Gurenko Andrey A.

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Gurenko
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Andrey A.
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  • 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
    Enriched, HIMU-type peridotite and depleted recycled pyroxenite in the Canary plume : a mixed-up mantle
    ( 2008-11-15) Gurenko, Andrey A. ; Sobolev, Alexander V. ; Hoernle, Kaj A. ; Hauff, Folkmar ; Schmincke, Hans-Ulrich
    The Earth’s mantle is chemically and isotopically heterogeneous, and a component of recycled oceanic crust is generally suspected in the convecting mantle [Hofmann and White, 1982. Mantle plumes from ancient oceanic crust. Earth Planet. Sci. Lett. 57, 421-436]. Indeed, the HIMU component (high μ = 238U/204Pb), one of four isotopically distinct end-members in the Earth’s mantle, is generally attributed to relatively old (≥1-2 Ga) recycled oceanic crust in the form of eclogite/pyroxenite, e.g. [Zindler and Hart, 1986. Chemical geodynamics. Ann. Rev. Earth Planet. Sci. 14, 493-571]. Although the presence of the recycled component is generally supported by element and isotopic data, little is known about its physical state at mantle depths. Here we show that the concentrations of Ni, Mn and Ca in olivine from the Canarian shield stage lavas, which can be used to asses the physical nature of the source material (peridotite versus olivine-free pyroxenite) [Sobolev et al., 2007. The amount of recycled crust in sources of mantle-derived melts. Science 316, 412-417], correlate strongly with bulk rock Sr, Nd and Pb isotopic ratios. The most important result following from our data is that the enriched, HIMU-type (having higher 206Pb/204Pb than generally found in the other mantle endmembers) signature of the Canarian hotspot magmas was not caused by a pyroxenite/eclogite constituent of the plume but appears to have been primarily hosted by peridotite. This implies that the old (older than ~1 Ga) ocean crust, which has more evolved radiogenic isotope compositions, was stirred into/reacted with the mantle so that there is not significant eclogite left, whereas younger recycled oceanic crust with depleted MORB isotopic signature (<1 Ga) can be preserved as eclogite, which when melted can generate reaction pyroxenite.
  • Preprint
    Source components of the Gran Canaria (Canary Islands) shield stage magmas : evidence from olivine composition and Sr–Nd–Pb isotopes
    ( 2009-09) Gurenko, Andrey A. ; Hoernle, Kaj A. ; Sobolev, Alexander V. ; Hauff, Folkmar ; Schmincke, Hans-Ulrich
    The Canary Island primitive basaltic magmas 31 are thought to be derived from a HIMU-type upwelling mantle containing isotopically depleted (NMORB) component and having interacted with an enriched (EM)-type component whose origin is still a subject of debate. We have studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6-90.0 mol.% Fo, 1722-3915 ppm Ni, 1085-1552 ppm Mn, 1222-3002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine basaltic) lavas with their bulk rock Sr-Nd-Pb isotope compositions (87Sr/86Sr = 0.70315- 0.70331, 143Nd/144Nd = 0.51288-0.51292, 206Pb/204Pb = 19.55-19.93, 207Pb/204Pb = 15.60- 15.63, 208Pb/204Pb = 39.31-39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source. Using the model [Sobolev et al. (2007) The amount of recycled crust in sources of mantle-derived melts. Science 316: 412-417] in which the reaction of Si-rich melts originated during partial melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free reaction pyroxenite, we obtain an endmember composition for peridotite with 87Sr/86Sr = 0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61, 208Pb/204Pb = 39.07 (EM-type endmember) and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289, 206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62, 208Pb/204Pb = 39.84 (HIMU-type endmember). Mixing of melts from these endmembers in proportions ranging from 70% peridotite and 30% pyroxenite to 28% peridotite and 72% pyroxenite can generate the compositions of the most primitive Gran Canaria shield stage lavas. Combining our results with those from the low silica rocks from the western Canary Islands [Gurenko et al. (2009) Enriched, HIMU-type peridotite and depleted recycled pyroxenite in the Canary plume: a mixed-up mantle. EPSL 277: 514-524], at least four distinct components are required. We propose that they are (1) HIMU-type pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component from the asthenosphere or lithosphere above the plume center.