Journal of Petrology | Volume 38 | Number 6 | Pages 677-702 | 1997
© Oxford University Press 1997
Cretaceous Basaltic Terranes in Western Columbia: Elemental, Chronological and Sr–Nd Isotopic Constraints on Petrogenesis
1 Department of Geology, University of Leicester University Road, Leicester LE1 7RH, UK
2 Department of Geology, Royal Holloway University of London Egham, London TW20 0EX, UK
3 Ingeominas—Regional Pacifico AA 9724, Cali, Colombia
4 College of Oceanography, Oregon State University Corvallis, OR 97331, USA
Received August 19, 1996; Revised typescript accepted January 10, 1997
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Abstract |
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Accreted terranes comprising Mid to Late Cretaceous picrites, basalts and dolerites occur in three north–south trending belts in western Colombia, in the Central Cordillera, Western Cordillera and along the Pacific coast. The geochemistry of these rocks is consistent with an oceanic plateau (plume-related) origin, and they most probably formed in the Pacific as part of the Caribbean oceanic plateau. These igneous rocks display small but significant inter-cordillera variations, being younger and more depleted in incompatible trace element ratios (and with more positive 
Nd values) to the west. The igneous rocks of the Pacific coast (Serranía de Baudó) are dated at 73–78 Ma (40Ar/39Ar), and those of the Western Cordillera at 
90 Ma, whereas the volcanics of the Central Cordillera are believed to be older than 100 Ma. Most of the igneous rocks are basaltic, and it is suggested that they have fractionated from picritic primary magmas, generated by partial melting within a hot mantle plume. Variable and positive Nd values reveal that the plume must have been heterogeneous, originating from a mantle source with a long-term history of depletion. Partial melt modelling suggests that the composition of the basalts requires at least some input from a mantle source region containing garnet and that the extent of partial melting required to reproduce the composition of the erupted basalts is of the order of 20%. Mixing of melts from different depths, either in the mantle melting column or during fractionation in lithospheric magma chambers, can explain the relative homogeneity of basaltic lavas erupted to form this (and other) oceanic plateaux. The Caribbean–Colombian oceanic plateau may have formed at an oceanic spreading centre, and valuable comparisons can be made between Iceland and the Caribbean–Colombian plateau.
KEY WORDS: basalt; Colombia; geochemistry; mantle plume; oceanic plateau
* Corresponding author. Telephone: +44 116 2523639. Personal fax: +44 116 2523639. Department fax: +44 116 2523918. e-mail: ack2{at}le.ac.uk
Present address: Graduate School of Oceanography, Rhode Island University, Narragansett, RI 02882, USA
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