Archaean basic magmas

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Authors:Cattell, A. C.; Taylor, R. N.
Author Affiliations:Primary:
Univ. Exeter, Dep. Geol., Exeter, United Kingdom
Univ. Southampton, United Kingdom
Volume Title:Early Precambrian basic magmatism
Volume Authors:Hall, R. P., editor; Hughes, D. J.
Source:Early Precambrian basic magmatism, edited by R. P. Hall and D. J. Hughes, p.11-39. Publisher: Chapman and Hall, New York, NY, United States
Publication Date:1990
Note:In English; 23 analys., 2 tables
Summary:Archaean basic magmatism is discussed, emphasis being given to komatiite, komatiitic basalt and tholeiitic basalt suites. Few, if any, products of Phanerozoic volcanism equate exactly with Archaean rocks. This in itself perhaps indicates a secular change in petrogenetic systems. Such a change could have been influenced by several factors which are not necessarily mutually exclusive, and include: 1) variations in the thermal regime under which melting occurred, 2) a temporal change in the chemistry of the upper mantle reflecting depletion events and 3) evolution of the tectonic setting of magmatism through time. Komatiites represent the products of high-degree partial melting of the mantle, and those preserved in greenstone belts were probably generated in sub- continental mantle. Associated komatiitic basalts are predominantly derivative magmas produced by interaction of komatiitic magma with continental crustal material. The virtual absence of komatiitic lavas from the Phanerozoic record reflects a secular decline in the T of the upper mantle. In the Archaean, komatiites could be generated only in hot rising plumes, while under present global thermal conditions even plumes with T 200 degrees C above ambient mantle values are only capable of producing basalt. At the present state of knowledge, it appears that Archaean komatiitic basalts and Phanerozoic boninites are only superficially similar. However, there is no reason why boninitic melts should not have been generated in the early Precambrian, and it would be dangerous to assume that all Archaean high-Si high-Mg lavas are contaminated komatiites. [J.M.H.]
Subjects:Archean; Basalts; Genesis; Geochemistry; Greenstone belts; IGCP; Igneous rocks; Komatiite; Mafic composition; Magmas; Metamorphic belts; Petrology; Precambrian; Tholeiitic basalt; Ultramafic composition; Volcanic rocks; Igneous activity; Komatiitic basalt
Abstract Numbers:91M/2091
Record ID:1991002605
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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