INCITAP   20787
INSTITUTO DE CIENCIAS DE LA TIERRA Y AMBIENTALES DE LA PAMPA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Ultramafic xenoliths suites from Patagonia extra back-arc, Argentine: Evidences of lithospheric mantle metasomatized by OIB-like melts and subduction related fluids
Autor/es:
GERVASONI F.; CONCEIÇÃO R.V.; JALOWITZKI, T.L.R.; BERTOTTO G.W.; PRESSI L.F.
Lugar:
Vancouver (Canada)
Reunión:
Conferencia; Goldschmidt Conference; 2008
Resumen:
Mantle ultramafic xenoliths from Patagonia, Argentine, related to Andes extra back arc tectonic setting, represented by Prahuaniyeu (41°20’09.4”S, 67°54’08.1”W) and Chenque volcanoes (43°38’39.3”S, 68°56’22”W), are the focus of this studies. Prahuaniyeu is sited in the Northern of Somun Curá Plateau and corresponds to pyroclastic events that host the xenoliths in ash cones and small lavas flow. Chenque is located further South of the Somun Curá Plateau, and corresponds to lava flows and Oligocene alkaline basalts that host the ultramafic xenoliths. Prahuaniyeu ultramafic xenoliths are classified as spinel-lherzolites, harzburgites and spinelwebsterites, while Chenque xenoliths are spinel-lherzolites, phlogopite-harzburgite, phlogopite-lherzolite and websterites. Xenoliths textures of both volcanos are porfiroclastic and type-I protogranular. Phlogopite in the Chenque xenoliths indicates a hydrated lithospheric mantle underneath that region. Trace elements analyses in both xenolith sets show that the litospheric mantle in the studied areas is depleted compared to primitive mantle, but with LREE enrichment compared to HREE. Spidergram shows that Prahuaniyeu xenoliths (CeN/YbN=16,14-26,87) are enriched in calchophile elements (W, Pb, Sn, Sb) and in LILE (Ba e Sr). The HFSE (Th, Zr, Hf and Y) are depleted, though Nb and Ta are enriched. Chenque xenoliths (CeN/YbN = 0,39-15,02) are also enriched in the same calchoplhile elements, but they exhibit Ba depletion and Th extreme depletion. Batch melting modeling for both ultramafic xenoliths suggest they are product of more than 50% of primitive mantle partial melting, which indicates that these lithopheric mantle may be very ancient or several time processed. High Nb/Hf ratios for both xenolith sets suggest metasomatic processes through carbonatitic or OIB-like melt percolation. However, high Pb/Ce ratios suggest that liquids associated to subduction events also played an important role in the metasomatic processes.