Concentration of rhenium and other rare metals in gases of the Kudryavy Volcano (Iturup Island,Kurile Islands)

Doklady Earth Sciences -     

Volborthite Occurrence at the Alaid Volcano (Atlasov Island,Kuril Islands,Russia)

Geology of Ore Deposits - Abstract—Yellow volborthite Cu2.95(V1.91P0.09)Σ2O7(OH)1.90·2H2O, and turquoise atacamite, Cu2[Cl0.98(OH)0.02]Σ1.00(OH)3 have been found incrusting...     

Evolution and Genesis of Magmas from Vico Volcano, Central Italy: Multiple Differentiation Pathways and Variable Parental Magmas

Vico volcano has erupted potassic and ultrapotassic magmas,ranging from silica-saturated to silica-undersaturated types,in three distinct volcanic periods over the past 0·5Myr. During Period I magma compositions changed from latiteto trachyte and rhyolite, with minor phono-tephrite; duringPeriods II and III the erupted magmas were primarly phono-tephriteto tephri-phonolite and phonolite; however, magmatic episodesinvolving leucite-free eruptives with latitic, trachytic andolivine latitic compositions also occurred. In Period II, leucite-bearingmagmas (⁸⁷Sr/⁸⁶Sr_initial = 0·71037–0·71115)were derived from a primitive tephrite parental magma. Modellingof phonolites with different modal plagioclase and Sr contentsindicates that low-Sr phonolitic lavas differentiated from tephri-phonoliteby fractional crystallization of 7% olivine + 27% clinopyroxene+ 54% plagioclase + 10% Fe–Ti oxides + 4% apatite at lowpressure, whereas high-Sr phonolitic lavas were generated byfractional crystallization at higher pressure. More differentiatedphonolites were generated from the parental magma of the high-Srphonolitic tephra by fractional crystallization of 10–29%clinopyroxene + 12–15% plagioclase + 44–67% sanidine+ 2–4% phlogopite + 1–3% apatite + 7–10% Fe–Tioxides. In contrast, leucite-bearing rocks of Period III (⁸⁷Sr/⁸⁶Sr_initial= 0·70812–0·70948) were derived from a potassictrachybasalt by assimilation–fractional crystallizationwith 20–40% of solid removed and r = 0·4–0·5(where r is assimilation rate/crystallization rate) at differentpressures. Silica-saturated magmas of Period II (⁸⁷Sr/⁸⁶Sr_initial= 0·71044–0·71052) appear to have been generatedfrom an olivine latite similar to some of the youngest eruptedproducts. A primitive tephrite, a potassic trachybasalt andan olivine latite are inferred to be the parental magmas atVico. These magmas were generated by partial melting of a veinedlithospheric mantle sources with different vein–peridotite/wall-rockproportions, amount of residual apatite and distinct isolationtimes for the veins. KEY WORDS: isotope and trace element geochemistry; polybaric differentiation; veined mantle; potassic and ultrapotassic rocks; Vico volcano; central Italy     

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.     

Crystallization Driven by Decompression and Water Loss at Stromboli Volcano (Aeolian Islands, Italy)

Stromboli, in the Aeolian Archipelago, is famous for its persistentvolcanic activity. The ‘normal’ activity, consistingof rhythmic explosions ejecting crystal-rich scoriae, is periodicallyinterspersed with more energetic explosions during which, inaddition to crystal-rich scoriae, crystal-poor pumices are alsoemitted. The scoriae contain     

Manam Island, Papua New Guinea: Petrology and Geochemistry of a Low-TiO2 Basaltic Island-Arc Volcano

