投稿时间：2012-05-10
修订日期：2012-06-28
中文摘要:随着同位素测试技术的发展,高温下重同位素分馏逐渐运用到地球化学领域。为了探索岩浆演化过程中是否会发生Cu同位素分馏,文章对西藏驱龙斑岩铜矿床同来源、不同演化阶段的两套岩浆岩(闪长岩包体和花岗闪长岩)进行了Cu同位素测试。测试结果显示,闪长岩包体的δ65Cu值集中在+0.08‰~+0.35‰之间,平均值为+0.25‰,花岗闪长岩的δ65Cu值为+0.42‰~+0.87‰,平均值为+0.60‰。Δ65Cu花岗闪长岩-闪长岩包体≈+0.4‰,并且δ65Cu值与样品ω(SiO2)变化存在一定的正相关性。结合地质学及同位素方面考虑,花岗闪长岩和闪长岩包体的Cu同位素组成差异可能是岩浆演化过程中发生了Cu同位素分馏所致。在驱龙矿区中新世岩浆演化过程中,随着岩浆去气作用,63Cu随HS-、Cl-等挥发分优先进入气相,导致残留岩浆熔体相对富集65Cu。此外,两者的Cu同位素组成差异也可能与岩浆演化过程中斜长石、角闪石、黑云母等矿物的不断结晶分离有关,矿物结晶分离时,基性矿物富集63Cu,而残余熔体则富集65Cu。
Abstract:In order to explore the problem that whether Cu isotope fractionation would happen in magmatic evolution process or not, this paper analyzed Cu isotope compositions of the granodiorite pluton and dioritic enclaves from the Qulong porphyry copper deposit, which have the same source but different evolutional stages. The results show that the δ65Cu values of dioritic enclaves are in the range of +0.08‰~+0.35‰, +0.25‰ on average, and the δ65Cu values of granodiorite pluton are +0.42‰~+0.87‰, +0.60‰ on average. The mean difference value is about +0.4‰, and the δ65Cu values are somewhat positively correlated with the SiO2 content. Considering the geological and isotope factors, the authors hold that the difference of Cu isotopic compositions between the dioritic enclaves and the granodiorite pluton might be attributed to the reason that the Cu isotope fractionation occurred during the magmatic evolution process. During the Miocene magmatic evolution process, 63Cu would first enter gas phase along with volatiles such as HS- and Cl- when the magma experienced the degassing process, which then led to the relative enrichment of 65Cu in remaining magmtic melt. In addition, the differences of Cu isotopic compositions might have also been related to the crystallization differentiation of such minerals as plagioclase, amphibole and biotite in the magmtic evolution process. In the mineral crystallization differentiation process, the 63Cu would enter mafic minerals whereas the residual melt was relatively enriched with 65Cu.
keywords:geochemistry Cu isotope fractionation magmatic evolution magma degassing process fractional crystallization Qulong Tibet
文章编号：
中图分类号：P618.41
文献标志码：
基金项目:本文得到国土资源部公益性行业科研专项(201011011);国家自然科学重点基金 (40730419)和国家自然科学基金(41040023)联合资助
引用文本：
聂龙敏,李振清,房小捷.2012.西藏驱龙斑岩铜矿床岩浆演化过程中的Cu同位素分馏[J].矿床地质,31(4):718~726NIE LongMin,LI ZhenQing,FANG XiaoJie.2012.Cu isotope fractionation during magma evolution process of Qulong porphyry copper deposit, Tibet[J].Mineral Deposits31(4):718~726
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