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- Deegan, Frances M, et al.
(författare)
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Sunda arc mantle source δ18O value revealed by intracrystal isotope analysis
- 2021
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 12:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) δ18O values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30 km at Merapi to ≤20 km at Agung. Here we show that mean clinopyroxene δ18O values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt δ18O values of 5.7 ‰ (±0.2 1 SD) indistinguishable from the δ18O range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member.
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- Deegan, Frances, et al.
(författare)
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Sunda arc mantle source delta O-18 value revealed by intracrystal isotope analysis
- 2021
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to <= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle.
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- Hickman-Lewis, Keyron, et al.
(författare)
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Metallomics in deep time and the influence of ocean chemistry on the metabolic landscapes of Earth’s earliest ecosystems
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Modern biological dependency on trace elements is proposed to be a consequence of their enrichment in the habitats of early life together with Earth’s evolving physicochemical conditions; the resulting metallic biological complement is termed the metallome. Herein, we detail a protocol for describing metallomes in deep time, with applications to the earliest fossil record. Our approach extends the metallome record by more than 3 Ga and provides a novel, non-destructive method of estimating biogenicity in the absence of cellular preservation. Using microbeam particle-induced X-ray emission (µPIXE), we spatially quantify transition metals and metalloids within organic material from 3.33 billion-year-old cherts of the Barberton greenstone belt, and demonstrate that elements key to anaerobic prokaryotic molecular nanomachines, including Fe, V, Ni, As and Co, are enriched within carbonaceous material. Moreover, Mo and Zn, likely incorporated into enzymes only after the Great Oxygenation Event, are either absent or present at concentrations below the limit of detection of µPIXE, suggesting minor biological utilisation in this environmental setting. Scanning and transmission electron microscopy demonstrates that metal enrichments do not arise from accumulation in nanomineral phases and thus unambiguously reflect the primary composition of the carbonaceous material. This carbonaceous material also has δ13C between −41.3‰ and 0.03‰, dominantly −21.0‰ to −11.5‰, consistent with biological fractionation and mostly within a restricted range inconsistent with abiotic processes. Considering spatially quantified trace metal enrichments and negative δ13C fractionations together, we propose that, although lacking cellular preservation, this organic material has biological origins and, moreover, that its precursor metabolism may be estimated from the fossilised “palaeo-metallome”. Enriched Fe, V, Ni and Co, together with petrographic context, suggests that this kerogen reflects the remnants of a lithotrophic or organotrophic consortium cycling methane or nitrogen. Palaeo-metallome compositions could be used to deduce the metabolic networks of Earth’s earliest ecosystems and, potentially, as a biosignature for evaluating the origin of preserved organic materials found on Mars.
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- Logan, Leslie, 1992-, et al.
(författare)
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Signatures of sulfide remobilization in the Kiruna mining district: a SIMS sulfur isotope and LA-ICP-MS trace element study
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Kiruna mining district in northern Norrbotten, Sweden, is situated in a region that is broadly described as an iron oxide-copper-gold (IOCG) district. Kiruna is well known for the iron oxide-apatite (IOA) deposits (Kiruna-type), but also hosts several Cu-bearing prospects including the Viscaria and Eastern Pahtohavare stratabound-stratiform Cu-(Fe-Zn), the Rakkurijärvi IOCG, and the Pahtohavare epigenetic Cu ± Au prospects. However the genesis of the Cu mineralization in the district has not been studied from a structural perspective in relation to the tectonic evolution of the region. Utilizing recent structural characterization of the Svecokarelian orogenic cycle as a framework, Cu- and Fe-bearing sulfides have been identified from the pre-, early, and late orogenic phases and assessed for primary and overprinting signatures with in situ δ34S and trace element data. Results indicate that the youngest stage of epigenetic mineralization (late orogenic) in the Pahtohavare area precipitated vein-hosted pyrite from a strongly Co-enriched hydrothermal fluid with δ34S values between 2‰ and 6 ‰. The late mineralization event occurred syn- to post-folding of the host rocks together with remobilization of sulfides from the younger Eastern Pahtohavare deposit. This remobilization is characterized by a fractionation of sulfur isotopes towards heavier values and dispersion of Co and Ni data towards higher and lower concentrations, respectively, and indicates redistribution of metals occurred as a result of the late orogenic mineralization and deformation. This implies a distinct Cu-forming event occurred in the late Svecokarelian orogeny both that introduced new metals and redistributed (and possibly incorporated) metals from a preexisting source. Metamorphic and low temperature remobilization is also recorded in samples from the district characterized by increases in Co and Ni, respectively.
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- Nemchin, Alexander, et al.
(författare)
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Pb-Pb ages of feldspathic clasts in two Apollo 14 breccia samples
- 2017
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 217, s. 441-461
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Tidskriftsartikel (refereegranskat)abstract
- Pb-Pb isochron ages of ca. 3.92 Ga for three K-feldspar-rich clasts from Apollo 14 breccias 14303 and 14083 were determinedusing Secondary Ion Mass Spectrometry (SIMS). These ages are interpreted to represent the resetting of the U-Pb systemin the clasts as a result of brecciation during the Imbrium impact. One of the clasts contains zircon grains that record asignificantly older crystallization age (ca. 4.33–4.35 Ga) for the rock represented by that clast. Initial Pb compositions determinedfor the clasts, combined with the previously measured Pb isotopic compositions of K-feldspar grains from severalApollo 14 breccia samples, constrain a range of initial Pb compositions in the ca. 3.9 Ga Fra Mauro formation at the Apollo14 landing site. This range in initial Pb compositions indicates that the rocks represented by these clasts, or the sources ofthose rocks, evolved with a high 238U/204Pb (µ-value) for substantial periods of time, although the precise crystallization agesof the rocks represented by at least two of the clasts investigated here are unknown.
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