Manam volcano consists of relatively mafic and compositionallysimilar tholeiitic basalts and low-SiO₂ andesites that are characterizedby notably low (mainly 0?3–0?35 weight per cent) TiO₂contents. These rocks provide an ideal opportunity to investigateboth the extent of depletion in their peridotite magma-sourceregions (which are evidently similar in many respects to thehighly depleted sources of boninitic magmas), and the interplayof the high-level processes of magma mixing, crystal fractionation,and upper crustal contamination, in an island-are volcano. Manamrocks have pronounced enrichments in Rb, Ba, K, and Sr relativeto the light rare-earth elements and, especially, to the high-field-strengthelements (Sr/Ti values are exceptionally high). However, thereis no compelling evidence that these enrichments were causedby addition of a hydrous, slab-derived component to the peridotitesource region. Nd and Sr-isotope ratios plot within the oceanicmantle array; ²⁰⁷Pb/²⁰⁴Pb values are only slightly higher thanthose for oceanic rocks; and the absence of hydrous minerals,the early crystallization and modal preponderance of plagioclaseover pyroxene, high estimated quenching temperatures, and lowwater contents in the Manam rocks, are all evidence that themagmas crystallized under markedly water-undersaturated conditions.Unusually anorthite-rich plagioclase phenoerysts in the morediffrentiated rocks may correspond to crystallization underhigher water-vapour pressures, possibly caused by influxes ofgroundwater, or they may be accidental xenocrysts. Fractionationof olivine, clinopyroxene, and spinel (early chromite followedby magnetite) has dominated the evolution of the magma series.However, clear correlations between incompatible trace-elementratios, ⁸⁷Sr/⁸⁶Sr, and 100 Mg/(Mg ? Fe^2?) values are convincingevidence for an accompanying mixing process—either of(1) two basaltic magma types (one more fractionated and lowerin ⁸⁷Sr/⁸⁶Sr than the other), or (2) pristine magmas and contaminantfrom basaltic conduit and reservoir wall rocks. Wall-rock contaminationis the less likely process, and is the more difficult one toidentify, particularly if it accompanied magma mixing.     

Geochemical Characteristics of Volcanogenic Deposits and Exhalation Mineralization in the Crater Part of the Active Kudryavy Volcano (Iturup Island of the Kuril Arc)

Geology of Ore Deposits - Exhalation ore mineralization is developing in the crater part of the active Kudryavy volcano. Lithogeochemical sampling results have revealed that Re, Au, Ag, As, Bi, Cd,...     

Selective Contamination of Basaltic Magmas and Genesis of Buchites (on the Example of Shufan Plateau,Primorye)

Doklady Earth Sciences - The problems of large-scale contamination of the Shufan volcanic plateau (Primorye) basalts with selective melts from xenoliths are discussed. Silico-alkaline liquids that...     

The Role of Pressure in Producing Compositional Diversity in Intraplate Basaltic Magmas

Basaltic magmas found in intraplate suites appear to followmore than one differentiation trend. Many ocean island suitesfollow the ocean island tholeiitic trend, with the basalts differentiatingfrom olivine tholeiite through basaltic andesite, andesite,and dacite to sodic rhyolite. Many continental intraplate magmaticregimes, such as those of the Snake River Plain and the plutonicsequences associated with massif anorthosites, follow the potassicsilica-saturated alkalic trend, in which basalt differentiatesfrom olivine tholeiite through ferrobasalt (jotunite or ferrodiorite),Fe-rich intermediate rocks (trachybasalt or monzonite), andtrachyte (syenite) to potassic rhyolites and granites. Crystallizationexperiments on an olivine tholeiite from the Snake River Plainshow that the basaltic portions of the ocean island tholeiitictrend and the potassic silica-saturated alkalic trend (whichleads to strong alkali, P, Ti, and Fe enrichment and silicadepletion) can arise from the same ‘dry’ tholeiiticparental magma. These compositional differences are inducedby changes in phase equilibria as a function of pressure, withthe ocean island tholeiitic series arising from crystal–liquiddifferentiation at low pressure and the potassic silica-saturatedalkalic series arising via differentiation at elevated pressures. KEY WORDS: tholeiite differentiation; experimental petrology; phase equilibria; ferrodiorite; ferrobasalt     

Rates of Thermal and Chemical Evolution of Magmas in a Cooling Magma Chamber: a Chronological and Theoretical Study on Basaltic and Andesitic Lavas from Rishiri Volcano, Japan

