夕线石成因讨论

本文通过夕线石的结构、成分及产出状态,系统讨论和总结了其变质形成过程.含夕线石的变质岩原岩未必对应泥质岩,富夕线石岩石成分上更不能与任何的泥质岩成分对应.原岩本身富铝如多数泥质岩是形成夕线石非常有利的成分条件,但是,即使有合适的温压条件,也未必能够形成夕线石,组分的差异性迁移才是夕线石形成的必要条件.夕线石的形成与变形...

Discussion on the origin of sillimanite

Through the structure, composition and occurrence of sillimanite, the formation process of sillimanite has been discussed and summarized in this paper. In composition, the protolith of the sillimanite-bearing metamorphic rocks is not necessarily pelite rocks, the sillimanite-rich rocks does not necessarily correspond to any pelite rocks. The Al-rich feature of the pelite is favorable for occurrence of sillimanite, but sillimanite may not occur in the rock even under appropriate metamorphic temperature and pressure condition. The differential migration of components is essential for sillimanite. The formation of sillimanite is closely related to deformation and metamorphism, especially anatexis in metamorphic rocks. Leucosome, pegmatite and granite all can evolve through metamorphism and anatexis. The key to the formation of sillimanite is the migration and leaching of alkaline(-earth) metals and their separation from sial components, resulting in the relative enrichment of Al₂O₃. Sillimanite, especially fibrolite, corresponds to the early differential deformation-metamorphism stage. In the process of component migration, the flow of solution or melt components leads to the false image of "stress orientation" of sillimanite, the aggregation of sillimanite and related minerals, and multiple evolution stages of different metamorphic minerals. Although different variants of Al₂SiO₅ have the same composition, their rock types or environments are still significantly different. On the one hand, their formation is not only controlled by temperature and pressure conditions, but also the acidity or alkalinity of the fluid or melt, which is critial in affecting the coordination state of aluminum.