华南富锂氟含稀有金属花岗岩的成冈分析

雪球结构的产出特征、钠长石电子探针分析及其它间接证据都说明，雪球结构是在岩浆结晶过程中形成的。雪球结构形成与否主要与岩浆熔体中Ｎａ２Ｏ／Ｋ２Ｏ比值和Ｆ、Ｈ２Ｏ含量有关。较大的Ｎａ２Ｏ／Ｋ２Ｏ比值（〉１）例钠长石首先从熔体中晶出；较高的Ｆ含量使岩浆固相线温度大大降低，有利于岩浆分异演化并形成接近端员组分的钠长石和钾长石同的Ｈ２Ｏ含量有利于石英以较快的速度生长并逐渐包裹钠长石形成雪球结构。自形的α－石英斑晶、接近各自端员组分的甲和工石和钠长石等说明该类花岗岩形成温度较低，众多的地质、地球化学依据都证明了，华南富锂氟含稀有金属花岗岩是从过铝富氟富钠的残余熔体中直接结晶而成的。

Genetic interpretation of Li-F-Rich rare metal-bearing granites in south China

The mode of occurrence of snow ball texture, the electron microprobe analysis of albite from quartz and K-feldspar phenocrysts as well as other evidence suggest that the snow ball texture might have been generated during the crystallization of magmatic melt. The formation of snowball texture was closely related to the Na2O/K2O ratio as well as the fluorine and H2O content of the granitic melt. The relative high Na2O/K2O ratio (> 1) probably caused the first crystallization of albite. The increase of fluorine content might have resulted in the decrease of solidus temperature and benefited the evolution of magma and the formation of K-feldspar and albite approximately with end-member composition. Comparatively high content of H2O was favorable for the faster growth of quartz than albite. Finally, the quartz phenocrysts which contained albite laths might form snow ball texture. Snow ball texture, together with low melting temperature of the granites, euhedral U= type quartz phenocrysts as well as K- feldspar and albite approximately with end-member composition, indicates that L-F- rich rare metal-bearing granites in South China were directly crystallized from the peraluminous F-N a- rich residual granitic melt.