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TitleMesozoic east North American alkaline magmatism. Part 1. Evolution of Monteregian lamprophyres, Québec, Canada
AuthorBédard, J H
SourceGeochimica et Cosmochimica Acta vol. 58, 1994 p. 95-112,
Alt SeriesGeological Survey of Canada, Contribution Series 44892
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
NTS31H/05NE; 31H/05NW; 31H/06NE; 31H/06NW; 31H/07NE; 31H/07NW; 31H/10; 31H/11; 31H/12
AreaMonteregian Hills
Lat/Long WENS -74.0000 -72.5000 45.7500 45.3333
Subjectsgeochemistry; igneous and metamorphic petrology; magmatism; lamprophyres; plutonic rocks; dykes, mafic; sills; camptonites; monchiquites; alnoites; magmatic deposits; petrography; trace element analyses; crystallization; Monteregian Intrusives; fractionation; Mesozoic; Cretaceous
Illustrationstables; diagrams; ternary diagrams
AbstractThe Cretaceous Monteregian alkaline igneous province is composed of shallowly emplaced plutonic complexes, and cogenetic dykes and sills. The mafic dykes are principally camptonites, monchiquites and alnöites, and sample the magmas that fed the plutons. The three principal dyke suites have different incompatible trace element ratios (YCe, ZrNb), and are not interrelated by closed-system fractional crystallization. Zonation of pyroxene grains imply a polybaric crystallization history, indicating that magmas ascended as mafic crystal-charged mushes. Intrasuite chemical variations among monchiquites are broadly consistent with segregation of the suspended phenocrysts from interstitial "syenitic" melts. Partial resorption of suspended amphibole megacrysts, assimilation of syenitic material (5-8%) and exsolution of carbonatitic melt are required to explain the variations of Ba, Rb, K2O, Th, La, and TiO2. Chemical variations among mafic camptonites are acceptably modelled by fractionation of pyroxene and olivine only, implying that their amphibole-rich character is the result of postfractionation crystallization under volatile-rich conditions. High-ZrNb camptonites and Rb-rich (AC) monchiquites could not unequivocably be linked to the main lineages and may represent distinct sources or have been affected by crustal contaminants.

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