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T-XCO2 stability relations and phase equilibria of a calcic carbonate scapolite

Geochimica et Cosmochimica Acta

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Abstract

At a total pressure of 5 kb, calcic, Cl-free scapolite (Me83) is stable relative to plagioclase-bearing assemblages at T ??? 625??C, XCO2 ??? 0.12. With decreasing temperature, scapolite breaks down to plagioclase + calcite. Scapolite is replaced by plagioclase + grossular + cancrinite + CO2 in the presence of H2O-rich fluids. The stable coexistence of scapolite and calcite, an assemblage typical of most natural occurrences of calcic scapolite, is limited by the reaction: scapolite + calcite ??? grossular + cancrinite + CO2, which occurs at 750??C, XCO2 = 0.46; 700??C, XCO2 = 0.33; 650??C, XCO2 = 0.18, for the chosen bulk composition. Generalization of the experimental results to encompass the complete range of fully carbonated scapolite compositions indicates that mizzonite (Me75) has the largest T-XCO2 stability field. For scapolite more calcic than mizzonite, stable growth is restricted to conditions of increasingly higher temperature and XCO2. The experimental results are consistent with various petrologic features of scapolite-bearing rocks, particularly scapolite-clinopyroxene granulites, and indicate that such rocks were formed in the presence of CO2-rich fluids. ?? 1983.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
T-XCO2 stability relations and phase equilibria of a calcic carbonate scapolite
Series title:
Geochimica et Cosmochimica Acta
Volume
47
Issue:
3
Year Published:
1983
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
351
Last page:
362
Number of Pages:
12