Petrology and geochemistry of Alkaline Basalts and Gabbroic xenoliths from Utila Island (Bay Islands, Honduras): Insights into back - Arc processes in the Central American Volcanic Arc

摘要

The island of Utila (Bay islands, Honduras), is situated in a back-arc environment, behind the Central American Volcanic Arc (CAVA). The Utila Volcanic Center (UVC) is Quaternary in age, based on geologic and stratigraphic relations with underlying carbonate rocks and is made up of three distinct, volcanic units: palagonite lapilli tuff, main lava flow and vent fades (in stratigraphic order). The UVC contains gabbroic xenoliths up to 5 cm in size embedded in lapilli and ash tuff. Alkaline basaltic (trachybasalt) flows are porphyritic extrusive rocks with phenocrysts composed of olivine, clinopyroxene, plagioclase and rare kaersutite. Gabbros are composed of amphibole, plagioclase, clinopyroxene, olivine, and Fe-Ti oxides. Primitive mantle normalized trace element patterns show enrichment in Ba, Nb, Ta and light rare earth elements (LREEs) similar to ocean island basalts (OIB) and share trace and major element characteristics similar to high-Nb basalt (HNB). Both basalts and gabbros Sr, Nd and Pb isotopes are distinct from OIB mantle sources in the Central American-Southern Caribbean region but similar to the Pacific MORB (Cocos Plate). A combination of OIB-like trace element characteristics and mid-ocean ridge basalt (MORB) -like isotopic ratios suggest that the UVC basalts originate from an enriched mantle source created by the hybridization of a depleted sub-arc mantle wedge in an earlier subduction stage of the CAVA. (C) 2019 Elsevier B.V. All rights reserved.