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The 7600 14C-year-old Kurile Lake caldera-forming eruption (KO) in southern Kamchatka, Russia, produced a 7-km-wide caldera now mostly filled by the Kurile Lake. The KO eruption has a conservatively estimated tephra volume of 140–170 km3 making it the largest Holocene eruption in the Kurile–Kamchatka volcanic arc and ranking it among the Earth''s largest Holocene explosive eruptions. The eruptive sequence consists of three main units: (I) initial phreatoplinian deposits; (II) plinian fall deposits, and (III) a voluminous and extensive ignimbrite sheet and accompanying surge beds and co-ignimbrite fallout. The KO fall tephra was dispersed over an area of >3 million km2, mostly in a northwest direction. It is a valuable stratigraphic marker for southern Kamchatka, the Sea of Okhotsk, and a large part of the Asia mainland, where it has been identified as a ∼6 to 0.1 cm thick layer in terrestrial and lake sediments, 1000–1700 km from source. The ignimbrite, which constitutes a significant volume of the KO deposits, extends to the Sea of Okhotsk and the Pacific Ocean on either side of the peninsula, a distance of over 50 km from source. Fine co-ignimbrite ash was likely formed when the ignimbrite entered the sea and could account for the wide dispersal of the KO fall unit. Individual pumice clasts from the fall and surge deposits range from dacite to rhyolite, whereas pumice and scoria clasts in the ignimbrite range from basaltic andesite to rhyolite. Ignimbrite exposed west and south of the caldera is dominantly rhyolite, whereas north, east and southeast of the caldera it has a strong vertical compositional zonation from rhyolite at the base to basaltic andesite in the middle, and back to rhyolite at the top. Following the KO eruption, Iliinsky volcano formed within the northeastern part of the caldera producing basalt to dacite lavas and pyroclastic rocks compositionally related to the KO erupted products. Other post-caldera features include several extrusive domes, which form islands in Kurile Lake, submerged cinder cones and the huge silicic extrusive massif of Dikii Greben'' volcano. [Copyright &y& Elsevier]

Abstract: The Kamchatka Peninsula in far eastern Russia represents the most volcanically active arc in the world in terms of magma production and the number of explosive eruptions. We investigate large-scale silicic volcanism in the past several million years and present new geochronologic results from major ignimbrite sheets exposed in Kamchatka. These ignimbrites are found in the vicinity of morphologically-preserved rims of partially eroded source calderas with diameters from ∼2 to ∼30km and with estimated volumes of eruptions ranging from 10 to several hundred cubic kilometers of magma. We also identify and date two of the largest ignimbrites: Golygin Ignimbrite in southern Kamchatka (0.45Ma), and Karymshina River Ignimbrites (1.78Ma) in south-central Kamchatka. We present whole-rock geochemical analyses that can be used to correlate ignimbrites laterally. These large-volume ignimbrites sample a significant proportion of remelted Kamchatkan crust as constrained by the oxygen isotopes. Oxygen isotope analyses of minerals and matrix span a 3‰ range with a significant proportion of moderately low-δ 18O values. This suggests that the source for these ignimbrites involved a hydrothermally-altered shallow crust, while participation of the Cretaceous siliceous basement is also evidenced by moderately elevated δ 18O and Sr isotopes and xenocryst contamination in two volcanoes. The majority of dates obtained for caldera-forming eruptions coincide with glacial stages in accordance with the sediment record in the NW Pacific, suggesting an increase in explosive volcanic activity since the onset of the last glaciation 2.6Ma. Rapid changes in ice volume during glacial times and the resulting fluctuation of glacial loading/unloading could have caused volatile saturation in shallow magma chambers and, in combination with availability of low-δ 18O glacial meltwaters, increased the proportion of explosive vs effusive eruptions. The presented results provide new constraints on Pliocene–Pleistocene volcanic activity in Kamchatka, and thus constrain an important component of the Pacific Ring of Fire. [Copyright &y& Elsevier]