V11D-3088
Variably Depleted Peridotites from Loma Caribe (Dominican Republic): A Possible Record of Subduction Initiation beneath the Greater Antilles Paleo-Arc
Monday, 14 December 2015
Poster Hall (Moscone South)
Claudio Marchesi1,2, Carlos J Garrido2, Joaquín A Proenza3, Lidia Butjosa3 and John F Lewis4, (1)University of Granada, Departamento de Mineralogía y Petrología, Granada, Spain, (2)CSIC-UGR, Instituto Andaluz de Ciencias de la Tierra, Armilla (Granada), Spain, (3)Universitat de Barcelona, Departament de Cristal•lografia, Mineralogia i Dipòsits Minerals, Barcelona, Spain, (4)George Washington University, Dept. of Earth and Environmental Sciences, Washington, DC, United States
Abstract:
Several mantle peridotite massifs crop out as isolated dismembered bodies in tectonic belts along the northern margin of the Caribbean plate. Among these bodies, the Loma Caribe peridotite forms the core of the Median Belt in central Dominican Republic. This peridotite massif is mainly composed of Cpx-bearing harzburgite, harzburgite, lherzolite and (Opx-bearing) dunite, locally intruded by gabbroic rocks of Barremian age (~ 125 Ma). Mg# of olivine increases from lower values in lherzolite (90), to higher values in Cpx-harzburgite (91), harzburgite (92) and dunite (92-94). Cr# of spinel spans from 0.23 in lherzolite to 0.87 in dunite, and progressively increases from fertile to refractory lithologies. These variations overlap the mineral compositions of both abyssal and supra-subduction zone peridotites. The sample/chondrite REE concentrations of whole rocks are variable (0.002 < LREEN < 0.11 and 0.003 < HREEN < 1.02), and the HREE contents generally reflect the fertility of the samples. Similar to mineral chemistry, these trace element abundances overlap the compositions of both highly depleted supra-subduction and more fertile abyssal peridotites. Peridotites are variably enriched in the most incompatible and fluid-mobile trace elements (Cs, Rb, Ba, Th, U and Pb), and show negative anomalies of Nb and Ta. MREE/HREE fractionations in whole rocks and clinopyroxene support that these rocks are residues after initial fractional melting (~ 4%) in the garnet stability field and additional melting (~ 5-15%) in the spinel peridotite facies. The relative enrichment in incompatible and fluid-mobile elements (e.g., LILE and LREE) probably resulted from interaction of melting residues with ascending fluids/melts. We interpret the compositional variability of the Loma Caribe peridotite as reflecting different stages of generation of sub-oceanic mantle lithosphere during the Lower Cretaceous initiation of subduction beneath the Greater Antilles Paleo-arc.
