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贵州碳酸盐岩风化壳中的晶体石英具有较强的测年潜力,其成因判别是年代学研究的前提和基础。对黔北、黔东地区3个碳酸盐岩风化壳剖面中的晶体石英和圆状石英进行了研究,拟通过晶体石英的δ18O值探讨其形成条件。结果表明,晶体石英的δ18O值在17.3‰～22.7‰范围内,平均为19.8‰,与火成岩、变质岩及热水(液)沉积中高温成因石英δ18O值明显不同;与砂岩中的碎屑石英、现代海滨砂中的石英以及风成沉积物中的石英等混合来源石英的δ18O值也有差异;尽管黔东大兴剖面中晶体石英和圆状石英的δ18O值相近,但它们的硅氧同位素相关关系不同,它们具有不同的成因;晶体石英的δ18O值分布在低温成因石英δ18O值范围内,这与其中未见两相包裹体的现象一致。结合实际资料和已有认识,推断晶体石英是包气带地表温度(15～25℃)条件下缓慢生长形成的;其形成过程与碳酸盐岩风化成土的两阶段模式密切相关:酸不溶物风化形成的含硅流体向下淋滤至风化壳底部后被圈闭在已形成的孔隙、空洞中,由于蒸发作用达到过饱和而缓慢结晶形成晶体石英。
Crystalline quartz in weathering crusts of carbonate rocks in Guizhou has strong dating potential, and its genetic differentiation is the precondition and basis of geochronology research. Crystalline quartz and round quartz in three carbonate weathering crust sections in northern Guizhou and eastern Guizhou were studied, and the formation conditions of quartz were discussed based on their δ18O values. The results show that the δ18O value of crystalline quartz is in the range of 17.3 ‰ ~ 22.7 ‰, with an average of 19.8 ‰, which is obviously different from the δ18O value of igneous quartz in igneous rocks, metamorphic rocks and hydrothermal (liquid) sediments. However, the δ18O values of quartz mixed in modern seashore sand and quartz in aeolian sediments are also different. Although the δ18O values of crystal quartz and round quartz in Qiaodong Daxing section are similar, their silicon-oxygen isotopic correlations They have different causes. The δ18O value of quartz is distributed in the δ18O value of low-temperature quartz, which is consistent with the fact that no two-phase inclusions exist in it. According to the actual data and previous understanding, it is deduced that the crystalline quartz is formed slowly by the surface temperature (15 ~ 25 ℃) in the aeration zone. The formation process is closely related to the two-stage model of carbonate weathering: The silicate fluid formed by weathering is leached down to the bottom of weathering crust and trapped in the formed pores and voids. Crystalline quartz crystallizes slowly as it reaches saturation due to evaporation.