Rates of magmatic processes in a cooling magma chamber wereinvestigated for alkali basalt and trachytic andesite lavaserupted sequentially from Rishiri Volcano, northern Japan, bydating of these lavas using ²³⁸U–²³⁰Th radioactive disequilibriumand ¹⁴C dating methods, in combination with theoretical analyses.We obtained the eruption age of the basaltic lavas to be 29·3± 0·6 ka by ¹⁴C dating of charcoals. The eruptionage of the andesitic lavas was estimated to be 20·2 ±3·1 ka, utilizing a whole-rock isochron formed by U–Thfractionation as a result of degassing after lava emplacement.Because these two lavas represent a series of magmas producedby assimilation and fractional crystallization in the same magmachamber, the difference of the ages (i.e. 9 kyr) is a timescaleof magmatic evolution. The thermal and chemical evolution ofthe Rishiri magma chamber was modeled using mass and energybalance constraints, as well as quantitative information obtainedfrom petrological and geochemical observations on the lavas.Using the timescale of 9 kyr, the thickness of the magma chamberis estimated to have been about 1·7 km. The model calculationsshow that, in the early stage of the evolution, the magma cooledat a relatively high rate (>0·1°C/year), and thecooling rate decreased with time. Convective heat flux fromthe main magma body exceeded 2 W/m² when the magma was basaltic,and the intensity diminished exponentially with magmatic evolution.Volume flux of crustal materials to the magma chamber and rateof convective melt exchange (compositional convection) betweenthe main magma and mush melt also decreased with time, from 0·1 m/year to 10^–3 m/year, and from 1 m/yearto 10^–2 m/year, respectively, as the magmas evolved frombasaltic to andesitic compositions. Although the mechanism ofthe cooling (i.e. thermal convection and/or compositional convection)of the main magma could not be constrained uniquely by the model,it is suggested that compositional convection was not effectivein cooling the main magma, and the magma chamber is consideredto have been cooled by thermal convection, in addition to heatconduction. KEY WORDS: convection; magma chamber; heat and mass transport; timescale; U-series disequilibria     

Behavior of rare earth elements during mixing of different types of water (Kunashir,the Kurile Islands)

The fractionation of rare earth elements (REE) was evaluated under the conditions of natural acidic water mixing with fresh and sea waters using the example of unique objects on Kunashir Island (the Kislaya and Lesnaya rivers). It was shown that the concentrations and fractionation of REE in the water types considered are diverse and controlled by a number of factors. The concentrations of dissolved REE normalized to the North American Shale Composite show an increase from the light to the heavy REE, which reflects both the character of the REE input with the thermal waters and the more active sorption of the light REE and their preferential removal to suspended solids. This is supported by the similar REE patterns in the suspended matter of the Kislaya River. The mixing of the waters of the Kislaya and Lesnaya rivers, which are assigned to different chemical types, is accompanied by active REE coprecipitation with Fe, Al, and Mn oxides and the more extensive removal of the light REE compared with the heavy REE. During acidic water mixing with seawater, more than 80% of the REE were precipitated at a salinity of 8‰.     

Role of climatic and volcanogenic factors in the formation of organogenic sediments and the development of landscapes on Simushir Island (Central Kurile Islands) in the middle-late Holocene

It is shown that the development history of landscapes on Simushir Island includes several stages marked by their reorganizations, which were caused by climate changes and volcanic eruptions. The stratigraphic data derived from sections of the soil-tephra cover in different areas of the island and from the peatland section on the Dushnaya Bay coast served as the basis for the paleogeographic reconstructions. They include data on the palynological spectra of the fossil and recent soils and peatland; the latter also yielded diatom assemblages. The radiocarbon dates and tephrostratigraphic record provided age estimates for the corresponding events.     

