A. V. Rybin

Geochemistry and Petrogenesis of Volcanic Rocks in the Kuril Island Arc

Newly obtained precise analytical data on trace elements and radiogenic Sr, Nd, and Pb isotopes testify to anomalous geochemical characteristics of mafic and intermediate Quaternary lavas in Paramushir (in the north of the Kuril arc), Kunashir and Iturup (in the south) islands, which are the largest three islands of the Kuril island arc. The high K and LREE concentrations in the volcanic products in Paramushir Island resulted from the southward expansion of the mantle thermal anomaly of the Kamchatka Peninsula and the involvement of melts related to the melting of oceanic sediments in magma generation. The depleted characteristics of the mafic volcanics are explained by the relatively young tectono-magmatic events during the opening of the Kuril backarc basin. The Kuril island-arc system developed on a heterogeneous basement. The northern islands are a continuation of the volcanic structures of southern Kamchatka, which were formed above an isotopically depleted and hot lithospheric mantle domain of composition close to that of the Pacific MORB type. The southern islands were produced above an isotopically enriched and cold lithospheric domain of the Indian-Ocean MORB type, which was modified in relation to relatively young backarc tectono-magmatic processes. Although issues related to the genesis of the transverse geochemical zoning were beyond the originally formulated scope of our research, the homogeneous enough isotopic composition of the rear-arc lavas in the absence of any mineralogical and geochemical lines of evidence of crustal contamination suggests an independent magmatic source.

Manifestations of the tsunami on November 15, 2006, on the central Kuril Islands and results of the runup heights modeling

ISSN 1028-334X, Doklady Earth Sciences, 2008, Vol. 419, No. 2, pp. 335–338.

Indian MORB-type mantle beneath the Kuril Island arc: Isotopic investigation of the mafic lavas of Kunashir Island

New data on the Hf, Pb, and Nd isotopes of the mafic rocks of various ages from Kunashir Island were used to address the nature of the sub-arc mantle of the southern segment of the Kuril island arc. At least since Late Cenozoic, its isotopic characteristics have been the MORB-type mantle of the Indian Ocean. Its boundary with the mantle reservoir of the Pacific MORB-type coincided probably with the Kuril-Kamchatka Trench.

Monitoring of the eruption of the Sarychev Peak Volcano in Matua Island in 2009 (central Kurile islands)

In June 2009, one of the greatest eruptions of the Sarychev Peak volcano in Matua Island (48°06′ N, 153°12′ E) for the recent historical period occurred. With the help of satellite sounding methods, the first signs of volcanic activity were recorded and all the stages of the explosive eruption were traced. During the expeditionary investigations in the active volcano, unique data on the character of the eruption were obtained. The volume of erupted material was 0.4 cubic km, which lead to an increased area of Matua Island by 1.4 square km. The GPS observation station set at the distance of 7 km from the volcano recorded the rapid displacement of the Earths’s surface during the first two days of the active phase of eruption. This eruption of the Sarychev Peak volcano occurred 2.5 years after the catastrophic Simushir earthquakes in the period of intensive relaxation of stresses in the middle of the central part of the Kurile island arc.

Felsic magmas of the caldera-forming eruptions on the Iturup Island: the first results of studies of melt inclusions in phenocrysts from pumices of the Lvinaya Past and Vetrovoy Isthmus calderas

The paper reports the first results of the petrological studies of magmatic melts that formed siliceous pyroclastic deposits related to voluminous eruptions on Iturup Island. The caldera-forming eruptions of the Lvinaya Past and the Vetrovoy Isthmus, having similar features, resulted from the evolution of silicic melts that originated from partial melting of metabasalts. According to the mineral thermometry results, the melt was crystallized at ~800°C. The phenocrysts from the Vetrovoy Isthmus pumices were crystallized at <1 kbar, while those from the Lvinaya Past were formed at higher pressures. The pyroclastic rock compositions in both calderas correspond to moderately aluminous dacite and rhyolitic dacite of the normal series, whose melts likely did not undergo significant crystallization differentiation before the eruptions. The main volatile components of the magma include H2O, CO2, S, F, and Cl. Degassing with emission of water–carbon-dioxide fluid accompanied the early crystallization of plagioclase in the Vetrovoy Isthmus pumice. Evidence of pre-eruption melt degassing in the Lvinaya Past were not found. Water release from the melts may be related to both the early magma degassing and the eruptions. The lack of data evidencing the deep differentiation and mixing of contrasting melts implies a relatively small time period between the acid melt appearance and eruptions.

Geochemical evolution of volcanism of Matua Island in the Central Kurils

The first comprehensive isotope-geochemical study of volcanogenic rocks of different ages from Matua Island made it possible to distinguish the general stages in the magmatic evolution of the subduction system. The petrological similarity of the rocks from the central and northern chains of the Kuril island arc testifies that they were formed above “hot” geochemically enriched but isotopically depleted lithospheric mantle. The compositional change of the volcanic rocks of Matua Island in the Pleistocene-Holocene suggests a geodynamic transition at that time. Taking into account the similar tendency previously established in the southern Kuril Range (Kunashir Island) and for the Mutnovsky and Gorelyi volcanoes of southern Kamchatka, a global Pleistocene-Holocene tectonic event may be proposed in the evolution of the Kuril-Kamchatka island arc. The finding of the “adakite-like” tephra on Matua Island indicates the presence of felsic adakite-like melts among the eruption products of Sarychev Peak Volcano.

Change of Landscape Structure of Matua Island after the Sarichev Volcano Peak Eruption June 12-15, 2009

Due to the Sarichev volcano peak eruption June 12–15, 2009, the landscape of Matua Island was modified greatly. On the basis of field data, the spatial structure of the island landscape before and after eruption was analyzed. Scale maps 1: 200 000 reflecting the landscape structure of the island before June 12 and on June 30 are presented. It was established that the landscape on the slope of the volcano cone was essentially restructured by the influence of pyroclastic flows and volcanic ash fall-out. Complication of the island structure was noted after the volcanic eruption.

Explosive Eruptions of the Sarychev Peak Volcano in the Holocene on Matua Island, the Central Kuriles: The Tephra Geochemistry

The first results of tephrochronological studies of the Sarychev Peak volcano on Matua Island in the Central Kuril Islands are presented and the eruptive evolution of the volcano in the Holocene is reconstructed. The volcanic products are typified and the general style of their geochemical evolution is reviewed on the basis of the distribution of the petrogenic oxides and trace elements in tephra samples taken bed-by-bed from the reference section of the soil-pyroclastic cover on Matua Island. The horizons of transit ashes are identified.