解石和毛石榴石形成了包晶的外缘。在 NaF+H2O 实验中,钛铁矿中的主要元素和微量元素被浸出,而在 Ca(OH)2+H2O 实验中,没有观察到主要元素或微量元素被浸出。作为热液过程的潜在指标,对 Nb/Ta、Th/U 和 Y/Ho 进行了研究。虽然在实验变质钛铁矿中 Nb/Ta 比率发生了改变,但两种流体的改变程度相同。相反,在这两次实验中,改变后的钛铁矿和原始钛铁矿之间的 Th/U 和 Y/Ho 比率都只有很小的变化。在 NaF+H2O 或 Ca(OH)2+H2O 流体中以牺牲榍石为代价形成了透辉石,这表明了在中上地壳 P-T 条件下,榍石如何与这些流体在简单的低硅活性体系中发生反应。
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来源期刊
Mineralogy and Petrology
Mineralogy and Petrology 地学-地球化学与地球物理
CiteScore
2.60
自引率
0.00%
发文量
0
审稿时长
1 months
期刊介绍: Mineralogy and Petrology welcomes manuscripts from the classical fields of mineralogy, igneous and metamorphic petrology, geochemistry, crystallography, as well as their applications in academic experimentation and research, materials science and engineering, for technology, industry, environment, or society. The journal strongly promotes cross-fertilization among Earth-scientific and applied materials-oriented disciplines. Purely descriptive manuscripts on regional topics will not be considered. Mineralogy and Petrology was founded in 1872 by Gustav Tschermak as "Mineralogische und Petrographische Mittheilungen". It is one of Europe''s oldest geoscience journals. Former editors include outstanding names such as Gustav Tschermak, Friedrich Becke, Felix Machatschki, Josef Zemann, and Eugen F. Stumpfl.
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