中国大陆科学钻探工程主孔榴辉岩中金红石微量元素地球化学特征

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• 其他题名：Trace Element Geochemistry of Rutiles in the Eclogites From the Chinese Continental Scientific Drilling Project Main Hole
• 作者：余金杰 ; 徐珏 ; 陈振宇 ; 王登红 ; 陈毓川 ; 王平安 ; 李晓峰
• 其他作者：YU Jinjie~ 1) ; XU Jue~ 1) ; CHEN Zhenyu~ 1) ; WANG Denhong~ 1) ; CHEN Yuchuan~ 2) ; WANG Pingan~ 3) ; LI Xiaofeng~ 1) 1) Institute of Mineral Resources ; Chinese Academy of Geological Sciences ; Beijing ; 1000372) Chinese Academy of Geological Sciences ; Beijing ; 1000373) Institute of Geomechanics ; Chinese Academy of Geological Sciences ; Beijing ; 100081
• 关键词：金红石 ; 微量元素 ; 榴辉岩 ; 原岩 ; 再平衡 ; 主孔 ; 大陆科学钻探工程
• 其他关键词：rutile ; trace elements ; eclogite ; provenance ; reequilibrium ; the Chinese Continental Scientific Drilling Project (CCSD) main hole
• 刊名：地质学报
• 出版日期：2006-12-15
• 年：2006
• 期：12
• 作者机构：中国地质科学院矿产资源研究所,中国地质科学院矿产资源研究所,中国地质科学院矿产资源研究所,中国地质科学院矿产资源研究所,中国地质科学院,中国地质科学院地质力学研究所,中国地质科学院矿产资源研究所 北京,100037,北京,100037,北京,100037,北京,100037,北京,100037,北京,100081,北京,100037
• 基金：国家重点基础研究发展规则“973”项目(编号2003CB716507)资助成果。

摘要

本文利用电子探针分析了中国大陆科学钻探工程主孔各种类型榴辉岩中金红石的Nb、Cr和Zr含量。Zack等(2002)的金红石Nb-Cr图解表明榴辉岩的原岩均为镁铁质岩,但不同类型榴辉岩具有不同的地球化学特征,即:1金红石榴辉岩、石英榴辉岩、角闪岩和钛铁矿榴辉岩中金红石的Nb和Cr含量大致相同,主孔中上述榴辉岩中金红石的Nb、Cr含量与区域上小焦金红石矿区金红石榴辉岩中金红石的Nb、Cr含量基本相同。总体来讲,区域和主孔榴辉岩中金红石以低Nb为特征,反映它们的原岩为镁铁质岩石。2蓝晶石多硅白云母榴辉岩中金红石具最高的Nb和Cr含量,其Nb和Cr均值分别为720×10-6和712×10-6,多硅白云母榴辉岩中金红石比金红石榴辉岩、石英榴辉岩、角闪岩和钛铁矿榴辉岩中金红石富集Cr。利用Zack等(2004)提出的金红石地质温度计,计算得出金红石榴辉岩的金红石形成温度介于608~746℃,石英榴辉岩的金红石温度介于629~680℃,钛铁矿榴辉岩金红石的形成温度介于629~704℃,蓝晶石多硅白云母榴辉岩的金红石形成温度为600℃,角闪岩的金红石形成温度为629℃。一种可能的解释是,榴辉岩在折返过程中退变质作用明显,流体活动强烈,导致金红石中Zr扩散丢失,金红石中Zr含量不同程度地受到角闪岩相退变质过程中再平衡作用的影响,致使计算的温度偏低。
Many kinds of eclogites (e.g., rutile eclogite, quartz eclogite, ilmenite eclogite, phengite eclogite and hornblendite) can be recognized in the main drillhole of Chinese Continental Scientific Drilling Project. Trace elements such as Nb, Cr and Zr in rutile are measured by electron microprobe with specific operating conditions. Provenance of all kinds of eclogites came from mafic rocks according to their Nb and Cr contents. All kinds of eclogites are characterized by low Nb concentrations. The Nb and Cr content of rutile is about identical from rutile eclogite, quartz eclogite, ilmenite eclogite, and hornblendite. Kyanite phengite eclogite has the highest Nb and Cr contents and its average Nb and Cr concentration is 720×10~ -6 and 712×10~ -6 , respectively. Compared to other eclogite, Kyanite phengite eclogite is more enriched in Cr. Based on a new Zr-in-rutile geothermometer by Zack et al. (2004), Rutile formation temperature of rutile eclogite varies from 608 to 746℃. Rutile formation temperature of quartz eclogite is between 629 and 680℃. Rutile formation temperature of ilmenite eclogite varies from 629 to 704℃.Rutile formation temperature of kyanite phengite eclogite is about 600℃ and Rutile formation temperature of hornblendite is about 629℃. When eclogite suffered amphibolite-facies retrograde metamorphism, Strong fluid activity resulted in Zr diffussional loss. So Zr content of rutiles became lower because of Zr diffusional resetting during amphibolite-facies retrograde metamorphism.