Geochemical Characteristics of Rodingite Derived from Eclogite in Western Tianshan, Xinjiang, China and Its Implication for Subduction Zone Fluid
详细信息
- 责任者：Shen TingTing(Laboratory of Crustal and Orogenic Evolution ; Peking University ; Beijing 100871 ; China) ; Zhang LiFei
- 刊名：Acta Petrologica Sinica
- 出版年：2012
- 卷期：28(7)
- 关键词：变火成岩 ; metaigneous rocks ; 天山 ; Tianshan Mountains
- 页码：p.2235-2249
- 图表：illus.,5 tables,39 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Rodingite in Changawuzi,Western Tianshan,China, is a new rodingite type derived from eclogite,and is the first occurrence that formed in the subduction zone.The fluid triggered rodingitization is subduction zone fluid.Compared with the rodingite formed during ocean-floor metamorphism,Changawuzi rodingite have similar petrology characteristic,but something different in elements migration.In order to infer the composition of the fluid,we tried three methods.First,we tested the chemical compositions of the main minerals garnet and pyroxene before and after rodingitization.Second,the ACF diagram,showing the bulk compostion changed from F side to C side,illustrate that Fe is decreasing and Ca is increasing.In addition,the bulk compositions of completely rodingited rocks are included in the area studied before.Third,assuming that Al is not moved during rodingitization,based on the method of Grant,we calculated the isocon diagrams of major elements,trace elements and REE.Based on the three methods we infer that the composition of the fluid is complicated and varied during rodingitization.In the stage of partial rodingitization,the fluid is rich in Ca,Si,Ti,Mn,Nb,Ta,Zr,Hf with high oxygen fugacity and Fe,Mg,Na,K,REE,Tb,Y are depleted.The fluid in this stage is not abundant so that a lot of unbalanced structures developed.In the stage of complete rodingitization,the fluid is rich in Ca,Mg,LREE,Ni,Cr and poor in Fe,Ti,Rb,Ba,MREE,HREE.The fluid process is strong and most of the elements migrate because of intense eluviation by the water-rich Ca bearing fluid.