| Summary: | ISBN : 978-1-897095-35-5 International audience The Barth Island Intrusive Complex (BIC) comprises spatially associated, concentric ovals of leucotroctolite, monzonite, and ferrodiorite, three members of the ‘anorthosite suite’. Concordance of contact orientations with structures in adjacent rock types, in all the rocks of the BIC, have resulted in previous interpretations of the BIC as either the result of differentiation of a single pulse of basic magma, or the result of pulses of different, broadly contemporaneous magmas. New mapping and ID-TIMS U-Pb zircon geochronology indicate that ferrodiorite and monzonite in the outer part of the BIC are closely contemporaneous, with emplacement ages of ca. 1318, while the central leucotroctolite unit is older, emplaced at ca. 1332 Ma. Spatial and geometric considerations suggest the magmas of the BIC were emplaced through the same conduit, as a cone structure. The difference in age between the inner and outer units of the BIC indicates that they were not part of the same melting event, suggesting that rock types of the anorthosite suite are not simply related by differentiation or AFC processes at any depth. Rock densities indicate the ferrodiorite and monzonite magmas could have been stably stratified together at depth; whole rock chemical results do not preclude their being products of conjugate immiscible liquids.
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