苏北榴辉岩中金红石的微量元素地球化学特征  

Trace elements geochemistry of eclogites in the northern Jiangsu province, eastern China.

作　　者：余金杰[1] 陈振宇[1] 王平安[2] 李晓峰[1] 黄建平[3] 王辉[3] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质科学院地质力学研究所,北京100081 [3]江苏省地质调查研究院,南京210018

出　　处：《岩石学报》2006年第7期1883-1890,共8页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规则项目(2003CB716507)资助成果.

摘　　要：本文利用电子探针分析了苏北地区三类榴辉岩中金红石的Nb、Cr和Zr含量,在Zack et al．(2002)的金红石Nb- Cr图解中,三类榴辉岩的原岩均为镁铁质岩,但它们具有不同的地球化学特征,即(1)小焦G类金红石榴辉岩中金红石的Nb含量最低,平均值为68ppm,而其它两类榴辉岩中金红石的Nb含量较高,平均值介于192～255ppm;(2)蓝晶石榴辉岩具有极高Cr含量,均值6106ppm,而许沟P类榴辉岩中金红石的Cr含量也较高,均值1233ppm,金红石榴辉岩中金红石Cr含量最低,均值为183ppm。利用Zaek et al．(2004)提出的金红石地质温度计,计算得出许沟P类榴辉岩的金红石形成温度介于600—751℃,平均温度689℃;演马厂M类榴辉岩的金红石温度介于507-641℃,平均温度557℃;小焦G类金红石榴辉岩金红石的形成温度介于541-673℃,平均温度613℃;新扬昌G类蓝晶石榴辉岩的金红石形成温度介于541-655℃,平均温度603℃。一种可能的解释是,榴辉岩在拆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。Three kinds of eclogites （ e. g. , M eclogite, P eclogite and G eclogite） can be recognized in the north of Jiangsu province. Trace elements in rutile such as Nb, Cr and Zr are measured by electron microprobe with specific operating conditions. Provenance of three kinds of eclogites came from mafic rocks according to their Nb and Cr contents. But three kinds of eclogites are distinguishable from Nb and Cr concentrations. The lowest average Nb content of rutile is discovered in rutile eclogite from the Xiaojiao futile deposits with an average value of 68 ppm. The average Nb contents of rutiles from other eclogites vary from 192 to 255 ppm, and are about identical. Rutile in kyanite eclogite are enriched in Cr with an average value of 6106ppm. Rutile in eclogite from the Xugou ultramafic rocks also has high Cr with an average value of 1233ppm. Rutile from the Xiaojiao rutile deposit has the lowest Cr content with an average value of 183ppm. Based on a new Zr-in-rutile geothermometer by Zack et al. （2004）, Rutile formation temperature of eclogite in the Xugou ultramafic rock varies from 600 to 751 ℃ with an average value of 689℃. Rutile formation temperature of phengite eclogite in the Yanmachang marble varies from 507 to 641℃ with an average value of 557℃. Rutile formation temperature of rutile eclogite in the Xiaojiao rutile deposit varies from 541 to 673℃ With an average value of 613℃. Rutile formation temperature of kyanite eclogite in the Xinyangchang kyanite prospect varies from 541 to 655℃ with an average value of 603℃. 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.

关 键 词：金红石 微量元素 榴辉岩 原岩 再平衡 苏北地区 

分 类 号：P588.348[天文地球—岩石学] P578.47[天文地球—地质学]