A potential method to confirm the previous existence of lawsonite in eclogite:the mass imbalance of Sr and LREEs in multistage epidote(Ganghe,Dabie UHP terrane)
作者单位：State Key Laboratory of Lithospheric EvolutionInstitute of Geology and GeophysicsChinese Academy of Sciences
会议名称：《中国科学院地质与地球物理研究所2013年度（第13届）学术年会》
会议日期：2014年
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]
基 金：supported by The National Key Basic Research Program of China(973 Program 2009CB825001) The National Science Foundation of China(Nos.41102034,41090371,40902023,and 40772051) China Postdoctoral Science Foundation funded project(2011M500384)
关 键 词：Dabie UHP terrane eclogite lawsonite multistage epidote Sr and LREEs
摘 要：Lawsonite is an important hydrous mineral that is stable at low-temperature(LT) and high-to ultrahigh -pressure(HP-UHP) conditions in subducted *** occurrence/absence of lawsonite in eclogite is a significant constraint for the construction of the metamorphic,tectonic and fluid/melt evolution histories of an HP-UHP ***,lawsonite is very rarely preserved in natural eclogites,and accurate judgment of its former existence is a significant challenge for *** present,whether lawsonite has ever existed in lawsonite-absent eclogite is mainly judged by(i) pseudomorphs after lawsonite, and(ii) phase equilibria *** this study,major element,and trace-element distributions in multistage minerals were examined in the Ganghe lawsonite-absent UHP eclogite in the Dabie UHP terrane,eastern *** work demonstrates that the whole-rock Sr and light rare earth elements (LREEs) are mainly dominated by epidote;other minerals(garnet,omphacite,quartz,kyanite,barroisite, phengite and accessory minerals) play a very limited role in the Sr and LREEs *** stages of epidote,which have noticeably different Sr and LREEs contents,were recognized in the eclogite:(i) Epidote porphyroblasts(Ep-P core),which are suspected to be the pseudomorphic mineral after lawsonite, contain significantly high Sr(7200-10 300 ppm) and LREEs(160-1300 ppm for La),(ii) An earlier stage epidote(Ep-In core) occurs as inclusions in matrix omphacite,or in omphacite inclusions in the suspected pseudomorphic minerals after lawsonite(SPMAL);this early epidote has significantly lower Sr(990-1890 ppm,average 1495 ppm,n = 17) and LREEs contents(60-110 ppm for La,average 91 ppm,n = 17).All of the existing early-stage minerals predating the SPMAL have very low contents of Sr and LREEs,and the total amounts of these elements in the early-stage minerals do not balance those in the *** indicates that a missing Ca-,Al-,Sr-and LREE-rich mineral,which was previously in equilibrium