Gurenko Andrey A.

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Gurenko
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Andrey A.
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  • Preprint
    Origin of volatiles emitted by Plinian mafic eruptions of the Chikurachki volcano, Kurile arc, Russia : trace element, boron and sulphur isotope constraints
    ( 2017-09-12) Gurenko, Andrey A. ; Belousov, Alexander B. ; Kamenetsky, Vadim S. ; Zelenski, Michael E.
    Chikurachki is a 1816-m high stratovolcano on Paramushir Island, Kurile arc, Russia, which has repeatedly produced highly explosive eruptions of mafic composition. The present work is aimed at constraining the origin of volatile components (CO2, H2O, F, S, and Cl), along with B and S isotopic compositions in a series of phenocryst-hosted melt inclusions and groundmass glasses from basaltic andesite pyroclasts of the 1853, 1986, and prehistoric Plinian eruptions of the volcano. The ranges of volatile concentrations in melt inclusions (47–1580 μg/g CO2, 0.4–4.2 wt% H2O, 399–633 μg/g F, 619–3402 μg/g S and 805–1240 μg/g Cl) imply a sudden pressure release from ~ 460 through ~ 35 MPa that corresponds to ~ 1.2–16-km-depth range of magma ascent upon decompression. We conclude that rapid ascent of the volatile-rich basaltic magmas from ~ 16-km initial depth accompanied by near-surface bubble nucleation and growth, and subsequent magma fragmentation appear to be a primary reason for the Plinian character of the Chikurachki eruptions. Significant negative correlations of S with K, Zr, Nb, Ba, La, Ce, Pr (R = − 0.8 to − 0.9), no clear relationships of S with H2O, CO2 and Cl, but strong positive correlations of S/K2O with H2O/K2O, Cl/K2O and F/K2O preclude magma degassing to be the only process affecting volatile concentrations dissolved in the melt. The δ34S values of the studied inclusion and groundmass glasses range from − 1.6 to + 12.3‰, decrease with decreasing S, show significant positive correlations with H2O/K2O, Cl/K2O and F/Zr, and negative correlations with a number of incompatible trace elements. Neither open- nor close-system magma degassing can account for the observed range of δ34S. The δ11B values of the melt inclusions range from − 7.0 to + 2.4‰ with 13–23 μg/g B. The relationships of δ11B with B/K2O and B/Nb are inconsistent with magma contamination at shallow crustal depths. Linear character of 1/S vs. δ34S relationship suggests two-component mixing. The possible mixing end-members could be the magmas having similar major and trace element compositions, but strongly contrasting volatile contents and S isotopes. Based on the behaviour of fluid-mobile vs. fluid-immobile incompatible trace elements, we conclude that the subduction component likely represents a mixture of subduction sediment-derived melt with up to 60% of slab-derived fluid. Admixture of ~ 1–8% of the inferred subduction component to the depleted mantle wedge source is required to account for the compositional range of the Chikurachki melt inclusions, and ~ 0.4–10% to constrain the composition of Kurile arc mafic magmas.
