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TitleEnclaves from the A-type granite of the Mégantic Complex, White Mountain Magma Series: clues to granite magmagenesis
AuthorBédard, J
SourceJournal of Geophysical Research vol. 95, no. B11, 1990 p. 17,797-17,819,
Alt SeriesGeological Survey of Canada, Contribution Series 28889
Mediapaper; on-line; digital
File formatpdf
NTS21E; 31G/01; 31G/08; 31G/09; 31G/16; 31H
AreaMonteregian Hills; mont Mégantic; lac Memphrémagog; White Mountains; Vermont; New Hampshire; Maine; New York; Massachussetts; Canada; United States of America
Lat/Long WENS -74.2500 -70.0000 46.0000 42.6667
Subjectsigneous and metamorphic petrology; igneous rocks; plutonic rocks; granites; hornblende; biotite; magmatism; magmas; inclusions; mafic rocks; intrusive rocks; microgranites; apatite; host rocks; aluminum; chromium; augite; phenocrysts; quartz; oligoclase; perthite; exsolution; anatexis; basalts; volcanic rocks; isotopic studies; strontium strontium ratios; rubidium-strontium ratios; petrographic analyses; mineralogical analyses; whole rock geochemistry; whole rock analyses; petrogenesis; pyroxene; amphibole; feldspar; mica; gabbros; syenites; dykes; diorites; lamprophyres; granophyres; recrystallization; models; mantle; monzonites; granodiorites; metasomatism; equilibrium; electron probe analyses; major element analyses; trace element analyses; White Mountain Magma Series; Mégantic Complex; leucocratic rocks; meladiorites; clots; pseudomorphs; microxenoliths; xenocrysts; megacrysts; magma hybridization; volatiles; residual melts; hawaiite; fractionation; crust; mixing; Mesozoic; Cretaceous
Illustrationsgeological sketch maps; photomicrographs; tables; ternary diagrams; plots; graphs
Released1990 01 01
AbstractThe subsolvus biotite-hornblende-granite at Mégantic contains mafic to leucocratic enclaves. The groundmass of leucocratic enclaves is microgranitic; that of mafic enclaves is meladioritic. Apatite is commonly acicular in the enclaves, suggesting quenching of mafic magmas commingled with the granitic host. Mafic enclaves contain mafic clots (hornblende cores, biotite rims), some with relic cores of viAl-Cr-rich diopsidic augite similar to phenocrysts in associated basaltic dykes. The clots are interpreted to be pseudomorphs after mafic phenocrysts. The enclaves also contain granitic microxenoliths, xenocrysts of quartz with hornblende reaction rims, partially resorbed oligoclase and perthite megacrysts and biotite xenocrysts. The xenocrysts record hybridization between a mafic enclave magma and a granitic magma and/or rock. Enclaves define mixing lines on many variation diagrams. However, Rb, Sr, Ba, Zr, Nb, Y, REE, Zn, Pb, and F do not fit this pattern and appear to have been redistributed by residual granitic melts or exsolved volatiles. The data suggest that the granite is anatectic, heat being provided by crystallization of associated basalts. Mixing calculations suggest that as little as 5% hybridization with basalt or hawaiite can account for the Sr isotopic heterogeneity of the granites.

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