大别造山带大陆深俯冲和折返过程中壳—幔相互作用信息 ——来自大理岩铅同位素的证据  

Information of Interaction of Crust and Mantle during Continent Subduction and Exhumation in Dabie Orogenic Belt:Evidencefrom Pb-Isotopes of Marbles

作　　者：刘富[1] 周汉文[2] 

机构地区：[1]中国地质大学研究生院 [2]中国地质大学地球科学学院

出　　处：《地质科技情报》2005年第1期14-18,共5页Geological Science and Technology Information

基　　金：国家重点基础研究发展规划项目(G1999075506)

摘　　要：对大别造山带不同产状大理岩的铅同位素研究表明,红安群王家店和双河大理岩分别经历过高压和超高压变质作用,具有较高的铅同位素变化范围和高的放射性成因铅,反映了上地壳铅同位素的特征;新店大理岩的铅同位素比值和变化范围很小,具有EM1型地幔铅同位素特征,表明有地幔铅同位素特征的记录;而位于剪切带的方高坪大理岩的铅同位素除了n(206Pb)/n(204Pb)值更高外,与新店大理岩的铅同位素特征相似,记录了放射性铅同位素的大量加入或丢失,导致本来具有与双河大理岩类似的铅同位素特征变得不明显。这些结果均表明大陆深俯冲及其折返过程对大理岩铅同位素组成的改造是相当复杂的。The Pb isotope compositions of marbles from different metamorphosed terranes in Dabie Mountains have been determined. The results show significant differences in different terranes. The UHP marble in Shuanghe shows a large range of n(^(206)Pb)/(n(^(204)Pb)) and high radiogenic Pb isotope composition ([n(^(206)Pb))/(n(^(204)Pb),)19.274—24.206,n(^(207)Pb)/n(^(204)Pb),15.708-16.440] similar to HP marble [n(^(206)Pb)/n(^(204)Pb),(19.011)-29.961,n(^(207)Pb)/n(^(204)Pb),15.601-16.432] in Wangjiadian,Hong'an Group. It is concluded that the high Pb isotope ratios in Shuanghe and Wangjiadian marbles,represent the Pb isotope character of upper crust.The Pb isotope of Xindian marble,however,shows low n(^(206)Pb)/n(^(204)Pb) ratios ((16.662)-(17.717)) and slightly varied n(^(207)Pb)/n(^(204)Pb) ratios (15.402-15.541) with respect to that of Shuanghe and Wangjiadian,same as EM1 features of Pb isotopic compositions.This suggests the interaction of Pb isotope of crust and mantle. The Pb features of low in n(^(207)Pb)/n(^(204)Pb) ratios but somewhat higher in n(^(206)Pb)/(n(^(204)Pb)) ratios (17.235-19.349) of marbles from Fanggaoping resemble those of Xindian ones,which may be caused by infiltration of tectonic fluids. The samples of marble from Fanggaoping collected in the shear zone,indicate that the reconstruction of Pb isotope compositions of marble is complicated during the subduction and exhumation.

关 键 词：大理岩 铅同位素 壳-幔相互作用 大别山 

分 类 号：P597[天文地球—地球化学]