Magma contamination, petrogenesis features and distribution of ore element in the rocks of nickeliferous formation in the Sredinny-Kamchatka massif

This is the final article that describes various for petro- and oreogenesis consequences of the contamination of nickel-bearing magma with siliceous material (quartzites), which led to the replacement of ultrabasic ore-hosting rocks (cortlandites) with ultramafic (amphibole orthopyroxenites). Besides, the paper describes the products of metamagmatic variations of pyroxene ore cumulates in biotite-amphibole rocks inported by water-potassium fluid. The author shows the unconventional results of fluid influence on similar cumulates with relics of quartzite xenoliths accompanied by the formation of ore granophyric autobreccies, as well as ore-bearing derivatives from the process of magma mixing (auto-contamination). We introduce an intraformational classification of copper-nickel ores by their associations with host rocks of different composition and origin — from juvenile magmatic ultrabasites, contaminated and ultramafites and melanodiorites to hybrid granitoids. The dynamics of the formation of intrusive ore-magmatic systems and the plausible reason of differences in the ore content of large and small intrusions are discussed

(Table 2) Absolute age of Magellan Seamount Guyots

This paper generalizes both original data and all available materials obtained by home and foreign researchers when studying guyots of the Magellan seamounts. The Magellan seamounts represent an extended arc-like chain of seamounts, mainly guyots within the middle part of the East-Mariana Trough. The guyots rise above the relatively flat floor of the East-Mariana Trough with depths about 5500-6000 m to the height up to 4500-4800 m and reach depth level from 1300 to 1200 m. In 1980s-1990s the Magellan seamounts become objects of permanent studies for both home and foreign researchers. First of all it is connected with the fact that considerable accumulations of Fe/Mn crusts and nodules were found at slopes and tops of the Magellan seamounts. Though having some similar features, the guyots of the Magellan seamounts differ considerably in their geological structure, time of formation and duration of volcanic activity. They were studied rather non-uniformly. The Ita-Maitai, Dalmorgeo, Roskomnedra, Vulkanolog, TIG, Hemler guyots and the Himu seamount were studied in detail, while the Nakhodka, IMGiG, TOI, DVGI guyots and the D-4 and Golden Dragonseamounts are less studied. The MA-3, MA-4, MA-10, MA-11, MA-27, MA-29, MA-31 and MA-38 guyots are very poorly studied

Evolution and genesis of volcanic rocks from Mutnovsky Volcano, Kamchatka

This study presents new geochemical data for Mutnovsky Volcano, located on the volcanic front of the southern portion of the Kamchatka arc. Field relationships show that Mutnovsky Volcano is comprised of four distinct stratocones, which have grown over that past 80 ka. The youngest center, Mutnovsky IV, has produced basalts and basaltic andesites only. The three older centers (Mutnovsky I, II, III) are dominated by basalt and basaltic andesite (60–80 by volume), but each has also produced small volumes of andesite and dacite. Across centers of all ages, Mutnovsky lavas define a tholeiitic igneous series, from 48–70 SiO2. Basalts and basaltic andesites have relatively low K2O and Na2O, and high FeO* and Al2O3 compared to volcanic rocks throughout Kamchatka. The mafic lavas are also depleted in the light rare earth elements (REEs), with chondrite-normalized La/Sm < 1.0. Andesites have generally higher REE abundances and are more enriched in light REEs, some showing negative Eu anomalies. All samples are depleted in field strength elements (HFSEs) relative to similarly incompatible REEs (e.g., low La/Ta, Nd/Hf compared to MORB), similar to island arc volcanic rocks worldwide. Radiogenic isotope ratios (Sr, Nd, Pb, Hf) are similar for samples from all four eruptive centers, and indicate that all samples were produced by melting of a similar source mixture. No clear age-progressive changes are evident in the compositions of Mutnovsky lavas. Mass balance and assimilation-fractional crystallization (AFC) modeling of major and rare earth elements (REEs) indicate that basaltic andesites were produced by FC of plagioclase, clinopyroxene and olivine from a parental basalt, combined with assimilation of a melt composition similar to dacite lavas present at Mutnovsky. This modeling also indicates that andesites were produced by FC of plagioclase from basaltic andesite, combined with assimilation of dacite. Dacites erupted from Mutnovsky I and II have low abundances of REEs, and do not appear to be related to mafic magmas by FC or AFC processes. These dacites are modeled as the products of dehydration partial melting at mid-crustal levels of a garnet-free, amphibole-bearing basaltic rock, which itself formed in the mid-crust by emplacement of magma that originated from the same source as all Mutnovsky magmas. Lead isotope data indicate that subducted sediment is likely present in the source beneath Mutnovsky and most Kamchatka volcanoes, but uniformly radiogenic Hf and Nd in mafic samples (εNd = 8.7–9.3, εHf = 15.4–15.9), and significant variation in trace element ratios at nearly constant εNd and εHf, indicate that sediment plays a minor roll in controlling subduction trace element patterns in Mutnovsky lavas. Mafic lavas with Ba/Th > 450 require an aqueous fluid source component from subducting oceanic crust, but mixing patterns in isotope versus trace element ratio plots for Hf and the REEs (εNd and εHf vs. ratios with Ce, Nd and Hf) demonstrate that a source component with radiogenic Nd and Hf, and fractionated (arc-type) trace element ratios must be present in the source of Mutnovsky lavas. This source component, which is interpreted to be a partial melt of subducted basalt in the eclogite facies (eclogite melt source component), appears to be present in the source of all Kamchatka volcanoes. Cross-arc geochemical patterns at Mutnovsky and in other arc systems (Isu-Bonin, Tonga-Kermadec) suggest that the aqueous fluid component diminishes and the eclogite melt component is increased from volcanoes at the arc front compared to those in rear-arc positions

