Iron isotope fractionation during fenitization:a case study of carbonatite dykes from Bayan Obo,Inner Mongolia,China  

作　　者：Zongyi Wu Jian Sun Xiaowei Li Xiangkun Zhu 

机构地区：[1]Institute of Geology,MNR Key Laboratory of Deep-Earth Dynamics,Chinese Academy of Geological Sciences MNR Key Laboratory of Isotope Geology,100037 Beijing,PR China [2]State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Science and Resources,University of Geosciences,100083 Beijing,China

出　　处：《Acta Geochimica》2022年第5期789-793,共5页地球化学学报（英文）

基　　金：the National Key R&D Programmes of China(Nos.2019YFA0708604 and 2019YFA0708404);the National Natural Science Foundation of China(No.41773018);the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources(No.J1901-29)。

摘　　要：As a powerful tracer in high-temperature geochemistry,Fe isotopes have been studied for their behaviour during fl uid exsolution and evolution related to felsic magma system,but that for carbonatite magma system remains unknown.Here we study the Fe isotope fractionation behaviour during fenitization–processes that widely occur associated with carbonatite or alkaline intrusions.Nine fenite/carbonatite samples from carbonatite dykes at Bayan Obo area are analyzed for their Fe isotope compositions as well as elemental compositions.Combined with previous reported carbonatite δ^(56)Fe data,the results show that carbonatites range from-0.35‰to 0.28‰,with an average of-0.10‰in δ^(56)Fe values,while fenites range from-0.17‰to 0.30‰,with an average of 0.11‰in δ^(56)Fe values.This indicates that fenitizing fl uids exsolved from carbonatite melts are enriched in heavier Fe isotopes.Such a Fe isotope fractionation trend is diff erent from that for fl uid exsolution from felsic magmatism.δ^(56)Fe values in fenites are negatively correlated with indicators of fenitization intensity such as(Na+K),Ti,Ba,Th,Nb,U or Pb abundances,likely refl ecting that Fe isotopes fractionate during the evolution of the fenitizing fl uids.Thus,Fe isotopes are a valuable tool for tracing fl uid exsolution and evolution relevant to carbonatite magmatism and related metal mineralization.

关 键 词：Iron isotopes Fenitization Fluid exsolution CARBONATITE Bayan Obo 

分 类 号：P588.245[天文地球—岩石学] P597[天文地球—地质学]