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Accurate determination of phase equilibrium diagrams by calorimetric measurements of high pressure silicate minerals and applications to structure of the earth's mantle.

通过高压硅酸盐矿物的量热测量准确确定相平衡图及其在地幔结构中的应用。

基本信息

批准号：
62540618
负责人：
AKAOGI Masaki
金额：
$ 1.54万
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 (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

The important scientific results of this research project are summarized as follows.1. Enthalpies of the olivine-modified spinel-spinel transitions in the system Mg_2SiO_4-Fe_2SiO_4 were measured by high temperature calorimetric techniques. The phase diagrams calculated form the present thermochemical data are not well consistent with those by Ringwood and Major (1970) and Kawada (1977), but agree very well with that determined with precise high pressure experiments by Katsura and Ito (1989). From the calculated phase diagrams, it is concluded that the olivine-modified spinel transition occurs at about 390-410 km in the mantle, while the modified spinel-spinel transition at about 490-540 km. Temperatures at 390 and 650 km are estimated to be 1400 and 1600 ﾟC, respectively.2. Enthalpy of the pyroxene-garnet transition in the system Mg_4Si_4O_<12>-Mg_3Al_2 Si_3O_<12> was measured by the same calorimetric techniques. The calculated phase diagram was in good agreement, with that by high pressure experiments by Akaogi and Akimoto (1977), when the pressure scale was revised. It was concluded from the phase diagram that the pyroxene-garnet transition in the mantle occurs gradually with depth in the depth range of about 300-500 km and shows no sharp seismic velocity discontinuity.3. High pressures over 18 GPa were generated by using new Bridgman-anvils (26 mm in diameter) with sintered diamond tips. The transition of beta-Zn_2SiO_4 to ZnSiO_3 ilmenite plus ZnO was examined using these new anvils.4. From the measured enthalpies of the pyroxene-ilmenite transition in ZnSiO_3 and of the disproportionation of Ni_2SiO_4 spinel, these phase equilibrium boundaries were calculated thermodynamically.

现将本研究项目的重要科学成果总结如下。用高温量热法测定了Mg_2SiO_4-Fe_2SiO_4体系中橄榄石修饰尖晶石-尖晶石相变的焓。从目前的热化学数据计算出的相图与Ringwood和Major（1970）和Kawada（1977）的相图不太一致，但与Katsura和Ito（1989）用精确的高压实验得出的相图非常一致。由相图可知，橄榄石-尖晶石相变发生在地幔内390 ~ 410 km处，而尖晶石-尖晶石相变发生在地幔内490 ~ 540 km处。390公里和650公里处的温度估计分别为1400和1600ºC。用同样的量热法测定了Mg_4Si_4O_<12>-Mg_3Al_2 Si_3O_<12>体系中辉石-石榴石转变的焓。计算得到的相图与Akaogi和Akimoto（1977）在修正压力标度时的高压实验相图吻合较好。相图表明，地幔中辉石岩-石榴石的转变是随深度逐渐发生的，在300-500 km左右的深度范围内，没有明显的地震速度不连续。采用新型bridgman - an砧（直径26毫米）和烧结金刚石尖端，可产生超过18 GPa的高压。用这些新试样考察了β - zn_2sio_4向ZnSiO_3钛铁矿+ ZnO的转变。根据测定的ZnSiO_3中辉石-钛铁矿转变焓和Ni_2SiO_4尖晶石歧化焓，计算了这些相平衡边界。