Partial Melting of Carbonate–Biotite Gneiss at the Conditions of the Continental Crust: Experimental and Thermodynamic Modeling

Mityaev, A.S.; Safonov, O.G.; Varlamov, D.A.; van Reenen, D.D.

Авторы: Mityaev A.S., Safonov O.G., Varlamov D.A., van Reenen D.D.
Журнал: Petrology
Том: 30
Номер: 3
Год издания: 2022
Издательство: Maik Nauka/Interperiodica Publishing
Местоположение издательства: Russian Federation
Первая страница: 278
Последняя страница: 304
DOI: 10.1134/s0869591122030067
Аннотация: One of the mechanisms explaining relationships between CO2-rich fluids and granitoid magmas athigh-temperature crustal metamorphism is the melting of protoliths that originally contained carbonate minerals.In order to study the coupled processes of dehydration/decarbonation and melting, experiments wereconducted with carbonate–biotite gneiss from an Archean greenstone belt at pressures of 6, 10, and 15 kbarin the temperature range of 800–950°C, and phase relations in this rock were modeled using the pseudo-sectionmethod. The experiments and modeling revealed a subvertical positive dP/dT slope of the solidus of therock. In comparison to the calculated solidus temperatures, the experiments showed higher melting temperatures(~800°C at 6 kbar and ~850°C at 10 and 15 kbar). The products of the experiments at pressures of 6 and10 kbar and temperatures >850°C were found out to contain assemblages of clinopyroxene, orthopyroxene,and ilmenite. The products of the experiments at 15 kbar did not contain either orthopyroxene or ilmenite,but calcium garnet and rutile were stable. The first portions of the near-solidus melts at 6 and 10 kbar werepoor in SiO2 (44–50 wt %) and were formed because carbonate phases were involved in the melting reactions.With a temperature increase, the melts acquired a granite composition that was close to the composition ofmelts formed during the melting of the carbonate-free plagioclase + biotite + quartz assemblage. An aqueous–carbonic fluid containing Ca–Mg–Fe carbonate components coexisted with the melts. The phaseassemblages and compositions of the granite melts obtained in the experiments are consistent with the modelingresults. Comparison of the experimental results with published data on the partial melting of the carbonate-free plagioclase + biotite + quartz assemblages led us to the preliminary conclusion that Ca–Mg–Fecarbonates are able to decrease the melting temperature. The experiments have demonstrated that granitemagmas can be derived together with aqueous–carbonic fluids from a carbonate-bearing protolith duringhigh-grade metamorphism in the middle and lower crust. The occurrence of clinopyroxene or two-pyroxeneassemblages in granitoids can be considered as a mineralogical indicator of this process.
Добавил в систему: Митяев Александр Сергеевич

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Partial Melting of Carbonate–Biotite Gneiss at the Conditions of the Continental Crust: Experimental and Thermodynamic Modelingстатья

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