南岭花岗岩类起源与稀土元素的分馏

南岭地区广泛发育的不同时代的各种花岗岩类是古老基底(1200—1800Ma)活化重熔的产物。在花岗岩的形成和演化过程中,有五种最主要的方式造成REE的分馏作用:(1)部分熔融作用;(2)分离结晶作用;(3)热重力扩散作用;(4)变质-混合岩化作用和(5)热液流体作用。其中第(2)和(3)种作用是引起HREE富集的最主要过程。地质构造背景、铅锶同位素组成和锆石群型资料一致表明:岩浆演化的局部物理化学环境是控制REE分馏的关键因素。

DifFerentiation of Rare Earth Elements and Origin of Granitic Rocks, Nanling Mountain Area

In Nanling Mountain area, a very important metallogenic province of China, the various granitic rocks with different ages are widely distributed. During the evolution of these granitoids which resulted from rejuvenation and anatexis of the old basement (1200-2000Ma), the main ways for REE differentiations were: (1) partial melting; (2) fractional crystalization; (3) thermogravitational diffusion; (4) differentiations of metamorphism and migmatism, and (5) hydrothermalism. Among them the (2) and (3) processes are the most important ones for HREE concentration in magma. Based on the data of tectonic setting, lead and strontium isotopic compositions and zircon population types, it is concluded that local physicochemical environment of magma is the key constraints to REE fractionations.