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  • 1. Bellucci, J. J.
    et al.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, A. A.
    Snape, J. F.
    Kenny, G. G.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Merle, Renaud E.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bland, P. A.
    Benedix, G. K.
    Tracing martian surface interactions with the triple O isotope compositions of meteoritic phosphates2020Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 531, artikkel-id 115977Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). The phosphates measured here have a range in δ18O [(18O/16O)sample/(18O/16O)Standard-1] × 103] from +1.0 to +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions taking place on the surface of Mars. Three samples have a Δ17O [δ17O-1000(1 + δ18O /1000)0.528-1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA 7533) have an elevated positive Δ17O outside of analytical uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ37Cl [(37Cl/35Cl)sample/(37Cl/35Cl)standard – 1] × 103] and enrichments in halogens not seen in the rest of the sample suite. Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ17O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ17O measurements from phosphate grains (n = 13) in NWA 7533, which are the explicit result of exchange reactions on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2σ, MSWD = 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.

  • 2. Bellucci, Jeremy
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Humayan, M
    Hewins, R
    Zanda, B
    Pb-isotopic evidence for an early, enriched crust on Mars2015Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 410, s. 34-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Martian meteorite NWA 7533 is a regolith breccia that compositionally resembles the Martian surface measured by orbiters and landers. NWA 7533 contains monzonitic clasts that have zircon with U–Pb ages of 4.428 Ga. The Pb isotopic compositions of plagioclase and alkali feldspars, as well as U–Pb isotopic compositions of chlorapatitein the monzonitic clasts of NWA 7533 have been measured by Secondary Ion Mass Spectrometry (SIMS). The U–Pb isotopic compositions measured from the chlorapatitein NWA 7533 yield an age of 1.357 ±81Ga(2σ). The least radiogenic Pb isotopic compositions measured in plagioclase and K-feldspar lie within error of the 4.428 Ga Geochron. These data indicate that the monzonitic clasts in NWA 7533 are a product of a differentiation history that includes residence in areservoir that formed prior to 4.428 Ga with a μ-value (238U/204Pb) of at least 13.4 ±1.7 (2σ)and aκ-value (232Th/238U) of ∼4.3. This μ-value is more than three times higher than any other documented Martian reservoir. These results indicate either the Martian mantle is significantly more heterogeneous than previously thought (μ-value of 1–14 vs. 1–5) and/or the monzonitic clasts formed by the melting of Martian crust with a μ-value of at least 13.4. Therefore, NWA 7533 may contain the first isotopic evidence for an enriched, differentiated crust on Mars.

  • 3.
    Bellucci, Jeremy
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Grange, Marion
    Collins, Gareth
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Snape, Joshua
    Norman, Marc
    Kring, David
    Terrestrial-like zircon in an Apollo 14 breccia.2019Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 510, s. 173-185Artikkel i tidsskrift (Fagfellevurdert)
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  • 4.
    Bellucci, Jeremy
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Snape, Joshua
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bland, Phil
    Benedix, Gretchen
    Roszjar, Julia
    Pb evolution in the Martian mantle2018Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 485, s. 79-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm–Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The μ-values (238U/204Pb) obtained for these two different stages of Pb growth are μ1 of 1.8 and a range of μ2 from 1.4–4.7, respectively. The μ1-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial μ-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sri, γ187Os, ε143Nd, and ε176Hf), the second stage mantle evolution range in observed mantle μ-values display excellent linear correlations (r2 > 0.85) and represent a spectrum of Martian mantle mixing-end members (depleted, intermediate, enriched).

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  • 5.
    Bellucci, Jeremy
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Snape, Joshua
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Halogen and Cl isotopic systematics in Martian phosphates: Implications for the Cl cycle and surface halogen reservoirs on Mars2017Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 458, s. 192-202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Cl isotopic compositions and halogen (Cl, F, Br, and I) abundances in phosphates from eight Martian meteorites, spanning most rock types and ages currently available, have been measured in situ by Secondary Ion Mass Spectrometry (SIMS). Likewise, the distribution of halogens has been documented by x-ray mapping. Halogen concentrations range over several orders of magnitude up to some of the largest concentrations yet measured in Martian samples or on the Martian surface, and the inter-element ratios are highly variable. Similarly, Cl isotope compositions exhibit a larger range than all pristine terrestrial igneous rocks. Phosphates in ancient (>4 Ga) meteorites (orthopyroxenite ALH 84001 and breccia NWA 7533) have positive d37Cl anomalies (+1.1 to +2.5 ‰).  These samples also exhibit explicit whole rock and grain scale evidence for hydrothermal or aqueous activity. In contrast, the phosphates in the younger basaltic Shergottite meteorites (<600 Ma) have negative d37Cl anomalies (-0.2 to -5.6 ‰).  Phosphates with the largest negative d37Cl anomalies display zonation where the rims of the grains are enriched in all halogens and have significantly more negative d37Cl anomalies indicating interaction with the surface of Mars during the latest stages of basalt crystallization. The phosphates with no textural, major element, or halogen enrichment evidence for mixing with this surface reservoir have an average d37Cl of -0.6 ‰, which suggests a similar Cl isotope composition between Mars, the Earth, and the Moon. The only process known to fractionate Cl isotopes, both positively and negatively, is formation of perchlorate, which has been detected in weight percent concentrations on the Martian surface. The age range and obvious mixing history of the phosphates studied here suggest perchlorate formation and halogen cycling via brines, which have also been observed on the Martian surface, has been active throughout Martian history. 

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  • 6.
    Bellucci, Jeremy
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Snape, Joshua
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    A Pb isotopic resolution to the Martian meteorite age paradox2016Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 433, s. 241-248Artikkel i tidsskrift (Fagfellevurdert)
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  • 7. Bolhar, Robert
    et al.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Milani, Lorenzo
    Magalhães, Nivea
    Golding, Suzanne D.
    Bybee, Grant
    LeBras, Loic
    Bekker, Andrey
    Atmospheric S and lithospheric Pb in sulphides from the 2.06 Ga Phalaborwa phoscorite-carbonatite Complex, South Africa2020Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 530, artikkel-id 115939Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lead and multiple sulphur isotope compositions were measured in-situ by SIMS on sulphide minerals from phoscorites and carbonatites of the ca. 2.06 Ga Phalaborwa Complex in South Africa. Additionally, sulphide mineral separates and bulk-rock samples were analyzed with IRMS methods to confirm SIMS data. Lead isotope ratios define a trend stretching from unradiogenic to highly radiogenic ratios corresponding to a Pb–Pb regression date of 2054 ± 99 Ma. This apparent date is consistent with the timing of emplacement and thus provides an age estimate for the sulphide mineralization. The least radiogenic Pb isotope compositions overlap, and the regression line intersects, a hypothetical mixing line between MORB mantle and an upper crustal reservoir at ca. 2.1 Ga, suggesting that either a significant quantity of crustal Pb contributed to sulphide mineralization, or that sulphidic xenomelts were derived from an isotopically enriched mantle source. Sulphur isotope ratios of individual sulphide minerals obtained by SIMS are highly variable (δ34S: −15 to +15‰ V-CDT) and, importantly, reveal the contribution of pre-Great Oxidation Event (GOE) atmospheric sulphur with mass-independent isotope fractionation (Δ33S = δ33S–[(1+δ34S)0.515-1]×1000 ≠0.0‰). Mass-independent sulphur isotope fractionation is also revealed by sulphur isotope ratios measured on sulphide mineral separates (Δ33S: 0.2 to 0.7‰) and bulk rock samples (Δ33S: 0.2 to 0.4‰). Generally, the range of sulphur isotope ratios obtained with SIMS is much larger than that observed in non-SIMS data, possibly reflecting isotopic variability at the μm scale, resolvable only with microbeam measurements. Various sources and mechanisms by which supracrustal material may have been incorporated into mantle-derived carbonatite-phoscorite magmas are assessed, taking into account that geological evidence for the presence of sedimentary material available for assimilation during shallow-level magma emplacement is lacking. Given the variability in S and Pb isotopic compositions, it is inferred that pre-GOE surficial Pb and S were not derived from asthenospheric mantle contaminated with supracrustal materials. Instead, whole rock trace element compositions, in concert with published geochemical and petrological evidence, are consistent with interaction of asthenospheric, plume-derived melt with compositionally heterogeneous lithospheric mantle that was metasomatically modified by fluids and melts released from a subducting slab. Despite geochemical and geochronological similarities with the 2055 Ma Busvheld Complex, lead and sulphur isotope data for both complexes are resolvably different, pointing to distinct lithospheric mantle sources involved in sulphide mineralization.

