Origin of two differentiation trends in the Emeishan flood basalts  

作　　者：XUYigang CHUNGSun-Lin 等 

机构地区：[1]GuangzhouInstituteofGeodchemistry,ChineseAcademyofSciences,Guangzhou510640,China [2]DepartmentofGeology,TaiwanUniversity,Taipei,Taiwan,ChinaCorrespondenceshouldbeaddressedtoXuYiagang

出　　处：《Chinese Science Bulletin》2003年第4期390-394,共5页

基　　金：supported by the Ministry of Science and Technology(Grant No.G1999043205);the Chinese Academy of Sciences(Grant No.KZCX2-101);the National Natural Science Foundation of China(Grant No.40234046).

摘　　要：Both the Bowen and Fenner differentiation trends have been recognized in the Emeishan flood basalts. While the Longzhoushan lavas in Panxi paleorift evolved on a trend of silica enrichment (Bowen trend), the lavas from Guizhou evolved along the Fenner trend leading to the magmas with high Fe2O3 (23%) and low SiO2 (44%) contents. This provides evidence for the existence of Fe-rich and Si-poor magmas in nature. Such contrasting differentiation trends, marked by different timing of crystallization of Fe-Ti oxides, are correlated with the extent of crustal contamina-tion of the magmas. Limited crustal contamination in the Guizhou lavas is coupled with the low oxygen fugacity which delayed the onset of magnetite crystallization. In contrast, significant involvement of crustal components in the Long-zhoushan lavas increased fO2 which in turn triggered early crystallization of magnetite. The close spatial association between the Longzhoushan lavas and the synchronous V-Fe- Ti deposit-bearing layered intrusions suggests a potential relationship between them.Both the Bowen and Fenner differentiation trends have been recognized in the Emeishan flood basalts. While the Longzhoushan lavas in Panxi paleorift evolved on a trend of silica enrichment (Bowen trend), the lavas from Guizhou evolved along the Fenner trend leading to the magmas with high Fe2O3 (23%) and low SiO2 (44%) contents. This provides evidence for the existence of Fe-rich and Si-poor magmas in nature. Such contrasting differentiation trends, marked by different timing of crystallization of Fe-Ti oxides, are correlated with the extent of crustal contamina-tion of the magmas. Limited crustal contamination in the Guizhou lavas is coupled with the low oxygen fugacity which delayed the onset of magnetite crystallization. In contrast, significant involvement of crustal components in the Long-zhoushan lavas increased fO2 which in turn triggered early crystallization of magnetite. The close spatial association between the Longzhoushan lavas and the synchronous V-Fe- Ti deposit-bearing layered intrusions suggests a potential relationship between them.

关 键 词：峨眉山 大型火成区 富铁岩浆 地壳污染 玄武岩 分化 

分 类 号：P588.145[天文地球—岩石学]