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The cation distribution of major and minor elements over the two non-equivalent sites in olivine and its temperature dependence.

橄榄石中两个非等价位点上主量元素和微量元素的阳离子分布及其温度依赖性。

基本信息

批准号：
02453050
负责人：
MATSUMOTO Takeo
金额：
$ 3.46万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

The cation distribution coefficients K_D (=(Fe/Mg)_<M1>/(Fe/Mg)_<M2>) were calculated from the X-ray site occupancy refinements for olivines. The K_D values of Mg, Feolivines obtained are 0.95-1.13 in basalt, 1.01-1.12 in ultramafic nodule, 1.18 in rhyolite, 0.95 in metamorphic rocks atid 0.91 in H6-chondolite. As a whole, the volcanic olivines have the slight preference of Fe for the Ml site, and the metamorphic olivines for the M2 site, as the previous investigators reported.In-situ high temperature X-ray experiments showed that the K_D values of the heated olivines increased with increasing temperature, and that values above 600 ﾟC increase with increasing fayalite content. Ttiese results suggest that tile cation exchange in olivine is not sluggish at high temperature and the cation distribution at high temperature is not preserved on cooling. Ttierefdre the K_D values at room temperature for olivines are riot obviously distinguished by the modes of occurrence.Using ALHEMI (Atomic Location by CHanneling Enhanced MIcroanalysis) technique, with an Akaslii EM-002B TEM having EDAX9100 and double tilt specimen holder, the distribution of cations over the two cation sites in olivine is determined. A suitable set of planes for electron clianrie. ling is(002)in Pbnm setting. Here, the new equation for the calculation to determine the site occupancies, using Si atom as reference atom, is derived. Mg and Fe show a slight preference for the M2 and M1 sites respectively. Minor elements Ni and Mn show a strong preference for the M1 site and the M2 site respectively.

由橄榄石的X射线占位精修计算了阳离子分配系数K_D（=（Fe/Mg）_<M1>/（Fe/Mg）_<M2>）。玄武岩、超镁铁结核、流纹岩、变质岩和H6球粒陨石中镁铁橄榄石的K_D值分别为0.95-1.13、1.01-1.12、1.18、0.95和0.91。原位高温X射线实验表明，加热橄榄石的K_D值随温度的升高而增大，600 ℃以上的K_D值随铁橄榄石含量的增加而增大。这些结果表明，橄榄石中的阳离子交换在高温下并不缓慢，高温下的阳离子分布在冷却时并不保持。由于橄榄石的室温K_D值与其赋存状态无明显区别，本文采用ALHEMI（Atomic Location by Channeling Enhanced Microanalysis）技术，在Akaslii EM-002 B透射电镜上，用EDAX 9100和双倾斜试样保持器，测定了橄榄石中两个阳离子位上的阳离子分布。一组适合于电子晶体的平面。在Pbnm设置中，ling为（002）。本文导出了以Si原子为参考原子计算占位比的新公式。Mg和Fe分别对M2和M1位点显示出轻微的偏好。微量元素Ni和Mn分别对M1位和M2位表现出强烈的偏好。