Earth's oldest mantle peridotites show entire record of late accretion

An important issue in Earth's earliest history is the timing and mixing history of the late accreted material that supplied highly siderophile elements to Earth's mantle after core segregation. Previously, constraints on ancient mantle processes could only be obtained indirectly from mantl...

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Bibliographic Details
Published in:Geology (Boulder) 2018-03, Vol.46 (3), p.199-202
Main Authors: van de Löcht, J, Hoffmann, J. E, Li, C, Wang, Z, Becker, H, Rosing, M. T, Kleinschrodt, R, Münker, C
Format: Article
Language:English
Subjects:
Accretion
Archean
Arctic region
Basalt
Depletion
Deposition
dunite
Earth
Earth mantle
Eoarchean
Geochemistry
Geochronometry
Geology
Greenland
harzburgite
igneous and metamorphic rocks
igneous rocks
Iridium
Isotope composition
isotope ratios
Isotopes
Komatiites
Magma
mantle
metals
Os-188/Os-187
Osmium
peridotites
Petrology
Platinum
platinum group
plutonic rocks
Precambrian
Preservation
radioactive isotopes
Radiometric dating
Re-187/Os-188
Rhenium
Rocks
Segregation
South Greenland
southwestern Greenland
stable isotopes
ultramafics
West Greenland
Zircon
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Summary:An important issue in Earth's earliest history is the timing and mixing history of the late accreted material that supplied highly siderophile elements to Earth's mantle after core segregation. Previously, constraints on ancient mantle processes could only be obtained indirectly from mantle-derived magmas such as basalts or komatiites. Relics of Eoarchean (older than 3.8 Ga) mantle were proposed to occur within the Eoarchean terrains of western Greenland. Here we provide geochemical evidence, including combined platinum group element (PGE) and Re-Os isotope data, showing that modern mantle-like peridotites occur at two localities in southwest Greenland. Rhenium-depletion model ages of these peridotites are mostly of Eoarchean age, in accord with U-Pb zircon ages of crosscutting granitoid intrusives. PGE abundances and patterns are similar to those of modern depleted mantle peridotites. For the first time, such patterns provide conclusive evidence for preservation of Eoarchean depleted mantle rocks that are clearly distinguishable from magmatic cumulates or komatiites. Abundances of Os, Ir, and Ru combined with Os isotope compositions in the Greenland peridotites reveal that primitive late accreted material appears to have been efficiently mixed into the sampled mantle domains by Eoarchean time.
ISSN:0091-7613
1943-2682
DOI:10.1130/G39709.1