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.
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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