摘要
沉积岩中的磷灰石是一类含CO_2量不等的碳氟磷灰石。在成岩作用过程中,随着成岩强度的增加,碳氟磷灰石结构中的CO_2逐渐丢失,从而引起矿物折光率、比重、晶胞参数和晶体化学性质的系统变化。作者在X-衍射和红外光谱研究的基础上,进一步提出了划分成岩阶段的磷灰石矿物结晶度指数和锐度指数两个参数,为成岩作用阶段划分提供了一种新的标尺。由于沉积岩中磷结核、条带和磷泥晶胶结物的广泛存在,这一新标尺可能有广泛应用的前景。
The apatites occurring in sedimentary rocks belong to carbonate-fluor-apatite (C-F aparite) with different CO_2 contents. In the diagenetic processes, the CO_2 content of C-F apatites becomes lower systematically with an increase in diagenetic strength; as a result, a whole evolutionary series of apatites, i.e. the higher C-F apatite-medial C-F apatite-lower C-F apatite-trace C-F apatite series, is formed, and finally it changes into fluorapatite.Owing to the loss of CO_2, the refraction indexes and specific gravities of apatite minerals gradually increase; furthermore, the cell dimension also increases and the chemical proporties of crystals change systematically too.With an increase in diagenetic strength, the shapes of apatite crystals change from colloid through cryptocrystalline and microcrystalline to fine and medium crystals; meanwhile, obvious changes take place in X-ray diffraction and IR spectra of apatites. The crystallinity of apatite gradually increases, its X-ray diffraction strengths of (211), (112), (300) and (002) peaks gradually rise, and the split of diffraction peaks becomes gradually complete. Its IR spectra strength and split degree also change in the same way as X-ray diffractions.Based on these studies, the author proposes two parameters for division of diagenetic stages, i.e. the crystallinity index (CR) and sharpness index (SH), which can measure the crystal strength of apatite minerals. The calculated formulas and the values of stage division of diagenesis are as follows:When SH<24.0 and CR<2.5, the diagenetic stage is indicated; when 54.0>SH≥24.0 and 6.0>CR≥2.5, it is the epigenetic stage; when SH≥54.0 and CR≥6.0, the stage enters metamorphic stage。
出处
《地质学报》
EI
CAS
CSCD
北大核心
1989年第4期310-323,共14页
Acta Geologica Sinica
基金
国家自然基金4861080项目资助
