摘要
花岗岩中锆石的电子荧光观察和微量元素分析表明,锆石中的韵律环带结构主要是以较宽的浅灰色条带与较窄的灰黑色条带交替重复出现而形成的。相应于条带灰度的变化,呈负相关性的锆与呈正相关性的铀的含量亦在起伏变化。由于锆石中铀与锆的类置同象置换是非常有限的,锆石中铀含量的变化主要取决于铀的分配系数的变化。因此,当含铀锆石的结晶过程处于非理想体系时,它以固溶体相变的形式来协调固液界面的局部体系与整个花岗质熔体的热力学平衡,从而形成含铀锆石的两种固溶体相交替生长的韵律环带结构。
Cathodoluminescent observations and trace elements analyses of zircon crystals from granitic rocks show that oscillatory zoning in zircon crystals is reflected by the repeated appearance of wide light-grey zones and narrow dark-grey zones. The greyness of each zone is correlated negatively with the content of Zr and positively with that of U. Because of the limited substitution of Zr by U in zircons, the variation in U content of zircons is dependent mainly on the partition coefficient of U between melt and zircon. In a nonideal system, the crystallization of U-bearing zircons might adjust the thermodynamic equilibrium between local melt at the solld-liquld interface and total granitic magma by the alternative change of solid-solutlon phases of U-Zr, hence giving rise to oscillatory zoning as observed in zircon crystals.
出处
《矿物学报》
CAS
CSCD
北大核心
1993年第2期124-129,共6页
Acta Mineralogica Sinica
关键词
锆石
韵律环带结构
铀
花岗岩
zircon
oscillatory zoning
uranium
limited solid solution
partition coefficient
