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J4 ›› 2012, Vol. 18 ›› Issue (2): 291-.

• 其他学科论文 • 上一篇    下一篇

秦岭早中生代壳幔岩浆混合作用——来自东江口花岗岩体闪长质包体的地球化学证据

李 雷,张成立,周 莹,田会全,李小菲   

  1. 西北大学 大陆动力学国家重点实验室,西北大学 地质学系,西安
  • 出版日期:2012-06-20 发布日期:2012-07-11
  • 通讯作者: 张成立,教授;E-mail:clzhang@nwu.edu.cn
  • 作者简介:李雷,男,1985年生,硕士研究生,岩石地球化学专业;E-mail:lilei19850730@163.com;

Early Mesozoic Crust- and Mantle-Derived Magmatic Mixing in the Qinling
Orogeny: Evidence From Geochemistry of Mafic Microgranular Enclaves
in the Dongjiangkou Pluton

LI Lei, ZHANG Chengli, ZHOU Ying, TIAN Huiquan, LI Xiaofei   

  1. Key Laboratory of Continental Dynamics of Northwest University, Department of Geology, Northwest University, Xi,an
  • Online:2012-06-20 Published:2012-07-11
  • Contact: Zhang Chengli, Professor;E-mail: clzhang@nwu.edu.cn

摘要:

      东江口花岗岩及闪长质包体分别获得了218 Ma 和224 Ma 的形成年龄,闪长质包体中存在岩浆不平衡结构并发育与寄
主花岗岩相同的钾长石斑晶及淬冷形成的针状磷灰石,揭示了花岗岩形成过程中曾发生二元岩浆混合作用。这种混合作用
已造成寄主花岗岩和闪长质包体化学组成的趋同,同时使得它们的Sr-Nd-Pb 同位素组成发生强烈均一化。但暗色闪长质包
体锆石具有较宽的εHf(t )值(-4.58~3.31),保留了二端元岩浆源区的特征。秦岭早中生代同期闪长质包体锆石εHf(t )>
10 及寄主花岗岩锆石εHf(t )< -10 的差异表明,它们分别来自相对亏损地幔源区和中元古代滞留于地壳的幔源基性物质,
而两个源区的岩浆,自224 Ma 以来发生强烈混合作用,形成大规模的壳幔混合花岗岩体。

关键词: 早中生代, 闪长质包体, 岩石地球化学, 壳幔岩浆混合作用

Abstract:

The zircon U-Pb ages of 218 Ma and 224 Ma have been obtained from the Dongjiangkou granitoids and their mafic
enclaves, respectively. The disequilibrium magmatic textures can be found in the mafic enclaves, which have some K-feldspars
similar to those of host granitoids and needle-like apatite formed under a quenching condition, indicating a two-end member
magmatic mixing in the early Mesozoic. The two-end member magmatic mixing resulted in similar geochemical compositions and
strong homogenization of Sr-Nd-Pb isotopes between host granitoids and their mafic enclaves. However, Hf isotopic composition
of the mafic enclaves shows a wide range of εHf(t) that varies from -4.58 to 3.31, registering the source features of two-end member
magma. Thus, the positive εHf(t) values (>10) of zircons from the contemporary mafic enclaves provide evidence that the mafic
magma was derived from the depleted mantle. While, host granitoids with negativeεHf(t ) values (<10) of zircons were products of
partial melting of the Mid-Proterozoic mantle-derived basic rocks. Since then, the distinct crust- and mantle-derived magmas were
mixed around 224 Ma, resulting in a large number of granitic intrusions with abundant mafic enclaves during the early Mesozoic
in the Qinling orogeny.

Key words: Early Mesozoic;mafic enclave;petro-geochemistry;crust- and mantle-derived magmatic mixing

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