Mantle-derived Archaean monzodiorites and trachyandesites

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Authors:Shirey, Steven Bottome; Hanson, Gilbert N.
Author Affiliations:Primary:
State Univ., N.Y. at Stony Brook, Earth and Space Sci., Stony Brook, NY, United States
Volume Title:Nature (London)
Source:Nature (London), 310(5974), p.222-224. Publisher: Macmillan Journals, London, United Kingdom. ISSN: 0028-0836
Publication Date:1984
Note:In English. 48 refs.; illus. incl. 1 table
Summary:The 2680-2750 m.y. old intrusive granite-greenstone terrains in the Rainy Lake region, Ontario, and in, and adjacent to, the Vermilion District, Minnesota, of the Superior Province in North America, include a wide variety of volcanic and intrusive rocks with initial Pb, Sr and Nd isotope ratios close to those for the mantle. The isotopic constraints require the production of large volumes of silica-oversaturated magmas from silica-undersaturated mantle within 100-200 m.y. Geochemical data on LILE-enriched monzodiorites and trachyandesites from the Rainy Lake area are given. It is concluded that they were derived by direct melting of the mantle at depths of <50 km in either anhydrous or hydrous conditions. Their REE abundances and initial 143Nd/144Nd ratios suggest that their mantle sources were enriched in LILE shortly before melting. The monzodiorites, trachyandesites and their granodioritic derivatives may comprise up to 20% of the exposed igneous rocks in the Rainy Lake region and Vermilion District. If these rocks are as abundant in other Archaean terrains, a significant part of the early continental crust could have formed by direct melting of LILE-enriched mantle. (Authors' abstract) [C.N.]
Subjects:Archean; Geochemistry; Greenstone belts; Igneous rocks; Isotopes; Magmas; Major elements; Mantle; Metals; Metamorphic belts; Monzodiorite; Nd-144/Nd-143; Neodymium; Petrology; Phase equilibria; Plutonic rocks; Precambrian; Rare earths; Stable isotopes; Trace elements; Trachyandesites; Volcanic rocks; Canada; Canadian Shield; Eastern Canada; Minnesota; North America; Ontario; Rainy Lake; Saint Louis County Minnesota; Superior Province; United States; Vermilion District
Coordinates:N480000 N490000 W0920000 W0933000
Abstract Numbers:86M/4686
Record ID:1985014113
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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