QUATERNARY VOLCANISM on THE KAMCHATKA PENINSULA, NORTHWEST PACIFIC REGION

The Kamchatka arc in the northwestern part of the Pacific ‘Ring of Fire’ is an area of high volcanic activity related to fast (~7.8 cm/y) subduction of the Pacific Plate beneath the Eurasian continental margin. Recent Kamchatka volcanoes are organized in two major volcanic belts: Eastern volcanic belt (EVB) and Sredinny Range. The northern (younger) part of the EVB extends into the Central Kamchatka Depression. Here, close to the edge of the slab, it bursts with the most productive arc volcanoes on Earth (Kliuchevskoi volcanic group and Shiveluch). Modern configuration of the volcanic belts reflects the evolution of the active subduction zone, which is believed to originate ~7 Ma ago in the southern part of the Kamchatka arc and then gradually extend to the north (Lander and Shapiro, 2007).

There is no evident spatial correlation between Quaternary volcanoes and fault systems that bound main neotectonic structures of the peninsula. The only regional fault system that may be linked to volcanism is found along the axis of the EVB. The faults exhibit dominantly normal displacement and form a ~130 km long graben-in-graben structure (Florensky and Trifonov, 1985).

Of all the volcanic arcs, Kamchatka has the largest number of collapse calderas per unit of arc length (Hughes and Mahood, 2008). Most of the calderas and associated ignimbrite fields are located in the southern part of the EVB. The largest Holocene explosive eruption was associated with the formation of Kurile Lake caldera in South Kamchatka. Its tephra volume of ≥140 km³ ranks it among Earth’s largest Holocene explosive eruptions (Ponomareva et al., 2004). Based on far larger caldera sizes and volumes of preserved ignimbrite sheets, some of the earlier caldera-forming eruptions might produce tephra volumes up to 400 km³ (Bindeman et al., 2010).

Different volcanic rock types in Kamchatka exhibit regular spatial pattern correlated to the present-day configuration of the subduction zone (Volynets, 1994). The volcanism in Kamchatka has thus mantle origin. Shallow fractionation accompanied by crustal assimilation enhanced geochemical variability and generated large volumes of silicic magmas (Bindeman et al., 2004). Correlation of erupted volumes, periodicity of volcanism, tectonics and rock geochemistry is an important direction of future studies in Kamchatka.