The Cambrian of Bennett Island (New Siberian Islands)

The paper presents new data on the Cambrian stratigraphy of Bennett Island, one of the least explored East Arctic islands. The section, about 500 m of total thickness, comprises four lithological units that store a record of the deposition history: (1) clastic sediments including storm sandstones; (2) shallow-marine mudstone; (3) lagoonal variegated mudstone and limestone; (4) black shale. It is suggested to classify the units as formations with their proper names. The section spans all epoches of the Cambrian stratigraphy constrained by trilobite fossils. In the Cambrian, territory of the island belonged to Siberia rather than to some exotic terrane, judging by abundant endemic Siberian trilobite species in the Bennett section. This inference is supported by synchronicity in recorded deposition events of Bennett Island and northeastern Siberia (Kharaulakh Mountains). The Cambrian sediments of the two areas were deposited in different parts of a single shallow sea which extended as far as Taimyr.     

Evolution of Deeper Basaltic and Shallower Andesitic Magmas during the AD 1469-1983 Eruptions of Miyake-Jima Volcano, Izu- Mariana Arc: Inferences from Temporal Variations of Mineral Compositions in Crystal-Clots

Miyake-jima volcano has erupted at least 13 times during theperiod 1469–1983. To understand the historic magmaticprocesses, we focus on the mineral assemblage and chemical compositionsof crystal-clots in single samples from each of the eruptions.Most of the historic lavas consist of nearly aphyric to weaklyporphyritic basalt to andesite, but there also exist megacryst-bearingrocks. The megacrysts are considered to be xenocrysts from adeep-seated plutonic body. Many samples of each eruption containtwo types of clots beside megacrysts, termed here B-type andA-type. The B-type clots are composed of olivine, clinopyroxeneand plagioclase, whereas the A-type clots additionally containmagnetite and orthopyroxene. Compositional relationships betweenthese mafic minerals suggest that the minerals in the same typeof clots are in equilibrium. Comparing the chemical compositionsof the minerals in the two types of clots in each sample, theyare derived from distinct magmas: the B-type clots from basalticmagma and the A-type clots from andesitic magma. During thehistoric activity, the magma plumbing system appears to haveincluded two magma storage systems: a deep-seated basaltic anda shallower andesitic one. In many cases, basaltic magma hasinjected into shallower andesitic magma to form mixed magma;however, andesitic magma has sometimes erupted alone withoutextensive injections of basaltic magma. Temporal variationsof mineral compositions in the clots and estimated whole-rockcompositions of the end-member magmas suggest that the basalticmagma has differentiated gradually since 1469, and that itsmagmatic temperature has fallen from 1220 to 1180°C. Conversely,the andesitic magma has changed in a complex fashion to becomemore mafic (the magmatic temperature rose from 1050 to 1100°C).As a result of this study, it is estimated that the basalticmagma after the 1983 eruption was the least mafic, and the andesiticmagma the most mafic, of the historic eruptions. KEY WORDS: andesite; basalt; crystal-clots; evolution of magma; Miyake-jima volcano; magma mixing     

Permian-Triassic trap magmatism in Bel'kov Island (New Siberian Islands)

The study was inspired by information on Paleozoic andesites, dacites, and diabases in Bel'kov Island in the 1974 geological survey reports used to reconstruct the tectonic evolution of the continental block comprising the New Siberian Islands and the bordering shelf. We did not find felsic volcanics or Middle Paleozoic intrusions in the studied area of the island. The igneous rocks are mafic subvolcanic intrusions, including dikes, randomly shaped bodies, explosion breccias, and peperites. They belong to the tholeiitic series and are similar to Siberian traps in petrography and trace-element compositions, with high LREE and LILE and prominent Nb negative anomalies. The island arc affinity is due to continental crust contamination of mantle magma and its long evolution in chambers at different depths. The 252±5 Ma K-Ar biotite age of magmatism indicates that it was coeval to the main stage of trap magmatism in the Siberian craton at the Permian-Triassic boundary. The terrane including the New Siberian Islands occurred on the periphery of the Siberian trap province where magmatism acted in a rifting environment. Magma intruded semiliquid wet sediments at shallow depths, shortly after their deposition. Therefore, the exposed Paleozoic section in Bel’kov Island may include Permian or possibly Lower Triassic sediments, of younger ages than it was believed earlier.     

