The Interplay between Melting, Refertilization and Carbonatite Metasomatism in Off-Cratonic Lithospheric Mantle under Zealandia: an Integrated Major, Trace and Platinum Group Element Study.
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| Title: | The Interplay between Melting, Refertilization and Carbonatite Metasomatism in Off-Cratonic Lithospheric Mantle under Zealandia: an Integrated Major, Trace and Platinum Group Element Study. |
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| Authors: | McCoy-West, Alex J.1,2 alex.mccoywest@gmail.com, Bennett, Vickie C.1, O'Neill, Hugh St. C.1, Hermann, Jörg1, Puchte, Igor S.3 |
| Source: | Journal of Petrology. Mar2015, Vol. 56 Issue 3, p563-604. 42p. |
| Subjects: | Melting, Carbonatites, Metasomatism, Cratons, Lithosphere, Earth's mantle |
| Geographic Terms: | Zealandia |
| Abstract: | It is widely accepted that stabilization of the continental crust requires the presence of sub-continental lithospheric mantle. However, the degree of melt depletion required to stabilize the lithosphere and whether widespread refertilization is a significant process remain unresolved. Here, major and trace element, including platinum group elements (PGE), characterization of 40 mantle xenoliths from 13 localities is used to constrain the melt depletion, refertilization and metasomatic history of lithospheric mantle underneath the micro-continent Zealandia. Our previously published Re-Os isotopic data for a subset of these xenoliths indicate Phanerozoic to Paleoproterozoic ages and, reinterpreted with the new major and trace element data presented here, demonstrate that a large volume (>2 million km³) of lithospheric mantle with an age of 1·99 ± 0·21 Ga is present below the much younger crust of Zealandia. A peritectic melting model using moderately incompatible trace elements (e.g. Yb) in bulk-rocks demonstrates that these peridotites experienced a significant range of degrees of partial melting, between 3 and 28%. During subsolidus equilibration clinopyroxene gains significant rare earth elements (REE), which then leads to the underestimation of the degree of partial melting by ≲12% in fertile xenoliths. A new approach taking into account the effects of subsolidus re-equilibration on clinopyroxene composition effectively removes discrepancies in the calculated degree of melting and provides consistent estimates of between 4 and 29%. The estimated amount of melting is independent of the Re-Os model ages of the samples. The PGE patterns record simple melt depletion histories and the retention of primary base metal sulfides in the majority of the xenoliths. A rapid decrease in Pt/IrN observed at c. 1·0 wt % Al2O3 is a direct result of the exhaustion of sulfide in the mantle residue at c. 20-25% partial melting and the inability of Pt to form a stable alloy phase. Major elements preserve evidence for refertilization by a basaltic component that resulted in the formation of secondary clinopyroxene and low-forsterite olivine. The majority of xenoliths show the effects of cryptic metasomatic overprinting, ranging from minor to strong light REE enrichments in bulk-rocks (La/YbN = 0·16-15·9). Metasomatism is heterogeneous, with samples varying from those with weak REE enrichment and notable positive Sr and U-Th anomalies and negative Nb-Ta anomalies in clinopyroxene to those that have extremely high concentrations of REE, Th-U and Nb. Chemical compositions are consistent with a carbonatitic component contributing to the metasomatism of the lithosphere under Zealandia. Notably, the intense metasomatism of the samples did not affect the PGE budget of the peridotites as this was controlled by residual sulfides. [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 |
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| Header | DbId: egs DbLabel: Engineering Source An: 102828115 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: The Interplay between Melting, Refertilization and Carbonatite Metasomatism in Off-Cratonic Lithospheric Mantle under Zealandia: an Integrated Major, Trace and Platinum Group Element Study. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22McCoy-West%2C+Alex+J%2E%22">McCoy-West, Alex J.</searchLink><relatesTo>1,2</relatesTo><i> alex.mccoywest@gmail.com</i><br /><searchLink fieldCode="AR" term="%22Bennett%2C+Vickie+C%2E%22">Bennett, Vickie C.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22O'Neill%2C+Hugh+St%2E+C%2E%22">O'Neill, Hugh St. C.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Hermann%2C+Jörg%22">Hermann, Jörg</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Puchte%2C+Igor+S%2E%22">Puchte, Igor S.</searchLink><relatesTo>3</relatesTo> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+Petrology%22">Journal of Petrology</searchLink>. Mar2015, Vol. 56 Issue 3, p563-604. 