  • 8.
    Bralower, Timothy
    et al.
    Pennsylvania State University.
    Cosmidis, Julie
    Pennsylvania State University.
    Heaney, Peter
    Pennsylvania State University.
    Kump, Lee
    Pennsylvania State University.
    Morgan, Joanna
    Imperial College London.
    Haroer, Dustin
    University of Kansas.
    Lyons, Shelby
    Pennsylvania State University.
    Freeman, Katherine
    Pennsylvania State University.
    Grice, Kliti
    Curtin University.
    Wendler, Jens
    Friedrich-Schiller-University Jena.
    Zachos, James
    University of California Santa Cruz.
    Artemieva, Natalia
    Planetary Science Institute, Tucson.
    Chen, Si Athena
    Pennsylvania State University.
    Gulick, Sean
    University of Texas.
    House, Christopher
    Pennsylvania State University.
    Jones, Heather
    Pennsylvania State University.
    Lowery, Christopher
    University of Texas at Austin.
    Nims, Christine
    Pennsylvania State University.
    Schaefer, Bettina
    Curtin University.
    Thomas, Ellen
    Yale University.
    Vajda, Vivi
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Department of Geology, Lund University, Sweden.
    Origin of a global carbonate layer deposited in the aftermath of the Cretaceous-Paleogene boundary impact2020Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 548, artikkel-id 116476Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microcrystalline calcite (micrite) dominates the sedimentary record of the aftermath of the Cretaceous–Paleogene (K–Pg) impact at 31 sites globally, with records ranging from the deep ocean to the Chicxulub impact crater, over intervals ranging from a few centimeters to more than seventeen meters. This micrite-rich layer provides important information about the chemistry and biology of the oceans after the impact. Detailed high-resolution scanning electron microscopy demonstrates that the layer contains abundant calcite crystals in the micron size range with a variety of forms. Crystals are often constructed of delicate, oriented agglomerates of sub-micrometer mesocrystals indicative of rapid precipitation. We compare the form of crystals with natural and experimental calcite to shed light on their origin. Close to the crater, a significant part of the micrite may derive from the initial backreaction of CaO vaporized during impact. In more distal sites, simple interlocking rhombohedral crystals resemble calcite precipitated from solution. Globally, we found unique calcite crystals associated with fossilized extracellular materials that strikingly resemble calcite precipitated by various types of bacteria in natural and laboratory settings. The micrite-rich layer contains abundant bacterial and eukaryotic algal biomarkers and most likely represents global microbial blooms initiated within millennia of the K–Pg mass extinction. Cyanobacteria and non-haptophyte microalgae likely proliferated as dominant primary producers in cold immediate post-impact environments. As surface-water saturation state rose over the following millennia due to the loss of eukaryotic carbonate producers and continuing river input of alkalinity, “whitings” induced by cyanobacteria replaced calcareous nannoplankton as major carbonate producers. We postulate that the blooms grew in supersaturated surface waters as evidenced by crystals that resemble calcite precipitates from solution. The microbial biomass may have served as a food source enabling survival of a portion of the marine biota, ultimately including life on the deep seafloor. Although the dominance of cyanobacterial and algal photosynthesis would have weakened the biological pump, it still would have removed sufficient nutrients from surface waters thus conditioning the ocean for the recovery of biota at highertrophic levels.

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  • 9. Callegaro, Sara
    et al.
    Marzoli, Andrea
    Bertrand, Hervé
    Chiaradia, Massimo
    Reisberg, Laurie
    Meyzen, Christine
    Bellieni, Giuliano
    Weems, Robert E.
    merle, Renaud E.
    Naturhistoriska riksmuseet.
    Upper and lower crust recycling in the source of CAMP basaltic dykes from southeastern North America2013Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 376, s. 186-199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The densest dykes swarm of the Central Atlantic magmatic province (CAMP) occur in southeastern North America (SENA) and were intruded between 202 and 195 Ma during Pangea break-up. New combined geochemical data (major and trace elements, Sr–Nd–Pb–Os isotopes) constrain the mantle source of these magmatic bodies and their evolution path. While Sr–Nd isotopic compositions for SENA rocks (87Sr/86Sr200Ma 0.70438–0.70880 and 143Nd/144Nd200Ma 0.51251–0.51204) fall within the low-Ti CAMP field, Pb–Pb isotopes (206Pb/204Pb200Ma 17.46–18.85, 207Pb/204Pb200Ma 15.54–15.65, 208Pb/204Pb200Ma 37.47–38.76) are peculiar to this area of the CAMP and cover a considerable span of compositions, especially in 206Pb/204Pb200Ma. Given the generally unradiogenic Os isotopic compositions (187Os/188Os200Ma 0.127–0.144) observed and the lack of correlation between these and other geochemical markers, crustal contamination during the evolution of SENA dykes must have been limited (less than 10%). Thus the isotopic variation is interpreted to reside primarily within the mantle source. These observations, coupled with typical continental signatures in trace elements (positive anomaly in Pb and negative anomalies in Ti and Nb), require another means of conveying a continental flavor to these magmas, which is here hypothesized to be the shallow recycling within the upper mantle of subducted lower and upper crustal materials. Pseudo-ternary mixing models show that a maximum of 10% recycled crust is enough to explain their trace element patterns as well as their isotopic heterogeneity. Looking at the larger picture of the origin of the CAMP, the thermal contribution of a mantle plume cannot be ruled out due to the relatively high mantle potential temperatures (1430–1480 °C) calculated for high-Fo SENA olivines. Nevertheless, our results suggest that the chemical involvement of a mantle plume is negligible (less than 5%) if either a C- or an EM-flavored plume is considered. Rather, the possibility of a PREMA-flavored mantle plume, enriched by 5–20% recycled crustal material, remains a possible, though less plausible, source for these tholeiites.

  • 10. Clift, Peter D.
    et al.
    Mark, Chris
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Alizai, Anwar
    Khan, Hawas
    Jan, M. Qasim
    Detrital U–Pb rutile and zircon data show Indus River sediment dominantly eroded from East Karakoram, not Nanga Parbat2022Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 600, s. 117873-117873, artikkel-id 117873Artikkel i tidsskrift (Fagfellevurdert)
    Fulltekst tilgjengelig fra 2024-11-01 00:00
  • 11.
    Danise, Silvia
    et al.
    Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Florence, Italy.
    Slater, Sam M
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Vajda, Vivi
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Department of Geology, Lund University, Sweden.
    Twitchett, Richard J.
    cDepartment of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK.
    Land-sea ecological connectivity during a Jurassic warming event2022Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 578, s. 117290-117290, artikkel-id 117290Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Knowledge on how climate change affects land-sea ecological connectivity in deep time is scarce. To fill this knowledge gap we have assembled a unique dataset through a Jurassic (early Toarcian) warming event that includes quantitative abundance data from pollen and spores, organic-walled marine plankton and benthic macro-invertebrates, in association with geochemical data derived from the same sampled horizons, from the Cleveland Basin, UK. Using this dataset we: (i) reconstruct the timing of degradation and recovery of land-plants, marine primary producers and benthic fauna in response to this event, and (ii) test for connectivity between changes in land and marine ecosystems. We find a discrepancy between the timing of the response of land-plant and marine ecosystems to the event. Land-plants were the first to be affected by initial warming, but also recovered relatively quickly after the peak of warmth to return to pre-event levels of richness and diversity. Plankton and benthic fauna instead experienced a delayed response to initial warming, but as warming peaked, they suffered a rapid and extreme turnover. Recovery in the shelf sea was also delayed (particularly for the benthos) compared to the vegetation. Ecological connectivity analyses show a strong link between changes in terrestrial and marine ecosystems. The loss of large trees on land contributed to changes in marine plankton, from dinoflagellate-to prasinophyte algal-dominated communities, by enhancing erosion, runoff and nutrient-supply into shallow seas. Eutrophication and changes in primary productivity contributed to the decrease of dissolved oxygen in the water column and in bottom waters, which in turn affected benthic communities. Such cause-effect mechanisms observed in the Cleveland Basin are likely to have occurred in other basins of the Boreal Realm, and in part also in basins of the Sub-Boreal and Tethyan realms. Although palaeolatitudinal and palaeoceanographic gradients may have controlled local and regional changes in land-plants and marine ecosystems during the Early Jurassic, the main climatic and environmental changes linked to rapid global warming, enhanced weathering and high primary productivity, are shared among all the examined realms.

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  • 12.
    Danise, Silvia
    et al.
    Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Florence, Italy.
    Slater, Sam M
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Vajda, Vivi
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Twitchett, Richard J.
    Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK.
    Land-sea ecological connectivity during a Jurassic warming event2021Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, s. 117290-117290, artikkel-id 117290Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Knowledge on how climate change affects land-sea ecological connectivity in deep time is scarce. To fill this knowledge gap we have assembled a unique dataset through a Jurassic (early Toarcian) warming event that includes quantitative abundance data from pollen and spores, organic-walled marine plankton and benthic macro-invertebrates, in association with geochemical data derived from the same sampled horizons, from the Cleveland Basin, UK. Using this dataset we: (i) reconstruct the timing of degradation and recovery of land-plants, marine primary producers and benthic fauna in response to this event, and (ii) test for connectivity between changes in land and marine ecosystems. We find a discrepancy between the timing of the response of land-plant and marine ecosystems to the event. Land-plants were the first to be affected by initial warming, but also recovered relatively quickly after the peak of warmth to return to pre-event levels of richness and diversity. Plankton and benthic fauna instead experienced a delayed response to initial warming, but as warming peaked, they suffered a rapid and extreme turnover. Recovery in the shelf sea was also delayed (particularly for the benthos) compared to the vegetation. Ecological connectivity analyses show a strong link between changes in terrestrial and marine ecosystems. The loss of large trees on land contributed to changes in marine plankton, from dinoflagellate- to prasinophyte algal-dominated communities, by enhancing erosion, runoff and nutrient-supply into shallow seas. Eutrophication and changes in primary productivity contributed to the decrease of dissolved oxygen in the water column and in bottom waters, which in turn affected benthic communities. Such cause-effect mechanisms observed in the Cleveland Basin are likely to have occurred in other basins of the Boreal Realm, and in part also in basins of the Sub-Boreal and Tethyan realms. Although palaeolatitudinal and palaeoceanographic gradients may have controlled local and regional changes in land-plants and marine ecosystems during the Early Jurassic, the main climatic and environmental changes linked to rapid global warming, enhanced weathering and high primary productivity, are shared among all the examined realms.

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  • 13. Deng, Kai
    et al.
    Yang, Shouye
    Lei, Bi
    Chang, Yuan-Pin
    Su, Ni
    Frings, Patrick J
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Xie, Xiaolei
    Small dynamic mountainous rivers in Taiwan exhibit large sedimentary geochemical and provenance heterogeneity over multi-spatial scales2019Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 505, s. 96-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Taiwan rivers are characterized by extremely rapid mass wasting and sediment transfer due to active tectonics and frequent typhoons. Various methods have been applied to constrain processes affecting their sediment source-to-sink routing. In most cases, the sediment at the outlet is considered to be a representative average of the whole upstream basin due to the short sediment routes (<200 km). However, this assumption may be inappropriate because huge compositional heterogeneity can exist even within such small dynamic river systems. To reveal their intra-station and basin-wide geochemical heterogeneity, we collected sediment samples along the Zhuoshui and Liwu Rivers in Taiwan. Multiple samples deposited in different locations or with different grain-sizes were collected at each station, and the <63 μm fractions were measured for their elemental and Sr–Nd isotopic compositions. Elemental ratios and dimension-reducing technique were firstly applied to discriminate the sediment provenances. They show that the large elemental heterogeneity exists between samples at the same station and also between stations along each river, explainable by variable sediment mixing and local lithological heterogeneity. When combining our Sr–Nd isotopic data with literature data from Taiwan rivers, five discrete clusters of river sediments can be distinguished, reflecting the inter-catchment heterogeneity of sediment provenance in Taiwan Island. We also applied a Sr–Nd isotopic mixing model coupled with Monte-Carlo simulations to quantify the provenance heterogeneity in both rivers. The sediment contribution of the Western Foothills/Tailuko Belt to the Zhuoshui/Liwu downstream can vary by a factor of ∼2 between sediment samples that were considered as spatial or temporal replicates. Combined with field in-situ observations, we propose that fast-changing sediment transport modes cause the provenance heterogeneity in small dynamic mountainous rivers attacked by frequent heavy storms or typhoons. Sediments transported during different events and with different provenances can be preserved at each station, which leads to the intra-station and basin-wide geochemical heterogeneity. This study shows that “small” dynamic mountainous rivers can exhibit “large” geochemical and provenance heterogeneity over multi-spatial scales, and thus the common assumption that “let nature do the averaging” should be treated cautiously in this kind of river. Therefore, we propose several effective sediment sampling approaches on small mountainous rivers for reference. Future studies relying on detrital sediments, e.g. applying cosmogenic nuclides or Li isotopes, should also be aware of the heterogeneous nature in small mountainous rivers, because fast-changing provenances can simultaneously bias the weathering and erosion signals and lead to unrepresentative results.

