The present paper reports first data on the Holocene explosive activity of Zavaritsky Volcano—a major caldera center on Simushir Island, Central Kurils. We have managed, for the first time ever, to reconstruct the chronology of explosive eruptions in this volcanic center for the last 10 thousand years, as well as to estimate the parameters of its larger eruptions. Overall, more than 40 tephra layers have been identified in pyroclastic soil sections, enabling us to estimate the frequency of eruptions, one event per every 250 years. The age model based on radiocarbon dates that we determined for proximal deposits and on published data for the tephra of Zavaritsky Volcano and for the CKr key tephra layer have enabled us to find the ages of most eruptions. It was found that the volcanic glasses of the Holocene pyroclastics have compositions corresponding to low-K basaltic andesites and rhyolites; the very low concentration of K2O is a reliable indicator to distinguish the Zavaritsky tephra, not only from that of adjacent medium-K volcanoes, but also from the tephra of the other low-K volcanoes in the Kuril–Kamchatka island arc. The Holocene activity of Zavaritsky Volcano began with two major eruptions whose conservative magnitude estimates (М) were 6.4 and 5.6. These events occurred about 9.5 ka and 9.2 ka ago. The tephra of the earlier eruption (ZV-1) propagated northeast, and was found as far as the northwestern North America. The tephra of the second large eruption (ZV-3) has traveled north, and was found in sediments of the Sea of Okhotsk. The ZV-1 pyroclastics is characterized by volcanic glass of rhyolitic composition with the highest concentration of SiO2 (72.5–74.0 wt

We present the results of an analysis of the chemical composition for the volcanic glasses discharged by the summit eruption and G.S. Gorshkov flank vent at Klyuchevskoi Volcano in 2020–2021. The data on the chemical and mineral compositions of basaltic andesites produced at the initial stage of the G.S. Gorshkov vent activity are given. The compositional variations of the volcanic glasses from the summit and the subsequent flank eruptions reflect the degree of crystallinity in the tephra particles and the successive change of microlite populations during crystallization of a single parental magma. Comparison of the volcanic glass chemistry from recent eruptions with similar data for the products of the preceding eruptive episodes in 2010 and 2016 shows their complete identity, which indicates a constant composition of the basaltic andesite magma that supplies the present-day volcanic eruptions.

The Mutnovskoe deposit is one of the largest and most prospective ore deposits in South Kamchatka. The northern and southern flanks within the main veining zone Opredelyayushchaya, composed of low-sulfi (goldsilver) and sulfide-polymetallic (gold-silver-polymetallic) types of ores, respectively, are distinguished. The paper presents the results of the complex mineralogical and geochemical studies of the gold-silver-polymetallic ores of the southern flank of the deposit. Features of textures and structures, mineral, chemical compositions and genesis of the ores, as well forms of precious and base metals occurrences are shown. Typomorphic features of pyrite, sphalerite, galena, chalcopyrite, tennantite-tetrahedrite, Au, Ag, Pb and Bi tellurides, native gold, Bi, Se and Ag sulfosalts are characterized. The pyrite-sphaleritequartz, sphalerite-galena-quartz, and chalcopyrite-tennantite-tetrahedrite mineral associations are distinguished. The temperatures and composition of ore-forming solutions are shown.

Банно-Карымшинский район, находящийся на территории Южно-Камчатского рудного района, содержит целую серию месторождений и рудопроявлений золотосеребряной формации, которые вытянуты полосой северо-западного простирания [Фролов и др. Карта полезных ископаемых..., 1999]. Большинство исследователей считают, что рудопроявления и месторождения этого района локализуются в зоне крупных сбросов северо-западного простирания, пересекающих Южную Камчатку вдоль границы поперечной Начикинской складчато-глыбовой зоны [Петренко, 1999]. В последние годы в Банно-Карымшинском районе были проведены геолого-структурные работы, которые позволили выделить крупную кальдеру, а внутри нее блоковое резургентное поднятие [Леонов, Рогозин, 2007], что позволяет в настоящее время пересмотреть структурные позиции золотосеребряных рудопроявлений и месторождений данного района. Предполагается, что их позиция контролируется разломами, ограничивающими кальдеру и расположенное в ней резургентное поднятие. В 70-х гг. ХХ века на территории Банно-Карымшинского района геологи выделяли одноименный Банно-Карымшинский рудный узел. В ходе проведенных ими геолого-поисковых работ были открыты основные участки золотосеребряных проявлений района содержащих рудоносные кварц-карбонатные жилы. Всего на территории Банно-Карымшинского района насчитывается восемь таких участков: Банный, Малыш, Верхне-Быстринский, ВерхнеКарымшинский Левый, Геофизический, Верхне-Карымшинский Правый, СреднеКарымшинский и Центральный (рис. 1).

