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La Désirade Island in the Cenozoic Lesser Antilles forearc region exposes a pre-Tertiary complex of oceanic volcanic, plutonic, and dike rocks. Previous work has established the stratigraphy and structure of the La Désirade igneous complex and also its late Mesozoic age. Dredge hauls from the nearby submerged Désirade fault scarp consist of similar volcanic and dike rocks plus greenstone, diabase, and gabbro. The composite section from island and submarine escarpment resembles upper oceanic crust but of controversial origin, original tectonic setting, and geodynamic significance.

More precise ages for the La Désirade igneous complex and its individual members provide important constraints on proposed tectonic models. We reanalyzed Radio-laria from intralava sediments in basaltic pillow lava and zircon from trondhjemite to pinpoint their age. The radiolarian assemblage correlates with those of formations in east-central and west-central Mexico. The Mexican radiolarian faunas are chronostratigraphically calibrated by co-occurring ammonites and Buchia. Abundant Mexican biostratigraphic and chronostratigraphic data (ammonites, Radiolaria, and Buchia) constrain the composite radiolarian assemblage from six localities on La Désirade to zone 4, upper subzone 4β (mid-upper Tithonian). Using the new chemical abrasion (CA) thermal ionization mass spectrometry zircon method of Mattinson, the results from three zircon fractions from trondhjemite provide a 143.74 ± 0.33 Ma U-Pb age for the La Désirade igneous complex. Combined biostratigraphic, chronostratigraphic, and geochronometric data put the geochronologic age for the mid-late Tithonian near 143.74 Ma, a maximum for the latest Jurassic.

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