1994 Fiscal Year Final Research Report Summary
Isotope Geodynamics of the Mantle-Crust System
| Project/Area Number |
05453011
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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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 | KUMAMOTO UNIVERSITY |
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Principal Investigator |
SHIMIZU Hiroshi Kumamoto Univ., Fac.Sci Assoc.Professor, 理学部, 助教授 (60090544)
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| Project Period (FY) |
1993 – 1994
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| Keywords | La-Ca system / Sm-Nd system / REE pattern / Sobaegsan Massif / Kamiaso conglomerate / Pilbara Block / Precambrian / Geochemical cycle |
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| Research Abstract |
Geochemical evolution of mantle and crust was isotopically studied. Some of the results are summarized as follows.
1.Ce and Nd isotopic ratios and rare earth element (REE) abundances were determined for Precambrian gneisses of the Sobaegsan Massif, Korea, and for Precambrian gneiss clasts in the Jurassic Kamiaso conglomerate from Centra I Japan. The results suggest the existence of LREE-depleted mantle in the Archean of the area under consideration and the formation of LREE-enriched coutinetal crust fron the depleted mantle at the late Archean in the east Asia.
2.Isotopic data of Sm-Nd, La-Ce and Rb-Sr systems and REE abundances were reported for the Archean Marble Bar chert from the Towers Formation of the Salgash Subgroup, Warrawoona Group, Pilbara Block, Western Anstralia. The obtained isotopic and chemical data suggest substantially large contribution of hydrothermal solution derived from chondritic-or depleted-mantle for the cherts and inorganic origin of the cherts which contrasts to Phanerozoic biogenic cherts.
3.Depth profiles of Ce and Nd isotopic ratios and REE abundances are reported for three water columns of the North Pacific Ocean. The obtained profiles prove that bottom water keepsepsilon_<Nd> value around -5 at the North Pacifc Ocean even if surface waters show extremely low epsilon_<Nd> values due to local source-inputs. MORB-like negative epsilon_<Ce> values are observed only for the surface waters of one the profiles, suggesting preferential photo-reduction of MORB-derived Ce to continental-derived Ce. This photo-reduction, together with a large aeolian-dust input, is suggested to responsible for surface maxima of Ce-anomaly observed for the surface of the prfile.
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Research Products
(6 results)
