Rodingite is a Ca-rich and Si-poor metasomatic rock commonly occurring in association with serpentinites. This rock is characterized by specific mineral assemblages consisting of hydrated garnet, diopside, vesuvianite, epidote-zoisite, chlorite, or prehnite. However, natural rodingites are significantly heterogeneous in mineral composition and vesuvianite occurs only in some extensively rodingitized rocks. Major factors controlling the mineral diversity as well as details on fluid-rock interactions leading to the evolution of mineral and chemical composition during rodingitization have not yet been fully constrained. In this work, we use PHREEQC software to present a geochemical model for the transformation of a mafic rock into vesuvianite-bearing rodingite at a temperature of 300 °C. Through these simulations, we investigate the effect of fluid composition and progress of the metasomatic process on rodingite formation. Our results show that rodingitization requires an open system with a high input of hydrothermal fluid. Additionally, a decrease in the Si/Ca ratio in the metasomatized rock is correlated to an increase in the volume of incoming fluid. Whole rock chemical and mineral composition in natural rodingites are well reproduced by the model. Furthermore, the diversity of mineral parageneses results mainly from different degrees of transformation and only to a lesser extent to the chemical composition of hydrothermal fluid or protolith. The hydrothermal fluid doesn't need to be especially rich in calcium to transform a mafic rock into rodingite, but it must be low in magnesium, silicon, and have a high pH, which is naturally controlled by serpentinization of surrounding ultramafic rocks.

中文翻译：

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辉长岩转变为含维苏威岩罗丁岩的地球化学模型


罗丁岩是一种富钙、贫硅的交代岩，通常与蛇纹岩伴生。这种岩石的特征是由水合石榴石、透辉石、维苏威石、绿帘石、黝帘石、绿泥石或葡萄石组成的特定矿物组合。然而，天然罗丁岩在矿物成分上具有显着的异质性，而维苏威岩仅出现在一些广泛的罗丁岩化岩石中。控制矿物多样性的主要因素以及导致罗金石化过程中矿物和化学成分演化的流体-岩石相互作用的细节尚未得到充分限制。在这项工作中，我们使用 PHREEQC 软件提出了一个地球化学模型，用于在 300 °C 的温度下将镁铁质岩石转变为含维苏威岩的 Rodingite。通过这些模拟，我们研究了流体成分和交代过程的进展对罗锌矿形成的影响。我们的结果表明，罗金石化需要一个具有高热液输入的开放系统。此外，交代岩石中硅/钙比的降低与进入流体体积的增加相关。该模型很好地再现了天然罗丁陨石中的整个岩石化学和矿物成分。此外，矿物共生体的多样性主要是由不同程度的转化造成的，而在较小程度上是由热液或原岩的化学成分造成的。热液不需要特别富含钙就能将镁铁质岩石转化为罗铜矿，但它的镁、硅含量必须较低，并且具有较高的pH值，这是由周围超镁铁质岩石的蛇纹石化自然控制的。