REE concentrations of garnet and omphacite in eclogites from the Dabie Mountain, central China  

作　　者：LI Jing DU Jianguo CHANG Qing LIU Lei CUI Yueju XIE Chao SUN Yutao 

机构地区：[1]Institute of Earthquake Science, China Earthquake Administration [2]Institute of Disaster Prevention [3]Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

出　　处：《Chinese Journal Of Geochemistry》2013年第1期85-94,共10页中国地球化学学报

基　　金：financially supported by the National Natural Science Foundation of China(Grant No.40873049) and Kyoto University,Japan

摘　　要：Distributions of the rare-earth elements (REE) in omphacite and garnet and REE behaviors during metamorphic processes were discussed. The REE concentrations of garnet and omphacite in six eclogite samples from the Dabie Mountain, central China, were measured by inductively coupled plasma-mass spectrometry (ICP-MS). The correlation of δEu ratios between garnet and omphacite indicated that chemical equilibrium of REE distribution between garnet and omphacite could be achieved during ultra-high pressure (UHP) metamorphism. Most of the partition coefficients (Kd=CiOmp/CiGrt) of light rare-earth elements (LREE) are higher than 1. However the partition coefficients of heavy rare-earth elements (HREE) are lower than 1. This indicated that the LREE inclined to occupy site M2 in omphacite, but the HREEs tended to occupy eightfold coordinated site in garnet during the eclogite formation. The REE geochemistry of the eclogites indicated that LREE could be partially lost during the prograde metamorphic process of protolith, but be introduced into the rocks during the symplectite formation. LREE are more active than HREE during the UHP metamorphism. The results are favorable to highlighting the REE behavior and evolution of UHP metamorphic rocks.Distributions of the rare-earth elements （REE） in omphacite and garnet and REE behaviors during metamorphic processes were discussed. The REE concentrations of garnet and omphacite in six eclogite samples from the Dabie Mountain, central China, were measured by inductively coupled plasma-mass spectrometry （ICP-MS）. The correlation of δSEu ratios between garnet and omphacite indicated that chemical equilibrium of REE distribution between garnet and omphacite could be achieved during ultra-high pressure （UHP） metamorphism. Most of the partition coefficients （Ka=Ci^Omp/Ci^Grt） of light rare-earth elements （LREE） are higher than 1. However the partition coefficients of heavy rare-earth elements （HREE） are lower than 1. This indicated that the LREE inclined to occupy site M2 in omphacite, but the HREEs tended to occupy eightfold coordinated site in garnet during the eclogite formation. The REE geochemistry of the eclogites indicated that LREE could be partially lost during the prograde metamorphic process of protolith, but be introduced into the rocks during the symplectite formation. LREE are more active than HREE during the UHP metamorphism. The results are favorable to highlighting the REE behavior and evolution of UHP metamorphic rocks.

关 键 词：稀土元素分布 石榴子石 元素浓度 绿辉石 榴辉岩 大别山 中国 电感耦合等离子体质谱 

分 类 号：P595[天文地球—地球化学] P578.947[天文地球—地质学]