| REE Geochemical Evolution and Its Significance of Early Precambrian Metamorphic Terrain,Wuyang,Henan |
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| 作者姓名： | 陈衍景 富士谷 |
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| 作者单位： | [1]InstituteofGeochemistry,AcademiaSinica,Guiyang [2]DepartmentofEarthSciences,NanjingUniversity |
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| 摘 要： | The supracrustal rocks of the Wuyang metamorphic terrain are divided into the Zhao anzhuang,Tieshanmiao and Yangshuwan Formations.These three Formations were dated at 3000-2550Ma,2550-2300Ma and 2300-2200Ma,respectively.∑REE and La/Yb)n of the Zhao anzhuang Formation volcanic rocks are obviously higher than those of the Tiesanmiao Formation equivalents,suggesting a sedimentary gap(2550 Ma boundary)between these two formations,The Zhao‘anzhuang Formation is older than the Tieshanmiao Formation.The sediments of these two Formations show no obvious differences in REE and are generally characterized by low ∑REE and positive Eu anomalies.On the contrary,the sediments of the Yangshuwan Formation are characterized by high ∑REE and negative Eu anomalies.Detailed discussions demonstrate that the Yangshuwan Formation was deposited in an oxidizing environment whereas the other two formations were formed in a reducing environment.At the end of the evolution of the Tieshanmiao Formation about 2300 Ma ago,the sedimentary environment was transformed from reducing to oxidizing .On the basis of the SHAB (soft/hard acid and base)theory,an oxidation-reduction model for sedimentary REE evolution has been established .It is proposed that the mantle tends to become gradually depleted in REE.especially in LREE,and the indices ∑REE and La/Yb) n of mantle-dervived volcanic rocks also tend to become lower and lower.
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| 关 键 词： | 稀土元素地球化学 前寒武纪 河南 变质地形 上地壳 岩石 火山岩 地质构造 |
REE geochemical evolution and its significance of early precambrian metamorphic terrain,Wuyang, Henan |
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| Yanjing Chen,Shigu Fu,Shouxi Hu,Yuanyou Zhang.REE Geochemical Evolution and Its Significance of Early Precambrian Metamorphic Terrain,Wuyang,Henan[J].Chinese Journal of Geochemistry,1992,11(2):133-139. |
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| Authors: | Yanjing Chen Shigu Fu Shouxi Hu Yuanyou Zhang |
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| Institution: | (1) Institute of Geochemistry, Academia Sinica, Guiyang;(2) Department of Earth Sciences, Nanjing University, China;(3) Geological Team 4, Henan Branch of China Non-ferrous Metal Industry Company, China |
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| Abstract: | The supracrustal rocks of the Wuyang metamorphic terrain are divided into the Zhao ’anzhuang, Tieshanmiao and Yangshuwan Formations.
These three Formations were dated at 3000–2550 Ma, 2550–2300 Ma and 2300–2200 Ma, respectively. ΣREE and La/Yb)n of the Zhao ’anzhuang Formation volcanic rocks are obviously higher than those of the Tieshanmiao Formation equivalents,
suggesting a sedimentary gap (2550 Ma boundary) between these two formations. The Zhao ’anzhuang Formation is older than the
Tieshanmiao Formation. The sediments of these two Formations show no obvious differences in REE and are generally characterized
by low ΣREE and positive Eu anomalies. On the contrary, the sediments of the Yangshuwan Formation are characterized by high
ΣREE and negative Eu anomalies. Detailed discussions demonstrate that the Yangshuwan Formation was deposited in an oxidizing
environment whereas the other two formations were formed in a reducing environment. At the end of the evolution of the Tieshanmiao
Formation about 2300 Ma ago, the sedimentary environment was transformed from reducing to oxidizing. On the basis of the SHAB
(soft/hard acid and base) theory, an oxidation-reduction model for sedimentary REE evolution has been established. It is proposed
that the mantle tends to become gradually depleted in REE, especially in LREE, and the indices ΣREE and La/Yb)n of mantle-derived volcanic rocks also tend to become lower and lower. |
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