1990 Fiscal Year Final Research Report Summary
Crustal Evolution : Evidence from Ce and Nd Isotope Ratios and REE Abundances
| Project/Area Number |
01470032
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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 |
分析・地球化学
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| Research Institution | The University of Tokyo |
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Principal Investigator |
SHIMIZU Hiroshi Univ. of Tokyo, Fac. of Sci., Assoc. Prof., 理学部, 助教授 (60090544)
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| Project Period (FY) |
1989 – 1990
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| Keywords | La-Ce systematics / Sm-Nd systematics / REE abundance pattern / Archean crust / Ce-anomaly / iron-formation / chert / ferromanganese nodule |
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| Research Abstract |
In order to make clear chemical evolution of continental crust, Ce and Nd isotopic ratios and rare-earth element (REE) abundances were presented for the Precambrian continental rocks as well as recent marine sediments and Cenozoic volcanic rocks. The obtained results are as follows.
1. Geochemical studies on the Archean gneisses and iron-formations from West Greenland show that the sources of these Archean rocks had a mainly chondritic or mantle-like light-REE-depleted nature rather than a continental-like light-REE-enriched nature. These results suggest that continental crust with light-REE-enriched nature had not been developed in the early stage of the Archean. Moreover, a long-term negative Ce-anomaly is not implied for the sources of Archean iron-formation.
2. Ce and Nd isotopic data on late Archean and early Proterozoic granites from the Canadian Shield suggest that both chondritic source and light-REE-enriched source had existed even in the same Superior Province.
3. Geochronological studies on East Asian Precambrian gneisses show that Precambrian continent in this area grew outward from northeastern China by addition of peripheral provinces.
4. It is disclosed that upper mantle beneath the Chinese continent had been chemically heterogeneous over a substantial period of time.
5. Ce and Nd isotopic ratios in marine sediments such as chert are proved to be a good indicator of their depositional environment.
6. Ce and Nd isotopic data of ferromanganese nodules from the Atlantic Ocean show light-REE-enriched continental nature. On the other hand, ferromanganese nodules from the Pacific Ocean have Ce isotopic ratios reflecting light-REE-depleted mantle-like nature in contrast to Nd isotopic ratios with light-REE-enriched nature. The difference of Ce isotopic ratios between samples from two Oceans indicates Ce source difference between them.
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[Publications] Hiroshi Shimizu: "REE, Ba, and Sr abundances and Sr, Nd, and Ce isotopic ratios in Hole 504B basalts, ODP Leg 111, Costa Rica Rift." Proc. Ocean Drilling Program, Sci. Results,. 111,. 77-83, (1989)
Description
「研究成果報告書概要(欧文)」より
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