HR: 10:45h
AN: V52A-02    [Abstracts]
TI: Tracing Mantle and Slab Contributions to the Proto Izu-Bonin-Mariana Arc Magmatism: Mineralogical and Geochemical Studies of a Volcaniclastic Sequence From the Palau-Kyushu Ridge, West Philippine Basin
AU: * D'Antonio, M
EM: masdanto@unina.it
AF: Dept. Scienze della Terra, Univ. Federico II, L.go S.Marcellino 10, Napoli, Italy, Napoli, 80138 Italy
AU: Savov, I P
EM: savovi@si.edu
AF: Dept. Mineral Sciences, National Museum of Natural History, Smithsonian Inst., Washington, DC 20560-0119 United States
AU: Hickey-Vargas, R
EM: hickey@fiu.edu
AF: Dept. Earth Sciences, Florida International Univ., 11200 SW 8th Street, Miami, FL 33199 United States
AU: Spadea, P
EM: piera.spadea@dgt.uniud.it
AF: Dept. Georisorse e Territorio, Univ. of Udine, Via Cotonificio 114, Udine, 33100 Italy
AU: Lockwood, J
EM: geohaz@aloha.net
AF: Geohazards Consultants, Inc., PO Box 479, Volcano, HI 96785 United States
AB: The submerged Palau-Kyushu Ridge (PKP) is the remnant of a proto-Izu-Bonin-Mariana (IBM) island arc, which was active since about 48 to 35 Ma ago, contemporaneously to subduction of the Pacific plate beneath the spreading West Philippine basin. Volcanic activity along the PKR stopped in response to plate reorganization, and renewed subduction which initiated with an E-W rifting, separating the PKR from the Iwo Jima ridge in the north and the West Mariana Ridge in the south. A 400 m- thick sequence of turbidites containing volcaniclastic sediments, underlain by basin basalt with a magnetic age of 49 Ma, was drilled during ODP Leg 195 at Site 1201, located about 200 km off the western slope of the PKR. These volcaniclastics represent a unique opportunity to sample the past activity of the PKR. Therefore, the mineralogical and geochemical features of these volcaniclastics are used to investigate the petrogenesis of the proto-IBM arc magmas, and the temporal evolution of the currently active intra-oceanic IBM island arc and related back-arc basins. From the recovered turbidite sequence, many volcaniclasts (mm- to cm- sized) and fresh pyroxene and plagioclase grains (xenocrysts) were collected and investigated from a petrological point of view. Most of the clasts are angular (breccias), and no rounded grains occur in the xenocrysts population, suggesting that these materials were incorporated in the turbidites fairly quickly after removal from the slopes of the PKR. The analyzed clasts range in composition from basalt (one sample) to basaltic andesite (the majority); a few samples showing a high total alkalis content like mugearite, are classified as altered basalts enriched in alkalis by hydrothermal alteration. Trace element abundance and distribution are indicative of a calk-alkaline affinity, also evidenced by high LILE/HFSE and LREE/HREE ratios. Initial Sr and Nd isotope ratios indicate derivation of the parental magmas from an arc-like mantle source, suggesting the involvement of a slightly enriched subduction-derived component, in agreement with the intra-oceanic character of the PKR.
DE: 1040 Isotopic composition/chemistry
DE: 3022 Marine sediments--processes and transport
DE: 3640 Igneous petrology
DE: 3670 Minor and trace element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly