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The chondritic neodymium stable isotope composition of the Earth inferred from mid-ocean ridge, ocean island and arc basalts.

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Title: The chondritic neodymium stable isotope composition of the Earth inferred from mid-ocean ridge, ocean island and arc basalts.
Authors: McCoy-West, Alex J.1,2,3 (AUTHOR) alex.mccoywest@gmail.com, Burton, Kevin W.2 (AUTHOR), Millet, Marc-Alban4 (AUTHOR), Cawood, Peter A.1 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Jan2021, Vol. 293, p575-597. 23p.
Subjects: Island arcs, Neodymium isotopes, Stable isotopes, Mid-ocean ridges, Internal structure of the Earth, Adakite, Chondrites, Basalt
Abstract: • First comprehensive study of Nd stable isotopes in wide range of terrestrial basalts. • Partial melting modelling demonstrates that δ146Nd is unfractionated upon melting. • Confirmation the bulk silicate Earth and chondrites have the indistinguishable δ146Nd. • Variations in δ146Nd induce no analytical artefacts when calculating radiogenic isotope compositions. Accurate knowledge of the composition of Earth's major chemical reservoirs is fundamental for constraining all modern geochemical cycles. Basaltic rocks provide a direct way of sampling the composition of Earth's inaccessible interior. Here, we present the first comprehensive neodymium (Nd) stable isotope analyses for a global compilation of mid-ocean ridge, ocean island, continental intraplate and island arc basalts using a double-spike technique. In these primitive magma compositions magmatic differentiation has no resolvable effect on δ146/144Nd. Mid-ocean ridge basalts possess an extremely homogenous δ146/144Nd with an average composition of δ146/144Nd = −0.025 ± 0.013‰ (±2 s.d.; n = 33). Ocean island and continental intraplate magmas possess more variable compositions (δ146/144Nd = 62 ppm) that are related to the variable incorporation of recycled components in their source regions. Island arc basalts from New Britain (δ146/144Nd = 61 ppm) reflect the complex interplay between source composition, degree of melting and slab-fluid inputs. Variations are uncorrelated with indicators of magmatic differentiation or slab-fluid addition, rather increasing δ146/144Nd with slab depth is attributed to a higher proportion of metasomatized sub-arc mantle in the melting region. A partial melting model for Nd stable isotopes has been constructed using Nd O force constants calculated using the Born-Lande approximation. Melting of typical mantle peridotite will induce no resolvable fractionations of Nd stable isotopes (Δ146/144Nd melt-mantle < 0.003‰ at 1200 °C). The lack of fractionation upon partial melting means primitive magmatic rocks can be used to calculate the average composition of the bulk silicate Earth (BSE), which is δ146/144Nd = −0.024 ± 0.031‰ (±2 s.d.; n = 80). This BSE composition is indistinguishable at the 95 % confidence level from that of chondritic meteorites, the building blocks of Earth. Therefore, sequestration of significant quantities of Nd into the sulfide matte did not occur, this combined with recent experimental evidence for no Sm-Nd fractionation means the sulfide matte cannot be considered a plausible solution for the 142Nd/144Nd offset between the Earth and chondrites. Despite resolvable variations in δ146/144Nd from the canonical value being widespread in terrestrial materials, they are not large enough to generate the difference in radiogenic Nd isotope ratios between the BSE and chondrites. [ABSTRACT FROM AUTHOR]
Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: The chondritic neodymium stable isotope composition of the Earth inferred from mid-ocean ridge, ocean island and arc basalts.
