1,721,053 research outputs found
Ruthenium and Tungsten isotopic composition of ocean island basalts and refrence materials
No full textThe dataset includes Ruthenium and Tungsten isotope data for mafic to ultramafic lava associated with the Hawaii, Réunion, Galápagos and Iceland plume systems. The data is supplemented by Ru isotope data for reference materials (OREAS 684) picrite derived from the upper mantle (Gönnern Quarry, Hessia) lherzolite preidotites (Eifel) and Eoarchean dunites (Isua, Greenland).
The data are supplementary to: Messling, Nils; Willbold, Matthias; Kallas, Leander; Elliott, Tim; Fitton, J. Godfrey; Müller, Thomas; Geist, Dennis (submitted) Core leakage revealed by Ru and W isotope systematics in ocean island basalts. Submitted to Natur
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No full textMolybdenum isotope and trace element data for samples from La Palma and Hawaii. All Mo isotope and Mo concentration as well as all trace element concentrations (in μg/g) for La Palma from this study. All major element data (in wt. %), trace element data for Hawaii as well as all Pb and Os isotopes from literature
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No full textMolybdenum and Nd isotope as well as trace element data for samples from the Kamchatka arc system. Trace element data in μg/g
Molybdenum isotope variations in magmatic rocks
Full text linkThe application of Mo isotopes to study geodynamic processes is a rather new development that has gained considerable momentum over the past few years. Its redox-sensitivity causes significant mass-dependent isotope variability in low-temperature environments – mainly during weathering, sediment deposition and seafloor alteration. Potentially, these fractionated Mo isotope characteristics of surface materials could be used to identify recycled crustal components in mantle sources. Here we provide an overview of the first studies on mass-dependent isotope variations of Mo in igneous rocks and the Mo isotopic characteristics of major geochemical reservoirs before assessing the potential of Mo isotope variations as a new tracer in mantle geochemistry.Mass-dependent Mo isotope variations induced by magmatic differentiation are in general muted owing to the incompatibility of Mo in common igneous minerals. However, fractionation of Mo isotopes by hydrous silicate mineral phases has been suggested. Sulphide fractionation can potentially have a marked influence on the Mo isotope composition of evolving magmatic systems but does not appear to be a major influence due to the limited modal abundance of sulphide phases precipitated during differentiation. The largest Mo isotope variations in igneous systems reported so far are found in arc-related rocks. Currently available data suggest that the δ98/95Mo values (i.e. the 98Mo/95Mo ratio relative to the reference material NIST SRM 3134) measured in arc basalts are higher than those of the upper mantle. This offset appears to be linked to the addition of isotopically heavy slab-derived fluid to the arc melts, whereby heavier Mo isotopes become enriched in the fluid as a result of the slab-dehydration. In contrast, lighter δ98/95Mo compositions found in some arc-related lavas could be linked to geochemical tracers commonly associated with sediment melt contribution. Overall, mass balance considerations suggest that the recycled crustal material has a Mo isotope composition equal to or most likely lighter than that of fresh oceanic crust.Chondritic meteorites display a remarkably homogeneous δ98/95Mo of − 0.16 ± 0.02‰ suggesting a similar bulk composition for the inner solar system and thus the Earth. Residual Mo in the mantle after core formation is expected to be isotopically heavy but for temperatures in excess of 2500 K, typically proposed for core-mantle equilibration, the difference in δ98/95Mo of the mantle relative to chondrite is < 0.1‰. Analyses of Mo isotopes in mid-ocean ridge basalts suggest a slightly sub-chondritic composition of the depleted mantle (δ98/95Mo = − 0.21 ± 0.02‰). Similarly, late Archean komatiites yield slightly sub-chondritic δ98/95Mo of ca. − 0.21 ± 0.06‰ suggesting that the mantle may have maintained a similar Mo isotope composition throughout the post-Archean. The Mo isotope composition of the continental crust is currently the least well-constrained value of major geochemical reservoirs. A preliminary estimate available for maximum value for the upper continental crust yields a super-chondritic δ98/95Mo of ca. + 0.15‰. The value of the bulk continental crust remains unknown but is likely to be lower. Assuming a chondritic bulk silicate Earth differentiates solely into continental crust and depleted mantle reservoirs, the δ98/95Mo of the average continental crust would range between + 0.1 and + 0.35‰. This is broadly compatible with the initial observations, making Mo the first non-radiogenic isotopic system to show such an apparent complementarity between the continents and mantle reservoirs. Given that deep recycled crust is characterised by δ98/95Mo lower than that of depleted mantle, subduction provides a mechanism by which to affect this change
