Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle
Abstract Ultramafic xenoliths from southeastern Arizona, USA, provide evidence for Cu‐isotope heterogeneity in the lithospheric mantle. We report new data on Type I (Cr‐, Mg‐rich) peridotites, but also the first Cu‐isotope data for Fe‐Ti‐Al‐rich Type II pyroxenite (±amphibole) xenoliths. Whole rock...
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| Language: | English |
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Wiley
2022-08-01
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| Series: | Geochemistry, Geophysics, Geosystems |
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| Online Access: | https://doi.org/10.1029/2022GC010436 |
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| author | Pamela D. Kempton Ryan Mathur Russell S. Harmon Aaron Bell Jochen Hoefs Barry Shaulis |
| author_facet | Pamela D. Kempton Ryan Mathur Russell S. Harmon Aaron Bell Jochen Hoefs Barry Shaulis |
| author_sort | Pamela D. Kempton |
| collection | DOAJ |
| description | Abstract Ultramafic xenoliths from southeastern Arizona, USA, provide evidence for Cu‐isotope heterogeneity in the lithospheric mantle. We report new data on Type I (Cr‐, Mg‐rich) peridotites, but also the first Cu‐isotope data for Fe‐Ti‐Al‐rich Type II pyroxenite (±amphibole) xenoliths. Whole rock δ65Cu values of the pyroxenites and cryptically metasomatized Type I lherzolites range to isotopically heavier compositions than asthenospheric mantle (i.e., up to +1.44‰ and +1.12‰, respectively, vs. ∼0‰ ± 0.2‰). Copper leached from the xenoliths using aqua regia, assumed to be hosted in interstitial sulfides, is even more variable (δ65Cu −0.78 to +3.88‰), indicating considerable isotopic heterogeneity within individual samples. Host basalts have low δ65Cu (−0.23‰ to −1.30‰), so basalt—xenolith interactions are not responsible for the compositional variations observed. While mass‐dependent fractionation may be partly responsible, metasomatism by fluids derived from recycled crustal materials is the predominant control on isotopic variations observed. Amphibole megacrysts and amphiboles separated from Type II amphibole‐bearing clinopyroxenite have normal, mantle‐like 18O/16O ratios but H‐isotope compositions (δ2HSMOW −82‰ to −45‰) that range between that of nominally anhydrous mantle (−80 ± 10‰) and seawater (0‰). Host basalts are also enriched in 34S relative to depleted asthenospheric mantle, having δ34SCDT values up to +8‰, i.e., compositions commonly attributed to a component of recycled seawater or hydrated oceanic crust. These new data suggest that formation of Type II metasomes in the lithospheric mantle beneath the Basin and Range Province was associated with subduction of the Farallon plate and not alkali basalt magmatism associated with Basin and Range extension. |
| format | Article |
| id | doaj-art-8aae1b77e6984ef1846ca77bd437bfd8 |
| institution | OA Journals |
| issn | 1525-2027 |
| language | English |
| publishDate | 2022-08-01 |
| publisher | Wiley |
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| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj-art-8aae1b77e6984ef1846ca77bd437bfd82025-08-20T02:08:11ZengWileyGeochemistry, Geophysics, Geosystems1525-20272022-08-01238n/an/a10.1029/2022GC010436Cu‐Isotope Evidence for Subduction Modification of Lithospheric MantlePamela D. Kempton0Ryan Mathur1Russell S. Harmon2Aaron Bell3Jochen Hoefs4Barry Shaulis5Department of Geology Kansas State University Manhattan KS USADepartment of Geology Juniata College Huntingdon PA USADepartment of Marine, Earth, and Atmospheric Sciences North Carolina State University Raleigh NC USADepartment of Geological Sciences University of Colorado Boulder Boulder CO USAGeowissenschaftliches Zentrum Göttingen Universität Göttingen GermanyTrace Element and Radiogenic Isotope Lab University of Arkansas Fayetteville AR USAAbstract Ultramafic xenoliths from southeastern Arizona, USA, provide evidence for Cu‐isotope heterogeneity in the lithospheric mantle. We report new data on Type I (Cr‐, Mg‐rich) peridotites, but also the first Cu‐isotope data for Fe‐Ti‐Al‐rich Type II pyroxenite (±amphibole) xenoliths. Whole rock δ65Cu values of the pyroxenites and cryptically metasomatized Type I lherzolites range to isotopically heavier compositions than asthenospheric mantle (i.e., up to +1.44‰ and +1.12‰, respectively, vs. ∼0‰ ± 0.2‰). Copper leached from the xenoliths using aqua regia, assumed to be hosted in interstitial sulfides, is even more variable (δ65Cu −0.78 to +3.88‰), indicating considerable isotopic heterogeneity within individual samples. Host basalts have low δ65Cu (−0.23‰ to −1.30‰), so basalt—xenolith interactions are not responsible for the compositional variations observed. While mass‐dependent fractionation may be partly responsible, metasomatism by fluids derived from recycled crustal materials is the predominant control on isotopic variations observed. Amphibole megacrysts and amphiboles separated from Type II amphibole‐bearing clinopyroxenite have normal, mantle‐like 18O/16O ratios but H‐isotope compositions (δ2HSMOW −82‰ to −45‰) that range between that of nominally anhydrous mantle (−80 ± 10‰) and seawater (0‰). Host basalts are also enriched in 34S relative to depleted asthenospheric mantle, having δ34SCDT values up to +8‰, i.e., compositions commonly attributed to a component of recycled seawater or hydrated oceanic crust. These new data suggest that formation of Type II metasomes in the lithospheric mantle beneath the Basin and Range Province was associated with subduction of the Farallon plate and not alkali basalt magmatism associated with Basin and Range extension.https://doi.org/10.1029/2022GC010436Cu isotopesH isotopes of mantle amphibolesS isotopes of alkali basaltsmantle xenolithsBasin and RangeFarallon subduction |
| spellingShingle | Pamela D. Kempton Ryan Mathur Russell S. Harmon Aaron Bell Jochen Hoefs Barry Shaulis Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle Geochemistry, Geophysics, Geosystems Cu isotopes H isotopes of mantle amphiboles S isotopes of alkali basalts mantle xenoliths Basin and Range Farallon subduction |
| title | Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle |
| title_full | Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle |
| title_fullStr | Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle |
| title_full_unstemmed | Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle |
| title_short | Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle |
| title_sort | cu isotope evidence for subduction modification of lithospheric mantle |
| topic | Cu isotopes H isotopes of mantle amphiboles S isotopes of alkali basalts mantle xenoliths Basin and Range Farallon subduction |
| url | https://doi.org/10.1029/2022GC010436 |
| work_keys_str_mv | AT pameladkempton cuisotopeevidenceforsubductionmodificationoflithosphericmantle AT ryanmathur cuisotopeevidenceforsubductionmodificationoflithosphericmantle AT russellsharmon cuisotopeevidenceforsubductionmodificationoflithosphericmantle AT aaronbell cuisotopeevidenceforsubductionmodificationoflithosphericmantle AT jochenhoefs cuisotopeevidenceforsubductionmodificationoflithosphericmantle AT barryshaulis cuisotopeevidenceforsubductionmodificationoflithosphericmantle |