  • Preprint
    Oxygen isotope heterogeneity of the mantle beneath the Canary Islands : insights from olivine phenocrysts
    ( 2010-11-16) Gurenko, Andrey A. ; Bindeman, Ilya N. ; Chaussidon, Marc
    A relatively narrow range of oxygen isotopic ratios (δ18O = 5.05.4‰) is preserved in olivine of mantle xenoliths, mid-ocean ridge (MORB) and most ocean island basalts (OIB). The values in excess of this range are generally attributed either to the presence of a recycled component in the Earth’s mantle or to shallow level contamination processes. A viable way forward to trace source heterogeneity is to find a link between chemical (elemental and isotopic) composition of the earlier crystallized mineral phases (olivine) and the composition of their parental magmas, then using them to reconstruct the composition of source region. The Canary hotspot is one of a few that contains ~1-2 Ga old recycled ocean crust that can be traced to the core-mantle boundary using seismic tomography and whose origin is attributed to the mixing of at least three main isotopically distinct mantle components i.e., HIMU, DMM and EM. This work reports ion microprobe and single crystal laser fluorination oxygen isotope data of 148 olivine grains also analyzed for major and minor elements in the same spot. The olivines are from 20 samples resembling the most primitive shield stage picrite through alkali basalt to basanite series erupted on Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro, Canary Islands, for which shallow level contamination processes were not recognized. A broad range of δ18Oolivine values from 4.6 to 6.1‰ was obtained and explained by stable, long-term oxygen isotope heterogeneity of crystal cumulates present under different volcanoes. These cumulates are thought to have crystallized from mantle derived magmas uncontaminated at crustal depth, representing oxygen isotope heterogeneity of source region. A relationship between Ni×FeO/MgO and δ18Oolivine values found in one basanitic lava erupted on El Hierro, the westernmost island of the Canary Archipelago, was used to estimate oxygen isotope compositions of partial melts presumably originated from peridotite (HIMU-type component inherited its radiogenic isotope composition from ancient, ~12 Ga, recycled ocean crust) and pyroxenite (young, <1 Ga, recycled oceanic crust preserved as eclogite with depleted MORB-type isotopic signature) components of the Canary plume. The model calculations yield 5.2 and 5.9±0.3‰ for peridotite and pyroxenite derived melts, respectively, which appeared to correspond closely to the worldwide HIMU-type OIB and upper limit N-MORB δ18O values. This difference together with the broad range of δ18O variations found in the Canarian olivines cannot be explained by thermodynamic effects of oxygen isotopic fractionation and are believed to represent true variations in the mantle, due to oceanic crust and continental lithosphere recycling.
  • Preprint
    Boron isotopic composition of olivine-hosted melt inclusions from Gorgona komatiites, Colombia : new evidence supporting wet komatiite origin
    ( 2011-09-11) Gurenko, Andrey A. ; Kamenetsky, Vadim S.
    A fundamental question in the genesis of komatiites is whether 30 these rocks originate from partial melting of dry and hot mantle, 400−500°C hotter than typical sources of MORB and OIB magmas, or if they were produced by hydrous melting of the source at much lower temperatures, similar or only moderately higher than those known today. Gorgona Island, Colombia, is a unique place where Phanerozoic komatiites occur and whose origin is directly connected to the formation of the Caribbean Large Igneous Province. The genesis of Gorgona komatiites remains controversial, mostly because of the uncertain origin of volatile components which they appear to contain. These volatiles could equally result from shallow level magma contamination, melting of a “damp” mantle or fluid-induced partial melting of the source due to devolatilization of the ancient subducting plate. We have analyzed boron isotopes of olivine40 hosted melt inclusions from the Gorgona komatiites. These inclusions are characterized by relatively high contents of volatile components and boron (0.2−1.0 wt.% H2O, 0.05−0.08 wt.% S, 0.02−0.03 wt.% Cl, 0.6−2.0 μg/g B), displaying positive anomalies in the overall depleted, primitive mantle (PM) normalized trace element and REE spectra ([La/Sm]n = 0.16−0.35; [H2O/Nb]n = 8−44; [Cl/Nb]n = 27−68; [B/Nb]n = 9-30, assuming 300 μg/g H2O, 8 μg/g Cl and 0.1 μg/g B in PM; Kamenetsky et al., 2010. Composition and temperature of komatiite melts from Gorgona Island constrained from olivine-hosted melt inclusions. Geology 38, 1003–1006). The inclusions range in δ11B values from −11.5 to +15.6 ± 2.2‰ (1 SE), forming two distinct trends in a δ11B vs. B-concentration diagram. Direct assimilation of seawater, seawater-derived components, altered oceanic crust or marine sediments by ascending komatiite magma cannot readily account for the volatile contents and B isotope variations. Alternatively, injection of <3% of a 11B enriched fluid to the mantle source could be a plausible explanation for the δ11B range that also may explain the H2O, Cl and B excess.