Journal ArticleDOI
Genesis of Archean Peridotitic Magmas and Constraints on Archean Geothermal Gradients and Tectonics
TLDR
In this article, a model of peridotitic komatiite magma was developed in which selective removal of garnet during ascent produces CaO/Al 2 O 3 > 1 and heavy rare-earth element depletion in the resultant peridoteitic or mafic extrusions.Abstract:
The experimentally determined extrusion temperature (1650° ± 20°C) for Archean peridotitic komatiite magma implies diapirism of upper mantle peridotite from a depth of at least 200 km. Models of magma genesis are developed in which selective removal of garnet during ascent produces CaO/Al 2 O 3 > 1 and heavy rare-earth element depletion in the resultant peridotitic or mafic extrusions. Magma genesis can be interpreted with a model of the Archean geotherm, lithosphere, and plate tectonics processes resembling the modern Earth, but this does not account for the distinctive preservation and character of Archean greenstone belts. A preferred model of a steeper Archean geotherm, thin lithosphere (≃50 km), and asthenosphere with approximately 5 percent melting does not allow eclogitization and subduction of basaltic oceanic crust, but it postulates scraping off of such crust against and between primitive sialic nucleii. This model may account for the distinctive characteristics of the Archean greenstone and “granite” terranes.read more
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Journal ArticleDOI
Trace-element geochemistry of archean greenstone belts
TL;DR: Agarwal et al. as mentioned in this paper investigated the trace-element distribution in Archean greenstone greenstone belts and found that most of the trace element distributions in greenstone volcanic rocks are enriched in transition metals compared to modern varieties.
Journal ArticleDOI
Hf isotope compositions of komatiites
TL;DR: Blichert-Toft et al. as discussed by the authors measured the Hf isotope compositions of four Al-depleted komatiites from the 3.45 Ga Barberton Greenstone Belt in South Africa and six Al-undepleted KOMATIITs from 2.7 to 1.9 Ga belts in Canada and Zimbabwe.
Journal ArticleDOI
Insights into early Earth from Barberton komatiites: Evidence from lithophile isotope and trace element systematics
Igor S. Puchtel,Janne Blichert-Toft,Mathieu Touboul,Richard J. Walker,Gary R. Byerly,Euan G. Nisbet,Carl R. Anhaeusser +6 more
TL;DR: In this article, major, minor, and lithophile trace element abundances and Nd and Hf isotope systematics are reported for two sets of remarkably fresh, by Archean standards, samples of komatiitic lavas from the 3.48-Ga Komati and 3.27-Ga Weltevreden Formations of the Barberton Greenstone Belt (BGB) in South Africa.
Journal ArticleDOI
Onset of plate tectonics by the Eoarchean
TL;DR: In this paper, a review of the main Eoarchean supracrustal belts of the world, constrained by relevant geochemical/isotopic data, is presented evidence that suggests that from at least ca. 4.0 -4.2 -Ga to 2.7 -2.5 -Ga Earth produced considerable juvenile mafic crust and consequent island arcs by Accretionary Cycle Plate Tectonics.
Journal ArticleDOI
The dynamic emplacement of cone sheets
TL;DR: In this article, the authors reviewed the explanations of the formation of radial dykes, ring dykes and cone sheets and found that they were unsatisfactory and suggested that the cone sheets occupied shear fractures formed as the result of dynamic stresses arising from the rapid expansion of a magma undergoing retrograde boiling.
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Shen-Su Sun,Robert W. Nesbitt +1 more