Petromagnetic and Geochemical Descriptions of Volcanics Discharged by Alaid Volcano, Kuril Islands, in 2015–2016

Alaid Volcano on Atlasov Island is the northernmost and highest volcano of the Kuril island arc. The first time lavas were discharged by the terminal eruption of 2015–2016 was in October 2018. The samples were studied by petromagnetic, petrogeochemical, and microprobe techniques. The chemical composition of the 2015–2016 ejecta is very similar to that of the 1933–1934, 1972, and 1981 eruptions, attesting to a common deep source of magmas. That source can be inferred to lie at a depth greater than 50 km, judging from their potassium–sodium products and from estimates of the P–T conditions that prevailed during the precipitation of rock-forming mineral phases from the melt. It was for the first time that data were obtained concerning the structure and composition of the magnetic fraction in the Alaid igneous rocks, and the depth was determined for the last equilibrium state of magma during the 2015–2016 eruption. A joint analysis of the petromagnetic and petrogeochemical characteristics of the Alaid trachybasalts studied here revealed significant correlative relationships between (a) concentrations of Ti and Cu and petromagnetic concentration characteristics, (b) alkali elements (Li, Rb, Cs) and rare-earth elements and coercive petromagnetic parameters.