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Fluid inclusion and thermobarometric study of interaction between mafic xenoliths and plagiogranites in the Lotta River Area, Lapland Granulite Beltтезисы доклада
- Авторы: Butvina V., Safonov O., Golunova M.
- Сборник: European Geosciences Union General Assembly 2020
- Тезисы
- Год издания: 2020
- Издательство: Copernicus GmbH on behalf of the European Geosciences Union
- Местоположение издательства: Germany
- Первая страница: 10
- Последняя страница: 5194
- DOI: 10.5194/egusphere-egu2020-294
- Аннотация: Thermobarometric data and fluid inclusions data of conditions of interaction between mafic xenolithes (granulites) and plagiogranites in the Lotta river area, Lapland Granulite Belt, confirm the conclusion that leucocratic garnet-bearing plagiogranites of the Lapland complex are associated with the anatexis of country khondalites during peak of metamorphism.The results of new thermobarometric studies, data on fluid inclusions in these rocks confirmed the conclusions of the researchers (Safonov et al., 2016, 2017).The formation of plagiogranitic magmas probably occurred at depths of about 25-30 km. As they ascended, they captured a variety of xenoliths (Kozlov, Kozlova, 1998). The most notable of these are the xenoliths of dipyroxene-plagioclase granulites (orthopyroxene ± clinopyroxene + plagioclase ± quartz + magnetite + ilmenite + pyrrotine). In the studied xenoliths amphibolization processes are widely manifested in the form of wide borders of potassium-containing pargasite-edenite amphibole and its coarse-grained symplecticites with quartz in contacts of pyroxenes, magnetite, ilmenite and pyrrhotite with plagioclase. The more basic composition of plagioclase and the lower magnesia of pyroxenes in amphibolized xenolith sites corresponds to the amphibole formation reaction: Opx + Ilm + Mt + Pl = Amph ± Qtz. Amphibolization is sometimes accompanied by the formation of biotite, indicating the introduction of additional components in xenoliths.A pressure of 6.0-6.4 kbar was estimated from the equilibrium of clinopyroxene + orthopyroxene + plagioclase + quartz in non-amphibolized xenolith sites. The temperatures corresponding to this association are 800-860°C and are within the range of plagiogranite crystallization temperatures (Kaulina et al., 2014) as well as peak temperatures of the M2 tectonic-thermal stage in the Lapland granulite belt (Mints et al., 2007). Amphibole-plagioclase equilibrium (Blundy, Holland, 1990) recorded the temperatures of the xenolith amphibolization process of 740-780°C at a pressure of 5.0-5.5 kbar. Variations in the composition of amphibole in the direction of decreasing temperature. It was probably due to the interaction of a substantially aqueous fluid from cooling plagiogranitic magma with xenoliths as they were captured and lifted.Indeed, xenoliths are crossed by veins of plagiogranitic composition. Abundance of water-salt (17-20 wt. % NaCl equivalent) inclusions and the subordinate amount of carbon dioxide inclusions in plagiogranite minerals confirm this assumption. Thus, plagiogranites of the Lapland complex and associated fluids were formed inside the complex at P-T parameters comparable to the peak conditions of granulite metamorphism of the complex. Rising to higher levels in the granulite complex, these granites could only produce fluid effects on the host rocks.
- Добавил в систему: Бутвина Валентина Григорьевна