'Postcumulus Processes Recorded in Whole Rock Geochemistry: A Case Study from the Mirabela Layered Intrusion, Brazil' by S.J. Barnes and M. Williams: Reply to Comment by A.E. Boudreau.
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| Title: | 'Postcumulus Processes Recorded in Whole Rock Geochemistry: A Case Study from the Mirabela Layered Intrusion, Brazil' by S.J. Barnes and M. Williams: Reply to Comment by A.E. Boudreau. |
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| Authors: | Barnes, Stephen J1 (AUTHOR), Williams, Morgan1 (AUTHOR) |
| Source: | Journal of Petrology. Sep2025, Vol. 66 Issue 9, p1-4. 4p. |
| Subjects: | Pyroxenite, Solidification, Microstructure, Geochemical surveys, Rock analysis |
| Geographic Terms: | Brazil |
| Abstract: | In our 2024 paper, we investigated a database of more than 60 000 whole-rock analyses of a pyroxenite–harzburgite–gabbronorite interval across the entire width on the Mirabela Layered Intrusion. We concluded that during the solidification of these cumulates they behaved as closed systems with respect to intercumulus components, where sufficiently large samples (3- to 10-m drill core composites) were considered. Boudreau (2025) reinterprets individual drill holes sampled at 1-m intervals to reach the opposite conclusion from ours. He claims that detailed geochemical trends in the plagioclase-excluded element P relative to plagioclase-compatible components Na and Sr indicate that residual trapped liquid was preferentially removed from the cumulate pile during compaction in the centre of the intrusion. We show that this conclusion is incompatible with trends in element ratios across the intrusion, particularly in the ratios of Al and Na to Ti. Concentrations of Ti show no evidence of depletion relative to Na and Al and correlate strongly with plagioclase-compatible elements throughout. Our original conclusion remains robust on this evidence. However, we find that Ti and P are decoupled to some extent and therefore agree that some selective mobility of P probably has occurred, although part of this apparent decoupling may be due to nugget effects in low-level P analyses. Detailed microstructural studies are needed to supplement a purely geochemical approach. [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of Petrology is the property of Oxford University Press / USA 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.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 188960827 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: 'Postcumulus Processes Recorded in Whole Rock Geochemistry: A Case Study from the Mirabela Layered Intrusion, Brazil' by S.J. Barnes and M. Williams: Reply to Comment by A.E. Boudreau. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Barnes%2C+Stephen+J%22">Barnes, Stephen J</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Williams%2C+Morgan%22">Williams, Morgan</searchLink><relatesTo>1</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+Petrology%22">Journal of Petrology</searchLink>. Sep2025, Vol. 66 Issue 9, p1-4. 4p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Pyroxenite%22">Pyroxenite</searchLink><br /><searchLink fieldCode="DE" term="%22Solidification%22">Solidification</searchLink><br /><searchLink fieldCode="DE" term="%22Microstructure%22">Microstructure</searchLink><br /><searchLink fieldCode="DE" term="%22Geochemical+surveys%22">Geochemical surveys</searchLink><br /><searchLink fieldCode="DE" term="%22Rock+analysis%22">Rock analysis</searchLink> – Name: SubjectGeographic Label: Geographic Terms Group: Su Data: <searchLink fieldCode="DE" term="%22Brazil%22">Brazil</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: In our 2024 paper, we investigated a database of more than 60 000 whole-rock analyses of a pyroxenite–harzburgite–gabbronorite interval across the entire width on the Mirabela Layered Intrusion. We concluded that during the solidification of these cumulates they behaved as closed systems with respect to intercumulus components, where sufficiently large samples (3- to 10-m drill core composites) were considered. Boudreau (2025) reinterprets individual drill holes sampled at 1-m intervals to reach the opposite conclusion from ours. He claims that detailed geochemical trends in the plagioclase-excluded element P relative to plagioclase-compatible components Na and Sr indicate that residual trapped liquid was preferentially removed from the cumulate pile during compaction in the centre of the intrusion. We show that this conclusion is incompatible with trends in element ratios across the intrusion, particularly in the ratios of Al and Na to Ti. Concentrations of Ti show no evidence of depletion relative to Na and Al and correlate strongly with plagioclase-compatible elements throughout. Our original conclusion remains robust on this evidence. However, we find that Ti and P are decoupled to some extent and therefore agree that some selective mobility of P probably has occurred, although part of this apparent decoupling may be due to nugget effects in low-level P analyses. Detailed microstructural studies are needed to supplement a purely geochemical approach. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Journal of Petrology is the property of Oxford University Press / USA 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: 10.1093/petrology/egaf078 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 4 StartPage: 1 Subjects: – SubjectFull: Pyroxenite Type: general – SubjectFull: Solidification Type: general – SubjectFull: Microstructure Type: general – SubjectFull: Geochemical surveys Type: general – SubjectFull: Rock analysis Type: general – SubjectFull: Brazil Type: general Titles: – TitleFull: 'Postcumulus Processes Recorded in Whole Rock Geochemistry: A Case Study from the Mirabela Layered Intrusion, Brazil' by S.J. Barnes and M. Williams: Reply to Comment by A.E. Boudreau. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Barnes, Stephen J – PersonEntity: Name: NameFull: Williams, Morgan IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 09 Text: Sep2025 Type: published Y: 2025 Identifiers: – Type: issn-print Value: 00223530 Numbering: – Type: volume Value: 66 – Type: issue Value: 9 Titles: – TitleFull: Journal of Petrology Type: main |
| ResultId | 1 |
