The sodic amphibole glaucophane is generally considered as indicative of blueschist-facies metamorphism. However, sodic amphiboles display a large range oin chemical compositions, due principally to the Fe²⁺Mg_-1 and Fe³⁺Al_-1 substitutions. Therefore, the whole-rock composition (namely its Na₂O and FeO* content, and the Fe²⁺-Fe³⁺ ratio), strongly control the stability field of the sodic amphiboles at the transition from greenschist- to blueschist-facies conditions. Neglecting these variables can lead to erroneous estimates of the metamorphic conditions and consequently the tectonic framework of the rocks. This paper explores the mechanisms that control the development of sodic amphibole and sodic pyroxene within the basement of the Dent Blanche Tectonic System (Western Alps), as a result of the Alpine metamorphic history. Field, petrographic and geochemical data indicate that sodic amphibole and sodic pyroxene form in different rock types: 1) In undeformed pods of ultramafic cumulates (hornblendite), sodic amphibole (magnesioriebeckite) forms coronas around magmatic pargasite; 2) Metatonalite displays patches of radiating sodic (magnesioriebeckite) and calcic (actinolite) amphiboles; 3) Sodic amphibole (magnesioriebeckite-glaucophane) occur with high-Si muscovite in fine-grained (blue) schists; and 4) In mylonitized granitoids (amphibole-gneiss) metasomatized along the contact with ultramafic cumulates, sodic amphibole (magnesioriebeckite-winchite) mainly forms rosettes or sheaves, generally without a shape-preferred orientation. Only locally are the needles aligned parallel to the stretching lineation. Pale green aegirine-augite is dispersed in an albite-quartz matrix or forms layers of fine-grained fibrous aggregates.The bulk-rock chemical composition of the different lithologies indicates that sodic amphibole and sodic pyroxene developed in Na- and Fe-rich systems or in a system with high Fe³⁺ / Fe*. Thermodynamic modelling performed for different rock types (taking into account the measured Fe₂O₃ contents) reveals that sodic amphibole appears at ∼ 8±1 kbar and 400-450 °C, i.e. at the transition between the greenschist- and blueschist-facies conditions, at lower pressure than previously proposed. To test the robustness of our conclusion, we performed a review of sodic amphibole compositions from a variety of terranes and P-T conditions. This shows (i) systematic variations of composition with P-T conditions and bulk-rock chemistry, and (ii) that the amphibole compositions reported from the studied area are consistent with those reported from other greenschist- to blueschist-facies transitions.

中文翻译：

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苏格角闪石在绿岩-蓝岩-相转变中的生长（Dent Blanche，西方阿尔卑斯山）：块岩化学控制和热力学模拟

钠闪石的葡糖二甲醚通常被认为是蓝片岩相变质的指示。但是，钠闪石的主要化学成分是Fe ²⁺ Mg _-1和Fe ³⁺ Al _-1取代，因此其化学组成范围很大。因此，整个岩石成分（即Na ₂ O和FeO *的含量以及Fe ²⁺ -Fe ³⁺比率），在从绿片岩相向蓝片岩相的过渡过程中，强烈地控制了钠双闪石的稳定性场。忽略这些变量会导致对变质条件的错误估计，从而导致岩石的构造框架的错误估计。本文探讨了由于高山变质史而在登特布兰奇构造系统（西阿尔卑斯山）的地下室控制钠闪石和钠辉石发展的机制。野外，岩相和地球化学数据表明，钠闪石和钠辉石在不同的岩石类型中形成：1）在未变形的超镁铁质堆积物（角闪石）中，钠闪石（镁硅锰矿）在岩浆辉石周围形成日冕；2）陨石显示出放射状的钠钙镁铝矾石和钙质（阳起石）闪石的碎片；3）高硅白云母与细晶（蓝色）片岩中出现钠闪石（镁铝辉石-葡甲铝）；和4）在沿与超镁铁质堆积物接触而变质的花岗岩化的类花岗岩（两栖类-片麻岩）中，钠闪石（镁铝闪石-温岭石）主要形成玫瑰花结或滑轮，通常没有形状优先的取向。针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。不同岩性的块状岩石化学成分表明，钠富铁体系或钠富铁体系中形成了钠闪石和钠辉石在高铁的体系中 3）高硅白云母与细晶（蓝色）片岩中出现钠闪石（镁铝辉石-葡甲铝）；和4）在沿与超镁铁质堆积物接触而变质的花岗岩化的类花岗岩（两栖类-片麻岩）中，钠闪石（镁铝闪石-温岭石）主要形成玫瑰花结或滑轮，通常没有形状优先的取向。针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。在高铁的体系中 3）高硅白云母与细晶（蓝色）片岩中出现钠闪石（镁铝辉石-葡甲铝）；和4）在沿与超镁铁质堆积物接触而变质的花岗岩化的类花岗岩（两栖类-片麻岩）中，钠闪石（镁铝闪石-温岭石）主要形成玫瑰花结或滑轮，通常没有形状优先的取向。针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。不同岩性的块状岩石化学成分表明，钠富铁体系或钠富铁体系中形成了钠闪石和钠辉石在高铁的体系中 和4）在沿与超镁铁质堆积物接触而变质的花岗岩化的类花岗岩（两栖类-片麻岩）中，钠闪石（镁铝闪石-温岭石）主要形成玫瑰花结或滑轮，通常没有形状优先的取向。针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。不同岩性的块状岩石化学成分表明，钠富铁体系或钠富铁体系中形成了钠闪石和钠辉石在高铁的体系中 和4）在沿与超镁铁质堆积物接触而变质的花岗岩化的类花岗岩（两栖类-片麻岩）中，钠闪石（镁铝闪石-温岭石）主要形成玫瑰花结或滑轮，通常没有形状优先的取向。针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。不同岩性的块状岩石化学成分表明，钠富铁体系或钠富铁体系中形成了钠闪石和钠辉石在高铁的体系中 针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。不同岩性的块状岩石化学成分表明，钠富铁体系或钠富铁体系中形成了钠闪石和钠辉石在高铁的体系中 针仅在局部平行于拉伸线对齐。淡绿色aegirine-augite分散在钠长石-石英基质中或形成细粒纤维状聚集体层。在高铁的体系中³⁺ /铁*。对不同类型的岩石进行热力学建模（考虑到测得的Fe ₂ O ₃含量）表明，钠闪石出现在约8±1 kbar和400-450°C的温度下，即在绿片岩和蓝片岩相条件之间的转变。 ，压力低于先前建议的压力。为了检验我们结论的稳健性，我们对来自各种地形和PT条件的钠闪石闪石成分进行了综述。这表明（i）PT条件和块岩化学组成的系统变化，以及（ii）研究区域报告的闪石成分与其他绿片相向蓝片相转变所报告的相一致。