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Petrology and Geochemistry of West Philippine Basin Basalts and Early Palau-Kyushu Arc Volcanic Clasts from ODP Leg 195, Site 1201D: Implications for the Early History of the Izu-Bonin-Mariana Arc |
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| Authors: | SAVOV IVAN P; HICKEY-VARGAS ROSEMARY; D'ANTONIO MASSIMO; RYAN JEFFREY G; SPADEA PIERA |
| Institution: | 1 GEOLOGY DEPARTMENT, UNIVERSITY OF SOUTH FLORIDA, TAMPA, FL 33620, USA 2 DEPARTMENT OF EARTH SCIENCES, FLORIDA INTERNATIONAL UNIVERSITY, MIAMI, FL 33199, USA 3 DIPARTIMENTO DI SCIENZE DELLA TERRA, UNIVERSITY FEDERICO II, NAPOLI 80138, ITALY, AND OSSERVATORIO VESUVIANO, ISTITUTO NAZIONALE DI GEOFISICA E VULCANOLOGIA, NAPOLI, ITALY 4 DIPARTIMENTO GEORISORSE E TERRITORIO, UNIVERSITY OF UDINE, UDINE 33100, ITALY |
| Abstract: | Site 1201D of Ocean Drilling Program Leg 195 recovered basalticand volcaniclastic units from the West Philippine Basin thatdocument the earliest history of the Izu–Bonin–Marianaconvergent margin. The stratigraphic section recovered at Site1201D includes 90 m of pillow basalts, representing the WestPhilippine Basin basement, overlain by 459 m of volcaniclasticturbidites that formed from detritus shed from the Eocene–Oligoceneproto-Izu–Bonin–Mariana island arc. Basement basaltsare normal mid-ocean ridge basalt (N-MORB), based on their abundancesof immobile trace elements, although fluid-mobile elements areenriched, similar to back-arc basin basalts (BABB). Sr, Nd,Pb and Hf isotopic compositions of the basement basalts aresimilar to those of basalts from other West Philippine Basinlocations, and show an overall Indian Ocean MORB signature,marked by high 208Pb/204Pb for a given 206Pb/204Pb and high176Hf/177Hf for a given 143Nd/144Nd. Trace element and isotopicdifferences between the basement and overlying arc-derived volcaniclasticsare best explained by the addition of subducted sediment orsediment melt, together with hydrous fluids from subducted oceaniccrust, into the mantle source of the arc lavas. In contrastto tectonic models suggesting that a mantle hotspot was a sourceof heat for the early Izu–Bonin–Mariana arc magmatism,the geochemical data do not support an enriched, ocean islandbasalt (OIB)-like source for either the basement basalts orthe arc volcanic section. KEY WORDS: back-arc basalts; Izu–Bonin–Marianas; Philippine Sea; subduction initiation; Ocean Drilling Program Leg 195 |
| Keywords: | : back-arc basalts Izu– Bonin– Marianas Philippine Sea subduction initiation Ocean Drilling Program Leg 195 |
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