铀系不平衡与洋中脊下的岩浆形成及其迁移过程  

U-SERIES DISEQUILIBRIUM ON MAGMA GENERATION AND TRANSPORTATION BENEATH MID-OCEAN RIDGE AXES

作　　者：张国良[1] 曾志刚[1] 殷学博[1] 

机构地区：[1]中国科学院海洋研究所海洋地质与环境重点实验室

出　　处：《海洋地质与第四纪地质》2008年第1期77-84,共8页Marine Geology & Quaternary Geology

基　　金：中国科学院知识创新工程重要方向项目(KZCX3-SW-223,KZCX2-YW-211);国家大洋专项课题(DYXM-115-02-1-03)

摘　　要：综述了20多年来洋中脊新生玄武岩中铀系不平衡研究成果,分析了铀系不平衡的形成机制和主要影响因素,并探讨了铀系不平衡研究中的一些问题。结果表明:(1)玄武质岩浆中230Th/238U不平衡可能产生于石榴子石稳定的深部源区,也可能来自230Th的"内部增长"(in-growth),过剩230Th更可能形成于含铝单斜辉石;(2)226Ra/230Th不平衡可能来自岩浆的形成过程,也可能来自岩浆迁移过程;(3)铀系不平衡与岩浆滞留时间和上升速率紧密相关,226Ra的大量过剩显示,这个不平衡事件形成于8ka以内,如果不考虑玄武质岩浆迁移过程的事件,则意味着岩浆迁移时间不超过8ka。提出当前亟待解决的问题:①准确模拟地幔部分熔融条件并测定铀系子体在熔体/地幔残留相间的分配系数;②提出更合理的结晶分异模型;③探索流体对226Ra/230Th不平衡的影响。The study of U-series disequilibrium in Mid Ocean Ridge basalts （MORB） of last 20 years has been comprehensively reviewed and the main results have revealed that：（1）^230 Th-^238U disequilibrium of the basalt may be generated in deep sources where garnet is stable and also from the in-growth of the ^230Th. The genesis of ^230 Th excess can be formed more likely in the presence of the clinopyroxene which contains aluminum. （2）The formation of ^226Ra-^230Th disequilibrium is attributed to the magma formation and also to its transportation. （3）Magma residence and transportation time can be reflected by U-series disequilibrium. Magma transportation time can not exceed 8 000 years regardless of other events during the magma transportation, because large ^226Ra excess must be generated within 8 000 years. Further work needs to be done to improve our understanding of the formation of U-series disequilibrium ： （1）Modeling of the partial melting of the mantle and determining the partition coefficients of the U-series daughters between the mantle solid and melt with accuracy. （2）Establishing suitable model of the fractional crystallization. （3）Unraveling the fluid influences on the ^226Ra-^230Th disequilibrium.

关 键 词：洋中脊玄武岩 铀系不平衡 岩浆形成 岩浆迁移 

分 类 号：P736.12[天文地球—海洋地质]