Schmincke Hans-Ulrich

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Schmincke
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Hans-Ulrich
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  • 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.