地学前缘 ›› 2009, Vol. 16 ›› Issue (2): 119-128.

• 论文 • 上一篇    下一篇

南秦岭印支期花岗岩带的“地幔印记”

田伟 董申保 陈咪咪 朱文萍   

  1. 造山带与地壳演化教育部重点实验室; 北京大学 地球与空间科学学院,  北京 100871
  • 收稿日期:2008-12-09 修回日期:2009-01-10 出版日期:2009-03-02 发布日期:2009-03-02
  • 作者简介:田伟（1976—）,男，博士，副教授，岩石学专业,主要从事岩浆岩岩石学研究。E-mail:davidtian@pku.edu.cn
  • 基金资助:

    国家科技支撑计划项目“西秦岭成矿地质背景与铅锌银铜金资源评价技术研究”(2006BAB01A11)

“Mantle signature” on the Indosinian granitoid belt in South Qinling, Central China.

  1. Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education; School of Earth and Space Sciences, Peking University, Beijing 100871, China
  • Received:2008-12-09 Revised:2009-01-10 Online:2009-03-02 Published:2009-03-02

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摘要：

南秦岭印支期花岗岩带的岩石组合包括闪长岩、二长闪长岩、英云闪长岩、花岗闪长岩和花岗岩等,岩体内广泛存在镁铁质微粒包体和脉体。大量(超过50％)样品具有高Mg＃(<076),高Cr(>100×10-6,最高为1 600×10-6)、Sr(>500×10-6)、Ba(>1 000×10-6)的“地幔印记(mantle signature)”。含石榴石基性岩部分重熔模型可以解释部分样品的高LREE、低HREE和高Sr低Y特征,但无法合理解释“地幔印记”的存在。简单的地幔上涌、减压熔融模型虽然可以产生幔源岩浆并解释基性酸性岩浆混合现象,但与具“地幔印记”样品的Sr、Nd同位素富集(ISr=0705 4~0708 5;εNd(t)=-152~-917)和区域地质特征相矛盾。具“地幔印记”样品与高Mg埃达克岩和太古宙sanukitoid岩系的相似性表明它们可以由含水富集地幔的直接熔融形成。

关键词: 高Mg埃达克岩;高Mg闪长岩;部分熔融;“地幔印记”;南秦岭

Abstract:

The Indosinian granitoid belt in South Qinling, Central China, is lithologically composed of diorite, monzodiorite, tonalite, granodiorite and granite, as well as widely distributed mafic microgranular enclaves and dykes within the intrusions. Majority (>50％) of samples have high Mg＃(<076), high Cr(>100×10-6,max=1 600×10-6), high Sr(>500×10-6) and high Ba(>1 000×10-6) content, i. e. having the “mantle signature”. The partial melting of garnet bearing metabasic rocks can explain high LREE, low HREE and high Sr, low Y characteristics of some samples, but cannot explain the “mantle signature”. Although simple mantle upwelling and adiabatic melting model is reasonable for producing mantlederived magma and mixing between basic and acidic magma, the enriched Sr, Nd isotope (ISr=0705 40708 5;εNd(t)=-152-917)of samples with mantle signature and the regional geological settings do not favor this model. Similarities to high Mg adakite and sanukitoid imply that the samples having mantle signature could be derived from direct partial melting of hydrous enriched mantle.

Key words: high Mg adakite; sanukitoid; partial melting; mantle signature; South Qinling

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