Reynaud C., Jaillard Etienne, Lapierre H., Mamberti M., Mascle G.H. (1999). Oceanic plateau and island arcs of Southwestern Ecuador : their place in the geodynamic evolution of Northwestern South America. Tectonophysics, 307, p. 235-254. ISSN 0040-1951.
Titre du document
Oceanic plateau and island arcs of Southwestern Ecuador : their place in the geodynamic evolution of Northwestern South America
Année de publication
1999
Type de document
Article
Auteurs
Reynaud C., Jaillard Etienne, Lapierre H., Mamberti M., Mascle G.H.
Source
Tectonophysics, 1999,
307, p. 235-254 ISSN 0040-1951
Coastal Ecuador is made up of an oceanic igneous basement overlain by Upper Cretaceous to Lower Paleocene (approximately 98-60 Ma) volcaniclastic and volcanic rocks of island-arc affinities. The igneous basement, known as the Pinon Formation, locally dated at 123 Ma, consists of olivine-free basalts and dolerites. Relative to N-MORB, both types of rocks exhibit high concentrations in Nb (0.3-10.75 ppm), Ta (0.03-0.67 ppm), Th (0.11-1.44 ppm), light and medium rare earth elements, and low Zr (22-105 ppm) and Hf (0.59-2.8 ppm) contents, thus showing oceanic plateau basalts affinities. Most of these oceanic plateau basalts tholeiites display rather homogeneous epsilonNd(T = 123 Ma) ratios (approximately +7), with the exception of two rocks with higher (+10) and lower (+4.5) epsilonNd(T = 123 Ma), respectively. All these basalts plot, with one exception, within the ocean island basalts field. Their (87Sr/86Sr)i ratios are highly variable (0.7032-0.7048), probably due to hydrothermal oceanic alteration or assimilation of altered oceanic crust. The rocks of the Pinon Formation are geochemically similar to the oceanic plateau tholeiites from Nauru and Ontong Java Plateaus and to the Upper Cretaceous (92-88 Ma) Carribbean Oceanic Plateau lavas. The basalts and dolerites of the Upper Cretaceous-Lower Paleocene island arcs show calc-alkaline affinities. The epsilonNd ratios to Cretaceous intra-oceanic are rocks from North, Central and South America and from the Greater Antilles. Since the Pinon oceanic plateau tholeiites are locally overlain by early-Late Cretaceous sediments (approximately 98-83 Ma) and yielded locally an Early Cretaceous age, they do not belong to the Late Cretaceous Caribbean Oceanic Plateau. The basement of coastal Ecuador is interpreted as an accreted fragment of an overthickened and buoyant oceanic plateau... (D'après résumé d'auteur)
