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

从尖晶石和橄榄石的化学成分看上地幔的演化.

基本信息

批准号：
06640611
负责人：
OZAWA Kazuhito
金额：
$ 1.41万
依托单位：
Univeristy of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06640611/
关键词：
upper mantle peridotite olivine spinel magma

项目摘要

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.

在本研究中明确了以下几点。橄榄石-尖晶石地幔阵列是上地幔的一种矿物学趋势，其特征是橄榄石的镁/(镁+铁)(镁#)与尖晶石的铬/(铬+铝)(铬#)呈正相关但非线性相关，可用分批熔融或分步熔融来解释，起始原始地幔组成分别为：橄榄石mg#=0.89，尖晶石Cr#=0.1.2。地幔橄榄石阵列是上地幔的一种矿物学趋势，其特征是镁与橄榄石中NiO含量呈正相关和近线性相关，应分为富镁部分和富铁部分。前一种趋势可由原始地幔批量熔融或分批熔融产生，Livine的Mg#=0.89，NiO=0.38wt.%，而后一种趋势是由于地幔橄榄石阵列上的橄榄岩与硅酸盐熔体之间的相互作用而产生的，其中橄榄石的Mg#和NiO含量比阵列上的橄榄石小。贫镁橄榄岩普遍存在于地幔橄榄石阵列中，表明这种反应在上地幔中相当普遍。根据观测到的单斜辉石和块状橄榄岩中的稀土和微量元素丰度，反演出了开放系统熔融过程的参数。估算的参数有：熔融程度、熔融过程中的熔体分数、流入熔体的微量元素组成、熔体流入速率与熔化速率的关系、熔融反应的化学计量系数。本项目的最终目标是构建橄榄石的镁和NiO含量的岩石成因网格，该网格基本完成。我们还没有完成构建尖晶石和橄榄石成分的网格，但已经彻底调查了两个极端的梅林案例(Batch和Fractiona)。在完成后一步网格并检验模型中的各项参数后，在不久的将来，我们就有可能在这样的岩石成因网格的基础上进行上地幔熔融过程的反演。