Bibliographic Citation
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Title | Petrogenesis of massif anorthosites: a perspective from St. Urbain, Quebec |
Creator/Author | Gromet, L.P. ; Dymek, R.F. |
Publication Date | 1985 Jan 01 |
OSTI Identifier | OSTI ID: 6576842 |
Report Number(s) | CONF-8510489- |
Other Number(s) | CODEN: GAAPB |
Resource Type | Conference |
Specific Type | Journal Article |
Resource Relation | Geol. Soc. Am., Abstr. Programs ; Vol/Issue: 17; 98. annual meeting of the Geological Society of America; 28 Oct 1985; Orlando, FL, USA |
Research Org | Brown Univ., Providence, RI (USA) |
Subject | 580300 -- Mineralogy, Petrology, & Rock Mechanics-- (-1989) ;580400 -- Geochemistry-- (-1989); ANORTHOSITES-- CHEMICAL COMPOSITION;ANORTHOSITES-- MINERALOGY;ANORTHOSITES-- PETROGENESIS;QUEBEC-- ANORTHOSITES; GEOCHEMISTRY;MAGMATISM |
Related Subject | CANADA;CHEMISTRY;GABBROS;IGNEOUS ROCKS;NORTH AMERICA;PLUTONIC ROCKS;ROCKS |
Description/Abstract | The St. Urbain massif is a post-orogenic anorthosite pluton (approx.^500 km/sup 2/) emplaced within the central high-grade granulite terrain of the Grenville structural province.^In contrast to other Grenville anorthosites, primary magmatic features are largely preserved.^The massif consists predominantly of andesine anorthosite (AA) of remarkable purity containing abundant plagioclase megacrysts.^AA has high K/sub 2/O (approx.^2 wgt.%), very high Sr contents (approx.^1200 ppm) and highly fractionated, low REE contents.^Features of AA provide the following insights into anorthosite origins: (1) Crystallization from anorthositic magmas, as evidenced by early crystallization of abundant antiperthitic plag, and igneous emplacement of AA dikes and veins into older, unrelated labradorite anorthosite; (2) in situ crystallization of pyroxene after plag, with no direct evidence of earlier crystallization of mafic minerals from a basaltic parent magma; (3) limited differentiation during crystallization, indicated by small variation in plag and opx and limited variations in plag Sr and REE contents; (4) the involvement of water, suggested by the late igneous crystallization of biotite and the localized grain-boundary replacement of plag by calcic myrmekite (An/sub 80/ + qtz).^(5) high temperature, relatively oxidizing conditions, indicated by magmatic hemoilmenite +/- rutile and rare ferropseudobrookite in AA and associated ores.^AA crystallized from highly feldspathic, relatively oxidized, somewhat hydrous parent magma with little trapped melt.^The development of a hyperfeldspathic parent magma with the requisite geochemical features can be ascribed to hydrous partial melting of mafic (to intermediate) rocks at deep crustal or greater depths, leaving a garnetiferous residue. |
Country of Publication | United States |
Language | English |
Format | Pages: 598 |
System Entry Date | 2001 May 13 |
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