华南陡山沱组磷块岩中微米级自形钠长石的发现及其可能成因

发布时间：2018-01-26 00:56

  本文关键词： 自生钠长石 陡山沱组 磷块岩 微生物　出处：《地学前缘》2017年01期 　论文类型：期刊论文

【摘要】：文中报道了在华南新元古代震旦纪陡山沱组磷块岩中首次发现的大量微米级自形长石。岩相学观察显示这些长石为自形-半自形板-柱状,呈团聚状或分散状产于砂级胶磷矿颗粒中,粒径大多在10~30μm,光学显微镜下无法观察到双晶。扫描电镜能谱(EDS)半定量分析表明这些自形长石为钠长石。电子探针(EPMA)分析显示所测样品钠长石端员(Ab)平均含量为97.96%,与典型自生钠长石成分一致。钠长石所包裹有机质的拉曼光谱特征指示其经历的最高温度不超过350℃,排除了其来源于高温的岩浆岩或高级变质岩的可能性。以上资料表明这些微米级自形长石为典型的自生成因高纯钠长石,可能形成于磷块岩的早期成岩阶段。自生钠长石与丝状化石常相伴出现,与前人通过嗜碱菌还原黏土矿物实验所获得微米级长石及微生物的产出关系相似;钠长石核部可见富含有机质,表明后者可能促进了矿物的生长。文中提出磷块岩中自生钠长石的成因模式:钠长石的Al和Si来自于黏土矿物的分解,该过程可能受嗜碱微生物介导;Al和Si与来源于海水或碳氟磷灰石晶格中的Na~+结合,在低温条件下结晶形成高纯度钠长石。微生物及其相关有机分子可能为钠长石结晶提供了成核点。
[Abstract]:In this paper, a large number of micron automorphic feldspar were first found in the Phosphorite of the Neoproterozoic Doushantuo formation in South China. It is agglomerated or dispersed in sand grade cemented phosphate rock particles, the particle size of which is mostly 10 ~ 30 渭 m. Double crystals could not be observed under optical microscope. The semi-quantitative analysis of scanning electron microscope (SEM) EDS showed that the eutectic feldspar was albite. The electron probe analysis (EPMA) showed that the measured sample was albite end member Ab). The average content was 97.96%. It is consistent with the composition of typical authigenic albite. The Raman spectra of the organic matter encapsulated in albite indicate that the highest temperature is not more than 350 鈩，

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