The Bannaya–Karymshina area is situated in southern Kamchatka west of the East Kamchatka Volcanic Belt in the backarc part of the Kuril–Kamchatka island arc. The area is unique in that it contains abundant ejecta of calc-alkaline, acid, mostly ignimbrite, volcanism for a period of 4 Ma. Three rock complexes can be identified with rhyolitic and rhyodacitic compositions: Middle Pliocene ignimbrites, crystalloclastic tuffs of Eopleistocene age that fill in the Karymshina caldera, and Early Pleistocene intrusions. All of these are composed of rocks with normal total alkalinity, while the concentration of potassium places them at the boundary between moderate and high-potassium rocks. We sought to determine the composition of primary acid melts by studying the composition of the silicate phase in homogeneous melt inclusions that were conserved in quartz phenocrysts hosted by volcanic rocks of varying ages. Practically all the melt inclusions we analyzed show increased total alkalies and are in the class of trachyrhyodacites and trachyrhyolites, with the varieties of the highest alkali content being alkaline rhyolites and comendites; the concentration of K 2 O classifies them as subalkaline rocks; one also notes the increased alumina of the acid melts. The compositions and spatial locations of the melt inclusions in quartz phenocrysts provide evidence of a three-phase crystallization in magma chambers at different depths. According to the experimental data, the quartz phenocrysts crystallized in a water-saturated melt at pressures of 0.1 to 3.5 kbars.

Предложена геолого-петрологическая модель формирования Белоголовского вулканического массива позднеплиоценового–раннеплейстоценового времени. Выделено две петрохимические серии пород разной щелочности: нормальной и умеренно-щелочной. Характер эволюции продуктов вулканизма и минералогический состав пород разной щелочности свидетельствуют о пространственной независимости и разной глубине очагов родительских магм их продуцирующих. Ведущим процессом, ответственным за образование расплавов, исходных для спектра пород внутри каждой серии, является кристаллизационная дифференциация. Эволюция щелочно-базальтовой магмы проходила ступенчато с образованием автономных дочерних расплавов состава: трахибазальты–трахиандезиты–трахиты–трахириолиты, комендиты, локализованных в разноглубинных промежуточных очагах.

We proposed a geological and petrologic model for the generation of the Belogolovskii Late Pliocene to Early Pleistocene volcanic massif. We identified two petrochemical series of rocks with varying alkalinities, viz., normal and moderate. The evolution of volcanic products and the mineralogic composition of rocks of varying alkalinities provide evidence that the sources of parent magmas are spatially independent and reside at different depths. Crystallization differentiation is the leading process that is responsible for the generation of the initial melts that give rise to the range of rocks within a series. The evolution of the alkaline basaltic magma occurred stepwise, producing autonomous daughter melts with the following compositions: trachybasalt-trachyandesite-trachyte-trachyrhyolite and comendite. These melts were localized in inter-mediate magma chambers at different depths.

The Kekuknai massif was formed in the course of tectono-magmatic activity that involved the origin of a shield volcano and a caldera depression with associated emplacement of extrusions that terminated in intense post-caldera areal volcanism. The mineralogical compositions of the massif’s rocks have been considered in detail. The use of previously known and newly developed indicator properties of rock-forming minerals allowed the reconstruction of the general picture of the magmatic melt evolution and conditions of rock crystallization (various fluid and water saturation levels, as well as the oxidation state of the system). Essentially island-arc or intraplate characteristics of the massif’s rock compositions are found at different stages of development of a single fluid-magmatic system. Decompression evolution of the parent deep-seated basanitic magma occurred via occurrence in intermediate magma chambers of daughter magmas of trachybasalt (pre-caldera stage) or hawaiite (areal volcanism) composition. Subsequent emanate-magmatic differentiation of these melts, combined with crystallization differentiation under changing P-T-conditions, resulted in the formation of the entire diversity of the Kekuknai rocks.

