藏东西藏岩的电气石

西藏岩是以发现地命名的一类新火成岩，相当于电英质火山岩。作为西藏岩最重要 造岩矿物之一的电气石，以其独特的产状、结构和构造等，显著有别于深成岩、交代岩和富电气石岩的电气石。所研究电气石产出的宏观、微观地质特征并借鉴富硼添加剂花岗岩体系 的岩石学实验资料表明，赋存在西藏岩内的电气石，大多数是由一类富硼和水的酸性岩浆- 热液过渡流体（但其总性质偏岩浆，即佤山岩浆），因近地表和内压大于外压，引发在一个较大而有限空间内隐爆、爆破，骤然冷凝结晶，并同石英及其晶屑一起胶结爆破角砾；佤山岩浆溢出期间，电气石与石英可各自聚集结晶并形成韵律状“层纹”。

Tourmaline from Xizangite, Eastern Tibet

Xizangite is a tourmalitic volcanic rocks， discovered and nam ed according to its locality by the authors. This is a new type of igne ous rock. As one of the most important rock-forming minerals within xizangite, the tourm aline from xizangite remarkably differs from that of plutonite, metasomatite a nd tourmalinite in occurrence, texture and structure. Based on the macroscop ic and microscopic mineralogical features of studied tourmaline, and the publish ed experimental data derived from studies of granitic system with added boron, t hi s paper suggests that the majority of tourmaline from xizangite was crystallized directly from a suddenly condensing B- and H2O-rich acid magmatic-hydr othermal transitional fluid. However, it bears even more analogy with magma in overall nature, or the washanite magma. While approaching the earth's surfac e, the internal pressure of washanite magma was much higher than the external p ressure and the space was limited. A cryptoexplosion-explosion took place, and tourmaline cemented the breccia together with quartz and crystals-clasts. Durin g washanite magma overflowing tourmaline and quartz could accumulatively crystal lize separately and form the rhythmic “layering structure.”