HR: 1340h
AN: V43B-1586    [Abstracts]
TI: Geochemical characteristics of turbidites in piston core samples from Western Hawaiian ridge
AU: * Fujimoto, Y
EM: fuji_yu1984@yahoo.co.jp
AF: Department of Earth Sciences, Kumamoto University, 2-39-1, Kurokami, Kumamoto, 860-8555 Japan
AU: Yokose, H
EM: yokose@sci.kumamoto-u.ac.jp
AF: Department of Earth Sciences, Kumamoto University, 2-39-1, Kurokami, Kumamoto, 860-8555 Japan
AU: Kanamatsu, T
EM: toshiyak@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15, Natsushima, Yokosuka, 237-0061 Japan
AU: Ishii, T
EM: ishii@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, Minamidai 1-15-1, Nakano-ku, Tokyo, 164-8639 Japan
AB: In order to understand the sequence of huge landslide on the submarine flank of the west Hawaii Island, two piston core samples, PC14 and PC15, were obtained from western offshore Hawaiian Ridge. The sampling sites, PC14 (20° 00.02'N, 158° 27.99'W, -4344 m) and PC 15 (20° 25.42'N, 159° 26.66'W, -4543 m), are 150 km SSW and 180 km SW of Oahu, respectively. The sample of PC14 is 963 cm long and the first magnetic polarity change is observed at 760.1 cm below sea floor (bsf). The sample of PC15 is 943 cm long and the first magnetic polarity change is observed at 625.3 cm bsf. Because Hawaii Island have been considered to construct last million years, normally magnetized upper samples of the cores are appropriate to our investigation. Remarkable volcaniclastic sand layers, which were originated from turbidites, are observed restrictedly between 60 and 369 cm bsf in the PC14 core sample and between 77 and 276 cm bsf in the PC15 core sample. Four remarkable turbidite layers, 2-5 cm thick, are observed in PC14 core sample:at 110 cm bsf, 140 cm bsf, 152 cm bsf, and 297 cm bsf. Light brown massive mud layers with laminas of very thin volcanic silty sand (< 1cm) are observed at 233 cm bsf and 297 cm bsf and the lamina zones are approximately 20 cm thick. Three remarkable turbidite layers, 2-5 cm thick, are observed in PC15 core sample:at 144 cm bsf, 244 cm bsf and 251 cm bsf. Some laminated volcanic silty sand layers are observed faintly. Major elements composition of representative volcanic glasses from both the PC 14 and 15 turbidite layers were analyzed using EPMA. Bulk rock chemical composition of the turbidite layers and massive mud, which were collected from the core samples 10 cm interval, were also determined with XRF. All the samples were washed with abundant distilled water to minimize sea water contamination. Although the lower turbidite layers in the PC14 core sample are little bit higher in MgO, the other samples are almost identical to each other both in glass compositions and bulk compositions. Analyzed bulk compositions indicate mixing trend between sandy turbidite layers and pelagic clay. Mud layer accompanied with turbidite flow can be distinguished from pelagic clay by MgO, CaO and K₂O variation diagram even in homogeneous appearances. All the volcanic glass compositions are poor in alkaline elements and are classified into tholeiitic basalt. Because most of their sulfur contents are less than 200 ppm, their source lavas were solidified at subaerial or shallow submarine conditions. The chemical variation of glass data from the turbidites are overlapped with previously reported Mauna Loa composition. Therefore, the turbidites of the PC14 and PC15 samples could be derived from Mauna Loa volcano in ancient shield stage.
DE: 3022 Marine sediments: processes and transport
DE: 3070 Submarine landslides
DE: 6063 Volcanism (5480, 8450)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005