Complex investigations of the mineral composition and petromagnetic properties of the rock samples constituting the Minami-Khiosi submarine volcano which is located in the Mariana island arc were carried out for the first time. The Minami-Khiosi submarine volcano is part of the Khiosi volcanic complex in the alkaline province of the Izu-Bonin and Mariana island arcs. The rocks analyzed are enriched in К2О (1.34-3.30 %), Ва - 370-806 ppm, and Sr - 204-748 ppm. Basalts exhibit a porphyric structure. Impregnations are mostly olivine, its single crystals or their concretions. In some samples olivine is very large in size (about 2 cm), but at the same time the grain-size of the main bulk is fine-crystalline. The studied samples include no less than 3 Fe-bearing oxide minerals. Among them are dominant titanomagnetite, and ilmenite and Fe hydroxides are less abundant. It has been established that the studied samples are mainly magnetically isotropic, have high values of natural remanent magnetization and Königsberger factor. As in other Late Cenozoic island arc submarine volcanoes of the Western Pacific the studied samples are highly differentiated by the amount of natural remanent magnetization and magnetic susceptibility. The main carriers of magnetization are low coercive magnetic minerals (titanomagnetite and magnetite) pseudosingle-domain structure and high coercivity (hematite). High values of natural remanent magnetization are due to psevdosingle-domain structure of titanomagnetite grains and high values of magnetic susceptibility are explained by a high concentration of ferromagnetic grains.

A multidisciplinary study of samples that were dredged during cruises of the R/V Vulkanolog was continued in order to interpret results from a survey of the anomalous magnetic field on the Pacific seafloor. We acquired data on the main ferromagnetic carrier and the nature of magnetization. The naturally occurring magnetic parameters and petromagnetic properties of the rocks that make up the edifices of the Sofu underwater volcanic cluster at the Izu-Bonin island arc have been studied. We provide the results of thermomagnetic, petrologic, and microprobe studies of the dredged samples. It is shown that the main magnetic mineral carriers of natural remanent magnetization are unaltered titanomagnetite and oxidized titanomagnetite. The differentiation of rocks over values of natural remanent magnetization was due to different crystallization conditions for titanomagnetite, while that over magnetic susceptibility was controlled by the magnetic grain size. The structural, mineralogic, and petrographic features of the samples show that they were taken from rocks that were discharged during different phases of eruptions.

Для решения задач систематизации, хранения и визуализации материалов, полученных в 1977-1991 гг. в 19 вулканологических экспедициях НИС "Вулканолог" в Тихом океане в Институте вулканологии и сейсмологии ДВО РАН, начиная с 2004 г., создается информационная система “Позднекайнозойские подводные вулканы Тихого океана”. Информационная система включает веб-сайт, базу данных и ГИС.

Происшедшие за последние годы многочисленные природные катастрофы, в целом, требуют разработки новой стратегии и тактики исследования современных геологических процессов. Одно из направлений исследований в этой области включает построение геодинамических моделей глубинного строения земной коры и верхней мантии на основе комплексной интерпретации геолого-геофизических данных. Регион исследования охватывает переходную зону от Евразийского континента к Тихому океану. Геодинамические модели глубинного строения построены через регионы Охотского, Японского, Филиппинского и Южно-Китайского морей, характеризующиеся повышенной сейсмичностью, частыми извержениями вулканов и другими природными катастрофами. Для построения геодинамических моделей использовались результаты геологических, геоморфологических, сейсмических, сейсмологических, петрологических, геотермических, магнитных, электромагнитных и гравиметрических исследований, данные GPS и палеотектонические реконструкции. Построение геодинамических моделей глубинного строения регионов природных катастроф может быть значительным вкладом в общую программу изучения глубинного строения и геодинамической обстановки районов исследований, необходимую для дальнейшей оценки рисков в той или иной зоне и подготовки действий населения на случай природной катастрофы.

For the first time in investigations of Klyuchevskoy, the sampling of gases was made directly in magma discharge during the flank eruption of 1988. High-temperature gases (1050—1100° C) are enriched in water and haloids, and impoverishen in sulphur; their compositions are close to that of chemical equilibrium at the temperature of sampling, the oxidizing state being formed in conditions that are close to redox conditions of NNO and QFM buffers. The isotopic composition of magmatic water (—71 %о<δD<—44%о; +6.3%о <δ18O< +8.4%о, SMOW) is in concordiance with the interval of «primary magmatic» waters. The isotopic composition of molecular hydrogen (—187%o<δD<— 160%о, SMOW) was formed in terms of isotopic equilibrium with water. Chemical composition of gases and isotopic composition of carbon in carbonic acid (δ13Cco2 = —11,6%о, PDB) indicate the significant degassing of magma of the 1988 flank eruption.
(Received October 4. 1989)

* Institute of Volcanology, Far East Division, USSR Academy of Sciences. Petro-pavtovsk-Kamchatskii, 683006, USSR
** Institute of Hydrous Problems, USSR Academy of Sciences, Moscow, 103064, USSR