Melt Inclusion Evidence for Magma Evolution at Mutnovsky Volcano, Kamchatka

Mutnovsky Volcano, located in Kamchatka, Russia, is a young volcano that has formed a series of four overlapping stratocones over its approximately 80 ka history. Erupted products at Mutnovsky range in composition from basalts to dacites; basalts are the most common. In this study, melt inclusions from representative samples of all erupted compositions from all four eruptive centers were analyzed to investigate the causes of the compositional heterogeneity, melt evolution, and pre‐eruptive magma dynamics. Melt inclusions from Mutnovsky were sampled in olivine, plagioclase, orthopyroxene, and clinopyroxene. The melt inclusion data represent a wide range of melt compositions, from basalt through rhyolite. Geochemical modeling of melt inclusion data, combined with field evidence and chemical zoning of plagioclase phenocrysts, indicates that fractional crystallization and magma mixing produced the range of erupted bulk rock compositions. The measured variability of melt inclusion compositions in each host mineral phase indicates that different host minerals trapped unique melts that evolved separately from one another. The melt inclusion data suggest that individual melt portions evolved by fractional crystallization, perhaps in different magma chambers, within the Mutnovsky plumbing system, and were mixed prior to eruption. Our data do not indicate whether the mixing events were the cause of eruption or are simply the manifestation of the eruption process. Melt inclusions trapped in plagioclase, clinopyroxene, orthopyroxene and olivine phenocrysts represent a wide range of melt compositions, from basalt through rhyolite. Melt inclusion data, combined with field evidence and chemical zoning of plagioclase phenocrysts, indicate that fractional crystallization and magma mixing produced the range of erupted bulk rock compositions. The melt inclusion data suggest that individual melt portions evolved by fractional crystallization, perhaps in different magma chambers, within the Mutnovsky plumbing system, and were mixed prior to eruption.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100313/1/gfl12060.pd

Middle to late Pleistocene record of explosive volcanic eruptions in marine sediments offshore Kamchatka (Meiji Rise, NW Pacific)

This paper presents the first detailed study of a late Pleistocene marine tephra sequence from the NW Pacific, downwind from the Kamchatka volcanic arc. Sediment core SO201-2-40, located on the Meiji Rise similar to 400 km offshore the peninsula, includes 25 tephras deposited within the last 215 ka. Volcanic glass from the tephras was characterized using single-shard electron microprobe analysis and laser ablation inductively coupled mass spectrometry. The age of tephras was derived from a new age model based on paleomagnetic and paleoclimate studies. Geochemical correlation of distal tephras to Kamchatkan pyroclastic deposits allowed the identification of tephras from the Karymsky, Gorely, Opala and Shiveluch eruptive centers. Three of these tephras were also correlated to other marine and terrestrial sites and hence are identified as the best markers for the north-west Pacific region. These are an early Holocene tephra from the Karymsky caldera (similar to 8.7 ka) and two tephras falling into the Marine Isotope Stage (MIS) 6 glacial time: an MIS 6.4 tephra from Shiveluch (similar to 141 ka) and the MIS 6.5 Rauchua tephra (similar to 175 ka) from Karymsky. The data presented in this study can be used in paleovolcanological and paleoceanographic reconstructions