  • 14.
    Donadini, Fabio
    et al.
    ETH Zürich.
    Elming, Sten-Åke
    Luleå Tekniska Universitet.
    Tauxe, Lisa
    University of California, La Jolla.
    Hålenius, Ulf
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Paleointensity determination on a 1.786 Ga old gabbro from Hoting, Central Sweden2011Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 309, s. 234-248Artikkel i tidsskrift (Fagfellevurdert)
  • 15. Ge, Rongfeng
    et al.
    Wilde, Simon
    Nemchin, Alexander
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Erickson, Timmons
    Mechanisms and consequences of intra-crystalline enrichment of ancient radiogenic Pb in detrital Hadean zircons from the Jack Hills, Western Australia2019Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 517, s. -49Artikkel i tidsskrift (Fagfellevurdert)
    Fulltekst (pdf)
    fulltext
  • 16. Kemp, Anthony I.S.
    et al.
    Vervoort, Jeffrey D.
    Petersson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Smithies, R. Hugh
    Lu, Yongjun
    A linked evolution for granite-greenstone terranes of the Pilbara Craton from Nd and Hf isotopes, with implications for Archean continental growth2023Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 601, s. 117895-117895, artikkel-id 117895Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In felsic igneous rocks, the parent and daughter elements in the widely used Sm–Nd and Lu–Hf isotope tracer systems are mainly hosted in accessory phases. Recrystallisation and/or breakdown of these minerals during metamorphism, deformation and weathering potentially compromises the chemical and isotopic composition of the respective whole rocks, impeding the utility of such information for deducing the timing, rates and processes of crust-mantle differentiation in the early Earth. The different abilities of zircon and REE-rich minerals to withstand metamorphism have been suggested as a reason for the decoupling of the Lu–Hf and Sm–Nd isotope systems observed in a number of ancient gneiss terranes. The controls on element mobility and subsequent isotopic disturbance during recrystallisation and breakdown of LREE-rich accessory minerals are, however incompletely understood. Here, we use petrography, element mapping, and microanalysis of accessory minerals, in tandem with whole rock Sm–Nd data, to assess the reliability of the Sm–Nd system in the 3.59–3.58 Ga Mount Webber Gabbros, the oldest rocks in the Pilbara Craton (Western Australia). We show that despite multiple thermal events, which reset the mineral Sm–Nd systematics, and decomposition of the REE-rich mineral allanite, the Mount Webber rocks retained the Sm–Nd isotope signatures of their magmatic protoliths at the whole-rock scale. We show that the allanite breakdown occurred during modern, near-surface weathering processes at low temperature, such that the REE were sequestered into secondary minerals rather than escaping in higher temperature metamorphic fluids. The whole rock Sm–Nd, and zircon O–Hf signatures, together with new 142Nd isotope data, suggest derivation of the Mount Webber rocks from undifferentiated mantle sources that preserve no evidence for Hadean silicate Earth differentiation. This study highlights the benefits of a combined analytical approach using both in-situ and whole-rock isotope analyses to obtain a more complete record of the source and thermal evolution of ancient, highly metamorphosed igneous rocks.

    Fulltekst (pdf)
    fulltext
  • 17.
    Kenny, Gavin
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Harrigan, Claire
    Boise State Universiry.
    Schmitz, Mark
    Boise State University.
    Crowley, James
    Boise State University.
    Wall, Corey
    Boise State University.
    Andreoli, Marco
    University of the Witwatersrand.
    Gibson, Roger
    University of the Witwatersrand.
    Maier, Wolfgang
    Cardiff University.
    Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa2021Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 567, artikkel-id 117013Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Impact cratering was a fundamental geological process in the early Solar System and, thus, constraining the timescales over which large impact structures cool is critical to understanding the thermal evolution and habitability of early planetary crusts. Additionally, impacts can induce mass extinctions and establishing the precise timing of the largest impacts on Earth can shed light on their role in such events. Here we report a high-precision zircon U–Pb geochronology study of the Morokweng impact structure, South Africa, which appears to have a maximum present-day diameter of ∼80 km. Our work provides (i) constraints on the cooling of large impact melt sheets, and (ii) a high-precision age for one of Earth's largest impact events, previously proposed to have overlapped the ca. 145 Ma Jurassic–Cretaceous (J–K) boundary. High-precision U–Pb geochronology was performed on unshocked, melt-grown zircon from five samples from a borehole through approximately 800 m of preserved impact melt rock. Weighted mean 206Pb/238U dates for the upper four samples are indistinguishable, with relative uncertainties (internal errors) of better than 20 ka, whereas the lowermost sample is distinguishably younger than the others. Thermal modeling suggests that the four indistinguishable dates are consistent with in situ conductive cooling of melt at this location within 30 kyr of the impact. The younger date from the lowest sample cannot be explained by in situ conductive cooling in line with the overlying samples, but the date is within the ∼65 kyr timeframe for melt-present conditions in footwall rocks below the impact melt sheet that is indicated by our thermal model. The Morokweng impact event is here constrained to 146.06 ± 0.16 Ma (2σ; full external uncertainty), which precedes current estimates of the age of the J–K boundary by several million years.

    Fulltekst (pdf)
    fulltext
  • 18.
    Kooijman, Ellen
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Smit, Matthijs
    Ratschbacher, Lothar
    Kylander-Clark, Andrew
    A view into crustal evolution at mantle depths2017Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 465, s. 59-69Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Crustal foundering is an important mechanism in the differentiation and recycling of continental crust. Nevertheless, little is known about the dynamics of the lower crust, the temporal scale of foundering and its role in the dynamics of active margins and orogens. This particularly applies to active settings where the lower crust is typically still buried and direct access is not possible. Crustal xenoliths derived from mantle depth in the Pamir provide a unique exception to this. The rocks are well-preserved and comprise a diverse set of lithologies, many of which re-equilibrated at high-pressure conditions before being erupted in their ultrapotassic host lavas. In this study, we explore the petrological and chronological record of eclogite and felsic granulite xenoliths. We utilized accessory minerals – zircon, monazite and rutile – for coupled in-situ trace-element analysis and U–(Th–)Pb chronology by laser-ablation (split-stream) inductively coupled plasma mass spectrometry. Each integrated analysis was done on single mineral zones and was performed in-situ in thin section to maintain textural context and the ability to interpret the data in this framework. Rutile thermo-chronology exclusively reflects eruption (), which demonstrates the reliability of the U–Pb rutile thermo-chronometer and its ability to date magmatic processes. Conversely, zircon and monazite reveal a series of discrete age clusters between 55–11 Ma, with the youngest being identical to the age of eruption. Matching age populations between samples, despite a lack of overlapping ages for different chronometers within samples, exhibit the effectiveness of our multi-mineral approach. The REE systematics and age data for zircon and monazite, and Ti-in-zircon data together track the history of the rocks at a million-year resolution. The data reveal that the rocks resided at 30–40 km depth along a stable continental geotherm at 720–750 °C until 24–20 Ma, and were subsequently melted, densified, and buried to 80–90 km depth – 20 km deeper than the present-day Moho – at . The material descended rapidly, accelerating from 0.9–1.7 mm yr−1to 4.7–5.8 mm yr−1 within 10–12 Myr, and continued descending after reaching mantle depth at 14–13 Ma. The data reflect the foundering of differentiated deep-crustal fragments (2.9–3.5 g cm−3) into a metasomatized and less dense mantle wedge. Through our new approach in constraining the burial history of rocks, we provided the first time-resolved record of this crustal-recycling process. Foundering introduced vestiges of old evolved crust into the mantle wedge over a relatively short period (c. 10 Myr). The recycling process could explain the variability in the degree of crustal contamination of mantle-derived magmatic rocks in the Pamir and neighboring Tibet during the Cenozoic without requiring a change in plate dynamics or source region.

