Sm-Nd, Rb-Sr isotope compositions of accretionary complex

Research Project

Project/Area Number	63540614
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	地質学一般
Research Institution	Kyushu University
Principal Investigator	HAMAMOTO Reiko Kyushu Univ., Science, Researcher, 理学部, 教務員 (40089917)
Co-Investigator(Kenkyū-buntansha)	YANAGI Takeru Kyushu Univ., Science, Professor, 理学部, 教授 (90037234)
Project Period (FY)	1988 – 1989
Project Status	Completed (Fiscal Year 1989)
Budget Amount *help	¥1,500,000 (Direct Cost: ¥1,500,000) Fiscal Year 1989: ¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1988: ¥1,100,000 (Direct Cost: ¥1,100,000)
Keywords	Sr isotope composition / Subduction complex / Pelagic sediment / Aeolian deposit / Shimanto terrain / Umber / Red shale / Pillow basalt / 赤色負岩 / Sm-Nd同位体比 / 島弧火山活動
Research Abstract	Aradani Formation of Hyuga Group in the Shimanto terrain is a subduction complex, Middle Eocene in age. 16 whole rock samples of greenstone-pelagic sequence (pillow basalt-umber-red shale-green shale black shale) in Aradani Formation were analyzed by Rb-Sr isotope dilution method. The results are as follows. (1) Average Rb concentration is 1.1 ppm, which is similar to average Rb content of MORB (Mid Oceanic Ridge Basalt). Rare elements pattern supported that the pillow basalt was MORB type. But its 87Sr/86Sr ratio(average 0.70876) is higher than MORB(average 87Sr/86Sr=0.703). It suggests that the basalt magma reacts to sea water. 87Sr/86Sr ratio of interpillow limestone indicate that the Sr ratio of sea water in Early Eocene is 0.70876. (2) 87Sr/86Sr variation of each umber and red shale samples relates to the distance from pillow basalt, and the variation indicates the umber is derived from mixing of basalic magma (hydrothermal) and red shale. (3) 87Sr/86Sr ratios of the pelagic sediments(red shale and black shale) are extremely higher than the ratio of sea water, therefore The pelagic sediments are aeolian deposits derived from old continental crusts.