摘要
碧口群火山岩系中部的基性熔岩以拉斑系列为主 ,基性火山岩的Sr同位素初始比值和Nd同位素初始比值较低 ,分别为 0 .70 12 4 8～ 0 .70 4 4 13和 0 .5 110 80～ 0 .5 12 341,大部分样品的εNd(t) >0 ,表明母岩浆主要来自地幔源区。岩石显示明显的富2 0 7Pb及2 0 8Pb特征。在以部分熔融作用为主的演化过程中岩浆发生了一定程度的分异 ,LREE、大离子亲石元素等表现了从亏损到富集的变化特点。基性熔岩的稀土与微量元素表现出与俯冲碰撞型的弧区玄武岩相同的特点。分析表明 :碧口群火山岩系形成于岛弧环境 ,它与横丹群浊积岩系在扬子板块西北缘构筑了一个弧盆系统 ,其时代为新元古代。
The Bikou volcanic terrane is predominated by tholeiitic marine lavas, with lower initial ratios of Sr and Nd, 0.701?248～0.704?413 and 0.511?080～0.512?341 respectively. Analyses also showed that most samples have negative εNd, which indicates that magma was probably derived from the mantle, while those with positive εNd perhaps resulted from magmatic contamination. In addition, rocks have significantly higher ^(207)Pb and ^(208)Pb. REE patterns and trace element spider diagrams indicate that magma generated by partial melting gave rise to some extent of differentiation during its evolution. Consequently, LREE and LILE demonstrated variation from depletion to enrichment. Besides, Basic lavas from the Bikou volcanic terrane showed the same characteristics as those from arcs in the background of subduction and collision with the consideration of ratios ofTh/Yb, Th/Nb and Hf/Th. New evidence showed that the Hengdan group is a turbidite terrane filled in a forearc basin, and both the Bikou and the Hengdan groups construct an arc-basin system developed on the north margin of Yangtze plate. SHRIMP ages indicated that the arc-basin system developed in the Neoproterozoic.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2004年第1期1-11,共11页
Acta Petrologica et Mineralogica
基金
国家自然科学基金资助项目 (4 0 172 071
49972 0 74)
国家自然科学基金国际合作交流资助项目 (4 0 2 1112 0 15 1)
中国地质调查局资助项目 (DKD2 0 0 10 0 2 )
973资助项目 (2 0 0 2CB412 60 8)
