| Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet |
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| 作者姓名： | 魏启荣 王江海 |
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| 作者单位： | [1]CollegeofMaterialsScience＆ChemicalEngineering,ChinaUniversityofGeosciences,Wuhan430074,China [2]GuangzhouInstituteofGeochemistry,ChineseAcademyofSciences,Guangzhou510640,China |
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| 基金项目： | 国家重点基础研究发展计划(973计划)，国家自然科学基金，中国科学院知识创新工程项目，中国博士后科学基金 |
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| 摘 要： | The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area, eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%-2.00%). These rocks may be classified as two groups, based on their Mg# numbers: one may represent primary magma (Mg# numbers from 68 to 69), and the other, the evolved magma(Mg# numbers from 49 to 57). Their REE contents are very high (∑REE = 155.06-239.04μg/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment (La/Yb)N =12.0-19.2], no Ce anomaly (Ce/Ce*=1.0), and weak negative Eu anomaly (Eu/Eu*=0.9). The rocks are highly enriched in Rb, Sr and Ba (59.5-93.8μg/g, 732-999 μg/g, and 450-632 g/g, respectively), high in U and Th (1.59-2.31μg/g and 4.73-8.16 μg/g, respectively), and high in Nb, Ta, Zr and Hf (70-118 μg/g,3.72-5.93 μg/g, 215-381 μg/g, and 5.47-9.03 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba, Ti and Y show negative anomalies. The 87Sr/86Sr ratios range from 0. 704029 to 0.704761; 143Nd/144Nd from 0. 512769 to 0. 512949; and εNd from 2.6 to 6.1. These geochemical features might suggest that the potential source of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mantle of Hawaii and Kergeulen volcanic rocks.
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| 关 键 词： | 地球化学 新生代 玄武岩 火山岩 同位素 |
Geochemical characteristics of Cenozoic basaltic high-K volcanic rocks from Maguan area,eastern Tibet |
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| Wei?Qirong,Wang?Jianghai.Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet[J].Chinese Journal of Geochemistry,2004,23(1):57-64. |
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| Authors: | Wei Qirong Wang Jianghai |
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| Institution: | (1) College of Materials Science & Chemical Engineering, China University of Geosciences, 430074 Wuhan, China;(2) Guangzhou Instaute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China |
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| Abstract: | The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area,
eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%–2.00%). These rocks may be classified as two groups, based on their Mg # numbers: one may represent primary magma
(Mg numbers from 68 to 69), and the other, the evolved magma (Mg* numbers from 49 to 57). Their REE contents are very high
(Σ REE = 155.06-239.04 μ/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment
(La/Yb)N = 12.0–19.2], no Ce anomaly (Ce/Ce* =1.0), and weak negative Eu anomaly (Eu/Eu* = 0.9). The rocks are highly enriched in
Rb, Sr and Ba (59.5-93.8 μ/g, 732–999 μ/g, and 450–632 ν/g, respectively), high in U and Th (1.59–2.31 μ/g and 4.73–8.16 μ/g,
respectively), and high in Nb, Ta, Zr and Hf (70-118 μ/g, 3.72–5.93 μ/g, 215–381 μ/g, and 5.47–9.03 μ/g, respectively). In
the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba,
Ti and Y show negative anomalies. The87Sr/86Sr ratios range from 0.704029 to 0.704761;143Nd/144Nd from 0.512769 to 0.512949; and εNd from +2.6 to + 6.1. These geochemical features might suggest that the potential source
of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mande of Hawaii and Kergeulen volcanic
rocks.
The study was supported jointly by the State Key Projects for Basic Research (No. Gl998040807), the National Natural Science
Foundation of China (No. 49972026), the Knowledge-innovation project of the Chinese Academy of Sciences (No. KZCX2-SW-117),
and the China Postdoctoral Science Foundation. |
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| Keywords: | Cenozoic basaltic high- K volcanic rocks geochemistry Nd-Sr isotope eastern Tibet Maguan area |
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