碳酸钙同质多象转变过程中氧同位素分馏的实验研究  

Experimental Studies of Oxygen Isotope Fractionation in the Polymorphic Transformation of CaCO_3 Minerals

作　　者：周根陶[1] 郑永飞[1] 

机构地区：[1]中国科学技术大学地球和空间科学系化学地球动力学研究实验室,合肥230026

出　　处：《地质学报》2001年第2期267-276,共10页Acta Geologica Sinica

基　　金：国家自然科学基金(编号49903001;49453003);中国科学院专项基金

摘　　要：本文通过“一步法”和“两步法”的“附晶生长法”分别合成了碳酸钙矿物,对其进行了同质多象转变过程中的氧同位素分馏行为的研究。同时通过真空条件下的同质多象转变实验,对文石和方解石的酸分馏系数的差异进行了实验验证。结果发现:①在50℃和70℃下,如果文石与水之间的氧同位素分馏未达到平衡,由母体文石经过同质多象转变生成的次生方解石完全继承了母体矿物的氧同位素组成。如果文石与水之间的氧同位素分馏达到平衡,由文石经过同质多象转变生成的次生方解石部分继承母体文石的氧同位素组成,并且次生方解石相对于母体文石富集^(18)O。②在0℃和25℃下,“一步法”的“附晶生长法”的实验结果表明,由六方方解石经过同质多象转变生成的次生方解石也完全继承母体矿物的氧同位素组成,并且在该温度下,矿物与水之间的氧同位素分馏与温度无关。CaCO3 polymorphs were experimentally synthesized by 'one-step' and 'two-step' overgrowth techniques, respectively, in order to study the oxygen isotope fractionation behaviors in polymorphic transformation of Ca-CO3 minerals. The difference in acid fractionation factor between calcite and aragonite were examined by polymorphic transformation experiment in vacuum. The results show that at 50 ℃ and 70 ℃ , if oxygen isotope fractionation between aragonite and water is out of equilibrium, secondary calcite can completely inherit the oxygen isotope feature of precursor aragonite. On contrary, if oxygen isotope fractionation for the aragonite-water system is at equilibrium at 50 ℃ and 70 ℃ , secondary calcite can only partly inherit the oxygen isotope feature of precursor aragonite. The secondary calcite tends to inherit the oxygen isotope feature of precursor aragonite more and more with decreasing temperature. The results from 'one-step overgrowth' at 0 ℃ and 25 ℃ show that secondary calcite has the same oxygen isotope composition as precursor vaterite, and that oxygen isotope fractionations between CaCO3 mineral and water are independent of temperature.

关 键 词：碳酸钙 氧同位素分馏 矿物合成 同质多象转变 氧继承性 温度 方解石 

分 类 号：P597[天文地球—地球化学]