Late Pleistocene basitic magmatism and Its Relation to large caldera-forming eruptions on Iturup Island on example of Klumba volcano, Kuril Islands

The basaltic andesite volcano Klumba is the only post-caldera volcano in the center of one of the most powerful explosive eruptions that occurred at the end of the Neopleistocene in Great Kuril Ridge (GKR) and formed a thick sequence of dacitic pumice tuffs on the Vetrovoy Isthmus on the Iturup Island. A detailed study of mineralogy and olivine-hosted fluid and melt inclusions in the rocks of the Klumba volcano, showed that the feeding magma evolved within the arc crust at depths between 15.5 and 7 km and was related to Mg-rich (up to 9.8 wt. % MgO), low-potassium and low-alumina basaltic andesite melts, which initially contained about 5–6 wt. % H2O. Olivine and Cr-Al spinel are the earliest minerals, which are later joined by plagioclase and pyroxenes. The crystallization of the basaltic andesites occurred at temperatures of about 1000–1200°C. The melt was saturated with carbon dioxide fluid, containing minor amounts of SO2. The Pleistocene basaltic andesitic magmatism in the central part of the Iturup Island was predominantly intrusive and resulted in the formation of a large trans-crustal magmatic system (TCMS), which could include the dacitic reservoir that fed the explosive eruption of the Vetrovoy Isthmus. The plumbing system of the Klumba volcano is considered to be a part of this TCMS with impulsive injections of variously differentiated basaltic andesite magmas. It is assumed that such systems may have been developed on the scale of the whole island. The processes duration and the amount of intruded magma may have been sufficient to cause partial melting in the upper parts of the island-arc crust and to form magma reservoirs of powerful explosive caldera-forming eruptions.