矿物氧同位素模式温度计算  

Calculation of oxygen isotope model temperature in minerals.

作　　者：王峥嵘[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：《岩石学报》2000年第1期67-82,共16页Acta Petrologica Sinica

基　　金：中国科学院项目! ( Nos.KZ95 2 -J1-4 0 9和 KZ95 1-A1-4 0 1);国家自然科学基金! ( Nos.4945 30 0 3和 497940 42 )

摘　　要：根据对现有氧扩散模型的解析分析 ,通过模拟矿物之间的氧同位素交换轨迹进行模式温度计算 ,改进了常规矿物对氧同位素地质温度计方法。将模式温度计算与矿物氧扩散封闭次序规则相结合 ,建立了一个系统独立的氧同位素温度计算方法 ,因此所得到的同位素温度能够更好地反映矿物在高温岩石冷却过程中的氧同位素交换行为。模式温度计算有如下优点 :( 1)考虑到了矿物之间氧扩散引起的同位素交换 ;( 2 )遵循质量守恒原理 ,更严格地适用于有限封闭体系 ;( 3)能够恢复岩石的高温历史 ;( 4)基本不依赖于具体的扩散模型 ;( 5 )地质含义更加明确 ,适用范围更广。通过对假想的封闭花岗岩体系、San Jose英云闪长岩和 Sybille采场橄长岩的实例分析可以看出 ,模式温度计算有良好的自洽性和应用前景。对大别山双河两种片麻岩所进行的模式温度计算得到副片麻岩中石榴石和榍石的模式温度为 6 95～ 930℃ ,正片麻岩中石榴石和磁铁矿的模式温度为 5 6 0～ 75 0℃。在高温下的降温阶段 ,副片麻岩与正片麻岩可能有着不同的冷却历史 。The conventional mineral pair isotope geothermometry is improved by simulating isotope exchange trajectories of minerals in terms of diffusion controlled isotope exchange. An independent approach is established by combining the calculation of oxygen isotope model temperature (OIMT) in minerals with the semi empirical sequence for oxygen diffusion blocking. The calculation method of model temperature is better than the conventional method in the following aspects: (1) oxygen isotope exchange in minerals due to diffusion is taken into account; (2) mass balance equation is satisfied, which fits to describe oxygen isotope exchange between minerals within a finite reservoir; (3) the record of high temperature can be recovered from high temperature rocks; (4) it is independent of concrete diffusion models; and (5) its geological meaning is more explicit, and calculation method can be widely applied. The tests with the ideal granite, San Jose tonalite and the troctolite from Sybille quarry have demonstrated that the OIMT concept and numerical method are promising to isotope geothermometry. The application to the two types of gneisses from Shuanghe in the Dabie Mountains obtains the model temperatures of 695 to 930℃ for garnet and titanite from the paragneiss, and 560 to 750℃ for garnet and magnetite from the orthogneiss. It appears that the paragneiss may have a different cooling history from that of the orthogneiss in the high temperature stage, and that both of them may have experienced the metamorphism of eclogite facies temperatures.

关 键 词：氧同位素 模式温度 地质温度计 矿物 片麻岩 

分 类 号：P588.345[天文地球—岩石学] P571[天文地球—地质学]