Abstract
Helium isotopes are used as a tracer for primitive reservoirs that have persisted in the Earth’s mantle. Basalts erupted at several intraplate oceanic islands, including Hawaii, Iceland, Galapagos, and Samoa, have hosted the highest 3He/4He ratios (>30 Ra, where Ra is atmospheric 3He/4He ratio) globally that are far in excess of the 3He/4He typical of the upper mantle sampled at mid-ocean ridges (8 Ra). These lavas have been suggested to be melts of a primitive, or possibly slightly depleted, mantle reservoir, i.e., either fertile or a depleted peridotite. Here we report evidence for geochemical enrichment in the high-3He/4He mantle sampled by lavas with the highest 3He/4He from Hawaii, Samoa, and possibly Galapagos. The titanium concentrations in high-3He/4He lavas from Samoa are too high to be explained by melts of a mantle peridotite, even at infinitesimally small degrees of melting, and the elevated Ti corresponds to elevated Pb-isotopic ratios. The highest 3He/4He lavas from Loihi, Hawaii, also have Ti concentrations that are too high to be melts of primitive mantle peridotite at the degrees of melt extraction proposed for this ocean island. Thus, Ti-rich material must have been added to the high-3He/4He mantle reservoir, and this material is likely to be recycled mafic crust similar to MORBlike eclogite, which is consistent with the elevated Pb-isotopic ratios. We show that fractionation corrected, major element compositions of high-3He/4He alkalic lavas can be satisfactorily modeled by melting and melt-rock interaction scenario in a fertile peridotite-MORB-eclogite hybrid system. Primitive peridotitic and recycled eclogitic reservoirs are suggested to be intimately associated in the deepest mantle and high-3He/4He lavas from several localities may sample a mantle source that hosts a component of recycled oceanic crust.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Reaching new boundaries for in-situ U-Th geochronology
- Normal to inverse transition in martian spinel: Understanding the interplay between chromium, vanadium, and iron valence state partitioning through a crystal-chemical lens
- Accuracy of timescales retrieved from diffusion modeling in olivine: A 3D perspective
- Phosphoran olivine overgrowths: Implications for multiple impacts to the Main Group pallasite parent body
- Diffusion of phosphorus in olivine and molten basalt
- Oceanic lavas sampling the high-3He/4He mantle reservoir: Primitive, depleted, or re-enriched?
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- Fe-Mg diffusion in spinel: New experimental data and a point defect model
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- Elastic softening of leucite and the lack of polar domain boundaries
- New thermobarometers for martian igneous rocks, and some implications for secular cooling on Mars
- An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites
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- Book Review: Arsenic: Environmental Geochemistry, Mineralogy, and Microbiology, RIMG Volume 79.
Articles in the same Issue
- Reaching new boundaries for in-situ U-Th geochronology
- Normal to inverse transition in martian spinel: Understanding the interplay between chromium, vanadium, and iron valence state partitioning through a crystal-chemical lens
- Accuracy of timescales retrieved from diffusion modeling in olivine: A 3D perspective
- Phosphoran olivine overgrowths: Implications for multiple impacts to the Main Group pallasite parent body
- Diffusion of phosphorus in olivine and molten basalt
- Oceanic lavas sampling the high-3He/4He mantle reservoir: Primitive, depleted, or re-enriched?
- U-Th baddeleyite geochronology and its significance to date the emplacement of silica undersaturated magmas
- Polycrystallinity of green rust minerals and their synthetic analogs: Implications for particle formation and reactivity in complex systems
- Fe pre-enrichment: A new method to counteract iron loss in experiments on basaltic melts
- Fe-Mg diffusion in spinel: New experimental data and a point defect model
- Age, petrochemistry, and origin of a REE-rich mineralization in the Longs Peak-St. Vrain batholith, near Jamestown, Colorado (U.S.A.)
- Laser-induced breakdown spectroscopy (LIBS) as a tool for in situ mapping and textural interpretation of lithium in pegmatite minerals
- Evidence for Nb2+ and Ta3+ in silicate melts under highly reducing conditions: A XANES study
- Elastic softening of leucite and the lack of polar domain boundaries
- New thermobarometers for martian igneous rocks, and some implications for secular cooling on Mars
- An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites
- Water effects on the anharmonic properties of forsterite
- Synthesis and structure of a stuffed derivative of α-quartz, Mg0.5AlSiO4
- Equation of state and elasticity of the 3.65 Å phase: Implications for the X-discontinuity
- Ca-Zn solid solutions in C2/c pyroxenes: Synthesis, crystal structure, and implications for Zn geochemistry
- Aluminum environments in synthetic Ca-Tschermak clinopyroxene (CaAlAlSiO6) from Rietveld refinement, 27Al NMR, and first-principles calculations
- Trioctahedral Fe-rich micas: Relationships between magnetic behavior and crystal chemistry
- High-pressure compressibility and phase stability of Mn-dolomite (kutnohorite)
- Composition dependence of spin transition in (Mg,Fe)SiO3 bridgmanite
- Oriented multiphase needles in garnet from ultrahigh-temperature granulites, Connecticut, U.S.A.
- Solubility and solution mechanisms of chlorine and fluorine in aluminosilicate melts at high pressure and high temperature
- Volatiles in magmas related to the Campanian Ignimbrite eruption: Experiments vs. natural findings
- Aluminosilicate melts and glasses at 1 to 3 GPa: Temperature and pressure effects on recovered structural and density changes
- Role of volatiles (S, Cl, H2O) and silica activity on the crystallization of haüyne and nosean in phonolitic magmas (Eifel, Germany and Saghro, Morocco)
- P-V-T equation of state and high-pressure behavior of CaCO3 aragonite
- A possible new Al-bearing hydrous Mg-silicate (23 Å phase) in the deep upper mantle
- Synthesis of large wadsleyite single crystals by solid-state recrystallization
- Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
- Earth’s “missing” minerals
- Magnetite-rutile symplectite derived from ilmenite-hematite solid solution in the Xinjie Fe-Ti oxide-bearing, mafic-ultramafic layered intrusion (SW China)
- New Mineral Names
- Book Review: Arsenic: Environmental Geochemistry, Mineralogy, and Microbiology, RIMG Volume 79.