Evolution of the upper mantle viewed from chemical composition of spinel and olivine.

本研究澄清了以下几点.橄榄石-尖晶石地幔阵列是上地幔的一种矿物学趋势，其特征是橄榄石的Mg/（Mg+Fe）（Mg#）与尖晶石的Cr/（Cr+Al）（Cr#）之间呈正的但非线性的相关性，可以用橄榄石Mg#=0.89和尖晶石Cr#=0.1.2的原始地幔成分开始的分批熔融或部分熔融来解释。地幔橄榄石阵列是上地幔中的一种矿物学趋势，其特征是橄榄石中Mg#与NiO含量呈正线性相关，应划分为富Mg和富Fe部分。前一种趋势可能是由橄榄石Mg#=0.89和NiO= 0.38wt.而后者的趋势是由于地幔橄榄石阵列上的橄榄岩和硅酸盐熔体之间的相互作用与橄榄石具有较小的Mg#和NiO含量比阵列上的橄榄石平衡。贫镁橄榄岩在地幔橄榄岩阵列上的普遍出现表明这种反应在上地幔中是相当普遍的.开放系统熔融过程的参数反演从观察到的稀土元素和微量元素丰度单斜辉石和橄榄岩块。估计参数为：熔融程度、熔融过程中的熔体分数、熔融熔体的微量元素组成、熔体相对于熔融速率的流入速率、熔融反应的化学计量系数等，最终建立了橄榄石的成岩格网。我们还没有完成对尖晶石和橄榄石组成的网格的构建，但是熔化的两种极端情况（批次和分数）已经被彻底研究。在完成后一个网格并检验模型中的各个参数后，我们可能在不久的将来就可以在这种成岩网格的基础上反演上地幔的熔融过程。

The following points are clarified in this research.1. Olivine-spinel mantle array, which is a mineralogical trend in the upper mantle and which is characterized by positive but nonlinear correlation between Mg/(Mg+Fe) (Mg#) of olivine and Cr/(Cr+Al) (Cr#) of spinel, can be explained by either batch or fractional melting with starting primitive mantle composoition of olivine Mg#=0.89 and spinel Cr#=0.1.2. Mantle olivine array, which is a mineralogical trend in the upper mantle and which is characterized by positive and near linear correlation between Mg# and NiO content of olivine, should be divided into Mg-rich and Fe-rich portion. The former trend can be produced by either batch or fractional melting from primitive mantle with livine Mg#=0.89 and NiO=0.38 wt. %, whereas the latter trend is due to interaction between peridotites on the mantle olivine array and silicate melt in equilibrium with olivine having smaller Mg# and NiO content than olivine on the array. Common occurrence of the Mg-poor peridotites on the mantle olivine array indicates that such reaction is quite general in the upper mantle.3. Parameters of open-system melting processes are inverted from observed REE and trace element abundances in clinopyroxene and bulk peridotite. Estimated parameters are : extent of melting, melt fraction during melting, trace element composition of influxed melt, melt influx rate relative to melting rate, stoichiometric coefficients for the melting reaction.The final goal of this project is to construct petrogenetic grid, which is nearly completed for Mg# and NiO content of olivine. We have not yet complete to construct the grid for spinel vs. olivine compositions, but two extreme cases of meling (batch and fractiona) have been throughly investigated. After completing the latter grid and examining each parameter in the model, we may be able to do inversion of melting opocesses in the upper mantl on the basis of such petrogenetic grid in near future.