Determination of Ce isotopes by TIMS and MC-ICPMS and initiation of a new, homogeneous Ce isotopic reference material
No full textRadiogenic 138Ce/ 136Ce ratios in geological and cosmological materials are a valuable tracer and dating tool in geo- and cosmochemistry. However, the variation in global 138Ce/ 136Ce ratios is small (e.g., 0.03% in ocean island basalts). In addition, the isobaric interference of 138Ba and the influence of the dominant 140Ce ion beam (88.5%) on 138Ce (ca. 0.251%) during mass spectrometric analysis present an analytical challenge. Hitherto employed methods generally dismiss the influence of the 140Ce low-mass peak-tail on the accuracy of the determined 138Ce/ 136Ce ratios. Therefore, the reported reproducibility ranges only from 0.05 to 0.004% (2RSD). In this study, TIMS and MC-ICPMS are used to determine 138Ce/ 136Ce ratios in reference materials. The results show that only the measurement of Ce as an oxide species by TIMS, combined with the accurate monitoring and correction of the background between the acquired ion intensities, can yield accurate and reproducible 138Ce/ 136C ratios. This method achieves a more than two-fold improvement in reproducibility (0.002%; 2RSD) compared to reported methods. The identification and quantification of individual sources of error resulted in a combined standard uncertainty of 0.002% (2RSE) for the method. A comparison of published data for the CeO 2 reference material JMC 304 reveals its isotopic heterogeneity. Therefore, a new reference material has been prepared from ultra-pure Ce metal from Ames Laboratory. It is now available for distribution. An initial characterization of the new reference material yielded a 138Ce/ 136C ratio of 1.33738 ± 0.000005 (2σ mean; N = 35) as a working value. © The Royal Society of Chemistry 2007
Molybdenum isotope evidence for subduction-modified, recycled mafic oceanic crust in the mantle sources of ocean island basalts from La Palma and Hawaii
No full texthttp://dx.doi.org/10.13039/100004807 California Department of Fish and Gamehttp://dx.doi.org/10.13039/501100000270 Natural Environment Research Councilhttp://dx.doi.org/10.13039/501100001659 Deutsche Forschungsgemeinschaf
Systematic Across‐Arc Variations of Molybdenum Isotopes in a Fluid‐Dominated Subduction Zone System
No full textAbstract Mass‐dependent Mo isotope variations are a promising new tracer to study magmatic processes in different geological settings. We report the first Mo isotope data for the Kamchatka arc system in the Northwest Pacific, comprising basaltic lavas of a complete Southeast‐Northwest traverse from the volcanic arc front through to the back arc region. The majority of volcanic centers investigated directly override the Hawaii‐Emperor Seamount Chain, which is currently being subducted underneath the arc system. Our Mo isotope data show systematic trends with Ce/Pb, Ce/Mo, Nb/Zr, La/Sm, and 143Nd/144Nd ratios from the volcanic arc front to the back arc. Arc front lavas have higher δ98/95Mo and lower Ce/Pb, Ce/Mo, Nb/Zr, La/Sm compared to back arc lavas. Because the involvement of subducted sediments can be excluded, we attribute the observed variations to a change in the mantle source composition from the arc front to the back arc regions. The isotopic and chemical budget of arc front lavas is dominated by a slab fluid component (high δ98/95Mo, low Ce/Pb, Ce/Mo), whereas mantle‐like Ce/Pb, Ce/Mo, elevated Nb/Zr and La/Sm in the back arc samples suggest an enriched mantle source. Combined δ98/95Mo, Nd, and Pb isotope data in back arc lavas are very similar to those observed for modern ocean island basalts from Hawaii. We thus explore the possibility that the back arc mantle was contaminated by a Hawaii‐type, enriched asthenospheric mantle component from the subducted Hawaii‐Emperor Seamount Chain
Formation of enriched mantle components by recycling of upper and lower continental crust
