HR: 18:00h
AN: V24A-07    [Abstracts]
TI: QUATERNARY ADAKITE - NB-ENRICHED BASALT ASSOCIATION IN THE WESTERN TRANS- MEXICAN VOLCANIC BELT: IS THERE ANY SLAB MELT EVIDENCE?
AU: * Petrone, C M
EM: chiara.petrone@unifi.it
AF: CNR - Istituto Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, Firenze, FI 50121, Italy
AU: Ferrari, L
EM: luca@geociecias.unam.mx
AF: Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AB: A spatial and temporal association between adakitic rocks and Nb-enriched basalts (NEB) has been recognised for the first time in the western sector of the Trans-Mexican Volcanic Belt in the San Pedro-Cerro Grande Volcanic Complex (SCVC). The SCVC is composed of subalkalic intermediate to felsic rocks, spanning in composition from high-silica andesites to rhyolites, and by the young transitional hawaiite and mugearite lavas of Amado Nervo shield volcano. Intermediate to felsic rocks of the SCVC show many geochemical characteristics of typical adakites, such as high Sr/Y ratios (up to 180) and low Y (< 18 ppm) and Yb contents. Mafic Amado Nervo rocks have high TiO2 (1.5-2.3 wt), Nb (14-27 ppm), Nb/La (0.5-0.9) and high absolute abundances of HFSE similar to those shown by NEB. However, the Sr and Nd isotopic signature of SCVC rocks is different from that shown by typical adakites and NEB. Although the adakites-NEB association has been traditionally considered as a strong evidence of slab-melting, we suggest that other processes can lead to its generation. Here we show that parental magmas of adakitic rocks of the SCVC derive their adakitic characteristic from high pressure crystal fractionation processes of garnet, amphibole and pyroxene of a normal arc basalt. On the other hand, Amado Nervo Na- alkaline parental magmas have been generated by sediment melting plus MORB-fluid flux melting of a heterogeneous mantle wedge, consisting of a mixture of depleted and an enriched mantle sources (90DM+10EM). We can not exclude a contribution to the subduction component of slab melts, because the component signature is dominated by sediment melt, but we argue that caution is needed in interpreting the adakites-NEB association in a genetic sense
DE: 8410 Geochemical modeling (1009, 3610)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly