Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications
The ~ 3700 Ma Inner Arc Group of the Isua supracrustal belt (Greenland) contains a 10 km long strip of ultramafic schists with two ≤ 1 km long meta-dunite lenses, preserving relict olivine + antigorite + titano-clinohumite and titano-chondrodite ~ 2.6 GPa ultra-high-pressure (UHP) assemblages. There...
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ftgfzpotsdam:oai:gfzpublic.gfz-potsdam.de:item_5006844 2023-05-15T16:28:45+02:00 Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications Nutman, A. Scicchitano, M. Friend, C. Bennett, V. Chivas, A. 2021 https://gfzpublic.gfz-potsdam.de/pubman/item/item_5006844 eng eng info:eu-repo/semantics/altIdentifier/doi/10.1016/j.precamres.2021.106249 https://gfzpublic.gfz-potsdam.de/pubman/item/item_5006844 Precambrian Research info:eu-repo/semantics/article 2021 ftgfzpotsdam https://doi.org/10.1016/j.precamres.2021.106249 2022-09-14T05:57:46Z The ~ 3700 Ma Inner Arc Group of the Isua supracrustal belt (Greenland) contains a 10 km long strip of ultramafic schists with two ≤ 1 km long meta-dunite lenses, preserving relict olivine + antigorite + titano-clinohumite and titano-chondrodite ~ 2.6 GPa ultra-high-pressure (UHP) assemblages. There are two distinct relict meta-peridotite variants: The southern lens ‘A’ variant is dominated by an aggregate of Fo91-92 olivine with δ18OVSMOW of + 5.4 ± 0.1‰ (95% confidence) in which are rare small clinopyroxene inclusions, plus rare interstitial accessory chrome spinel partly altered to magnetite. The olivine grains are bounded by serpentine domains, which are intergrown with the olivine margins with a marginally more iron-rich composition of Fo90.5. The northern lens ‘B’ contains coarser-grained Fo96-98 olivine which encloses magnetite as clusters and trails, some arranged with 60◦-120◦ conjugate intersections. The Fo96-98 olivine has δ18OVSMOW of + 3.2 ± 0.2‰ and is in equilibrium with high-Al antigorite and the accessory UHP Ti-rich minerals. We interpret that the Fo90-92 versus the Fo96-98 olivine assemblage variants are caused by a varying degree of fluid influx during ca. 3700 Ma serpentinisation, prior to peak UHP metamorphism. The Fo90-92 variant was a rock-dominated system with a postulated early serpentine + ferroan brucite alteration assemblage, with abundant relict mantle-like δ18OVSMOW + 5.4‰ olivine. The Fo96-98 variant was a fluid-dominated system, where obliteration of the protolith olivine formed serpentine + magnetite + brucite ± magnesite. During prograde UHP metamorphism consumption of brucite by reaction with serpentine gave rise to a lower δ18OVSMOW Fo96-98 olivine + serpentine assemblage. Both varieties have similar bulk chemistry, interpreted as depleted mantle that was enriched in LILE and LREE by a melt or fluid, prior to varying degrees of serpentinisation and superimposed UHP metamorphism. In Phanerozoic abyssal peridotites similar textural, chemical and isotopic variations are the ... Article in Journal/Newspaper Greenland GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) Greenland Precambrian Research 361 106249 |
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ftgfzpotsdam |
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English |
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The ~ 3700 Ma Inner Arc Group of the Isua supracrustal belt (Greenland) contains a 10 km long strip of ultramafic schists with two ≤ 1 km long meta-dunite lenses, preserving relict olivine + antigorite + titano-clinohumite and titano-chondrodite ~ 2.6 GPa ultra-high-pressure (UHP) assemblages. There are two distinct relict meta-peridotite variants: The southern lens ‘A’ variant is dominated by an aggregate of Fo91-92 olivine with δ18OVSMOW of + 5.4 ± 0.1‰ (95% confidence) in which are rare small clinopyroxene inclusions, plus rare interstitial accessory chrome spinel partly altered to magnetite. The olivine grains are bounded by serpentine domains, which are intergrown with the olivine margins with a marginally more iron-rich composition of Fo90.5. The northern lens ‘B’ contains coarser-grained Fo96-98 olivine which encloses magnetite as clusters and trails, some arranged with 60◦-120◦ conjugate intersections. The Fo96-98 olivine has δ18OVSMOW of + 3.2 ± 0.2‰ and is in equilibrium with high-Al antigorite and the accessory UHP Ti-rich minerals. We interpret that the Fo90-92 versus the Fo96-98 olivine assemblage variants are caused by a varying degree of fluid influx during ca. 3700 Ma serpentinisation, prior to peak UHP metamorphism. The Fo90-92 variant was a rock-dominated system with a postulated early serpentine + ferroan brucite alteration assemblage, with abundant relict mantle-like δ18OVSMOW + 5.4‰ olivine. The Fo96-98 variant was a fluid-dominated system, where obliteration of the protolith olivine formed serpentine + magnetite + brucite ± magnesite. During prograde UHP metamorphism consumption of brucite by reaction with serpentine gave rise to a lower δ18OVSMOW Fo96-98 olivine + serpentine assemblage. Both varieties have similar bulk chemistry, interpreted as depleted mantle that was enriched in LILE and LREE by a melt or fluid, prior to varying degrees of serpentinisation and superimposed UHP metamorphism. In Phanerozoic abyssal peridotites similar textural, chemical and isotopic variations are the ... |
format |
Article in Journal/Newspaper |
author |
Nutman, A. Scicchitano, M. Friend, C. Bennett, V. Chivas, A. |
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Nutman, A. Scicchitano, M. Friend, C. Bennett, V. Chivas, A. Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications |
author_facet |
Nutman, A. Scicchitano, M. Friend, C. Bennett, V. Chivas, A. |
author_sort |
Nutman, A. |
title |
Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications |
title_short |
Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications |
title_full |
Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications |
title_fullStr |
Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications |
title_full_unstemmed |
Isua (Greenland) ~3700 Ma meta-serpentinite olivine Mg# and δ18O signatures show connection between the early mantle and hydrosphere: Geodynamic implications |
title_sort |
isua (greenland) ~3700 ma meta-serpentinite olivine mg# and δ18o signatures show connection between the early mantle and hydrosphere: geodynamic implications |
publishDate |
2021 |
url |
https://gfzpublic.gfz-potsdam.de/pubman/item/item_5006844 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
Precambrian Research |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1016/j.precamres.2021.106249 https://gfzpublic.gfz-potsdam.de/pubman/item/item_5006844 |
op_doi |
https://doi.org/10.1016/j.precamres.2021.106249 |
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Precambrian Research |
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361 |
container_start_page |
106249 |
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1766018428982788096 |