Fluid Infiltration and Mass Transfer along a Lamprophyre Dyke–Marble Contact: An Example from the South-Western Korean Peninsula

Abstract

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 (aK2O)–temperature pseudosection shows that at aK2O~−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.

Role of acidic fluids in Earth’s deep lithosphere: Insights from the Neoarchean magmatic roots of the Nilgiri Block, southern India

“…It is challenging to test these results due to limitations in availability of natural fluid inclusions representing deep Earth, and also experimental, modelling, and spectroscopic methods to detect and interpret speciation in H 2 O-CO 2 -Cl system in high P-T conditions. Our approach to improve our knowledge is exploring factors controlling mineral reactions and partitioning of fluid components in natural minerals in the Earth's interior (Samuel et al, 2019;Kwon et al, 2020;Noh et al, 2020;Samuel et al, 2021).…”

Editorial for Special Issue “Microtexture Characterization of Rocks and Minerals”

“…The articles published in the issue can be divided into several topics. The articles by Park et al [1], Mao et al [2] and Noh et al [3] are the case studies investigating some geological processes at the regional scale, based on microtextural characterization. Park et al [1] present new microstructural data from two ductile shear zones, constrain the kinematics and deformation conditions of ductile shearing, and provide an improved understanding of the tectonic process of the Mesozoic East Asian continental margin.…”

“…Mao et al [2] investigated the microstructures of rhyolitic lavas filled by solidified crude oil from a Basin in NE China using quantitative image analysis, and defined the type, morphology, pore-size distribution, and pore-volume contribution of different pores, which can be beneficial to the further understanding of the microstructure and pore system of the rhyolites as a potential hydrocarbon reservoir. Noh et al [3] examined the formation of an olivine-bearing serpentinized metasomatic zone developed on dolomitic marble through microtextural and geochemical characterization and phase equilibria modelling, and they tried to understand the infiltration metasomatism caused by a lamprophyre dyke-marble contact zone from the southwestern Korean Peninsula.…”