Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling
Abstract Kimberlite‐borne eclogite xenoliths having Precambrian oceanic crustal protoliths and entrained from ≥100 km depth can retain pristine geochemical features despite extended residence in the cratonic lithospheric mantle, making them valuable archives of deep chemical cycling including that o...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Wiley
2023-12-01
|
| Series: | Geochemistry, Geophysics, Geosystems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2023GC011170 |
| _version_ | 1797368051220348928 |
|---|---|
| author | Sonja Aulbach Roland Stalder Malcolm Massuyeau Richard A. Stern Dmitri A. Ionov Andrey V. Korsakov |
| author_facet | Sonja Aulbach Roland Stalder Malcolm Massuyeau Richard A. Stern Dmitri A. Ionov Andrey V. Korsakov |
| author_sort | Sonja Aulbach |
| collection | DOAJ |
| description | Abstract Kimberlite‐borne eclogite xenoliths having Precambrian oceanic crustal protoliths and entrained from ≥100 km depth can retain pristine geochemical features despite extended residence in the cratonic lithospheric mantle, making them valuable archives of deep chemical cycling including that of water. We determined, by Fourier Transform Infrared Spectroscopy, structural OH contents in clinopyroxene and garnet from 15 unmetasomatized eclogite xenoliths. Calculated total c(H2O) is 100–510 wt.ppm for clinopyroxene and below detection (∼2 wt.ppm) to 200 wt.ppm for garnet, while garnet δ18O, determined by Secondary Ion Mass Spectrometry, ranges from +5.0‰ to +7.3‰, (similar to high‐ and low‐temperature seawater‐altered oceanic crust). Estimated electrical conductivity in pristine eclogites increases with temperature (i.e., depth for conductive geotherms), while clinopyroxene‐garnet H2O partition coefficients decrease with increasing temperature and garnet grossular component (i.e., Ca#), similar to other incompatible components. Various considerations suggest the retention of primary H2O in the samples, likely occurring in km‐sized pods of coarse‐grained eclogite. High Al2O3 in clinopyroxene as omphacite component, stabilized during high‐pressure metamorphism, facilitates H2O uptake. Therefore, the high bulk c(H2O) estimated for samples with plagioclase‐rich, deep crustal protoliths (median 290 wt.ppm) may indicate an interaction with fluids expelled at depth from serpentinites. The c(H2O) of ancient and modern subducted bulk oceanic crust (∼220–240 wt.ppm) are similar, suggesting constant mantle ingassing since at least 3 Ga ago. This places constraints on factors, such as mantle temperatures, that determine the efficiency of deep water cycling. |
| first_indexed | 2024-03-08T17:26:52Z |
| format | Article |
| id | doaj.art-a4b758e009ae494ea1451d04b4711b77 |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-08T17:26:52Z |
| publishDate | 2023-12-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-a4b758e009ae494ea1451d04b4711b772024-01-02T19:00:35ZengWileyGeochemistry, Geophysics, Geosystems1525-20272023-12-012412n/an/a10.1029/2023GC011170Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O RecyclingSonja Aulbach0Roland Stalder1Malcolm Massuyeau2Richard A. Stern3Dmitri A. Ionov4Andrey V. Korsakov5Institut für Geowissenschaften Goethe‐Universität Frankfurt Frankfurt GermanyUniversität Innsbruck Institut für Mineralogie und Petrographie Innsbruck AustriaInstitute for Mineralogy University of Münster Münster GermanyCanadian Centre for Isotopic Microanalysis Department of Earth and Atmospheric Sciences University of Alberta Edmonton AB CanadaGeosciences Montpellier University of Montpellier Montpellier FranceSobolev Institute of Geology and Mineralogy Siberian Branch Russian Academy of Science Novosibirsk Russian FederationAbstract Kimberlite‐borne eclogite xenoliths having Precambrian oceanic crustal protoliths and entrained from ≥100 km depth can retain pristine geochemical features despite extended residence in