摘要
li-F花岗质岩石以超酸性、过铝、富含H2O、F、B、P等挥发性组分和富含Li、Rb、Cs、Be、Ta、Nb、Sn、W等亲石稀有金属元素为主要特征,以黄玉-锂云母-钠长石花岗岩为典型代表。从该类岩石地质产状的多样性和可对比性、空间分布的规律性、矿物岩石的结构构造、硅酸盐-熔体包裹体特征以及实验岩石学的研究成果等方面,综合论证该类岩石主要是从经过分异演化而形成的残余熔浆中直接结晶而成的;充分的分离结晶作用,是产生这种残余熔浆的主要机制;岩体的空间分带特征和各带之间的渐变过渡关系,为分离结晶作用的途径和演化方向提供了重要信息;熔体中挥发性组分的大量存在,是分离结晶作用能充分进行的关键因素;亲石稀有金属元素在流/熔配分中倾向于进入熔体相,是残余熔体中逐步富集这些稀有金属元素的主要原因;岩浆-热液过渡阶段出溶的流体相与已晶出的共存固相之间的相互作用,造成了广泛的交代蚀变现象;残余熔浆在不同地质和物理化学环境中的侵位、结晶和演化,造成了Li-F花岗质岩石在产状、结构构造和矿物组合等方面的多样性。
Li F rich and rare metal bearing granitic rocks are characterized by ultra acidity, aluminium oversaturation, enrichment in volatile components, such as H2O, F, B and P etc., and high concentration of lithophile rare metal elements, such as Li, Rb, Cs, Be, Ta, Nb, Sn and W etc., and are represented by the topaz lepidolite albite granites. Based on the similarity in chemical compositions, significant variation in geological occurrences, regularities in spatial distribution, structures and textures of rocks and mineral constituents, silicate melt inclusions in minerals, and results of experimental petrological studies, these rocks are essentially the products of crystallization from the Li F rich and rare metal bearing residual granitic melts. Well evolved fractional crystallization is the major mechanism in generation of this kind of residual melts. The spatial zonation and gradual transition between different zones provides an important clue for the path and progressive evolution of the fractionation. Existence of large amounts of volatile components in the melts is an important factor for well evolved fractional crystallization. Tentative partitioning of lithophile rare metal elements into the melts is the major control for their enrichment in residual granitic melts. Interaction of exsolved fluid phase with coexisting solid phase during the magmatic hydrothermal transition stage yields a widespread metasomatic alteration. Emplacement, crystallization and evolution of these melts at different geological and physico chemical environments result in large varieties of Li F granitic rocks in geological occurrences, structures and textures, and mineral associations.
出处
《地球化学》
CAS
CSCD
北大核心
2002年第2期141-152,共12页
Geochimica
基金
国家自然科学基金(49873017
49973022)
高校博士点基金(1999028420)
