DOI: 10.1016/j.epsl.2020.116331
论文题名: >2.7 Ga metamorphic peridotites from southeast Greenland record the oxygen isotope composition of Archean seawater
作者: Peters S.T.M. ; Szilas K. ; Sengupta S. ; Kirkland C.L. ; Garbe-Schönberg D. ; Pack A.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 544 语种: 英语
中文关键词: Archean oceans
; deserpentinisation
; Ivnartivaq
; Nagssugtoqidian Orogenic Belt
; Rae craton
; triple oxygen isotopes
英文关键词: Binary alloys
; Clay alteration
; Gallium
; Geochronology
; Isotopes
; Lead alloys
; Magnesite
; Metamorphic rocks
; Olivine
; Oxygen
; Temperature
; Trace elements
; Uranium alloys
; Weathering
; Zircon
; Hydrothermal alterations
; Mineral composition
; Oxygen isotope composition
; Seawater compositions
; Steady-state values
; Trace element concentrations
; Triple oxygen isotopes
; Ultramafic cumulate
; Seawater
; Archean
; hydrothermal alteration
; isotopic composition
; metamorphic rock
; oxygen isotope
; peridotite
; seawater
; ultramafic rock
; Arctic
; Greenland
英文摘要: The δ18O value of seawater is presently buffered by high-temperature hydrothermal alteration and low-temperature weathering of lithospheric rocks. It is much debated whether the δ18O of seawater has been buffered to this steady-state value throughout Earth's history or, alternatively, whether it gradually increased towards the present value since the Archean. A third possibility is that the δ18O of seawater was buffered at a higher value before continents emerged, and has been buffered at its current value (δ18O ∼ −1‰) since the emergence of continents. In this contribution, we reconstruct the δ18O of Archean seawater from triple oxygen isotope (δ17O, δ18O) variations in >2.7 Ga ultramafic rocks that reacted with fluids that, in turn, had been derived from seawater in the Archean. The samples that were studied are peridotites from the Ivnartivaq complex, an ultramafic lens in the Archean Kuummiut terrane (Rae craton, southeast Greenland) that have unusually low δ18O values for peridotites (in olivine, 1.7‰≤δ18O≤4.6‰, relative to VSMOW). Bulk rock trace element concentrations, mineral compositions and U-Pb dating of zircon grains in the peridotites indicate that these samples are metamorphic peridotites, that formed by the dehydration of serpentinites ∼2.7 Ga ago. The serpentinite protoliths, in turn, had formed by alteration of ultramafic cumulate rocks at high temperatures (250–450 °C) by fluids that were derived from seawater. Triple oxygen isotope variations in olivine from the peridotites indicate that the fluids could not have been derived from seawater with a significantly higher or lower δ18O value than that of seawater in the Phanerozoic, but could have been derived from seawater with a value of δ18O ∼ −1‰, i.e., the modern (ice-free) seawater composition. We conclude that the δ18O of seawater had reached its current steady state value by 2.7 Ga ago. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165210
Appears in Collections: 气候变化与战略
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作者单位: University of Göttingen, Geosciences Centre, Department of Isotope Geology, Goldschmidtstraße 1, Göttingen, 37077, Germany; University of Copenhagen, Department of Geosciences and Natural Resource Management, Øster Voldgade 10, København K, 1350, Denmark; School of Earth and Planetary Sciences, Timescales of Mineral Systems, Centre for Exploration Targeting–Curtin Node, Curtin University, Perth, WA, Australia; Kiel University, Institute of Geosciences, Ludewig-Meyn-Strasse 10, Kiel, 24118, Germany
Recommended Citation:
Peters S.T.M.,Szilas K.,Sengupta S.,et al. >2.7 Ga metamorphic peridotites from southeast Greenland record the oxygen isotope composition of Archean seawater[J]. Earth and Planetary Science Letters,2020-01-01,544