HR: 1340h
AN: T13C-1479    [Abstracts]
TI: Onset of subduction in eastern Cuba (Sierra del Convento melange): geochemical evidences for a partially melted young slab.
AU: Lazaro, C
EM: clazaro@ugr.es
AF: Departamento de Mineralogía y Petrología. Universidad de Granada, Avda. Fuentenueva s/n, Granada, 18002, Spain
AU: * Garcia-Casco, A
EM: agcasco@ugr.es
AF: Departamento de Mineralogía y Petrología. Universidad de Granada, Avda. Fuentenueva s/n, Granada, 18002, Spain
AB: Geochronological and regional geological arguments indicate the onset of subduction of the Protocaribbean (Atlantic) lithosphere during the Aptian (ca. 120 Ma). Exotic blocks of MORB-like amphibolite and associated tonalite-trondhjemite from Sierra del Convento melange in eastern Cuba document this early stage of subduction. Major and trace element geochemical signatures and Sr-Nd isotope data of these blocks indicate that oceanic crust underwent partial melting processes during subduction. Theoretical melting models suggest that the trondhjemites are not oceanic plagiogranite formed after differentiation or partial melting of MORB at oceanic ridges, but instead that they formed by 1-30 wt % water-saturated melting of epidote±garnet amphibolite. REE patterns of the trondhjemites are fractionated (1 < (La/Yb)n < 16.8), with LREE enrichment and flat or slightly depleted HREE patterns which compare well with adakitic melts formed by partial melting of mafic material at moderate to high pressure. Indeed, trondhjemites from Sierra del Convento have some of the geochemical features of Cenozoic adakites, including SiO2>56%, 3.5%<Na2O<7.5%, (K2O/Na2O) ~ 0.42, Mg# ~ 50, Ni =20-40 ppm, Cr =30-50 ppm, LREE enrichment, HREE depletion, and high La/Yb and Sr/Y. However, the trondhjemites from Sierra del Convento are more comparable to acid rocks from Catalina Schist melange (California) considered to be primary slab melts which did not react with the mantle wedge. In agreement with major and trace element geochemistry, the Sr-Nd isotope systematic of selected amphibolites and trondhjemites can be explained by a two stage model involving a) generation of MORB-like basalts and b) partial melting of subducted MORB. Partial melting of amphibolite in the Sierra del Convento melange is consistent with the onset of subduction of young oceanic lithosphere of the Protocaribbean.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting