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Mafic Pegmatites Intruding Oceanic Plateau Gabbros and Ultramafic Cumulates from Bolivar, Colombia: Evidence for a 'Wet' Mantle Plume? |
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| Authors: | KERR ANDREW C; TARNEY JOHN; KEMPTON PAMELA D; PRINGLE MALCOLM; NIVIA ALVARO |
| Institution: | 1 DEPARTMENT OF EARTH SCIENCES, CARDIFF UNIVERSITY, PARK PLACE, CARDIFF CF10 3YE, UK 2 DEPARTMENT OF GEOLOGY, UNIVERSITY OF LEICESTER, UNIVERSITY ROAD, LEICESTER LE1 7RH, UK 3 NERC ISOTOPE GEOSCIENCES LABORATORY, c/o BRITISH GEOLOGICAL SURVEY, KEYWORTH, NOTTINGHAM NG12 5GG, UK 4 SCOTTISH UNIVERSITIES ENVIRONMENTAL RESEARCH CENTRE, EAST KILBRIDE, GLASGOW G75 0QF, UK 5 INGEOMINAS—REGIONAL PACIFICO, AA 9724, CALI, COLOMBIA |
| Abstract: | The fault-bounded Bolívar Ultramafic Complex (BUC) onthe eastern fringes of the Western Cordillera of Colombia wastectonically accreted onto the western coast of South Americain the late Cretaceous–early Tertiary, along with pillowbasalts of the Caribbean–Colombian Oceanic Plateau (CCOP).The complex consists of a lower sequence of ultramafic cumulates,successively overlain by layered and isotropic gabbroic rocks.The gabbros grade into, and are intruded by, mafic pegmatitesthat consist of large magnesiohornblende and plagioclase crystals.These pegmatites yield a weighted mean 40Ar–39Ar step-heatingage of 90·5 ± 0·9 Ma and thus coincidewith the timing of peak CCOP volcanism. The chemistry of theBUC is not consistent with a subduction-related origin. However,the similarity in Sr–Nd–Pb–Hf isotopes betweenthe CCOP and the BUC, in conjunction with their indistinguishableages, suggests that the BUC is an integral part of the plume-derivedCCOP. The parental magmas of the Bolívar complex wereprobably hydrous picrites that underwent 20–30% crystallization.The residual magmas from this fractionation contained |
| Keywords: | : mantle plume Caribbean Colombia wet melting oceanic plateau pegmatite |
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