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Synthetic Sr-Ca margarite, anorthite and slawsonite solid solutions and solid-fluid Sr-Ca fractionation

Axel Liebscher, Maik Thiele, Gerhard Franz, Guido Doersam and Matthias Gottschalk
Synthetic Sr-Ca margarite, anorthite and slawsonite solid solutions and solid-fluid Sr-Ca fractionation
European Journal of Mineralogy (April 2009) 21 (2): 275-292

Abstract

Calcium-strontium solid-solutions of margarite, anorthite, slawsonite, calcite and strontianite were synthesized from oxide-hydroxide-fluid mixtures by way of hydrothermal experiments at 400-500 degrees C and 390-500 MPa. The fractionation of Ca and Sr between the coexisting phases was investigated via electron microprobe and X-ray diffraction analyses of the solids and inductively coupled plasma-optical emission spectrometry of the fluids. A complete solid-solution series of margarite is indicated and the lattice parameters a, b, c, and V increase linearly with increasing Sr content. The lattice parameters of (Ca,Sr)-anorthite show a likewise linear increase with increasing Sr content. The formation of Sr-Ca slawsonite and Sr-Ca strontianite is restricted to high bulk Sr contents. The fractionation of Ca and Sr between minerals and fluid expressed as K (sub D(Sr-Ca)) (super mineral-fluid) increases in the following sequence: calcite-fluid<anorthite-fluid< or =margarite-fluid nearly equal 1< or =strontianite-fluid<slawsonite-fluid. At low X (sub Sr) (i.e., for common metamorphic bulk-rock compositions), K (sub D(Sr-Ca)) (super calcite-fluid) = 0.09, K (sub D(Sr-Ca)) (super anorthite-fluid) = 0.51, and K (sub D(Sr-Ca)) (super margarite-fluid) = 0.56; the Sr/Ca ratio of the fluid is therefore generally higher than that of the coexisting minerals. This suggests that during prograde metamorphism and probably continuous dehydration, the Sr/Ca ratio of the rock decreases continuously with time. But, owing to the roughly equal Sr-Ca mineral-fluid fractionation for margarite and anorthite, which was also determined for zoisite/clinozoisite and lawsonite, this decrease will result in only moderate changes of whole-rock and fluid Sr-composition as long as these phases are the main Sr-bearing minerals.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 21
Serial Issue: 2
Title: Synthetic Sr-Ca margarite, anorthite and slawsonite solid solutions and solid-fluid Sr-Ca fractionation
Affiliation: Technical University Berlin, Section Mineralogy-Petrology, Berlin, Federal Republic of Germany
Pages: 275-292
Published: 200904
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 45
Accession Number: 2009-048516
Categories: Mineralogy of silicatesIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables
Secondary Affiliation: German Research Centre for Geosciences, DEU, Federal Republic of Germany
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200926
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