大别山双河超高压变质矿物O同位素平衡及其对Sm-Nd和Rb-Sr等时线年龄有效性的制约  

Oxygen Isotope Equilibrium between UHP Metamorphic Minerals at Shuanghe in the Dabie Orogenic Belt and Its Constraints on Sm-Nd and Rb-Sr Chronometers

作　　者：赵子福[1] 郑永飞[1] 李曙光[1] 龚冰[1] 

机构地区：[1]中国科学院壳幔物质与环境重点实验室中国科学技术大学地球和空间科学学院,安徽合肥230026

出　　处：《地球学报》2005年第B09期98-101,共4页Acta Geoscientica Sinica

基　　金：本文为国家973项目（编号：G1999075503）研究成果.

摘　　要：对大别造山带双河超高压榴辉岩和片麻岩Sm-Nd和Rb-Sr等时线矿物进行了O同位素地质测温。尽管Sm-Nd等时线给出一致的三叠纪年龄（213～238Ma），同一样品Rb-Sr等时线却给出侏罗纪年龄（171～174Ma）。片麻岩、榴辉岩和榴闪岩矿物对0同位素测温得到600-720℃和420-550℃两组温度，分别对应于约225±5Ma榴辉岩相变质和约175±5Ma角闪岩相退变质条件下停止同位素扩散交换的温度。同一样品三叠纪Sm-Nd等时线年龄的保存、侏罗纪Rb-Sr等时线年龄的出现以及有规律的O同位素温度，表明在角闪岩相退变质过程中，Sr和O在含水矿物（如黑云母和角闪石）中的扩散速率在手标本尺度上比石榴石Nd和多硅白云母Sr的扩散速率快。As the rates of Nd, Sr and O diffusion in metamorphic minerals are comparable in many cases, the state of O isotope equilibrium between metamorphic minerals can provide a test for the validity of mineral Sm-Nd and Rb-Sr chronometers. In order to illustrate this applicability, the authors carried out O isotope geothermometry for Srn-Nd and Rb-Sr isochron minerals from UHP eclogites and gneisses at Shuanghe in Dabie terrane of eastern Central China. Although the Sm-Nd isochrons give consistent Triassic ages of 213-238 Ma for eclogite-facies metamorphism, the Rb-Sr isochrons give Jurassic ages of 171 - 174 Ma for the same samples. O isotope geothermometry of the gneiss, eclogite and amphibolite minerals yields two sets of temperatures of 600-720℃ and 420-550℃, respectively, corresponding to the cessation of isotopic exchange by diffusion at about 225 ± 5 Ma during eclogite-facies recrystallization and that at about 175 ± 5 Ma during amphibolite-fades retrogression.

关 键 词：榴辉岩和片麻岩 O同位素 Sr-Nd同位素 矿物等时线 扩散平衡 RB-SR等时线年龄 SM-ND等时线年龄 超高压榴辉岩 同位素平衡 变质矿物 

分 类 号：P618.51[天文地球—矿床学] P597[天文地球—地质学]