Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Journal of the Geological Society

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by FURNES, H. Articles by STILLMAN, C. J. Search for Related Content GeoRef GeoRef Citation

The geochemistry and petrology of an alkaline lamprophyre sheet intrusion complex on Maio, Cape Verde Republic

C. J. STILLMAN²

¹ Geologisk Institutt avd.A, Allegt. 41, 5041 Bergen, Norway
² Department of Geology, Trinity College, Dublin 2, Ireland

The Atlantic island of Maio in the Cape Verde archipelago has a Basement Complex of Mesozoic and Tertiary age which is invaded by an intense swarm of sheet intrusions ranging in age from c. 16 to 8 Ma. These cut an alkaline ultramafic, mafic and felsic plutonic complex (Central Igneous Complex) and its host, a segment of Jurassic ocean floor with pillow lavas and abyssal sediments. The Basement Complex is dissected and unconformably overlain by a sequence of lavas of basanitic and nephelinitic composition.

The sheet intrusions comprise sills and dykes of alkaline lamprophyre, many of which are aphyric or sparsely porphyritic. Phenocrysts are predominantly clinopyroxene, with smaller amounts of olivine and Ti-magnetite. Microphenocrysts are kaersutite, apatite and biotite. The groundmass is dominated by potassium feldspar and analcime. Calcic plagioclase is extremely rare. Chemically the intrusions are basanitic, with major and minor element compositions directly comparable with the Neogene and Pleistocene basanitic lavas which cap the island. Calculations based on observed phenocryst phases suggest that the liquids involved in the crystallization of the sheet intrusions may have been derived by crystal fractionation from a range of basanitic parents. These were similar to those from which the later lavas were generated, but modified to some extent by variable water-rock interactions enhanced by trapped volatiles.

This article has been cited by other articles:

				G.H.-N. CHAN, J. MALPAS, C. XENOPHONTOS, and C.-H. LO Magmatism associated with Gondwanaland rifting and Neo-Tethyan oceanic basin development: evidence from the Mamonia Complex, SW Cyprus Journal of the Geological Society, May 1, 2008; 165(3): 699 - 709. [Abstract] [Full Text] [PDF]

				V. V. Ivanikov, A. S. Rukhlov, and K. Bell Magmatic Evolution of the Melilitite-Carbonatite-Nephelinite Dyke Series of the Turiy Peninsula (Kandalaksha Bay, White Sea, Russia) J. Petrology, November 1, 1998; 39(11-12): 2043 - 2059. [Abstract] [Full Text] [PDF]