42p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Melting%22">Melting</searchLink><br /><searchLink fieldCode="DE" term="%22Carbonatites%22">Carbonatites</searchLink><br /><searchLink fieldCode="DE" term="%22Metasomatism%22">Metasomatism</searchLink><br /><searchLink fieldCode="DE" term="%22Cratons%22">Cratons</searchLink><br /><searchLink fieldCode="DE" term="%22Lithosphere%22">Lithosphere</searchLink><br /><searchLink fieldCode="DE" term="%22Earth's+mantle%22">Earth's mantle</searchLink> – Name: SubjectGeographic Label: Geographic Terms Group: Su Data: <searchLink fieldCode="DE" term="%22Zealandia%22">Zealandia</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: It is widely accepted that stabilization of the continental crust requires the presence of sub-continental lithospheric mantle. However, the degree of melt depletion required to stabilize the lithosphere and whether widespread refertilization is a significant process remain unresolved. Here, major and trace element, including platinum group elements (PGE), characterization of 40 mantle xenoliths from 13 localities is used to constrain the melt depletion, refertilization and metasomatic history of lithospheric mantle underneath the micro-continent Zealandia. Our previously published Re-Os isotopic data for a subset of these xenoliths indicate Phanerozoic to Paleoproterozoic ages and, reinterpreted with the new major and trace element data presented here, demonstrate that a large volume (>2 million km³) of lithospheric mantle with an age of 1·99 ± 0·21 Ga is present below the much younger crust of Zealandia. A peritectic melting model using moderately incompatible trace elements (e.g. Yb) in bulk-rocks demonstrates that these peridotites experienced a significant range of degrees of partial melting, between 3 and 28%. During subsolidus equilibration clinopyroxene gains significant rare earth elements (REE), which then leads to the underestimation of the degree of partial melting by ≲12% in fertile xenoliths. A new approach taking into account the effects of subsolidus re-equilibration on clinopyroxene composition effectively removes discrepancies in the calculated degree of melting and provides consistent estimates of between 4 and 29%. The estimated amount of melting is independent of the Re-Os model ages of the samples. The PGE patterns record simple melt depletion histories and the retention of primary base metal sulfides in the majority of the xenoliths. A rapid decrease in Pt/IrN observed at c. 1·0 wt % Al2O3 is a direct result of the exhaustion of sulfide in the mantle residue at c. 20-25% partial melting and the inability of Pt to form a stable alloy phase. Major elements preserve evidence for refertilization by a basaltic component that resulted in the formation of secondary clinopyroxene and low-forsterite olivine. The majority of xenoliths show the effects of cryptic metasomatic overprinting, ranging from minor to strong light REE enrichments in bulk-rocks (La/YbN = 0·16-15·9). Metasomatism is heterogeneous, with samples varying from those with weak REE enrichment and notable positive Sr and U-Th anomalies and negative Nb-Ta anomalies in clinopyroxene to those that have extremely high concentrations of REE, Th-U and Nb. Chemical compositions are consistent with a carbonatitic component contributing to the metasomatism of the lithosphere under Zealandia. Notably, the intense metasomatism of the samples did not affect the PGE budget of the peridotites as this was controlled by residual sulfides. [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/egv011 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 42 StartPage: 563 Subjects: – SubjectFull: Melting Type: general – SubjectFull: Carbonatites Type: general – SubjectFull: Metasomatism Type: general – SubjectFull: Cratons Type: general – SubjectFull: Lithosphere Type: general – SubjectFull: Earth's mantle Type: general – SubjectFull: Zealandia Type: general Titles: – TitleFull: The Interplay between Melting, Refertilization and Carbonatite Metasomatism in Off-Cratonic Lithospheric Mantle under Zealandia: an Integrated Major, Trace and Platinum Group Element Study. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: McCoy-West, Alex J. – PersonEntity: Name: NameFull: Bennett, Vickie C. – PersonEntity: Name: NameFull: O'Neill, Hugh St. C. – PersonEntity: Name: NameFull: Hermann, Jörg – PersonEntity: Name: NameFull: Puchte, Igor S. IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 03 Text: Mar2015 Type: published Y: 2015 Identifiers: – Type: issn-print Value: 00223530 Numbering: – Type: volume Value: 56 – Type: issue Value: 3 Titles: – TitleFull: Journal of Petrology Type: main |
| ResultId | 1 |
