Low Crustal Fluid Reservoirs in Ultramafic Cumulates of Kamchatka

• Published in: Petrology 2023-12, Vol.31 (6), p.705-717
• Main Authors: Simakin, A. G., Shaposhikova, O. Yu
• Format: Article
• Language: English
• Subjects: Anomalies; Earth and Environmental Science; Earth Sciences; Fluids; Fractionation; Fractures; Geochemistry; High temperature; Inclusions; Lava; Localization; Magma; Mechanical failure; Microfracture; Mineralogy; Olivine; Reservoirs; Topology; Volatiles; Volcanic activity; Volcanism; Volcanoes
• ISSN: 0869-5911; 1556-2085
• DOI: 10.1134/S0869591123060036

Based on published geophysical and petrological data, lower crustal fluid reservoirs have been proposed below the Klyuchevskoy Volcano, expressed as a low V p / V s anomaly. A high V p / V s anomaly under the proposed fluid reservoir is interpreted as a zone of magma accumulation. The localization of fluids in these reservoirs in the ductile lower crust can vary from isolated inclusions to filling of microfractures over a time scale of several months. Using a simplified poroelastic model, it is shown that the transition in the topology of pore space filled with fluid or melt can provide the observed changes in V p / V s in the anomalies of high and low values at a melt content of several vol % and fluid content less than 1 vol %, respectively. In zones of active volcanism, such as the Klyuchevskaya group of volcanoes (KGV), fluid reservoirs are localized in ultramafic cumulates formed during the early high-temperature stage of magma fractionation. Ultramafic xenoliths in the products of eruptions of the KGV and Avachinsky volcanoes, often interpreted as mantle rocks, formed at pressures of about 5 kbar or depths of about 18–20 km in accordance with two-pyroxene geo-thermobarometry and the content of volatiles in melt inclusions in olivine and spinel. When crossing by ascending magmas, the fluid-containing reservoir experiences mechanical failure and injects a certain amount of fluid into the magma, which then captures pieces of crushed magmatic cumulates. The composition of melt inclusions in olivine can reveal records of the magma-fluid interaction.