摘要
变形作用可以引起Rb－Sr同位素较大的活动性，但是Sm－Nd同位素相对保持稳定。流体在剪切带活动期间以渗透方式沿着糜棱叶理面运移为主，在活动期结束后则以孔隙流体方式保留在岩石中。Rb、Sr同位素可以在垂立于糜棱叶理方向上十分短的距离内（厘米尺度）达到再平衡。因此，通过选择适当的样品和采用“薄板”技术，Rb－Sr全岩等时线方法可以测定剪切带发生糜棱岩化作用的时间。在低级对中级变形变质作用环境下，流体／岩石反应对Sin、Nd同位素体系的干扰作用较小，但是，在高级变形变质条件下，一些REE未发生分馏的岩石中，Sin、Nd同位素可以测定岩石的成岩年龄．然而．在另外一些REE元素发生分馏的岩石中，Sm、Nd同位素发生了一定程度的重调。
Deformation can cause Rb-Sr isotopes to be more active, but Sm-Nd isotopes keep relatively im-mobile. During the shear zone activiting, fluid migration is mainly by means of infiltrative fluid trans-porting along mylonitic foliation; after the active period, the fluid is kept in the rock as pore fluid. Rb-Sr isotopic reequilibrium will reach over short distance (on a centimeter scale) perpendicular to the my-lonitic foliation. Therefore, by selecting proper samples and using 'thin-slab' technique, whole-rock Rb-Sr isochron method can be used to date the timing of mylonitization in the shear zone. Under the circumstance of low- to medium-grade deformation and metamorphism, fluid/rock interaction has less disturbance to the Sm-Nd isotopic system. In contract, under high-grade deformation and metamor-phism, Sm-Nd isotopes can be used to date the timing of formation of the rock if no fractionation of some REE elements happened, but in those rocks where the fractionation happened, Sm-Nd isotopes will be reset to some extent.
出处
《地质地球化学》
CSCD
北大核心
1997年第3期70-75,共6页
Geology-Geochemistry
关键词
韧性剪切带
铷
锶
钐
钕
同位素体系
ductile shear zone
Rb-Sr
Sm-Nd
infiltrative fluid
'thin-slab' technique