Кекукнайский массив сформировался в результате тектоно-магматической деятельности, выразившейся образованием щитообразного вулкана, кальдерной депрессии с сопутствующим внедрением экструзий, и завершившейся интенсивным посткальдерным ареальным вулканизмом. Проведено детальное рассмотрение особенностей минералогического состава пород массива. Использование уже имеющихся и дополнительно выявленных индикаторных возможностей породообразующих минералов позволило восстановить общую картину эволюции магматических расплавов и условия кристаллизации пород (различная флюидонасыщенность-обводненность и окисленность системы). Существенно островодужные или внутриплитные характеристики в составе пород массива проявлены на разных стадиях развития единой флюидно-магматической системы. Декомпрессионная эволюция материнской глубинной базанитовой магмы была реализована появлением в промежуточных очагах дочерних магм трахибазальтового (докальдерный этап развития системы) или гавайитового (ареальный вулканизм) состава. Дальнейшая эманационно-магматическая дифференциация этих расплавов в сочетании с кристаллизационной дифференциации в условиях меняющейся P-T-f02 обстановки и привела к образованию всего многообразия пород Кекукнайского массива.

The evolution of the Quaternary Kekuknai volcanic massif (the western flank of the Sredinnyi Range in Kamchatka) has been subdivided into five stages: (1) the pre-caldera trachybasaltbasaltic andesite, (2) the extrusive trachyandesite-trachydacite, (3) the early trachybasalt, (4) the middle hawaiitemugearite (with occasional occurrences of basaltic andesites), and (5) the late trachybasalt-hawaiitemugearite (with occasional andesites) of areal volcanism. On the basis of petrologic data we identified the island arc and the intraplate geochemical types of rocks in the massif. The leading part in petrogenesis was played by dynamics of the fluid phase with a subordinated role of fractional crystallization and hybridism. Successive saturation of rocks with the fluid phase in the course of melt evolution stopped at the time of caldera generation when most fluid mobile elements and silica had been extracted. The geological and petrologic data attest to the formation of the massif in the environment of a backarc volcanic basin during the beginning of rifting with active participation of mantle plume components.

On page 498, in the caption to Fig. 5, description of (7) and (8) should read (7) compositional field of the Mount Khukhch basanitic groundmass; (8) average composition of the Mount Khukhch basa-nitic groundmass.The diagram is based on our and literature data.2.

Neogene (N 1 2 -N 2 1 ?) K-Na alkaline rocks were found in western Kamchatka as a subvolcanic basanite body at Mount Khukhch. The basanites have a microphyric texture with olivine phenocrysts in a fine-grained doleritic groundmass. The olivine contains inclusions of Al-Cr spinel. The microlites consist of clinopyroxene, plagioclase, magnetite, and apatite, and the interstitial phases are leucite, nepheline, and analcime. The Mount Khukhch basanites are characterized by elevated concentrations of MgO, TiO2, Na2O, and K2O, high concentrations of Co, Ni, Cr, Nb, Ta, Th, U, LREE (LaN/YbN = 10.8−12.6, DyN/YbN = 1.4−1.6) at moderate concentrations of Zr, Hf, Rb, Ba, Sr, Pb, and Cu. The values of indicator trace-element ratios suggest that basanites in western Kamchatka affiliate with the group of basaltoids of the within-plate geochemical type: Ba/Nb = 10−12, Sr/Nb = 17−18, Ta/Yb = 1.3−1.6. The basanites of western Kamchatka show many compositional similarities with the Miocene basanites of eastern Kamchatka, basanites of some continental rifts, and basalts of oceanic islands (OIB). The geochemistry of these rocks suggests that the basanite magma was derived via the ∼6% partial melting of garnet-bearing peridotite source material. The crystallization temperatures of the first liquidus phases (olivine and spinel) in the parental basanite melt (1372–1369°C) and pressures determined for the conditions of the “mantle” equilibrium of the melt (25–26 kbar) are consistent with the model for the derivation of basanite magma at the garnet depth facies in the mantle. The geodynamic environment in which Neogene alkaline basaltic magmas occur in western Kamchatka was controlled by the termination of the Oligocene—Early Miocene subduction of the Kula oceanic plate beneath the continental margin of Kamchatka and the development of rifting processes in its rear zone. The deep faulting of the lithosphere and decompression-induced magma generation simultaneous with mantle heating at that time could be favorable for the derivation of mantle basite magmas.

(1990). MINERAL ZONING OF THE QUATERNARY LAVAS OF THE KURILE ISLAND ARC. International Geology Review: Vol. 32, No. 2, pp. 128-142.