A refined technique for measuring crystal size distributions in thin section
A refined technique for measuring crystal size distributions in thin section
复制标题
测量薄片中晶体尺寸分布的精细技术
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
T. Peterson
中科院分区：
文献类型：
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作者：
T. Peterson
Abstract Log-normal size distributions are of the form n=noe−L/α, where n=number density, L=crystal length, and α is a constant. A method for measuring three-dimensional log-normal crystal or grain size distributions (CSDs) in thin section has been deduced from computer experiments, in which 2D sections were cut through assemblages of 3D solids. The size ranges and distributions studied were appropriate for igneous microphenocryst to megacryst populations. Conversion from 2D to 3D is based on an exact correction for spheres of uniform diameter. Cumulate numbers of polygons with length≥L (N2D) are converted to N3D by the equation:ln(N3D)=ln(N2D/[L·S])+ln(γ)−β/[L·S] The number density is then obtained as n=−dN/dL. The parameters S and γ correct the measured lengths and no (no=number density at L=0) respectively, and are functions of crystal shape. The parameter β is a weak function of the degree of spatial orientation of the crystals. Highly symmetrical shapes such as cubes, octahedra, and elongated prisms can be accurately measured when randomly oriented; however, rectangular solids with a≠b≠c cannot be accurately measured because they produce bimodal length distributions in cross section. Strongly oriented textures (trachytic or lineated) can be accurately measured regardless of crystal shape. New CSD data from alkaline rocks and a kimberlite give examples of CSDs modified by megacryst retention, xenocryst addition, phenocryst accumulation, and groundmass nucleation.