  • 19. Kovaleva, Elizaveta
    et al.
    Kusiak, Monika A.
    Kenny, Gavin G.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Habler, Gerlinde
    Schreiber, Anja
    Wirth, Richard
    Nano-scale investigation of granular neoblastic zircon, Vredefort impact structure, South Africa: Evidence for complete shock melting2021Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 565, artikkel-id 116948Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Granular neoblastic zircon (ZrSiO4) with systematically oriented granules has been proposed as evidence for extreme shock pressures (>30 GPa) and subsequent high temperatures (>1200 ◦C). It is widely agreed to reflect the solid-state phase transition from zircon to its high-pressure polymorph reidite and subsequent reversion to zircon. This model is based on crystallographic relationships between granules of a single type of granular zircon and does not explain the formation of other types of granular zircon textures, for example, grains with randomly oriented granules or with large, often euhedral granules. Here we report the first nano-scale observations of granular neoblastic zircon and the surrounding environment. We conducted combined microstructural analyses of zircon in the lithic clast from an impact melt dike of the Vredefort impact structure. Zircon granules have either random or systematic orientation with three mutually orthogonal directions of their c-axes coincident with [110] axes. Each1-2 μm zircon granule is a mosaic crystal composed of nanocrystalline subunits. Granules contain round inclusions of baddeleyite (monoclinic ZrO2) and amorphous silica melt. Tetragonal and cubic ZrO2 also occur as sub-μm-sized inclusions (<50 nm). Filament-like aggregates of nanocrystalline zircon are present as “floating” in the surrounding silicate matrix. They are aligned with each other, apparently serving as the building blocks for the mosaic zircon crystals (granules). Our results indicate shock-related complete melting of zircon with the formation of immiscible silicate and oxide melts. The melts reacted and crystallized rapidly as zircon granules, some of which experienced growth alignment/twinning and parallel growth, causing the characteristic systematic orientation of the granules observed for some ofthe aggregates. In contrast to the existing model, in which this type of granular zircon is considered to be a product of reversion from the high-pressure polymorph reidite, our nano-scale observations suggesta formation mechanism that does not require phase transition via reidite but is indicative of instant incongruent decomposition, melting and rapid crystallization from the melt

  • 20. Nikogosian, I.K.
    et al.
    Ersoy, Ö.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Mason, P.R.D.
    de Hoog, J.C.M.
    Wortel, R.
    van Bergen, M.J.
    Multiple subduction imprints in the mantle below Italy detected in a single lava flow.2016Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 449, s. 12-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western–Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  • 21. Olierook, Hugo K. H.
    et al.
    Jourdan, Fred
    Whittaker, Joanne M.
    Merle, Renaud E.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Jiang, Qiang
    Pourteau, Amaury
    Doucet, Luc S.
    Timing and causes of the mid-Cretaceous global plate reorganization event2020Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Global plate reorganization events (GPREs) can have profound impact on plate velocities, climate and the biotic cycle but the timing and triggers for GPREs remain debated. The timing and causes of the mid-Cretaceous GPRE, one of only two GPREs since the breakup of Pangea, remains poorly constrained because it occurred during the Cretaceous Normal Superchron. Here, we provide a new plagioclase Ar-40/Ar-39 age of 103.82 +/- 0.54 Ma (2 sigma) at DSDP site 256 along the world's clearest curved fracture zones in the Wharton Basin, off NW Australia. Using Monte Carlo simulations, we compute that the mid-Cretaceous GPRE commenced at 111.2(-1.2)(+1.3) Ma (95% confidence). The mid-Cretaceous GPRE was associated with a significant plate deceleration (minimum similar to 26%), similar to the Eocene GPRE, implying that this process is fundamental to plate reconfigurations. We propose that the mid-Cretaceous GPRE was caused by slab-breakoff and cessation of the south-dipping subduction zone in the Mesotethys Ocean at ca. 111 Ma. Ultimately, we posit that subduction zone initiations and cessations are the primary triggers for both post-Pangean GPREs and that top-down processes may be the fundamental drivers for GPREs. (C) 2020 Elsevier B.V. All rights reserved.

  • 22. Olierook, Hugo K.H.
    et al.
    Jourdan, Fred
    Merle, Renaud
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Timms, Nicholas E.
    Kusznir, Nick
    Muhling, Janet R.
    Bunbury Basalt: Gondwana breakup products or earliest vestiges of the Kerguelen mantle plume?2016Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 440, s. 20-32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this contribution, we investigate the role of a mantle plume in the genesis of the Bunbury Basalt using high-precision 40Ar/39Ar geochronology and whole-rock geochemistry, and by using crustal basement thickness of the eastern Indian Ocean and the western Australian continent. The Bunbury Basalt is a series of lava flows and deep intrusive rocks in southwestern Australia thought to be the earliest igneous products from the proto-Kerguelen mantle plume. Nine new plateau ages indicate that the Bunbury Basalt erupted in three distinct phases, at 136.96±0.43 Ma, 132.71±0.43 Ma and 130.45±0.82 Ma. All Bunbury Basalt samples are enriched tholeiitic basalts with varying contributions from the continental lithosphere that are similar to other Kerguelen plume-products. Based on plate reconstructions and the present geochronological constraints, the eruption of the oldest Bunbury Basalt preceded the emplacement of the Kerguelen large igneous province by at least 10–20 m.y. Such age differences between a precursor and the main magmatic event are not uncommon but do require additional explanation. Low crustal stretching factors beneath the Bunbury Basalt (β≈1.4) indicate that decompression melting could not have been generated from asthenospheric mantle with a normal chemistry and geotherm. An elevated geotherm from the mantle plume coupled with the geochemical similarity between the Bunbury Basalt and other Kerguelen plume-products suggests a shared origin exists. However, new age constraints of the oldest Bunbury Basalt are synchronous with the breakup of eastern Gondwana and the initial opening of the Indian Ocean at ca. 137–136 Ma, which may mean an alternative explanation is possible. The enriched geochemistry can equally be explained by a patch of shallow mantle beneath the southern Perth Basin. The patch may have been enriched during Gondwana suturing at ca. 550–500 Ma, during early rifting events by magmatic underplating or by intruded melts into the subcontinental lithospheric mantle. This enriched geochemical signature would then be sufficient to trigger decompression melting from passive rifting between Greater India and Australia with no contribution from the Kerguelen hotspot. We conclude that although the proto-Kerguelen hotspot is certainly a possible explanation for the genesis of the Bunbury Basalt, decompression melting of an enriched patch of subcontinental lithospheric mantle is an alternative theory.

  • 23. Panieri, G.
    et al.
    Lepland, A.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Wirth, R.
    Raanes, M.P.
    James, R.H.
    Graves, C.A.
    Crémière, A.
    Schneider, A.
    Diagenetic Mg-calcite overgrowths on foraminiferal tests in the vicinity of methane seeps.2017Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 458, s. 203-212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera. Here, we present structural, geochemical, and stable carbon isotope data from single foraminiferal calcite tests and authigenic Mg-calcite overgrowths in a sediment core recovered from an area of active methane seepage in western Svalbard at ca. 340 m water depth. The foraminifera are from intervals in the core where conventional bulk foraminiferal δ13C values are as low as −11.3 ‰. Mg/Ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain Mg-rich interlayers with Mg/Ca up to 220 mmol/mol. Transmission electron microscopy (TEM) of the contact point between the biogenic calcite and authigenic Mg-calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation. Secondary ion mass spectrometry (SIMS) analyses reveal that the Mg-rich layers are strongly depleted δ13C (δ13C as low as −34.1 ‰). These very low δ13C values indicate that the authigenic Mg-calcite precipitated from pore waters containing methane-derived dissolved inorganic carbon at the depth of the sulfate–methane transition zone (SMTZ). As the depth of the SMTZ can be located several meters below the sediment-seawater interface, interpretation of low foraminiferal δ13C values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care.

