Geochemistry and genesis of behind-arc basaltic lavas from eastern Nicaragua

The petrology and chemistry of the Behind the Volcanic Front (BVF) lavas from eastern mainland Nicaragua and the adjacent Great Corn Island in the Caribbean Sea illustrate the complex nature of sources and processes operating in such a tectonic setting The older, Early Miocene (similar to 17 Ma) group of low-Ti (<1 wt %) basalts-andesites is characterized by a strong LILE/I-IFSE depletion The low-Ti lavas from El Rama and El Bluff areas are interpreted as relics of Early Miocene volcanic arc, largely analogous to the nowadays extinct Coyol arc further west However, these rocks differ in some parameters from the modern volcanic front lavas, most notably in having lower delta(7) Li values, Ba/Yb ratios and lower U contents The younger high-Ti (Ti> 15%) lavas, rich in other HFSE as well, are represented both by alkaline (Quaternary trachybasalts Volcan Azul and Kukra Hill) and subalkaline (basalts-basaltic andesttes Late Miocene, similar to 11 Ma Great Corn Island and Quaternary, Pearl Lagoon) volcanic rocks. The Lae Miocene and Quatemary high-T1 BVF lavas probably represent small-volume decompression melts of a source similar to that of the OIB-like magmas, most likely upwelling asthenosphere having a strong Galapagos mantle imprint. The positive Sr-Nd isotopic correlation indicates an interaction between this 01B component and a depleted lithospheric mantle modified by a subduction-relatecl influx of Sr and, to a lesser extent, other hydrous fluid-mobile elements However, the rocks show no recognizable influence of the modern subduction The feeble trace-element (e g., slightly elevated Ba, K, and Sr at some localities) and a more pronounced Sr-Li isotopic subduction-related signal stems most likely from the Miocene convergence episode Subduction of the Galapagos hot-spot tracks in Costa Rica produces magmas that can be readily recognized by their elevated Sr isotopic ratios due to seafloor alteration. the Nd isotopic signature remains unaffected Such a component with relatively unradiogenic Nd and radiogenic Sr is required in the source of the modern volcanic front lavas but is not needed to explain the variation in the studied BVF dataset Terrains with multiepisodic subduction history should be considered with caution, as the lavas generated by decompression melting of the asthenosphenc source in the back-arc region may bear a geochemical Imprint of the fossil and not the modern subduction component stored in the local lithospheric mantle (C) 2010 Elsevier B.V. All rights reserved