夕线石成因讨论
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P578.94+5

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国家自然科学基金项目(41941004,41472172)


Discussion on the origin of sillimanite
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    摘要:

    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、变质作用,尤其是深熔作用密切相关。浅色体、伟晶岩及花岗岩等均可通过变质、深熔作用演化而成。夕线石形成的关键是深熔作用中碱(土)金属的迁移、淋滤及其与硅铝组分的分离,从而造成局部Al2O3相对增加。夕线石尤其是毛发状夕线石对应于早期差异性变形-变质作用阶段。组分迁移过程中溶液或熔体组分的流动导致夕线石出现"应力定向"的假像、夕线石和相关矿物的聚集以及不同变质矿物的多个演化阶段。铝硅酸盐Al2SiO5的不同变体虽然成分相同,其所产出的岩石类型或环境仍有显著的差别,其形成不仅受温压条件控制,流体或熔体的酸碱性质也很重要,介质成分可影响到铝的配位。

    Abstract:

    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.

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任留东,2022,夕线石成因讨论[J].岩石矿物学杂志,41(2):437~445. REN Liu-dong,2022,Discussion on the origin of sillimanite[J]. Acta Petrologica et Mineralogica,41(2):437~445.

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  • 收稿日期:2021-11-19
  • 最后修改日期:2022-02-10
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  • 在线发布日期: 2022-03-21
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