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  Data: &lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22McCoy-West%2C+Alex+J%2E%22&quot;&gt;McCoy-West, Alex J.&lt;/searchLink&gt;&lt;relatesTo&gt;1,2,3&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; alex.mccoywest@gmail.com&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Burton%2C+Kevin+W%2E%22&quot;&gt;Burton, Kevin W.&lt;/searchLink&gt;&lt;relatesTo&gt;2&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Millet%2C+Marc-Alban%22&quot;&gt;Millet, Marc-Alban&lt;/searchLink&gt;&lt;relatesTo&gt;4&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Cawood%2C+Peter+A%2E%22&quot;&gt;Cawood, Peter A.&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)
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  Data: &lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Island+arcs%22&quot;&gt;Island arcs&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Neodymium+isotopes%22&quot;&gt;Neodymium isotopes&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Stable+isotopes%22&quot;&gt;Stable isotopes&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Mid-ocean+ridges%22&quot;&gt;Mid-ocean ridges&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Internal+structure+of+the+Earth%22&quot;&gt;Internal structure of the Earth&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Adakite%22&quot;&gt;Adakite&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Chondrites%22&quot;&gt;Chondrites&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Basalt%22&quot;&gt;Basalt&lt;/searchLink&gt;
– Name: Abstract
  Label: Abstract
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  Data: • First comprehensive study of Nd stable isotopes in wide range of terrestrial basalts. • Partial melting modelling demonstrates that δ146Nd is unfractionated upon melting. • Confirmation the bulk silicate Earth and chondrites have the indistinguishable δ146Nd. • Variations in δ146Nd induce no analytical artefacts when calculating radiogenic isotope compositions. Accurate knowledge of the composition of Earth&#39;s major chemical reservoirs is fundamental for constraining all modern geochemical cycles. Basaltic rocks provide a direct way of sampling the composition of Earth&#39;s inaccessible interior. Here, we present the first comprehensive neodymium (Nd) stable isotope analyses for a global compilation of mid-ocean ridge, ocean island, continental intraplate and island arc basalts using a double-spike technique. In these primitive magma compositions magmatic differentiation has no resolvable effect on δ146/144Nd. Mid-ocean ridge basalts possess an extremely homogenous δ146/144Nd with an average composition of δ146/144Nd = −0.025 &#177; 0.013‰ (&#177;2 s.d.; n = 33). Ocean island and continental intraplate magmas possess more variable compositions (δ146/144Nd = 62 ppm) that are related to the variable incorporation of recycled components in their source regions. Island arc basalts from New Britain (δ146/144Nd = 61 ppm) reflect the complex interplay between source composition, degree of melting and slab-fluid inputs. Variations are uncorrelated with indicators of magmatic differentiation or slab-fluid addition, rather increasing δ146/144Nd with slab depth is attributed to a higher proportion of metasomatized sub-arc mantle in the melting region. A partial melting model for Nd stable isotopes has been constructed using Nd O force constants calculated using the Born-Lande approximation. Melting of typical mantle peridotite will induce no resolvable fractionations of Nd stable isotopes (Δ146/144Nd melt-mantle &lt; 0.003‰ at 1200 &#176;C). The lack of fractionation upon partial melting means primitive magmatic rocks can be used to calculate the average composition of the bulk silicate Earth (BSE), which is δ146/144Nd = −0.024 &#177; 0.031‰ (&#177;2 s.d.; n = 80). This BSE composition is indistinguishable at the 95 % confidence level from that of chondritic meteorites, the building blocks of Earth. Therefore, sequestration of significant quantities of Nd into the sulfide matte did not occur, this combined with recent experimental evidence for no Sm-Nd fractionation means the sulfide matte cannot be considered a plausible solution for the 142Nd/144Nd offset between the Earth and chondrites. Despite resolvable variations in δ146/144Nd from the canonical value being widespread in terrestrial materials, they are not large enough to generate the difference in radiogenic Nd isotope ratios between the BSE and chondrites. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
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  Data: &lt;i&gt;Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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    Identifiers:
      – Type: doi
        Value: 10.1016/j.gca.2020.09.038
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 23
        StartPage: 575
    Subjects:
      – SubjectFull: Island arcs
        Type: general
      – SubjectFull: Neodymium isotopes
        Type: general
      – SubjectFull: Stable isotopes
        Type: general
      – SubjectFull: Mid-ocean ridges
        Type: general
      – SubjectFull: Internal structure of the Earth
        Type: general
      – SubjectFull: Adakite
        Type: general
      – SubjectFull: Chondrites
        Type: general
      – SubjectFull: Basalt
        Type: general
    Titles:
      – TitleFull: The chondritic neodymium stable isotope composition of the Earth inferred from mid-ocean ridge, ocean island and arc basalts.
        Type: main
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            NameFull: McCoy-West, Alex J.
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            NameFull: Burton, Kevin W.
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            NameFull: Millet, Marc-Alban
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            NameFull: Cawood, Peter A.
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            – D: 15
              M: 01
              Text: Jan2021
              Type: published
              Y: 2021
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              Value: 293
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