白云石成因研究新方法——白云石晶体结构分析
- 收稿日期:
2013-12-09
- 修回日期:
2014-03-17
- 刊出日期:
2014-06-10
摘要: 传统的白云石研究方法对于白云石成因分析具有多解性，对于已有白云石成因模式的套用或重新建立新的白云石成因模式将白云石的形成机理过于简单化、模式化。白云石的晶体结构保存了晶体的形成环境、结晶速度、晶体生长与变化特征、流体特征的证据，白云石晶体结构分析是进行白云石成因分析的有效手段，之前很少有研究者从晶体结构角度进行白云石成因分析。在岩石学和地球化学研究的基础上，本文对四川盆地灯影组—寒武系鞍状白云石、纤状白云石、残余颗粒细晶白云石、孔洞充填粗晶白云石和泥晶白云石五种白云石进行了微组构取样，并利用X衍射仪、透射电镜等晶体结构研究手段，从晶体结构角度对五种白云石组构的有序度、晶胞参数、晶格条纹、晶面间距、晶格缺陷等晶体结构参数进行了差异性研究，分析了它们不同的形成环境和成岩演化特征，初步建立了不同类型白云石晶体结构判识标志。
New Approach on the Study of Dolomite Origin: The crystal structure analysis of dolomite
- Received Date:
2013-12-09
- Rev Recd Date:
2014-03-17
- Publish Date:
2014-06-10
Abstract: There is multiplicity during the study of dolomite origin with conventional methods. It is over simple and patternized using the existing dolomite models or establishing new models. The crystal structures of dolomite preserved the forming environments, crystallizing velocity, crystal growing and diversification characteristics of dolomite crystals and the fluid characteristics, and so on. The crystal structure analysis of dolomite is an effective method to explore the origin of dolomite, which was concerned by few researchers. Based on petrographic and geochemical studies, this paper used X-ray diffraction, TEM and EPM methods and focused on the different characteristics of ordering degrees, crystal cell parameters, crystal lattice stripes, interplanar distances, and lattice defects of 5 different kinds of dolomite crystals (saddle dolomite, fibrous dolomite, fine crystal dolograinstone, coarse crystal dolomite in vugs and micritic dolomite) from Sinian Dengying Formation-Cambrian in Sichuan Basin after micro-fabric sampling and discussed the variation of the forming environments and upgrowth features. Different dolomites with varial crystal forms, sizes, burial depths and petrographic characteristics have disparate crystal structures. Saddle dolomites from hydrotherm have low ordering degrees (0.42~0.68), higher cell parameter c value and abnormal distribution in crystal cell parameter chart, curved lattice stripes, notable branched and ribbon-like lattice defects and narrower interplanar distances. Fibrous dolomites cements from seawater have absolute order structures (ordering degree=1), ideal cell parameters, exquisite lattice stripes, few lattice defects and narrow interplanar distances. Fine crystal dolograinstones with burial replacement origin have high ordering degrees (0.96~0.97), high cell parameters c values, regular lattice stripes, few lattice defects and near-dial interplanar distances. Coarse crystal euhedral dolomites cements from pores have higher ordering degrees (0.905~0.97), various cell parameter c values because of different burial depth, straight lattice stripes, unfrequent lattice defects and near-ideal interplanar distances. Authigenic micritic dolomites from nearsurface environment has lower ordering degrees (0.64~0.832), a little lower cell parameter c values, inlaid lattice stripes, equable lattice defects, a little narrow interplanar distances. Based on 5 kinds of dolomites crystal structure assemblages, the crystal structure identification marks of different dolomites were preliminarily established.
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