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
Exhalative origins of iron formations
TL;DR: In this paper, a detailed review of the literature on the formation of all iron formations is presented, concluding that deep weathering has been the source of all the known iron formations.
Journal ArticleDOI
The geology and petrogenesis of a greenstone belt and related nickel sulfide mineralization at Yakabindie, Western Australia
A.J. Naldrett,A.R. Turner +1 more
TL;DR: Two major rock sequences, the Lower and Upper Greenstones, separated by an unconformity and associated conglomerate, are exposed in a narrow (5-30 km) elongate (130 km) greenstone belt in the Lawlers-Mt Keith area of the Eastern Goldfields of Western Australia.
Journal ArticleDOI
Generation of komatiite magma and gravitational differentiation in the deep upper mantle
TL;DR: In this article, it was suggested that aluminium-depleted komatiite with a high Ca/OAl2O3 ratio may be derived from diapirs which originated in the deep upper mantle at pressures from 70 kbar to at least 140 kbar, where selective separation of pyropic garnet occurs effectively.
Journal ArticleDOI
Plate tectonics and continental basaltic geochemistry throughout Earth history
TL;DR: In this paper, the authors use weighted bootstrap resampling to minimize sampling bias over the heterogeneous rock record and obtain maximally representative average basaltic compositions through time.
Journal ArticleDOI
Early Archaean rocks and geochemical evolution of the earth's crust
R.K. O'Nions,Robert J. Pankhurst +1 more
TL;DR: The trace element chemistry of these very old rocks is reviewed in an attempt to establish the mechanism of formation of early crust and place constraints on the chemical evolution of the earth's mantle as mentioned in this paper.
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