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峨眉山玄武岩属典型低渗透介质,其岩体风化是通过结构体风化实现的。风化玄武岩结构体具有一层或多层腐岩壳包围核心石形成的壳状结构;从表面向内,越靠近结构体几何中心,玄武岩风化程度越低。玄武岩风化可分为初期和中后期两个阶段,第一阶段仅存在二价铁向三价铁的转变而无明显组分流失与相对富集,第二阶段二价铁氧化与活动性组分(Si、Ca、Mg、Na、K)淋失和惰性组分(Al、Ti、∑Fe)相对富集同时发生。风化初期,随着风化程度的提高,FeO和Fe2O3相对含量此消彼长,但∑Fe相对含量变化不大;风化中后期,随着风化程度的提高,SiO2、CaO、MgO、Na2O、K2O、FeO相对含量单调降低,Al2O3、TiO2、Fe2O3、LOI单调升高。玄武岩风化过程中,FeO和Fe2O3相对含量对风化程度变化最为敏感。贯穿整个风化过程的含铁矿物氧化引起的铁种相对含量变化应成为峨眉山玄武岩风化程度评价需要考虑的关键因素。
Emeishan basalt is a typical low-permeability medium, and its rock weathering is achieved through structural weathering. The weathered basaltic structure has one or more layers of shell-shaped structure formed by the core surrounded by saprolite shells. The basalts are weathered inwardly and closer to the geometric center of the structure. Basalt weathering can be divided into two stages: early stage and late stage. In the first stage, there is only the change of ferrous iron to ferric iron without significant loss and relative enrichment. In the second stage, ferrous iron oxidation and active component (Si, Ca, Mg, Na, K) leaching and inert components (Al, Ti, ΣFe) relative enrichment occurs simultaneously. In the initial stage of weathering, the relative content of FeO and Fe2O3 increased with the degree of weathering increasing, but the relative content of ΣFe changed little. During the middle and late weathering stages, the content of SiO2, CaO, MgO, Na2O, K2O, The relative content of FeO monotonically decreased, and the content of Al2O3, TiO2, Fe2O3 and LOI monotonically increased. During basalt weathering, the relative contents of FeO and Fe2O3 are most sensitive to the change of weathering degree. The change of the relative content of iron species caused by oxidation of iron-bearing minerals throughout the weathering process should be the key factor to be considered in the evaluation of the weathering degree of basalt Emeishan.