广东凡口地区泥盆系碳酸盐岩化学成岩作用

Chemical Diagenesis of the Devonian Carbonate Rock in the Fankou LeadZinc Mine Area

阴极发光技术揭示了碳酸盐岩成岩作用的多阶段性。主要成岩作用发生于浅埋条件。这种环境的Ｅｈ、ｐＨ值较低，矿物中含锰，导致弱发光。岩石的碳、氧同位素值偏离了海相环境的值域。根据Ｓｒ／Ｃａ比推算，成岩溶液相当于淡水中加入不足１０％的海水。基于这些研究，作者提出一种新的成岩作用方式—溶实作用。

The multiplestage diagenesis was revealed by the cathodoluminescence of carbonate rock samples. The minerals precipitated in shallowburial condition where the primary diagenesis occured are higha in a Mn content with weak luminescence, which resulted from the drop of Eh and pH values due to the decomposition of organic substances. With further falling of the Eh and pH values, the increase of Fe 2+ contained in the minerals quenched the luminescence. Being in a deepburial condition, the pH value was controlled by the equilibrium between carbonate minerals and water, so the environment is alkalescent. The condition is favourable to the formation of Mn(Ⅱ) cation and contrary to Fe(Ⅱ) cation. As a result, this precipitated minerals have a bright luminousness. The carbon and oxygen isotope compositions of the whole rocks deviated from the range of marine environment but weve close to that of freshwater diagenetic environment. Diagenetic solution based on the Sr/Ca ratio in the minerals was analogous to that of freshwater mixed with less than 10% marinewater. This solution made the minerals in limemud sediments dissolved and brougt about dissolvedreprecipitatlon a dynamic equilibrium with the increase of saturation. Baced on the studies above, the authors suggested “dissolvedsolidification” is a new diagenetic pattem of limemud sediments solidified in freshwater by way of dissolvedreprecipitation, which made the new minerals arranged inseparably.