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Study on deep structure and dynamics of the mantle by calorimetric measurements of high pressure silicates

高压硅酸盐量热测量研究地幔深层结构和动力学

基本信息

批准号：
03453058
负责人：
AKAOGI Masaki
金额：
$ 5.18万
依托单位：
Gakushuin 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：
1991
资助国家：
日本
起止时间：
1991 至 1993
项目状态：
已结题

项目摘要

Main research results of this project are as follows.1. Heat capacity and enthalpy of MgSi0_3 perovskite were mesured, using the perovskite sample synthesized at very high pressure and high temperature. Based on the measured thermo dynamic properties, phase boundary of dissoication of Mg_2SiO_4 spinel to MgSiO_3 perovskite plas MgO was precisely determined. The slope of the boundry suggests that the upper mantle and lower mantle convect separatery but intermittant convection occurs between them. An adiabatic geotherm in the lower mantle and the temperature at the lowermost mantle were estimated, using the heat capacity of MgSiO_3 perovskite.2. Transition enthalpy of MgSiO_3 garnet was measured using the sampie synthesized at very high pressure and high temperature, and the phase equiliblium boundar were calculated. It eas suggetsed from the phase diagram that the garnet-perovskite transition which occurs in the descending lithoshere promotes the subduction.3. Effect of pressure was observed on the partition coefficients of Ni, Mn and Co between metallic iron and silicates at high pressure and hgih temparature. This result suggests that the pressure effect should be incoporated in geochemical model of the core-mantle separation.Enthalpy measurements of MgSio_4-Fe_2SiO_4 olivine solid solution showed that nonideality of the olivine solid solution was symmteric with to respect to composition and the nonideality parameter was detemined.5. Stability fields of hollandite solid solution in the system KAISi_3O_8-NaAISi_3O_8 and of a new hexagonal(Mg, Ca)AI_2O_4 phase were detemined at high pressure and high temparature.These aluminous phases may be stable in the transition zone and the lower mantle.

本课题的主要研究成果如下：1.用高温高压合成的钙钛矿型MgSiO_3样品测定了其热容和焓。根据所测的热力学性质，精确地确定了Mg_2SiO_4尖晶石向MgSiO_3钙钛矿相转变的相界。边界的斜率表明，上地幔和下地幔对流是分离的，但它们之间的对流是不连续的。利用MgSiO_3钙钛矿的热容量估算了下地幔的绝热地温和地幔最低温度.用高温高压合成的样品测定了MgSiO_3石榴石的相变焓，并计算了相平衡边界。从相图中可以看出，下降岩石层中发生的石榴石-钙钛矿转变促进了俯冲作用.在高温高压条件下，研究了压力对Ni、Mn、Co在金属铁和硅酸盐之间分配系数的影响。对MgSiO_4-Fe_2SiO_4橄榄石固溶体的热焓测量表明，橄榄石固溶体的非理想性与成分有关，并确定了非理想性参数.在高压高温条件下测定了KAlSi_3O_8-NaAlSi_3O_8系统中的Hollandite固溶体和一种新的六方相（Mg，Ca）Al_2O_4相的稳定场，这些铝相可能在过渡带和下地幔中是稳定的。