Here, the petrological features of numerous primitive achondrites and highly equilibrated chondrites are evaluated to review and expand upon our knowledge of the chondrite–achondrite transition, and primitive achondrites in general. A thermodynamic model for the initial silicate melting temperature and progressive melting for nearly the entire known range of oxidation states is provided, which can be expressed as T _m = 0.035Fa²−3.51Fa + 1109 (in °C, where Fa is the proportion of fayalite in olivine). This model is then used to frame a discussion of textural and mineralogical evolution of stony meteorites with increasing temperature. We suggest that the metamorphic petrology of these meteorites should be based on diffusive equilibration among the silicate minerals, and as such, the chondrite–achondrite transition should be defined by the initial point of silicate melting, not by metal–troilite melting. Evidence of silicate melting is preserved by a distinctive texture of interconnected interstitial plagioclase ± pyroxene networks among rounded olivine and/or pyroxene (depending on ƒO₂), which pseudomorph the former silicate melt network. Indirectly, the presence of exsolution lamellae in augite in slowly cooled achondrites also implies that silicate melting occurred because of the high temperatures required, and because silicate melt enhances diffusion. A metamorphic facies series is defined: the Plagioclase Facies is equivalent to petrologic types 5 and 6, the Sub‐calcic Augite Facies is bounded at lower temperatures by the initiation of silicate melting and at higher temperatures by the appearance of pigeonite, which marks the transition to the Pigeonite Facies.

中文翻译：

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球粒陨石-闪长岩过渡以及平衡原始石质陨石的变质相系列综述

在此，我们评估了许多原始斜纹岩和高度平衡的斜纹岩的岩石学特征，以回顾和扩展我们对球粒-斜方晶石转变以及原始斜纹岩的认识。提供了一个热力学模型，用于初始硅酸盐的熔融温度和几乎在整个已知氧化态范围内的逐步熔融，可以表示为T _m  = 0.035Fa ²−3.51Fa + 1109（以°C为单位，其中Fa是橄榄石中铁橄榄石的比例）。然后，使用该模型对石质陨石随温度升高的组织和矿物学演化进行讨论。我们建议，这些陨石的变质岩石学应基于硅酸盐矿物之间的扩散平衡，因此，球粒陨石-陨石转变应由硅酸盐熔化的起始点定义，而不是由金属-三菱沸石熔化定义。硅酸盐熔化的证据是由一个独特的结构保留互连间隙斜辉石±（取决于ƒO圆形橄榄石和/或辉石之间的网络₂），将原来的硅酸盐熔体网络假变形。间接地，在缓慢冷却的长晶体中的闪锌矿中存在析出片晶，这也意味着由于所需的高温以及发生的硅酸盐熔体促进扩散，导致发生了硅酸盐熔体。定义了变质相系列：斜长岩相相当于岩石学类型5和6，亚钙质硬质岩相在较低的温度下通过硅酸盐融化而受到限制，而在较高的温度下通过皂石的出现而受到限制，这标志着过渡鸽子岩相。