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Mineral distribution within polymineralic veins in the Sanbagawa belt,Japan: implications for mass transfer during vein formation
Authors:Atsushi Okamoto  Taketo Kikuchi  Noriyoshi Tsuchiya
Institution:(1) Graduate School of Environmental Studies, Tohoku University, Sendai, Japan;(2) Present address: E & E Solutions Inc., Tokyo, Japan
Abstract:Pelitic schists of the Sanbagawa metamorphic belt contain several types of polymineralic veins that formed during the late stages of exhumation. The vein mineral assemblages are quartz + albite + K-feldspar + chlorite ± calcite (Type I, II) and quartz + albite + calcite (Type III). Type I and II veins contain quartz and albite with stretched-crystal and elongate-blocky textures, respectively. The mineral species within Type I veins vary with compositional bands within the host rocks. Type III veins are characterized by euhedral to subhedral quartz grains with concentric zoning and a homogeneous distribution along the vein length. The vein textures vary depending on the crack aperture during multiple crack-seal events: <0.08 mm for Type I, and 0.5–10 mm for Type III. Type II veins show intermediate features between Type I and III veins in terms of mineral distribution (weak dependence on the host rock composition) and apparent crack aperture (less than 1–15 mm). These observations suggest a transition in the dominant transport mechanism of vein components with increasing crack aperture, from diffusion from host rocks to fluid advection along cracks.
Keywords:Polymineralic vein  Mass transfer  Mineral distribution  Vein texture  Sanbagawa metamorphic belt
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