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中南大学学报(自然科学版)

Journal of Central South University

第49卷    第9期    总第289期    2018年9月

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文章编号:1672-7207(2018)09-2280-12
湘东王仙花岗闪长斑岩的岩石地球化学、锆石U-Pb年代学和Hf同位素组成
杨立志1, 2,吴湘滨1, 2,胡斌1, 2,李杰1, 2,王玺凯1, 2

(1. 中南大学 有色金属成矿预测与地质环境监测教育部重点实验室,湖南 长沙,410083;
2. 中南大学 地球科学与信息物理学院,湖南 长沙,410083
)

摘 要: 王仙花岗闪长斑岩出露于湖南省东部,通过地球化学和地质年代学方法对其岩石元素质量分数和锆石U-Pb-Hf同位素组成进行研究。研究结果表明:该岩体为富SiO2(其质量分数w(SiO2)为74.46%~75.79%)和Al2O3(w(Al2O3)为12.47%~12.83%),贫TFe2O3(w(TFe2O3)为0.96%~1.09%)和MgO(w(MgO)为0.17%~0.27%),且相对贫钠富钾(w(Na2O)/w(K2O)为0.39~0.57)的高钾钙碱性、强过铝质花岗岩;稀土元素质量分数较低,具有明显四组分配分曲线特征,相对富集Rb,Th,U,K,Nd,Hf和Sm,而亏损Ba,Eu,Sr,Ti和P;王仙花岗闪长斑岩的侵位年龄为(224.7±4.4) Ma,锆石的εHf(t)较稳定,为-6.83~-3.44,这表明王仙花岗闪长属于S型花岗岩,是华夏地块中元古代较成熟的泥质地壳部分熔融并有少量幔源物质侵入,经高程度分离结晶作用形成的;印支晚期华南板块同时受到古特提斯洋闭合和古太平洋板块向北西俯冲的影响,在碰撞后的伸展环境中,幔源物质底侵,造成地壳物质部分熔融并与幔源物质混合,形成王仙花岗闪长斑岩。

 

关键词: 王仙花岗闪长斑岩;锆石U-Pb年代学;Hf同位素;湘东;印支期

Geochemistry, geochronology and zircon Hf isotope of Wangxian granodiorite-porphyry in eastern Hunan Province and its geological significance
YANG Lizhi1, 2, WU Xiangbin1, 2, HU Bin1, 2, LI Jie1, 2, WANG Xikai1, 2

1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China

Abstract:The Wangxian granodiorite-porphyry is exposed at the eastern Hunan Province, rock element mass fraction and zircon Pb-Hf isotopes were studied by geochemical methods and geochronology. The results show that the Wangxian granodiorite-porphyry is characterized by strongly peraluminous composition and high potassium Ca-alkalineseries with high w(SiO2) (74.46%—75.79%) and w(Al2O3) (12.47%—12.83%), and low w(TFe2O3) (0.96%—1.09%), w(MgO) (0.17%—0.27%) and w(Na2O)/w(K2O)(0.39—0.57). The trace elements of the Wangxian granodiorite-porphyry has low total REE contents, strong enrichment of Rb, Th, U, K, Nd, Hf and Sm, and relative depletion of Ba, Eu, Sr, Ti and P- REE distribution curve presents as four groups of different curves. The emplacement age of the Wangxian granodiorite- porphyry is determined in (224.7±4.4) Ma. The primary zircons have uniform and negative εHf(t) (-6.83— -3.44), which indicates that the Wangxian granodiorite-porphyry belongs to S-type granites, and is formed by partial melting of mesoproterozoic crustal material of the Cathaysia block and mixed with some mantle-sourced magma. The magma experiences a strong crystal fractionation process. Combined with the Indosinian period tectonic development of South China, the Wangxian granodiorite-porphyry formed in an extensional rift intraplate environment, which is related to the closure of the paleo-Asian Ocean and NW-trending flat subduction of paleo-Pacific plate. The extensional setting induces the underplating of the basaltic magma, leading to partial melting of crustal rocks.

 

Key words: Wangxian granodiorite-porphyry; zircon U-Pb dating; Hf isotope; eastern Hunan Province; Indosinian period

中南大学学报(自然科学版)
  ISSN 1672-7207
CN 43-1426/N
ZDXZAC
中南大学学报(英文版)
  ISSN 2095-2899
CN 43-1516/TB
JCSTFT
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