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2018) 'The Fe and Zn isotope composition of deep mantle source regions : insights from Ban Island picrites.', Geochimica et cosmochimica acta., 238 . pp. 542-562. Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

We present a method for the determination of δ146Nd, 143Nd/144Nd and Sm–Nd ratios from a single spiked aliquot.

Arc lavas display elevated Fe 31 /RFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidized or oxidizing components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride, and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex, and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S-bearing and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilized from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in proximity to metasediments display a significant Fe isotope fractionation. The covariation of d 56 Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction.

Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE-and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their δ 49 Ti variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a 47 Ti-49 Ti double spike. Our data reveal significant variations in δ 49 Ti for KREEPrich samples (+0.117 to +0.296 ‰) and intra-group variations in the mare basalts (-0.030 to +0.055 ‰ for low-Ti and +0.009 to +0.115 ‰ for high-Ti basalts). We modelled the δ 49 Ti of KREEP using previously published HFSE data as well as the δ 49 Ti evolution during fractional crystallisation of the LMO. Both approaches yield δ 49 Ti KREEP similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and Th, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data.

composition of the modern continental crust based on molybdenites, granites and primitive arcrelated basalts yield super-chondritic δ Mo values ranging from +0.05‰ to +0.3‰ [13][14][15] . If the bulk Earth is chondritic with respect to Mo stable isotopes and Mo is not fractionated during its partitioning into Earth's core (cf. 16 ), then an isotopically light, sub-chondritic Mo reservoir must exist in the mantle 17,18 . Arc lavas show extremely variable δ 98 Mo (−0.88‰ to +0.24‰) but the consensus is that subduction zones appear to be fluxing isotopically light Mo into the mantle [19][20][21] . However, whether this material is efficiently recycled or has enough mass to affect the composition of the bulk mantle remains to be established. Previous Mo isotope analyses of Archean komatiites 17 have slightly sub-chondritic compositions, but within error of 46 chondrites 11 , while five of the most depleted ( 143 Nd/ 144 Nd >0.5131) mid-ocean ridge basalts 47 (MORB) measured are resolvably sub-chondritic 22 . Therefore, it is possible that a 48 complementary light sub-chondritic Mo isotope reservoir is present within the mantle 18 , but its 49 composition and nature remains poorly constrained. 50Here, we focus on komatiite and picrite samples from four well characterized suites: 51 two from the Archean, the 3.5 Ga Komati (South Africa) and 2.7 Ga Munro (Canada) komatiites 23 , and two from the Phanerozoic, the 89 Ma Gorgona (Colombia) komatiites 24 and 53 the 61 Ma Baffin Island (NE Canada) picrites 25,26 , to better constrain the Mo isotope 54 composition of the mantle throughout Earth's history. The selection of rock samples for this purpose is non-trivial due to the complex behaviour of Mo during mantle melting. Although none of the major silicate phases in the mantle host significant Mo 27 , Mo is chalcophile and the presence of residual sulfides will strongly affect the Mo concentration of a melt 18 . Furthermore, isotopic studies of Mo isotopes in ultramafic lithologies are hampered by the low concentrations of Mo (<50 ng/g) and the significant isotopic variability observed in mantle lithologies 12,17 . The ultramafic lavas studied here formed at elevated temperatures (>1400 °C) by high-degrees of partial melting (>25%), which would have led to complete sulfide extraction 65 volumes, during Hadean-Archean times. ESTABLISHING A SUB-CHONDRITIC MO ISOTOPE RESERVIOROur measurements show sub-chondritic values for unaltered Archean Komati and Munro komatiites with δ Mo varying from −0.22 to −0.18‰ (Fig. 1; Table S1). Previous analyses of Archean komatiites presented in Greber et al. 17 define a wide range (−0.32‰ < δ 98 Mo < +0.07‰) with an average δ 98 Mo of the four investigated localities calculated as −0.210 ±0.098‰. Combing these results is not straightforward. For example, previously analysed samples from the Vetreny Belt, Fennoscandia have experienced significant crustal assimilation 29 and consequently display resolvably heavier δ 98 Mo (−0.077 ±0.083‰). We thus disregard these samples in subsequent interpr...

Zealandia is a largely submerged, continental fragment in the southwest Pacifi c, generally considered to be derived from East Gondwana, but whose origins, age, structure, and relationships with other continental masses are poorly known. To explore the development of this microcontinent, a suite of mantle xenoliths was assembled from 12 localities throughout New Zealand, an emergent part of Zealandia. The 187 Re-188 Os isotopic systematics of the xenoliths yield model ages (T RD2 ) between 0 and 2.3 Ga. Six samples from the newly defi ned Waitaha domain, South Island, have a narrow range of T RD2 ages from 1.6 to 1.9 Ga, in agreement with an aluminochron model age for this mantle domain of ca. 1.95 Ga, and with a three-point Re-Os isochron age of 2.26 ± 0.10 Ga. These ages are >500 m.y. older than T RD2 ages preserved in other regions of mantle lithosphere from the eastern margin of Gondwana (e.g., southeastern Australia and Marie Byrd Land, Antarctica) and >1 b.y. older than the oldest crustal rocks exposed in New Zealand. Thus, the lithospheric mantle of Zealandia has a complex age structure, including a region of Paleoproterozoic cratonic mantle with a minimum extent of ~45,000 km 2 . This ancient mantle resided at the margins of several supercontinents during the past ~2 b.y., attesting to the durability of subcontinental lithospheric mantle domains, even when decoupled from overlying contemporaneous crust and in an oceanic setting distanced from stable cratonic nuclei.

Nd in Oceanic Crust composition of the oceanic crust (δ 146 Nd = −0.067) and MORB, combined with limited evidence of melt extraction to the upper crust at Hole 735B, led to the conclusion that melts involved in RPF have not contributed in a substantial way to the Nd isotope composition of erupted MORB.