Magma Origin and Evolution of White Island (Whakaari) Volcano, Bay of Plenty, New Zealand

White Island is an active composite stratovolcano in the Bayof Plenty, New Zealand, that comprises many small volume (<0·1km³) andesite–dacite lava flows and pyroclastic depositswith phenocryst contents of     

The Occurrence of Forsterite and Highly Oxidizing Conditions in Basaltic Lavas from Stromboli Volcano, Italy

We report the occurrence of unusual, high-magnesium (Fo₉₆) olivinephenocrysts in a basaltic lava and an ejected lithic block fromthe Upper Vancori period (13 ka) and the recent activity (2002–2003)of Stromboli volcano, Italy. The samples that contain this distinctivemineral chemistry are a shoshonitic basalt and a basaltic andesitewith anomalous bulk-rock chemical characteristics in which theiron is highly oxidized (6–8 wt % Fe₂O₃ and <1 wt %FeO). In other respects these samples are similar to the majorityof Stromboli basalts, characterized by the coexistence of olivine,clinopyroxene, plagioclase and Fe–Ti oxides as phenocrysts,and clinopyroxene, plagioclase and Fe–Ti oxides in thegroundmass. In the high-magnesium olivine samples, Fe–Tioxides (pseudobrookite) typically occur as symplectitic intergrowthswith the olivine phenocrysts, indicating simultaneous growthof the two phases. We propose, as a paragenetic model, thatthe Fo₉₆ olivine phenocrysts crystallized from a highly oxidizedbasaltic magma in which most of the iron was in the ferric state;hence, only magnesium was available to form olivine. The highlyoxidized state of the magma reflects sudden degassing of volatilephases associated with instantaneous, irreversible, transientdegassing of the magma chamber; this is postulated to occurduring periods of sudden decompression induced by fracturingof the volcanic edifice associated with paroxysmic activityand edifice collapse. KEY WORDS: Stromboli; Mg-rich olivine; oxygen fugacity; redox state of magmas; irreversible processes     

Petrogenesis and Implications of Calc-Alkaline Cryptic Hybrid Magmas from Washburn Volcano, Absaroka Volcanic Province, USA

The petrogenesis of calc-alkaline magmatism in the Eocene AbsarokaVolcanic Province (AVP) is investigated at Washburn volcano,a major eruptive center in the low-K western belt of the AVP.New ⁴⁰Ar/³⁹Ar age determinations indicate that magmatism atthe volcano commenced as early as 55 Ma and continued untilat least 52 Ma. Although mineral and whole-rock compositionaldata reflect near equilibrium crystallization of modal phenocrysts,petrogenetic modeling demonstrates that intermediate compositionmagmas are hybrids formed by mixing variably fractionated andcontaminated mantle-derived melts and heterogeneous siliciccrustal melts. Nd and Sr isotopic compositions along with traceelement data indicate that silicic melts in the Washburn systemare derived from deep-crustal rocks broadly similar in compositionto granulite-facies xenoliths in the Wyoming Province. Our preferredexplanation for these features is that mantle-derived basalticmagma intruded repeatedly in the deep continental crust leadingto fractional crystallization, silicic melt production, andhomogenization of magmas, followed by ascent to shallow reservoirsand crystallization of new plagioclase-rich mineral assemblagesin equilibrium with the intermediate hybrid liquids. The implicationsof this process are that (1) some calc-alkaline magmas may onlybe recognized as hybrids on purely chemical grounds, particularlyin systems where mixing precedes and is widely separated fromcrystallization in space and time, and (2) given the role ascribedto crustal processes at Washburn volcano, the variation betweenrocks that follow calc-alkaline trends in the western AVP andthose that follow shoshonitic trends in the east cannot simplyreflect higher pressures of fractionation to the east in Moho-levelmagma chambers in the absence of crustal interaction. KEY WORDS: petrogenesis; magma mixing; calc-alkaline; Absaroka Volcanic Province; ⁴⁰Ar/³⁹Ar dates     

Trace elements in phosphorites from Kotelny Island (New Siberian Islands)

Doklady Earth Sciences - The first study of the full chemical composition of Triassic phosphorites from Kotelny Island and Jurassic–Cretaceous phosphorite from the Egorjevsk deposit showed...