HR: 09:15h
AN: V51B-04    [Abstracts]
TI: Is there a link between the shallow forearc devolatilization processes, island arc magma generation and deeply subducted metamorphic slabs?
AU: * Savov, I P
EM: savovi@si.edu
AF: Smithsonian Institution, National Museum of Natural History Dept.Mineral Sciences Constitution Ave./10th street, Washington, DC 20560 United States
AU: Ryan, J G
EM: ryan@chuma.cas.usf.edu
AF: University of South Florida, Department of Geology 4202 E.Fowler Ave.,SCA 528, Tampa, FL 33620 United States
AU: D'Antonio, M
EM: masdanto@unina.it
AF: University Federico II of Napoli, Dipartimento di Scienze della Terra, Napoli, 80138 Italy
AU: Fryer, P
EM: pfryer@soeast.hawaii.edu
AF: University of Hawaii, Department of Geology and Geophysics/SOEST 2525 Correa Road, Honolulu, HI 96822 United States
AB: Shallow slab devolatilization is not only witnessed through fluid expulsion at accretionary prisms, but is also evidenced by the occurrence of serpentinized mantle domains and/or mud volcanism in the forearc regions of the Izu-Bonin, Mariana and South Sandwich intraoceanic arc-basin systems. The protoliths of these forearc serpentinites are mantle harzburgites that have suffered large volume melt extraction (up to 25 %) prior to interactions with fluids released from downgoing plates.These forearc serpentinites all show U-shaped REE patterns and very low REE abundances (0.001-0.1 X chondrites). Relative to global depleted mantle values these rocks typically have one to two orders of magnitude lower HFSE, REE, Th and U contents. Interestingly, all forearc rocks thus far examined show extreme enrichments of fluid mobile elements (FME: B, As, Sb, Cs). Because the 11/10B, 7/6Li and 87/86Sr isotope systematics in forearc serpentinites point to non-seawater-related processes, studies of elemental excesses and anomalous isotopic signatures recorded in the forearc serpentinites allow assessment of how much of the subducted inventory is lost between 10 and 40 km depths. Based on similar but substantial enrichments of FME in the Mariana forearc serpentinites recovered at ODP Legs 125 and 195, we report large slab inventory depletions of B (75%); Cs (25%); As (15%); Li (15%) and Sb (8%); surprisingly low (generally less than 2%) depletions of Rb, Ba, Pb, U, Sr, and no depletions in REE and the HFSE. Such slab-metasomatized mantle wedge materials may be dragged to depths of arc magma generation, as proposed by Tatsumi (1986) and Straub and Layne (2001), and thus represent an unexplored class of mantle material, different in its origins and geochemical fingerprint from mantle rocks such as may be represented by arc xenoliths, or the basal ultramafic sections of high-pressure ophiolites.
DE: 1020 Composition of the crust
DE: 1025 Composition of the mantle
DE: 1030 Geochemical cycles (0330)
DE: 3660 Metamorphic petrology
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly