Japan Geoscience Union Meeting 2016

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International Session (Oral)

Symbol S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT09] Hard-Rock Drilling: Oceanic Lithosphere to Continental Crust Formation

Mon. May 23, 2016 10:45 AM - 12:15 PM Convention Hall A (2F)

Convener:*Yoshihiko Tamura(R & D Center for Ocean Drilling Science, Japan Agency for Maine-Earth Science and Technology), Tomoaki Morishita(School of Natural System, Colleage of Science and Technology, Kanazawa University), Susanne Straub(Lamont-Doherty Earth Observatory, Columbia Univ., USA), Takashi Sano(Department of Geology and Paleontology, National Museum of Nature and Science), Susumu Umino(Department of Earth Sciences, Kanazawa University), Eiichi TAKAZAWA(Department of Geology, Faculty of Science, Niigata University), Katsuyoshi Michibayashi(Institute of Geosciences, Shizuoka University), Chair:Eiichi TAKAZAWA(Department of Geology, Faculty of Science, Niigata University), Takashi Sano(Department of Geology and Paleontology, National Museum of Nature and Science)

11:15 AM - 11:30 AM

[SIT09-09] A seamount on top of Ontong Java Plateau was created by remelting of plateau lithosphere by plate flexure

★Invited papers

*Takeshi Hanyu1, Maria Luisa Tejada1, Kenji Shimizu1, Osamu Ishizuka2, Jun-Ichi Kimura1, Qing CHANG1, Ryoko Senda1, Takashi Miyazaki1, Kosuke T. Goto2, Akira Ishikawa3 (1.Japan Agency for Marine-Earth Science and Technology, 2.Geological Survey of Japan, AIST, 3.The University of Tokyo)

Keywords:oceanic plateau, lithosphere, recylced material

The Ontong Java Plateau (OJP) was formed by a main volcanism occurred at ca. 120 Ma, followed by several pulses of the late-stage volcanism on and along the margins of the plateau. The origin of the late-stage volcanism is poorly understood because of limited rock sampling. We present the age and geochemical composition of basalts dredged from Nuugurigia Atoll that stands on the plateau basement, possibly erupted in the late-stage volcanism. The 40Ar/39Ar age of dredged basalts is ca. 20 Ma, younger than any other known late-stage volcanism on OJP (down to 34 Ma), and is coincided with the collision of the plateau with the proto-Solomon arc. These basalts have enriched isotopic signatures pointing towards EM1 distinct from any other rocks thus far collected from OJP. Moreover, they show unusual trace element composition with Sr enrichment and Zr-Hf depletion relative to the elements with similar incompatibility. Such isotopic and trace elemental feature are shared with quartz-bearing garnet pyroxenite xenoliths rarely found from Solomon Islands (Ishikawa et al., 2007). Ishikawa et al. inferred that such pyroxenite was derived from delaminated granulitic lower crust and was part of the OJP lithosphere underplated beneath the plateau lithosphere via the mantle upwelling responsible for the main plateau-forming volcanism. We suggest that the basalts in the late-stage volcanism at Nuugurigia were products of rejuvenated melting of such pyroxenite. Melt transport through the lithosphere may have been facilitated by plate flexure occurred just south of the atoll when the plateau collided with the proto-Solomon arc around 20 Ma.