Tectonostratigraphic complexes of the southern Kronotskii paleoarc (Eastern Kamchatka): Structure,age, and composition

The eastern peninsulas of Kamchatka are mostly composed of tectonostratigraphic complexes, which were formed within the Late Cretaceous-Eocene Kronotskii-Kamchatka arc. The accretion of this paleoarc to the Kamchatka margin of northeastern Asia in the terminal Cenozoic represented the last collisional event in the formation of the present-day structure of Kamchatka. The article presents new data on the age, composition, and structure of the tectonostratigraphic complexes constituting the southern segment of the Kronotskii-Kamchatka paleoarc. It is shown that the oldest rocks of these complexes are the Campanian in age and represented by volcano-sedimentary rocks that were formed in different geodynamic environments. The investigated igneous rocks are attributed to two types: (1) the tholeiite series of a mid-oceanic ridge (MOR) (Vetlovaya Complex); (2) tholeiite and calc-alkaline series of island arcs (Shipunskii Sequence of the Kronotskii Group).     

Miocene foraminifer complexes of Karaginsky Island,East Kamchatka

Investigation of Miocene foraminifers in Karaginsky Island allowed recognition of 13 complexes. In all, three complexes were recognized in the Variegated Formation, eight complexes were found in the Plosky Cape Formation, and three were recorded in the Yunyun’vayam Creak Formation. The changes in their nature were related to changes in paleoenvironments. The composition of complexes indicates their accumulation under conditions of the outer shelf and continental slope. The recognized foraminifer complexes allow correlating successions in Karaginsky Island with Lower-Upper Miocene successions of the Northern Pacific.     

The study of unfrozen water in volcanic ashes (Kamchatka)

The results of the study of unfrozen water in frozen volcanic ashes of different ages and mineral compositions from Kamchatka are discussed. The results of thermal analysis of chemical and granulometric composition are presented and discussed.     

U-Pb SHRIMP dating of zircons from metamorphic complexes in eastern Kamchatka

The metamorphic complexes of eastern Kamchatka exposed on the Khavyven Highland and Karaginsky Island, as well as on the Kamchatka and Ozernoi peninsulas, compose large (up to 1.5 km) elongated blocks spatially associated with ophiolitic peridotite and gabbroic rock bodies (the Khavyven Highland and Karaginsky Island) or make up isolated fragments and blocks among serpentinite melange (the Ozernoi and Kamchatka peninsulas). The degree of metamorphism of the primary rocks varies from the greenschist/amphibolite boundary facies (Karaginsky Island and the Khavyven Highland) to the high-pressure amphibolite facies (the Ozernoi and Kamchatka peninsulas).     

Garnet-bearing basites of the Kuvalorog massif (Kamchatka Peninsula )

The petrographic, petrochemical, and mineralogical compositions of the Kuvalorog Ni-bearing cortlandite-norite intrusion and endocontact leucodiorites hosting pyrope-almandine garnet are considered. Lamprophyre dikes with scarce pyrope-almandine garnet, first discovered in the massif, and plagioclase-pyroxene symplectites in garnet porphyroblast areas are studied. Judging from the petrography of rocks and the composition of inclusions rich in incompatible elements in the garnet, the mineral was produced by the reaction of orthopyroxene with the anorthite component of plagioclase at the subsolidus stage of formation of endocontact diorites. This reaction was probably favored by the fluid phase abundant in the parental magma of the Kuvalorog intrusion and, especially, in the zones near its contact with relics of terrigenous rocks, where it was produced as a result of the rock dehydration under the thermal effect of the intrusion.     

Specific mineral associations of hydrothermal shale (South Kamchatka)

The sequence of hydrothermal shale from the East Pauzhet thermal field within the Pauzhet hydrothermal system (South Kamchatka) was studied in detail. It was established that the formation of shale resulted from argillization of an andesitic lava flow under the influence of an acidic sulfate vapor condensate. The horizons with radically different compositions and physical properties compared to those of the overlying homogeneous plastic shale were distinguished at the base of the sequence. These horizons are characterized by high (up to two orders of magnitude in comparison with average values in hydrothermal shale) concentrations of F, P, Na, Mg, K, Ca, Sc, Ti, V, Cr, Cu, and Zn. We suggested a geological–geochemical model, according to which a deep metal-bearing chloride–hydrocarbonate solution infiltrated into the permeable zone formed at the root of the andesitic lava flow beneath plastic shale at a certain stage of evolution of the hydrothermal system.     

Neogene basanites in western Kamchatka: Mineralogy,geochemistry, and geodynamic setting

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 (La_N/Yb_N = 10.8?12.6, Dy_N/Yb_N = 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.     

Variations of Seismicity in the Avachinsky Gulf (Kamchatka, Russia)

Variations of seismic mode in the region of the Avachinsky Gulf (Kamchatka, Russia) are considered. Observed anomalies (seismic quiescence, the ring seismicity, reduction of the slope of the earthquake recurrence diagram) provide a basis to consider this region as a place of strong earthquake preparation. The Kamchatka regional catalogues of earthquakes between 1962–1995 were used in the analysis. A reduced seismicity rate is observed during 10 years in an area of 150 km × 60 km in size. During the last five years, in the vicinity of the area considered, earthquakes with M > 5 occurred three times more often than the average over thirty years. It is interpreted as ring seismicity. The block of 220 km × 220~km in size, including the quiescence zone, is characterized by a continuous decrease of the recurrence diagram slope, which has reached a minimum value for the last 33 years in this region.     

The Paleogene in the southern part of Karagin Island (Eastern Kamchatka)

On the basis of foraminifers In the section through the Cenozoic deposits of Karagin Island, we distinguish the Eocene (the Cape Tons and Mt. Peresheyek suites), Oligocene (the Il'khatun suite and the Laternula sandstones), and Miocene deposits and describe their paleontological characteristics. We identify 18 assemblages of foraminifera, correlating the Paleogene deposits on Karagin Island with the synchronous deposits to Japan and California. The Cape Tons and Mt. Peresbeyek suites are correlated with the Sakasegawa and Poronai formations in Japan and with deposits of the Narizian and Refugian stages to California. —Authors.     

Possible precursors in groundwater ions and gases content in Kamchatka (Russia)

For many years, hydrogeochemicals have been collected with a mean sampling frequency of three days in the form of the most common ions and gases in the groundwater of five deep wells in the Southern area of the Kamchatka peninsula. In the last decade, five earthquakes with M > 6.5 occurred at distances less than 250 km from these wells. In order to reveal possible precursors of these earthquakes we analysed the hydrogeochemicals collected. The quasi-periodic annual variation was filtered out, together with other slow trends, and then we smoothed out the high frequency fluctuations that arise from the errors in a single measurement. When examining the filtered and smoothed data, we labelled each signal with an amplitude greater than three times the standard deviation as an irregularity and we made a first attempt at defining an anomaly as an irregularity which occurs simultaneously in more than one type of ion or gas at each well. In a second definition we used the existence of an irregularity occurring simultaneously in each type of ion or gas at more than one well. Then we chose the minimum time interval between two successive earthquakes as the maximum temporal window between a possible anomaly and the subsequent earthquake. Concerning the ions content, we identified a total of 16 anomalies with 11 successes and 5 failures; for the gases content we identified a total of 25 anomalies with 9 successes and 16 failures. On the basis of the criteria chosen we find the possibility that the successes of ion contents as earthquake precursors is high; but in contrast there is a only small possibility that the successes in gases content are precursors.     

Late Cretaceous-Paleocene magmatic complexes of central Kamchatka: Geological settings and compositional features

A comparative analysis of the Late Cretaceous-Paleocene volcanism was conducted for four areas of Kamchatka: the Pravyi Tolbachik-Levaya Shchapina-Adrianovka interlfuve (the northern part of the Tumrok Range), the area south of the Ipuin River and Mt. Khrebtovaya (the northern Valaginsky Range), the area of Mt. Savul’ch (the upper reaches of the Kitil’gina River, northern Valaginsky Range), and the Kirganik-Levaya Kolpakova interfluve (the Sredinny Range). New petrochemical, geochemical, and isotopic data on the volcanic rocks from these areas are reported. The examination of this material, together with already published data on volcanic and plutonic rocks of similar composition and age, made it possible to establish the following: (1) the considered basaltoids are ascribed to the subalkali basalt-trachyandesite series with transition toward a meymechite-picrite rock association; (2) the alkali content in the rocks of the Valaginsky-Tumrok-Sredinny ranges increases simultaneously with the increase of the Rb content, while the contents of HFSE and radioactive elements decrease and then again increase. Two trends are identified in the Yb_n-Ce_n diagram: a positive trend spanning most of the volcanic and plutonic rocks and a negative trend defined by the data points of the meymechite-picrite association. The first trend reflects the rock evolution during crystallization differentiation, while the second trend was produced by different degrees of melting of initial protolith. The possible geodynamic reconstructions of this volcanism are discussed as well.     

Age of Ichinsky and Khangar Stratovolcanoes (Sredinny Range,Kamchatka)

Doklady Earth Sciences - The K–Ar isotopic age of the beginning of formation of Ichinsky (0.35) and Khangar (0.4) stratovolcanoes is established for the first time, as well as the age of the...