Effects of retrograde-zoning of garnet on Sm-Nd isotopic dating of eclogite and oxygen isotopic disequilibrium between eclogitic minerals

作     者：李曙光 刘贻灿 徐树桐 郑永飞 

作者机构：School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China Anhui Institute of Geology Hefei 230001 China 

出 版 物：《Science China Chemistry》 (中国科学（化学英文版）)

年 卷 期：2002年第45卷第z1期

页      面：28-37页

核心收录：

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 0703[理学-化学] 

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.40033010 and 49794041) the Major State Research Program of China(Grant No.G1999075503) Anhui Bureau of Geology and Mineral Resources 

主　　题：eclogite, Sm-Nd isotopic dating, oxygen isotope, zonation of garnet, Dabie Mountains. 

摘      要：The compositional zoning of the garnet in a strongly deformed eclogite from Raobazhai foliated peridotite has been recognized. The CaO concentrations of the garnet are decreased from the core to the rim, while its MnO concentrations are increased, suggesting the retrograde origin of such CaO-MnO zoning. The tie line of garnet+omphacite from this eclogite gives a Sm-Nd age of (187±5) Ma, which is less significant than the Sm-Nd ages of (221±5)-(228±3) Ma and (210 ±6)-(214±6) Ma for ultrahigh-pressure eclogites in the southern Dabie zone and in the northern Dabie zone, respectively. This younger Sm-Nd age could result from the ^(143)Nd/^(144)Nd ratio decrease of the retrograde zone in the garnet. The δ^(80)O values of the garnet and omphacite show that their fractionation values are less than the equilibrium fractionation value between the garnet and om- phacite at 500-900℃, which suggests an oxygen isotopic disequilibrium between them.