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J4 ›› 2011, Vol. 17 ›› Issue (3): 436-.

• 岩浆作用、成矿作用与地球动力学专栏 • 上一篇    下一篇

广东北部早白垩世粗面岩的成因:Sr-Nd-Pb同位素制约

 项媛馨,  巫建华   

  1. 东华理工大学 地球科学学院,抚州
  • 收稿日期:2010-10-09 修回日期:2010-11-23 出版日期:2011-09-20 发布日期:2011-09-20
  • 通讯作者: 巫建华,男,1960年生,博士,教授,主要从事火山地质学与铀矿地质学的研究;E-mail:jhwu@ecit. cn
  • 作者简介:项媛馨,女,1986年生,硕士研究生,主要从事岩浆岩与成矿作用的研究;E-mail:xiangyuanxin@163.com
  • 基金资助:

      中国核工业总公司“中国中、新生代铀成矿作用”(中核计2008-74号)项目资助

Origin of the Early Cretaceous Trachyte in Northern Guangdong Province Constraints of Sr-Nd-Pb Isotopes

 XIANG Yuan-Xin,  Wu-Jian-Hua   

  1. School of  Earth Sciences, East China Institute of  Science and  Technology, Fuzhou
  • Received:2010-10-09 Revised:2010-11-23 Online:2011-09-20 Published:2011-09-20
  • Contact: Wu Jianhua, Professor. E-mail: jhwu@ecit. cn

摘要:

     广东北部大长沙盆地粗面岩锆石SHRIMP U-Pb 年龄为(135.3±1.5) Ma,形成于早白垩世早期,其Sr-Nd-Pb
同位素组成为:富放射性成因铅,(206Pb/204Pb)  i=18.23~18.39,(207Pb/204Pb) i=15.78~15.88,(208Pb/204Pb) i  = 38.83~39.14,中等的εNd (t)(=-3.35~-3.21)及较高的(87Sr/86Sr)  i (=0.706871~ 0.709074) ;在Pb-Pb图解上均位于NHRL上方,△Sr值为99.1~247.0 (平均140.5),表明存在典型的Dupal同位素异常。Sr-Nd,Sr-Pb,Nd-Pb和Pb-Pb同位素特征表明,大长沙盆地粗面岩起源于年轻下地壳的部分熔融,但年轻下地壳曾受到深俯冲上地壳析出流体的交代作用,粗面岩岩浆是源区混合的产物,在上升的过程中没有受到上地壳物质的混染。

关键词: 粗面岩, Sr-Nd-Pb同位素, 下地壳, 部分熔融, 大长沙盆地

Abstract:

 The trachyte in the Dachangsha basin of the northern Guangdong province was formed in the Early Cretaceous (SHRIMP
zircon U-Pb dating shows an age of  trachyte as 135.3±1.5 Ma). The Sr-Nd-Pb  isotopic composition cnaracteristics of  trachyte are as  follows: enriched  in  radiogenic  lead,(206Pb/204Pb)i=18.23~18.39,(207Pb/204Pb)i = 15.78~15.88,(
208Pb/204Pb)i=38.83~39.14; moderate initial Nd isotopic ratios, εNd( t )=-3.35~-3.21; and higher initial Sr isotopic rations, (
87Sr/86Sr)i= 0.706871~0.709074. On the Pb-Pb diagrams, the trachyte is plotted above NHRL line and △Sr = 99.1~247.0  (140.5 in average), which indicates that the trachyte has obvious Dupal anomaly. The Sr-Nd, Sr-Pb, Nd-Pb and Pb-Pb relationship of the trachyte suggests that the trachyte should be originated from partial melting of the young lower crust, while the lower crust should be influenced by metasomatism of fluids from dehydration of subducted upper crust,and there was no upper crust contamination in the process of magma rising.

Key words:  trachyte, Sr-Nd-Pb isotopes, lower crust, partial melting, Dachangsha basin

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