  • 24.
    Petersson, Andreas
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kemp, Anthony I.S.
    Boyet, Maud
    Whitehouse, Martin J.
    Boyce, Matilda
    Roberts, Malcolm
    Kennedy, Allen
    Response of Sm–Nd isotope systematics to complex thermal histories: A case study from 3.58 Ga gneisses of the Pilbara Craton2023Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 620, s. 118346-118346, artikkel-id 118346Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In felsic igneous rocks, the parent and daughter elements in the widely used Sm–Nd and Lu–Hf isotope tracer systems are mainly hosted in accessory phases. Recrystallisation and/or breakdown of these minerals during metamorphism, deformation and weathering potentially compromises the chemical and isotopic composition of the respective whole rocks, impeding the utility of such information for deducing the timing, rates and processes of crust-mantle differentiation in the early Earth. The different abilities of zircon and REE-rich minerals to withstand metamorphism have been suggested as a reason for the decoupling of the Lu–Hf and Sm–Nd isotope systems observed in a number of ancient gneiss terranes. The controls on element mobility and subsequent isotopic disturbance during recrystallisation and breakdown of LREE-rich accessory minerals are, however incompletely understood. Here, we use petrography, element mapping, and microanalysis of accessory minerals, in tandem with whole rock Sm–Nd data, to assess the reliability of the Sm–Nd system in the 3.59–3.58 Ga Mount Webber Gabbros, the oldest rocks in the Pilbara Craton (Western Australia). We show that despite multiple thermal events, which reset the mineral Sm–Nd systematics, and decomposition of the REE-rich mineral allanite, the Mount Webber rocks retained the Sm–Nd isotope signatures of their magmatic protoliths at the whole-rock scale. We show that the allanite breakdown occurred during modern, near-surface weathering processes at low temperature, such that the REE were sequestered into secondary minerals rather than escaping in higher temperature metamorphic fluids. The whole rock Sm–Nd, and zircon O–Hf signatures, together with new 142Nd isotope data, suggest derivation of the Mount Webber rocks from undifferentiated mantle sources that preserve no evidence for Hadean silicate Earth differentiation. This study highlights the benefits of a combined analytical approach using both in-situ and whole-rock isotope analyses to obtain a more complete record of the source and thermal evolution of ancient, highly metamorphosed igneous rocks.

    Fulltekst (pdf)
    fulltext
  • 25. Rasmussen, Maja B.
    et al.
    Halldórsson, Sæmundur A.
    Jackson, Matthew G.
    Bindeman, Ilya N.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Helium and oxygen isotopic variations in the Iceland plume source controlled by entrainment of recycled oceanic lithosphere2022Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 594, s. 117691-117691, artikkel-id 117691Artikkel i tidsskrift (Fagfellevurdert)
  • 26.
    Roberts, Nick M.W.
    et al.
    British Geological Survey.
    Salminen, Johanna
    University of Helsinki and Geological Survey of Finland.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Mitchell, Ross N.
    Institute of Geology and Geophysics, Chinese Academy of Sciences.
    Palin, Richard M.
    University of Oxford.
    Condie, Kent C.
    New Mexico Institute of Mining and Technology.
    Spencer, Christopher J.
    Queen's University, Ontario.
    On the enigmatic mid-Proterozoic: Single-lid versus plate tectonics2022Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 594, s. 1-12, artikkel-id 117749Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mid-Proterozoic (ca. 1850–850 Ma) is a peculiar period of Earth history in many respects: ophiolites and passive margins of this age are rare, whereas anorthosite and A-type granite suites are abundant; metamorphic rocks typically record high thermobaric (temperature/pressure) ratios, whereas ultrahigh pressure (UHP) rocks are rare; and the abundance of economic mineral deposits features rare porphyry Cu-Au and abundant Ni-Cu and Fe-oxide Cu-Ag (IOCG) deposit types. These collective observations have been used to propose that a stagnant-lid, or single-lid, tectonic regime operated at this time, between periods of plate tectonics in the Paleoproterozoic and Neoproterozoic. In our reappraisal of the mid-Proterozoic geological record, we not only assess the viability of the single-lid hypothesis for each line of evidence, but also that of the plate tectonic alternative. We find that evidence for the single-lid hypothesis is equivocal in all cases, whereas for plate tectonics the evidence is equivocal or supporting.We therefore find no reason to abandon a plate tectonic model for the mid-Proterozoic time period. Instead, we propose that the peculiarities of this enigmatic interval can be reconciled through the combination of two processes working in tandem: secular mantle cooling and the exceptionally long tenure and incomplete breakup of Earth’s first supercontinent, where both of these phenomena had a dramatic effect on lithospheric behaviour and its resulting imprint in the geological record

  • 27. Roszjar, J.
    et al.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Srinivasan, G.
    Mezger, K.
    Scherer, E.E.
    Van Orman, J.A.
    Bischoff, A.
    Prolonged magmatism on 4 Vesta inferred from Hf–W analyses of eucrite zircon2016Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 452, s. 216-226Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The asteroid 4 Vesta is the second most massive planetesimal in the Solar System and a rare example of a planetary object that possibly can be linked to a specific group of differentiated meteorites, the howardite–eucrite–diogenite suite. The 182Hf–182W chronometry of individual zircon grains from six basaltic eucrites revealed distinct growth episodes ranging from 4532 −11/+6 Ma−11/+6 Ma to 4565.0±0.9 Ma4565.0±0.9 Ma and constrains the early thermal history of 4 Vesta, indicating that its mantle generated basaltic melts for at least 35 million years (Myr). Initially, the energy needed for melting was provided by decay of short-lived isotopes, mostly 26Al. The long duration of magmatism despite the short lifetime of 26Al implies that the asteroid must have accreted within the first ∼4 Myr of Solar System formation, similar to the formation of iron meteorite parent bodies, and that its interior must have been thermally well insulated by an early-formed crust that prevented heat loss.

  • 28. Sarafian, A.R.
    et al.
    John, T.
    Roszjar, J.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Chlorine and hydrogen degassing in Vesta's magma ocean.2017Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 459, s. 311-319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The hydrophilic nature of halogens makes these elements ideal for probing potential hydrous geologic processes. Generally, in magmatic settings the stable isotopes of Cl may fractionate when H is in low concentrations and little fractionation occurs when the H concentration is high. We determined the Cl isotope composition and halogen content (F, Cl, Br, and I) of apatite and merrillite in seven basaltic eucrites, which are meteorites linked to the asteroid 4-Vesta, by using secondary ion mass spectrometry. We compare our halogen results with H isotope data, existing bulk rock concentrations, and petrologic models. The inferred Cl isotope composition of eucrites from this study, expressed in standard  δ37Cl notation, which ranges from −3.8 to 7.7‰, correlates with the bulk major- and trace-element content, e.g., the Cl isotope composition positively correlates with Mg and Sc, while Cl isotope composition negatively correlates with K, V, and Cr. Here we suggest that eucrites preserve evidence of a degassing magma ocean as evidenced by the decreasing bulk rock K content with increasing δ37Cl. If the eucrite parent body, 4-Vesta, accreted with a negative δ37Cl of −3.8±1.1‰, at least some parts of the solar nebula would have been isotopically light compared to most estimates of the Earth, which on average is close to 0‰.

