Contrib Mineral Petrol (1996) 124: 29 — 43  Springer-Verlag 1996 Andrew C. Kerr · John Tarney · Giselle F. Marriner · Gerard Th. Klaver Andrew D. Saunders · Matthew F. Thirlwall The geochemistry and petrogenesis of the late-Cretaceous picrites and basalts of Curac  ao, Netherlands Antilles: a remnant of an oceanic plateau Received: 1 September 1995/Accepted: 5 February 1996 Abstract The island of Curaiao in the southern Cari- bbean Sea is composed mainly of a thick sequence ('5 km) of pillow lavas, grading upwards from pic- rites at the base of the exposed section, to basalts nearer the top. Modelling suggests that picrites are related to the basalts by fractional crystallisation. Initial radiogenic isotope ratios of the picrites have a re- stricted compositional range:   "#6.1 to #6.6, Sr/Sr"0.70296—0.70319; whereas the basalts dis- play a wider range of compositions:   "#6.6 to #7.6, Sr/Sr"0.70321—0.70671. This variation in isotope ratios between basalts and picrites may be due to the assimilation of altered oceanic crust (or possibly partial melts of such crust) by a picritic magma along with fractional crystallisation. The relatively narrow range of Nd and Pb isotopic compositions in the Curaiao lavas suggests either that the source region was homogeneous, or that melts from a heterogeneous mantle source were well mixed before eruption. Chon- dritic to slightly light rare earth element enriched pat- terns, combined with long-term light rare earth element depletion (positive   ), suggest that the lavas were formed by polybaric melting of spinel lherzolite, with small a contribution from garnet lherzolite melts. High- MgO lavas, the absence of a subduction related chemi- stry, and the chemical similarity to other oceanic pla- teaux, suggest a mantle plume origin for the Curaiao A.C. Kerr ( ) · J. Tarney · A.D. Saunders Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK G.Th. Klaver Rijks Geologische Dienst, Richard Holkade 10, 2000 AD, Haarlem, Holland G.F. Marriner · M.F. Thirlwall Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK Editorial responsibility: A Hofmann lava succession. The Curaiao volcanic sequence is part of an oceanic plateau formed at about 88—90 Ma, fragments of which are dispersed around the Caribbean as well as being obducted onto the western margin of Colombia and Ecuador. The occur- rence of high-Mg lavas throughout this Cretaceous Caribbean—Colombian igneous province requires anomalously hot mantle ('200° C hotter than ambient upper mantle) over a large part of a putative plume head, which is inconsistent with some mantle plume models. Introduction Oceanic plateaux such as Ontong Java, the Manihiki Rise and Kerguelen represent large areas of thickened (15—40 km) oceanic crust, and are caused by volumi- nous outpourings of basaltic magma (Mahoney 1987; Coffin and Eldholm 1993). Despite the obvious volu- metric importance of such vast volcanic provinces, our knowledge of the geochemistry of these plateaux is still limited, with most available data coming from the top few hundred metres of drill holes. Petrogenetic models for the origin of these plateaux therefore literally only ‘‘scratch the surface’’ (Coffin and Eldholm 1993). However if, through tectonic reconstructions and geochemical observations, the uplifted remnants of similar plateaux can be identified in the geological record, then the potential exists to examine in greater detail the roots of these large igneous bodies. This paper focuses on the geo- chemistry of a part of the Cretaceous Caribbean— Colombian oceanic plateau (Kerr et al. in press a, b), the volcanic succession of the island of Curaiao, along the southern margin of the Caribbean (Fig. 1). We will discuss the petrogenesis of these lavas, as well as reviewing the evidence for an original oceanic plateau setting.