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From crustal protoliths to mantle garnet pyroxenites: insights from Os isotopes and highly siderophile elements.

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Title: From crustal protoliths to mantle garnet pyroxenites: insights from Os isotopes and highly siderophile elements.
Authors: Montanini, Alessandra1 (AUTHOR) alessandra.montanini@unipr.it, Luguet, Ambre2 (AUTHOR), van Acken, David3 (AUTHOR), Tribuzio, Riccardo4,5 (AUTHOR), Schuth, Stephan6 (AUTHOR), Nowell, Geoff M.7 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Aug2025, Vol. 402, p217-233. 17p.
Subjects: Siderophile elements, Metal sulfides, Isotopic signatures, Eclogite, Pyroxenite, Garnet
Abstract: Recycled pyroxenites are a key component of mantle heterogeneity, influencing magma generation and contributing to the radiogenic Os signature of oceanic basalts. However, natural examples of pyroxenites as proxies for crust-derived heterogeneities in the convective mantle are rare and recycling mechanisms remain debated. Here we report abundances of highly siderophile (HSE: Os, Ir, Pt, Pd, Re) and chalcogen (S, Se, Te) elements, along with Os isotope compositions, for garnet clinopyroxenites and websterites enclosed in fertile peridotites from the Jurassic Northern Apennine ophiolites. The pyroxenites provide fractionated HSE patterns—depleted in Os and Ir and enriched in Pt, Pd, and Re compared to host lherzolites. Present-day 187Os/188Os ratios range from moderately to highly radiogenic (0.154–2.475). Garnet clinopyroxenites have lower Os, higher Pd/Ir, and more radiogenic Os than websterites. Model calculations based on bulk HSE data indicate the garnet clinopyroxenites reflect sulfur saturation and base metal sulfide (BMS) crystallization from partial melts of eclogites derived from MORB-type gabbroic protoliths. Their Os isotope signature indicates long-term Re/Os enrichment and derivation from ancient mafic protoliths, likely older than 1.0 Ga. The HSE distribution and Os isotopic signature of the websterites, along with their sulfide mineralogy, support a hybrid origin involving contributions from both peridotite- and eclogite-derived components. The websterites may represent natural analogues of the second-stage pyroxenites involved in OIB magma genesis. Host lherzolites exhibit flat CI chondrite-normalized HSE patterns and near-chondritic Se/Te and Pd/Ir ratios, implying initial depletion of incompatible HSEs like Pd and Re, followed by BMS addition during melt percolation that also affected some pyroxenites. Se (78–539 ppb) and Te (13–44 ppb) are significantly enriched in the pyroxenites compared to the lherzolites. The low Se/Te ratios (6–15) in garnet clinopyroxenites could explain the Se–Te signature of plume-influenced E-MORB. We show that mantle pyroxenites with a crustal fingerprint display wide HSE and Os isotope variability, reflecting heterogeneity of crustal protoliths, melt–peridotite interactions, and late melt percolation during their decompression history. [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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  Label: Title
  Group: Ti
  Data: From crustal protoliths to mantle garnet pyroxenites: insights from Os isotopes and highly siderophile elements.
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  Data: <searchLink fieldCode="AR" term="%22Montanini%2C+Alessandra%22">Montanini, Alessandra</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> alessandra.montanini@unipr.it</i><br /><searchLink fieldCode="AR" term="%22Luguet%2C+Ambre%22">Luguet, Ambre</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22van+Acken%2C+David%22">van Acken, David</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Tribuzio%2C+Riccardo%22">Tribuzio, Riccardo</searchLink><relatesTo>4,5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Schuth%2C+Stephan%22">Schuth, Stephan</searchLink><relatesTo>6</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Nowell%2C+Geoff+M%2E%22">Nowell, Geoff M.</searchLink><relatesTo>7</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Aug2025, Vol. 402, p217-233. 17p.
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  Data: <searchLink fieldCode="DE" term="%22Siderophile+elements%22">Siderophile elements</searchLink><br /><searchLink fieldCode="DE" term="%22Metal+sulfides%22">Metal sulfides</searchLink><br /><searchLink fieldCode="DE" term="%22Isotopic+signatures%22">Isotopic signatures</searchLink><br /><searchLink fieldCode="DE" term="%22Eclogite%22">Eclogite</searchLink><br /><searchLink fieldCode="DE" term="%22Pyroxenite%22">Pyroxenite</searchLink><br /><searchLink fieldCode="DE" term="%22Garnet%22">Garnet</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Recycled pyroxenites are a key component of mantle heterogeneity, influencing magma generation and contributing to the radiogenic Os signature of oceanic basalts. However, natural examples of pyroxenites as proxies for crust-derived heterogeneities in the convective mantle are rare and recycling mechanisms remain debated. Here we report abundances of highly siderophile (HSE: Os, Ir, Pt, Pd, Re) and chalcogen (S, Se, Te) elements, along with Os isotope compositions, for garnet clinopyroxenites and websterites enclosed in fertile peridotites from the Jurassic Northern Apennine ophiolites. The pyroxenites provide fractionated HSE patterns—depleted in Os and Ir and enriched in Pt, Pd, and Re compared to host lherzolites. Present-day 187Os/188Os ratios range from moderately to highly radiogenic (0.154–2.475). Garnet clinopyroxenites have lower Os, higher Pd/Ir, and more radiogenic Os than websterites. Model calculations based on bulk HSE data indicate the garnet clinopyroxenites reflect sulfur saturation and base metal sulfide (BMS) crystallization from partial melts of eclogites derived from MORB-type gabbroic protoliths. Their Os isotope signature indicates long-term Re/Os enrichment and derivation from ancient mafic protoliths, likely older than 1.0 Ga. The HSE distribution and Os isotopic signature of the websterites, along with their sulfide mineralogy, support a hybrid origin involving contributions from both peridotite- and eclogite-derived components. The websterites may represent natural analogues of the second-stage pyroxenites involved in OIB magma genesis. Host lherzolites exhibit flat CI chondrite-normalized HSE patterns and near-chondritic Se/Te and Pd/Ir ratios, implying initial depletion of incompatible HSEs like Pd and Re, followed by BMS addition during melt percolation that also affected some pyroxenites. Se (78–539 ppb) and Te (13–44 ppb) are significantly enriched in the pyroxenites compared to the lherzolites. The low Se/Te ratios (6–15) in garnet clinopyroxenites could explain the Se–Te signature of plume-influenced E-MORB. We show that mantle pyroxenites with a crustal fingerprint display wide HSE and Os isotope variability, reflecting heterogeneity of crustal protoliths, melt–peridotite interactions, and late melt percolation during their decompression history. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>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.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1016/j.gca.2025.05.034
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 17
        StartPage: 217
    Subjects:
      – SubjectFull: Siderophile elements
        Type: general
      – SubjectFull: Metal sulfides
        Type: general
      – SubjectFull: Isotopic signatures
        Type: general
      – SubjectFull: Eclogite
        Type: general
      – SubjectFull: Pyroxenite
        Type: general
      – SubjectFull: Garnet
        Type: general
    Titles:
      – TitleFull: From crustal protoliths to mantle garnet pyroxenites: insights from Os isotopes and highly siderophile elements.
        Type: main
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            NameFull: Montanini, Alessandra
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            NameFull: Luguet, Ambre
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            NameFull: van Acken, David
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            NameFull: Tribuzio, Riccardo
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            NameFull: Schuth, Stephan
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            – D: 01
              M: 08
              Text: Aug2025
              Type: published
              Y: 2025
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              Value: 402
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