  • 29.
    Snape, Joshua
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Curran, Natalie
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Joy, Katherine
    Hopkinson, Tom
    Mahesh, Anand
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kenny, Gavin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Ancient volcanism on the Moon: Insights from Pb isotopes in the MIL 13317 and Kalahari 009 lunar meteorites2018Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 502, s. 84-95Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lunar meteorites provide a potential opportunity to expand the study of ancient (>4000 Ma) basaltic volcanism on the Moon, of which there are only a few examples in the Apollo sample collection. Secondary Ion Mass Spectrometry (SIMS) was used to determine the Pb isotopic compositions of multiple mineral phases (Ca-phosphates, baddeleyite K-feldspar, K-rich glass and plagioclase) in two lunar meteorites, Miller Range (MIL) 13317 and Kalahari (Kal) 009. These data were used to calculate crystallisation ages of 4332 ± 2 Ma (95% confidence level) for basaltic clasts in MIL 13317, and 4369 ± 7 Ma (95% confidence level) for the monomict basaltic breccia Kal 009. From the analyses of the MIL 13317 basaltic clasts, it was possible to determine an initial Pb isotopic composition of the protolith from which the clasts originated, and infer a 238 U/204 Pb ratio (μ-value) of 850 ± 130 (2σ uncertainty) for the magmatic source of this basalt. This is lower than μ-values determined previously for KREEP-rich (an acronym for K, Rare Earth Elements and P) basalts, although analyses of other lithological components in the meteorite suggest the presence of a KREEP component in the regolith from which the breccia was formed and, therefore, a more probable origin for the meteorite on the lunar nearside. It was not possible to determine a similar initial Pb isotopic composition from the Kal 009 data, but previous studies of the meteorite have highlighted the very low concentrations of incompatible trace elements and proposed an origin on the farside of the Moon. Taken together, the data from these two meteorites provide more compelling evidence for widespread ancient volcanism on the Moon. Furthermore, the compositional differences between the basaltic materials in the meteorites provide evidence that this volcanism was not an isolated or localised occurrence, but happened in multiple locations on the Moon and at distinct times. In light of previous studies into early lunar magmatic evolution, these data also imply that basaltic volcanism commenced almost immediately after Lunar Magma Ocean (LMO) crystallisation, as defined by Nd, Hf and Pb model ages at about 4370 Ma.

    Fulltekst (pdf)
    fulltext
  • 30.
    Snape, Joshua
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Curtin University.
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Tartèse, Romain
    Muséum National d'Histoire Naturelle, France.
    Barnes, Jessica
    Open University, United Kingdom.
    Anand, Mahesh
    Open University, United Kingdom.
    Crawford, Ian
    Birkbeck College, University of London, United Kingdom.
    Joy, Katherine
    University of Manchester, United Kingdom.
    Lunar basalt chronology, mantle differentiation and implications for determining the age of the Moon2016Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 451, s. 149-158Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite more than 40 years of studying Apollo samples, the age and early evolution of the Moon remain contentious. Following the formation of the Moon in the aftermath of a giant impact, the resulting Lunar Magma Ocean (LMO) is predicted to have generated major geochemically distinct silicate reservoirs, including the sources of lunar basalts. Samples of these basalts, therefore, provide a unique opportunity to characterize these reservoirs. However, the precise timing and extent of geochemical fractionation is poorly constrained, not least due to the difficulty in determining accurate ages and initial Pb isotopic compositions of lunar basalts. Application of an in situion microprobe approach to Pb isotope analysis has allowed us to obtain precise crystallization ages from six lunar basalts, typically with an uncertainty of about ±10Ma, as well as constrain their initial Pb-isotopic compositions. This has enabled construction of a two-stage model for the Pb-isotopic evolution of lunar silicate reservoirs, which necessitates the prolonged existence of high-μreservoirs in order to explain the very radiogenic compositions of the samples. Further, once firm constraints on U and Pb partitioning behaviour are established, this model has the potential to help distinguish between conflicting estimates for the age of the Moon. Nonetheless, we are able to constrain the timing of a lunar mantle reservoir differentiation event at 4376 ±18Ma, which is consistent with that derived from the Sm–Nd and Lu–Hf isotopic systems, and is interpreted as an average estimate of the time at which the high-μurKREEP reservoir was established and the Ferroan Anorthosite (FAN) suite was formed.

    Fulltekst (pdf)
    Snape et al. (2016) Lunar basalt ages
  • 31. Stern, R.J.
    et al.
    Ali, K.A.
    Ren, M.
    Jarrar, G.H.
    Romer, R.L.
    Leybourne, M.I.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Ibrahim, K.M.
    Cadomian (∼560 Ma) crust buried beneath the northern Arabian Peninsula: Mineral, chemical, geochronological, and isotopic constraints from NE Jordan xenoliths.2016Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 436, s. 31-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to better understand the nature and formation of the lower continental crust beneath northern Arabia, we studied lower crustal xenoliths brought up by Neogene basalts in NE Jordan. Most of these xenoliths are comprised of primary phases plagioclase + two-pyroxenes with magnetite and ilmenite. Most clinopyroxene are augite whereas orthopyroxene mostly are hypersthene (Mg# = 50–80). Plagioclase feldspar is dominantly andesine–labradorite; pyrope-rich garnet and Fe-rich olivine (Fo75 to Fo62) are rare. These xenoliths represent cumulates formed from intermediate magmas that pooled in the lower crust. Many xenoliths also contain small, fine-grained K-rich zones interpreted as melt pockets reflecting late magmatic infiltration of the lower crust. The xenoliths display a wide range in major element compositions (37–51 wt.% SiO2, 4–15 wt.% MgO and 0.1–6.3 wt.% TiO2), enrichment in Ba, K, Sr, Pb and Eu, and some trace element ratios atypical of bulk continental crust (e.g., K/Rb=1265±565, K/U=63000±60080 and Th/U=0.96±0.56); these extreme ratios reflect widespread K-metasomatism associated with melt pockets. The magmas from which these cumulates formed may have been generated at a reararc convergent margin setting. Four U–Pb zircon populations yield indistinguishable ages of 554±4 Ma; 559±5 Ma; 559±6 Ma, and 563±5 Ma. Initial 87Sr/86Sr values (0.70260–0.70352) and positive εNd(560)εNd(560) (with the exception of a single, more radiogenic sample (+9.6), range=+1.3 to +4.8) indicate that the lower crust sampled by the xenoliths originated in the asthenospheric mantle, with little or no interaction with older crust, although Pb isotopic compositions allow for some interaction with older or subducted crustal materials. We interpret the geochemistry and mineralogy of these xenoliths to indicate that the lower crust beneath NE Jordan is mafic and comprised of plagioclase-rich 2-pyroxene igneous rocks. The lower crust of this area formed by magmatic underplating over less than 18 Ma. The crust of NE Jordan is significantly younger than the crust of the northernmost Arabian–Nubian Shield and represents a fragment of Cadomian (600–520 Ma) crust that may make up the NE margin of the Arabian Plate.

