碾子山晶洞碱性花岗岩矿物-水氧同位素交换反应动力学  

Kinetics of oxygen isotope exchange between water and minerals of miarolitic alkaline granite from Nianzishan

作　　者：赵子福[1] 郑永飞[1] 魏春生[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,安徽合肥230026

出　　处：《地球化学》2001年第2期177-185,共9页Geochimica

基　　金：国家自然科学基金资助项目! (40033010; 49603043

摘　　要：对黑龙江碾子山碱性花岗岩的全岩及其主要单矿物进行了氧同位素分析。结果表明，全岩和单矿物不仅δ 18O值变化范围较大 (全岩－ 2.4‰～ 2.0‰， 石英 0.0‰～ 5.8‰， 碱性长石－ 3.8‰～ 0.1‰， 磁铁矿－ 8.5‰～ － 1.0‰ )，而且强烈亏损 18O。共生矿物之间表现出明显不平衡的氧同位素分馏特征，指示在花岗岩侵位之后与水之间发生了同位素交换。根据锆石和现代大气降水的氧同位素组成，对岩石与外来流体的δ 18O值进行了估计。多维矿物相-水氧同位素交换反应动力学模型定量模拟表明， 碾子山岩体流体流动速率约为 1× 10－ 15～ 3× 10－ 14 mol/s， 水-岩反应时限约为 0.3～ 3 Ma， 水 /岩比 (氧摩尔比 )介于 0.11～ 1.02之间。水-岩反应温度较高 (约 400℃ )和反应时间较长是导致石英δ 18O降低的主要原因。The oxygen isotopic compositions of whole rocks and single minerals were measured for alkaline granites from Nianzishan in Heilongjiang Province. The results show that the whole rocks and single minerals have widely variableδ 18O values (－ 2.4‰～ 2.0‰ for whole rock, 0.0‰～ 5.8‰ for quartz,－ 3.8‰～ 0.1‰ for alkaline feldspar, and－ 8.5‰～－ 1.0‰ for magnetite), and depleted in 18O. Oxygen isotope disequilibrium is observed between the coexisting minerals, indicating water- rock exchange for the alkaline granite during its emplacement. The initialδ 18O values of rock and external fluid are estimated according to the oxygen isotopic compositions of zircons and modern meteoric water. Quantitative simulation was carried out by using the kinetic model of oxygen isotope exchange between multi- minerals and water. It is obtained that the flow rate of fluid is about 1× 10－ 15～ 3× 10－ 14 mol/s , the time of water- rock interaction is about 0.3～ 3 Ma, and ratio of water to rock is about 0.11～ 1.02. Significant decrease in quartzδ 18O is ascribed to water- rock interaction of higher temperatures (～ 400℃ ) and longer time (>1 Ma).

关 键 词：碱性花岗岩 氧同位素 水-岩反应 交换动力学 黑龙江 矿物分析 

分 类 号：P588.12[天文地球—岩石学] P597.2[天文地球—地质学]