No full textThe origin of enriched mantle (EM) sources remains an unsolved problem for constraining the composition and chemical evolution of the Earth's mantle, because a wealth of different, often mutually exclusive models has been suggested. To address this predicament and to re-investigate the origin of EM sources on a global scale, this study is based on combined chemical and isotopic literature data for more than 530 samples from 16 key locations from worldwide ocean islands. The combined Sr, Nd, Pb isotope and trace element systematics of global ocean island basalts suggest that each EM source contains a unique enriched additive. Systematic variations between Th/Nb, K/La, Rb/La, and Ce/Pb ratios and 87Sr/86Sr ratios in all EM basalts suggest that all EM-type end-members share a common heritage from the continental crust. The observed coupling of relative Eu enrichments or deficits with 87Sr/86Sr isotope ratios further indicates that the inferred compositional differences of EM-type sources are caused by the addition of different proportions of lower and upper continental crust. Recycling of marine sediment and oceanic lithosphere in subduction zones accounts for the isotopic and chemical composition of EM sources with high 87Sr/86Sr and relatively constant 206Pb/204Pb ratios (e.g. Samoa), which have a high affinity for the upper continental crust. Sources with a coupled 87Sr/86Sr-206Pb/204Pb isotope evolution that extend to low 206Pb/204Pb but less radiogenic 87Sr/86Sr ratios (e.g. Pitcairn) are dominated by lower continental crust. Transfer of the lower continental crust into the mantle can occur either by subduction erosion or by crustal delamination. Here we propose that one common process, the recycling of upper and lower continental crust and oceanic lithosphere at destructive plate margins and their subsequent re-melting as part of the mantle sources of ocean island basalts, can account for the entire range of chemical and isotopic signatures in EM-type oceanic basalts. This implies that the compositional heterogeneity in the Earth's mantle is induced by, and intrinsic to the recycling process and not principally dependent on intra-mantle stirring of a limited number of originally distinct and physically separate mantle reservoirs. © 2010 Elsevier B.V
Trace element composition of mantle end-members: Implications for recycling of oceanic and upper and lower continental crust
No full textRecycling of oceanic crust together with different types of marine sediments has become somewhat of a paradigm for explaining the chemical and isotopic composition of ocean island basalts. New high-precision trace element data on samples from St. Helena, Gough, and Tristan da Cunha, in addition to recent data from the literature, show that the trace element and isotope systematics in enriched mantle (EM) basalts are more complex than previously thought. EM basalts have some common characteristics (e.g., high Rb/La, Ba/La, Th/U, and Rb/Sr and low Nb/La and U/Pb) that distinguish them from HIMU basalts (high μ = 238U/204Pb). The isotopically distinct EM-1 and EM-2 basalts, however, cannot be clearly distinguished on the basis of incompatible trace element ratios. Ultimately, each suite of EM basalts carries its own specific trace element signature that must reflect different source compositions. In contrast, HIMU basalts show remarkably uniform trace element ratios, with a characteristic depletion in incompatible trace elements (Rb, Ba, Th, U, and Pb) and enrichment in Nb and Ta relative to EM basalts. Compositional similarities between HIMU and EM basalts (e.g., Nb/U, La/Sm, La/Th, Sr/Nd, Ba/K, and Rb/K) suggest that their sources share a common precursor, most likely recycled oceanic lithosphere. The compositional differences between HIMU and EM basalts, on the other hand, can only be explained if the EM sources contain an additional heterogeneous component. Parent-daughter ratios in subducted marine sediments have a unimodal distribution. Recycling of sediments alone can therefore not account for the isotopic bimodality of EM basalts. The upper and lower continental crust have similarly variable trace elements ratios but are systematically distinct in their Rb/Sr, U/Pb, Th/Pb, and Th/U ratios. Thus the upper and lower continental crust evolve along two distinct isotopic evolution paths but retain their complex trace element characteristics, similar to what is observed in EM basalts. We therefore propose that recycling of oceanic lithosphere together with variable proportions of lower and upper continental crust, which are introduced into the mantle together with the oceanic lithosphere via subduction erosion and/or subduction of marine sediments, respectively, provides a plausible explanation for the trace element and isotope systematics in ocean island basalts. Copyright 2006 by the American Geophysical Union
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