| Project/Area Number |
06640635
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
地球化学
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| Research Institution | OKAYAMA UNIVERSITY |
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Principal Investigator |
OKANO Osamu OKAYAMA UNIV., GRADUATE SCHOOL OF NATURAL SCIENCE & TECHNOLOGY,RESEARCH ASSOCIATE, 大学院自然科学研究科, 助手 (10233355)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Noboru KOBE UNIVERSITY,DEPT.EARTH SCIENCES,PROFESSOR, 理学部, 教授 (90030791)
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| Project Period (FY) |
1994 – 1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1995: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1994: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Keywords | METEORITE / LL-CHONDRITE / ALKALI DIFFERENTIATION / DATING / RB-SR AGE / アルカリ分化 / 年代 |
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| Research Abstract |
Yamato-74442, a brecciated LL-group chondrite, consists of fragments with igneous texture, chondrules, mineral fragments, and host. The fragments involve K-rich fragments as well as normal ones. Typically, both fragments consist mainly of euhedral porphyritic olivines and a few orthopyroxenes in a glassy groundmass. EPMA analyzes for these fragments indicate that olivines and orthopyroxenes have a range of Fe/Fe+Mg ratio of 27.19-31.33 and 20.10-26.91 mol%, respectively. There is no significant difference in these ratios between K-rich (Na_2O/K_2O<less than or equal>1) and normal fragments. The K_2O contents of groundmass for K-rich fragments range from 0.51 to 4.89 wt% and that of the normal fragments is 0.38-0.90 wt%. K_2O contents of groundmass very from fragment to fragment but are rather homogeneous in a single fragment.
Rb-Sr isotopic determination on eighteen K-rich fragments (1.5 to 9.5mg in weight) gave an internal isochron age of 4.516 (]SY.+-。[) 0.028 Ga and initial <@D187@>D1Sr/<@D186@>D1Sr ratio of 0.70025 (]SY.+-。[) 0.00168. This age is somewhat old compared with a whole rock isochron age of LL chondrites (4.493 (]SY.+-。[) 0.018 Ga ; Minster and Allegre, 1981). From a comparison of the present result with others so far reported, it is inferred that the alkali differentiation as observed in Yamato-74442 probably occurred during a process of accumulation from LL chondrite parent material in the early solar nebula.
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