In this contribution, we report the metasomatic characteristics of a lamprophyre dyke–marble contact zone from the Hongseong–Imjingang belt along the western Gyeonggi Massif, South Korea. The lamprophyre dyke intruded into the dolomitic marble, forming a serpentinized contact zone. The zone consists of olivine, serpentine, calcite, dolomite, biotite, spinel, and hematite. Minor F and Cl contents in the serpentine and biotite indicate the composition of the infiltrating H₂O-CO₂ fluid. SiO₂ (12.42 wt %), FeO (1.83 wt %), K₂O (0.03 wt %), Sr (89 ppm), U (0.7 ppm), Th (1.44 ppm), and rare earth elements (REEs) are highly mobile, while Zr, Cr, and Ba are moderately mobile in the fluid. Phase equilibria modelling suggests that the olivine, spinel, biotite, and calcite assemblage might be formed by the dissolution of dolomite at ~700 °C, 130 MPa. Such modelling requires stable diopside in the observed conditions in the presence of silica-saturated fluid. The lack of diopside in the metasomatized region is due to the high K activity of the fluid. Our log activity K₂O (a_K2O)–temperature pseudosection shows that at a_K2O~−40, the olivine, spinel, biotite, and calcite assemblage is stable without diopside. Subsequently, at ~450 °C, 130 MPa, serpentine is formed due to the infiltration of H₂O during the cooling of the lamprophyre dyke. This suggests that hot H₂O-CO₂ fluids with dissolved major and trace elements infiltrated through fractures, grain boundaries, and micron-scale porosity, which dissolved dolomite in the marble and precipitated the observed olivine-bearing peak metasomatic assemblage. During cooling, exsolved CO₂ could increase the water activity to stabilize the serpentine. Our example implies that dissolution-reprecipitation is an important process, locally and regionally, that could impart important textural and geochemical variations in metasomatized rocks.

中文翻译：

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沿煌斑岩堤-大理石接触的流体渗透和传质：以朝鲜西南半岛为例

在这项贡献中，我们报告了韩国京畿道西部洪城—临金刚带的煌斑岩脉—大理石接触带的交代特征。煌斑岩堤侵入白云岩大理石中，形成蛇形接触区域。该区域包括橄榄石，蛇纹石，方解石，白云石，黑云母，尖晶石和赤铁矿。蛇纹石和黑云母中的少量F和Cl含量表明渗透的H ₂ O-CO ₂流体的组成。SiO ₂（12.42 wt％），FeO（1.83 wt％），K ₂O（0.03 wt％），Sr（89 ppm），U（0.7 ppm），Th（1.44 ppm）和稀土元素（REE）具有很高的流动性，而Zr，Cr和Ba在流体中具有中等流动性。相平衡模型表明，橄榄石，尖晶石，黑云母和方解石组合可能是由白云石在〜700°C，130 MPa下的溶解所形成的。这样的模型需要在二氧化硅饱和流体存在下在观察到的条件下稳定的透辉石。交代区域中透辉石的缺乏是由于液体的高K活性。我们的对数活动K ₂ O（_K2O）–温度伪截面表明，在_K2O处约-40，橄榄石，尖晶石，黑云母和方解石组合稳定，没有透辉石。随后，在〜450°C，130 MPa时，由于在蛇眼石堤冷却期间H ₂ O的渗透而形成蛇纹石。这表明具有溶解的主要和微量元素的热H ₂ O-CO ₂流体会通过裂缝，晶界和微米级孔隙率渗透，从而使白云石溶解在大理石中并沉淀出观察到的含橄榄石的峰交代组合。冷却期间，溶解的CO ₂可以增加水活度以稳定蛇纹石。我们的例子表明，溶解-再沉淀是局部和区域性的重要过程，可以在交代岩石中赋予重要的质地和地球化学变化。