the cratonic lithospheric mantle, making them valuable archives of deep chemical cycling including that of water. We determined, by Fourier Transform Infrared Spectroscopy, structural OH contents in clinopyroxene and garnet from 15 unmetasomatized eclogite xenoliths. Calculated total c(H2O) is 100–510 wt.ppm for clinopyroxene and below detection (∼2 wt.ppm) to 200 wt.ppm for garnet, while garnet δ18O, determined by Secondary Ion Mass Spectrometry, ranges from +5.0‰ to +7.3‰, (similar to high‐ and low‐temperature seawater‐altered oceanic crust). Estimated electrical conductivity in pristine eclogites increases with temperature (i.e., depth for conductive geotherms), while clinopyroxene‐garnet H2O partition coefficients decrease with increasing temperature and garnet grossular component (i.e., Ca#), similar to other incompatible components. Various considerations suggest the retention of primary H2O in the samples, likely occurring in km‐sized pods of coarse‐grained eclogite. High Al2O3 in clinopyroxene as omphacite component, stabilized during high‐pressure metamorphism, facilitates H2O uptake. Therefore, the high bulk c(H2O) estimated for samples with plagioclase‐rich, deep crustal protoliths (median 290 wt.ppm) may indicate an interaction with fluids expelled at depth from serpentinites. The c(H2O) of ancient and modern subducted bulk oceanic crust (∼220–240 wt.ppm) are similar, suggesting constant mantle ingassing since at least 3 Ga ago. This places constraints on factors, such as mantle temperatures, that determine the efficiency of deep water cycling.https://doi.org/10.1029/2023GC011170kimberlite‐borne eclogite xenolithsnominally anhydrous mineralsFourier transform infrared spectroscopyelectrical conductivitydeep Earth water cycle |
| spellingShingle | Sonja Aulbach Roland Stalder Malcolm Massuyeau Richard A. Stern Dmitri A. Ionov Andrey V. Korsakov Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling Geochemistry, Geophysics, Geosystems kimberlite‐borne eclogite xenoliths nominally anhydrous minerals Fourier transform infrared spectroscopy electrical conductivity deep Earth water cycle |
| title | Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling |
| title_full | Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling |
| title_fullStr | Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling |
| title_full_unstemmed | Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling |
| title_short | Water in Omphacite and Garnet From Pristine Xenolithic Eclogite: T‐X‐fO2 Controls, Retentivity, and Implications for Electrical Conductivity and Deep H2O Recycling |
| title_sort | water in omphacite and garnet from pristine xenolithic eclogite t x fo2 controls retentivity and implications for electrical conductivity and deep h2o recycling |
| topic | kimberlite‐borne eclogite xenoliths nominally anhydrous minerals Fourier transform infrared spectroscopy electrical conductivity deep Earth water cycle |
| url | https://doi.org/10.1029/2023GC011170 |
| work_keys_str_mv | AT sonjaaulbach waterinomphaciteandgarnetfrompristinexenolithiceclogitetxfo2controlsretentivityandimplicationsforelectricalconductivityanddeeph2orecycling AT rolandstalder waterinomphaciteandgarnetfrompristinexenolithiceclogitetxfo2controlsretentivityandimplicationsforelectricalconductivityanddeeph2orecycling AT malcolmmassuyeau waterinomphaciteandgarnetfrompristinexenolithiceclogitetxfo2controlsretentivityandimplicationsforelectricalconductivityanddeeph2orecycling AT richardastern waterinomphaciteandgarnetfrompristinexenolithiceclogitetxfo2controlsretentivityandimplicationsforelectricalconductivityanddeeph2orecycling AT dmitriaionov waterinomphaciteandgarnetfrompristinexenolithiceclogitetxfo2controlsretentivityandimplicationsforelectricalconductivityanddeeph2orecycling AT andreyvkorsakov waterinomphaciteandgarnetfrompristinexenolithiceclogitetxfo2controlsretentivityandimplicationsforelectricalconductivityanddeeph2orecycling |