Abstract

New radiolarian assemblages of Late Jurassic age were extracted from seven chert localities of the basement complex of La Désirade Island (Guadeloupe), the oldest geological unit of the Lesser Antilles arc and the eastern Caribbean region. These fauna range in age from Kimmeridgian or early Tithonian to early or early late Tithonian, showing that La Désirade cherts are not all coeval, contrary to what was established by previous studies. Furthermore, the close spatial association of cherts and volcanic elements composed of basaltic flows and volcaniclastics suggests a mixed setting of hydrothermal siliceous deposits and biogenous sedimentation consistent with an arc-related oceanic setting rather than an ophiolite-type oceanic crust. As the youngest age is obtained to the northwest of the basement complex whereas older data are found to the southeast, it also suggests that La Désirade basement complex may have undergone some structural stacking consistent with an accretion-type geodynamic setting. Our biochronological data provide a preliminary tectonic model of an eastward subduction zone for Lesser Antilles arc basement emplacement during the Mesozoic.

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