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Earth and Planetary Science Letters
North-Holland
Earth and Planetary Science Letters

North-Holland

0012-821X

Earth and Planetary Science Letters/Journal Earth and Planetary Science LettersSCIEIAHCIISTP
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    Did an asteroid impact cause temporary warming during snowball Earth?

    Lan, ZhongwuMitchell, Ross N.Gernon, Thomas M.Nordsvan, Adam R....
    6页
    查看更多>>摘要：The ca. 717 Ma low-latitude Sturtian "snowball Earth " glaciation lasted similar to 56 Myr. However, sedimentological evidence for transient, open ocean conditions during the glaciation appears to contradict the concept of a global deep freeze. We demonstrate multiple lines of geologic evidence from five continents for a temporary, localized sea-ice retreat during the middle of the Sturtian glaciation, which coincides with one, perhaps two, asteroid impacts, and arguably more terrestrial impacts as inferred from the lunar impact record. The well-dated Janisjarvi impact (ca. 687 Ma) is synchronous with repeated volcanic ash falls whose deposition is most parsimoniously interpreted to indicate a partially ice-free ocean. Temporary greenhouse warming caused by the vaporization of sea ice can explain localized glacial retreat within restricted seaways between these continents, where ice flow would have been constricted and sea ice thinnest before impact. (c) 2022 The Author(s). Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    Potassium incorporation and isotope fractionation in cultured scleractinian corals

    Li, WenshuaiLiu, Xiao-MingWang, KunHu, Yongfeng...
    11页
    查看更多>>摘要：Potassium (K) participates in coral biological activities and accumulates in their skeletons, driving the fractionation of stable K isotopes (K-41/K-39). Constraining the influences of biotic and abiotic controls on K isotope fractionation is important for interpreting coral records. However, the processes and mechanisms regulating K incorporation into coral skeletons and K isotope fractionation between seawater and coral skeletons remain unknown. Here, we combined isotopic and synchrotron-based spectroscopic analyses to evaluate the phase distribution and corresponding isotope variation of K in the skeleton of scleractinian (Porites australiensis) corals at a seawater temperature range from 20 to 29 degrees C in aquaria culture experiments. Potassium in coral skeletons exists mainly as organic-K (K hosted in soluble and insoluble organic matrices) and carbonate-K (K incorporated into K2CO3 and aragonite) phases of various proportions. Coral delta K-41 values vary substantially in both direction and magnitude from the modern seawater delta K-41 composition (similar to 0.12 parts per thousand), showing marked deviations ( delta K-41(Coral-Sea)) from -2.00 to 0.67 parts per thousand. As seawater temperature increases, the organic-K fraction increases, whereas delta K-41(Coral) decreases. The variation in delta K-41(Coral) reflects the relative proportions of organic-bound K to carbonate-associated K. In most cases, coral intracrystalline organic matrices preferentially sequester isotopically lighter K whereas carbonate phases prefer heavier K. Distinguishable inter-colony difference in skeletal delta K-41 of corals growing under the same culturing conditions reveals the influence of physiological controls on K partitioning and isotope fractionation. Although calcification rate correlates with temperature to different degrees in the studied corals, likely reflecting control of the difference in zooxanthellae density, we infer that calcification rate is not a major controlling factor on skeletal delta K-41. Rather, skeletal delta K-41 correlates closely with K phase partitioning, which is ascribed to temperature-sensitive physiological modulation (c) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Chlorine isotope behavior in subduction zone settings revealed by olivine-hosted melt inclusions from the Central America Volcanic Arc

    Bouvier, A. -S.Portnyagin, M. V.Flemetakis, S.Hoernle, K....
    12页
    查看更多>>摘要：The isotopic composition of Cl, a highly hydrophilic and incompatible element, can provide new insights into the processes of element recycling in subduction zone settings. Samples from 13 localities in Guatemala, El Salvador, Nicaragua and Costa Rica, representing a ca. 1000 km long NW-SE segment along the Central American Volcanic Arc (CAVA), were selected. Ninety-seven melt inclusions, hosted by olivine Fo(90-70), were measured for Cl isotope ratios and trace element concentrations. Melt inclusions from samples from Guatemala to northwest Nicaragua have a restricted range of delta Cl-37 values (range < 1%o within a sample) with values decreasing from Santa Maria (Guatemala) to San Miguel (El Salvador), whereas melt inclusions from Nicaragua and Costa Rica display larger variation within a sample (delta Cl-37 value range > 1%o, up to 3.8%o) and do not show any systematic variation along the arc. For some samples, the delta Cl-37 in the melt inclusions is shifted by up to 2%o to higher values compared to bulk rock data from the same volcanic center, for which the extent of Cl degassing is not known. The combination of delta Cl-37 values in melt inclusions with trace elements and the existing knowledge about the slab contributions along the arc allows us to elucidate the Cl isotope composition of different endmembers in this subduction zone. From Guatemala to northwest Nicaragua, a fluid component, originating from serpentinite, has a delta Cl-37 value close to +0.6%o. This value, similar to lithospheric serpentinites, confirms that despite the aqueous fluid migration through the entire slab, Cl isotopes do not fractionate significantly during transport. A melt-like component, present in the southern part of the arc, has negative delta Cl-37, possibly down to -2.5%o. This component has lower delta Cl-37 than values of the oceanic crust but similar to sediments currently subducting beneath CAVA. Finally, a common component, most likely amphibole-bearing metasomatized mantle, is identified in samples with the highest delta Cl-37 values (up to +3.0%o). The melting of amphibole, a mineral concentrating 37Cl over 35Cl, could explain the high delta Cl-37 values. The difference between melt inclusions and bulk rock delta Cl-37 in some volcanic centers probably results from late-stage processes such as mixing of different batches of magma at shallower levels after melt inclusions entrapment. Melt inclusions thus give a more comprehensive picture of Cl isotope systematics along the CAVA and in primitive subduction-related magmas. (c) 2022 The Author(s). Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier