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Title Petrogenesis of massif anorthosites: a perspective from St. Urbain, Quebec
Creator/Author Gromet, L.P. ; Dymek, R.F.
Publication Date1985 Jan 01
OSTI IdentifierOSTI ID: 6576842
Report Number(s)CONF-8510489-
Other Number(s)CODEN: GAAPB
Resource TypeConference
Specific TypeJournal Article
Resource RelationGeol. Soc. Am., Abstr. Programs ; Vol/Issue: 17; 98. annual meeting of the Geological Society of America; 28 Oct 1985; Orlando, FL, USA
Research OrgBrown Univ., Providence, RI (USA)
Subject580300 -- Mineralogy, Petrology, & Rock Mechanics-- (-1989) ;580400 -- Geochemistry-- (-1989); ANORTHOSITES-- CHEMICAL COMPOSITION;ANORTHOSITES-- MINERALOGY;ANORTHOSITES-- PETROGENESIS;QUEBEC-- ANORTHOSITES; GEOCHEMISTRY;MAGMATISM
Related SubjectCANADA;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 PublicationUnited States
LanguageEnglish
FormatPages: 598
System Entry Date2001 May 13

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