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TitleThe lower crust of the Bay of Islands ophiolite, Canada: petrology, mineralogy, and the importance of syntexis in magmatic differentiation in ophiolites and at ocean ridges
AuthorBedard, J H; Hébert, R
SourceJournal of Geophysical Research vol. 101, no. B11, 1996 p. 25105-25124, https://doi.org/10.1029/96jb01343
Year1996
Alt SeriesGeological Survey of Canada, Contribution Series 1996106
PublisherWiley-Blackwell
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNewfoundland and Labrador
NTS12H/04NW; 12H/05; 12G/08
AreaNorth Arm Mountain
Lat/Long WENS -58.5000 -57.5000 49.5000 49.0000
Subjectsmineralogy; igneous and metamorphic petrology; tectonics; ophiolites; magma differentiation; mid-ocean ridges; peridotites; pyroxenites; gabbros; sills; fractional crystallization; deformation; textures; hydrothermal alteration; geothermometry; magmatism; crustal studies; Bay of Island Ophiolites; North Arm Mountain Massif; syntexis
Illustrationsphotomicrographs; graphs; histograms
Released1996 11 10
AbstractThe lower crust of the North Arm Mountain massif (Bay of Islands ophiolite) is composed of interfolded, porphyroclastic-textured peridotite, pyroxenite, and gabbro, belonging to several differentiation series. Low-Ti pyroxenes, high An/Fo, abundant orthopyroxene, and high spinel Cr/Al suggest arc affinities. Discordant contacts and inclusion relationships show that many peridotites are synkinematic sills. Some host rocks were altered to sulphide-bearing, greenschist-grade assemblages prior to intrusion. Most feldspathic peridotites and melagabbros are hybrids formed by disaggregation of host gabbros into primitive intrusions. Many pyroxenites and chromitites are by-products of incongruent dissolution reactions. Much of the pyroxene component of peridotites and olivine pyroxenites is xenolithic. Synmagmatic shear augmented the efficiency and extent of hydridization and assimilation reactions. Syntexis (the melting and dissolution of xenocrysts) was as important as fractional crystallization in generating petrological diversity and controlling melt evolution. Synmagmatic extension at spreading ridges could produce similar results, and so account for many enigmatic features of mid-ocean ridge basalts (xenocrysts of anorthite and aluminous spinel, excess chlorine in basalts, and the pyroxene paradox). If syntexis is an important ridge-axis process, then assuming that fractional crystallization alone controls melt evolution may generate incorrect calculated parental melt compositions, and so lead to erroneous conclusions about mantle sources and processes.
GEOSCAN ID207560

 
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