Petrology of the unbrecciated eucrites
Petrology of the unbrecciated eucrites
复制标题
DOI：
10.1016/j.gca.2008.10.035
复制
发表时间：
2009-02
影响因子：
5
通讯作者：
R. Mayne;H. McSween;T. Mccoy;A. Gale
中科院分区：
文献类型：
--
作者：
R. Mayne;H. McSween;T. Mccoy;A. Gale
根据影响其光谱的岩石学因素，如矿物化学、模态优势、粒度和结构，对29种非角砾岩进行了彻底的表征。我们进行了一项岩石学和光谱研究，旨在深入了解灶神星玄武岩地壳的岩石成因和存在于其中的各种岩石类型，并帮助对黎明号轨道航天器收集的光谱进行岩石学解释。本文详细介绍了研究的岩石学部分。为了避免伴随的光谱研究中岩性混合的复杂性，选择了未角化的长晶岩样品。在玄武岩长辉长岩中可以看到各种各样的结构类型，包括淬火、粗粒和花岗母岩样品。长绿长岩中的分带辉石和那些保存了最初快速冷却历史的辉石是罕见的。几乎所有的长晶石样品都发生了热变质，通常可归为平衡态；然而，该术语仅反映辉石的四边形（Mg， Fe和Ca）组成，并且在辉石和斜长石组成中的少量元素（Al， Ti和Cr）中可以看到相当大的变化。辉石和斜长石组成的测定与辉石的地热测量相结合，可以更好地估计辉长岩所经历的相对热变质程度。这里观察到的岩石学差异可能使不同的绿长岩在光谱上得到区分。这对于不同的辉石成分来说尤其如此，因为辉石的光谱主要是由辉石的吸收特征决定的。
Twenty-nine unbrecciated eucrites have been thoroughly characterized in terms of the petrologic factors that affect their spectra, such as mineral chemistry, modal adundances, grain sizes, and textures. We have conducted a combined petrologic and spectral study designed to provide insight into the petrogenesis of the basaltic crust of Vesta and the variety of rock-types that exist within it, as well as aid in the petrologic interpretation of spectra to be collected by the Dawn orbiting spacecraft. This paper details the petrology part of the study. Unbrecciated eucrite samples were selected to avoid the complications of lithologic mixing in the accompanying spectral study. A wide variety of textural types are seen within the basaltic eucrites, encompassing quenched, coarse-grained, and granoblastic samples. Zoned pyroxenes in eucrites and those that preserve a history of initial rapid cooling are rare. Nearly all eucrite samples have been thermally metamorphosed and would commonly be classified as equilibrated; however, this term reflects only the quadrilateral (Mg, Fe, and Ca) compositions of pyroxenes, and considerable variations are seen within the minor elements (Al, Ti, and Cr) in pyroxenes as well as plagioclase compositions. Determination of both pyroxene and plagioclase compositions together with pyroxene geothermometry provides a better estimate for the relative degree of thermal metamorphism a eucrite has experienced. The petrologic differences observed here might allow different eucrites to be distinguished spectrally. This is especially true for the varying pyroxene compositions as the spectra of eucrites are dominated by absorption features attributed to pyroxene.