  • 32. Stern, Robert J.
    et al.
    Ren, Minghua
    Ali, Kamal
    Forster, Hans-Jürgen
    Al Safarjalani, Abdulrahman
    Nasir, Sobhi
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Leybourne, Matthew I.
    Romer, Rolf L.
    Early Carboniferous (∼357 Ma) crust beneath northern Arabia: Tales from Tell Thannoun (southern Syria)2014Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 393, s. 83-93Artikkel i tidsskrift (Fagfellevurdert)
  • 33.
    Vajda, Vivi
    et al.
    Naturhistoriska riksmuseet, Enheten för paleobiologi. Department of Geology, Lund University, Sweden.
    McLoughlin, Stephen
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Mays, Chris
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Frank, Tracy
    University of Nebraska.
    Fielding, Christopher
    University of Nebraska.
    Tevyaw, Allen
    University of Nebraska.
    Lehsten, Veiko
    Lund University,.
    Bocking, Malcolm
    Bocking Associates.
    Nicoll, Robert
    Geoscience Australia.
    End-Permian (252 Mya) deforestation, wildfires and flooding—Anancient biotic crisis with lessons for the present2020Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 529, artikkel-id 115875Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Current large-scale deforestation poses a threat to ecosystems globally, and imposes substantial and prolonged changes on the hydrological and carbon cycles. The tropical forests of the Amazon and Indonesia are currently undergoing deforestation with catastrophic ecological consequences but widespread deforestation events have occurred several times in Earth’s history and these provide lessons for the future. The end-Permian mass-extinction event (EPE; ∼252Ma) provides a global, deep-time analogue for modern deforestation and diversity loss. We undertook centimeter-resolution palynological, sedimentological, carbon stable-isotope and paleobotanical investigations of strata spanning the end-Permian event at the Frazer Beach and Snapper Point localities, in the Sydney Basin, Australia. We show that the typical Permian temperate, coal-forming, forest communities disappeared abruptly, followed by the accumulation of a 1-m-thick mudstone poor in organic matter that, in effect, represents a ‘dead zone’ hosting degraded wood fragments, charcoal and fungal spores. This signals a catastrophic scenario of vegetation die-off and extinction in southern high-latitude terrestrial settings. Lake systems, expressed by laterally extensive but generally less than a few-metres-thick laminated siltstones, generally lacking bioturbation, hosting assemblages of algal cysts and freshwater acritarchs, developed soon after the vegetation die-off. The first traces of vascular plant recovery occur ∼1.6m above the extinction horizon. Based on analogies with modern deforestation, we propose that the global fungal and acritarch events of the Permo-Triassic transition resulted directly from inundation of basinal areas following water-table rise as a response to the abrupt disappearance of complex vegetation from the landscape. The δ13Corg values reveal a significant excursion toward low isotopic values, down to −31ppt (a shift of ∼4deg), across the end-Permian event. The magnitude of the shift at that time records a combination of changes in the global carbon cycle that were enhanced by the local increase in microbial activity, possibly also involving cyanobacterial proliferation. We envisage that elevated levels of organic and mineral nutrients delivered from inundated dead forests, enhanced weathering and erosion of extra-basinal areas, together with local contributions of volcanic ash, led to eutrophication and increased salinity of basinal lacustrine–lagoonal environments. We propose that the change in acritarch communities recorded globally in nearshore marine settings across the end-Permian event is to a great extent a consequence of the influx of freshwater algae and nutrients from the continents. Although this event coincides with the Siberian trap volcanic activity, we note that felsic–intermediate volcanism was extensively developed along the convergent Panthalassan margin of Pangea at that time and might also have contributed to environmental perturbations at the close of the Permian.

    Fulltekst (pdf)
    fulltext
  • 34. Virtasalo, J.J.
    et al.
    Laitala, J.J.
    Lahtinen, R.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Pyritic event beds and sulfidized Fe (oxyhydr)oxide aggregates in metalliferous black mudstones of the Paleoproterozoic Talvivaara formation, Finland2015Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 432, s. 449-460Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Paleoproterozoic, 2.0–1.9 Ga Talvivaara formation of Finland was deposited during the Shunga Event, a worldwide episode of enhanced accumulation of organic-rich sediments in the aftermath of the Lomagundi–Jatuli carbon isotope excursion. Sulfidic carbonaceous mudstones in the Talvivaara formation contain one of the largest known shale-hosted nickel deposits. In order to gain new insight into this Shungian sedimentary environment, sedimentological, petrographical and in situ S and Fe isotopic microanalyses were carried out on samples representing depositional and early-diagenetic conditions. The event-bedded lithology with tidal signatures in the organic-rich mudstones strongly indicates deposition from predominantly river-delivered mud on a highly-productive coastal area, below storm-wave base. The riverine supply of phosphorus, sulfate and iron supported high primary productivity and resulted in strong lateral and vertical chemical gradients in the nearshore waters with a shallow oxic surface layer underlain by euxinic water. The stratigraphic upper part of the Talvivaara formation contains banded intervals of thin alternating pyrite beds and carbonaceous mudstone beds. The pyrite beds were deposited by seaward excursions of the concentrated, acidic Fe-rich river plume subsequent to droughts or dry seasons, which led to intense pyrite precipitation upon mixing with euxinic waters. δS34 and δFe56 values of the bedded pyrite (median δS34=−10.3‰ and δFe56=−0.79‰) are consistent with the reaction of dissolved Fe(II) with H2S from bacterial sulfate reduction. Organic-rich clayey Fe-monosulfide-bearing granules were transported from the muddy estuary, and enclosed in Fe (oxyhydr)oxide aggregates that were forming by wave and current reworking in nearshore accumulations of river-delivered iron. The isotopic composition of these presently pyrrhotitic inclusions (median δS34=−3.3‰ and δFe56=−1.6‰) indicates microbial iron reduction. The Fe (oxyhydr)oxide aggregates were transported in muddy debris flows to the distal euxinic seafloor. Their Fe (oxyhydr)oxide matrix was replaced by pyrite (median δS34=+5.8‰ and δFe56=+0.81‰) at shallow sediment depths with 34S and 56Fe-enriched porewater. Wavy-crinkly laminae of possible microbial origin developed on the euxinic seafloor during low sedimentation. These results indicate episodic deposition at seasonal to multiannual time scales. δS34 and δFe56 values in the studied Fe-sulfides provide evidence of microbial isotope fractionation processes and syndepositional and early-diagenetic origin, finding no support for the previously proposed local hydrothermal activity in the Talvivaara mudstones.

  • 35. Visser, Robbin
    et al.
    John, Timm
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Patzek, Markus
    Bischoff, Addi
    A short-lived 26Al induced hydrothermal alteration event in the outer solar system: Constraints from Mn/Cr ages of carbonates2020Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 547, artikkel-id 116440Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A key process in the early solar system that significantly affects the further evolution and transport of highly volatile elements throughout the solar system hydrothermal parent body alteration. To determine whether hydrothermal alteration in outer solar system parent bodies occurred more or less simultaneously or due to a sequence of multiple different events, we investigated low-temperature hydrothermally altered CM and CI chondrites along with volatile-rich CM-like clasts and C1 clasts with abundant mineral phases that contain volatiles. In this respect, C1 clasts are particularly important as they closely resemble the CI chondrites but originate from isotopically different parent bodies. Specifically, we applied the SIMS-based Mn/Cr in situ dating technique to carbonates, a common hydrothermally formed phase in low-temperature hydrothermally altered meteorites. The Mn/Cr ages of dolomites in CI chondrites and C1 clasts as well as calcites in CM chondrites and CM-like clasts reveal that nearly all carbonates in low-temperature hydrothermally altered clasts and chondrites were formed within a brief period between 2-6 Ma after CAI formation. Given this sharp separation, and that hardly any material contains carbonates formed later than ∼6 Ma after CAI formation, hydrothermal alteration likely occurred near-contemporaneously among different parent bodies in the outer solar system. Further, the timing of hydrothermal alteration matches peak heating of 26Al decay that ceased at ∼5 Ma after CAI formation. Hereby, these results are consistent with a model in which the carbonates in low-temperature hydrothermally altered parent bodies precipitated from the fluid produced by melting ice. The results also show that other potential heating events (e.g., impacts) only negligibly contributed to creating environments where fluid-mediated dissolution and precipitation of carbonates was possible. Additionally, the isotopic (H, O, Cr, and S) differences between C1 clasts and CI chondrites are most likely not caused by differences in timing of hydrothermal aqueous alteration and, thus, are best explained by spatially different isotopic reservoirs.

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