Fluorite alignments cutting metasomatic textures in trachyte feldspars from Oki-Dogo Island, Sea of Japan

Abstract

Feldspar internal textures in a pyroclastic trachyte from Oki-Dogo, Sea of Japan, were examined to expand the understanding of feldspar reactions during the cooling through magmatic to hydrothermal stages, beyond the previous information of feldspars in Oki-Dogo alkaline lava and sheet rocks, using the methods of an electron microprobe and cathodoluminescence. Two types of micron-size internal microtextures were found to coexist in individual feldspar phenocrysts: clear domain textures, formed during a high-temperature magmatic stage, and turbid microperthitic textures, formed during a low-temperature subsolidus stage. The both microtextures are products of metasomatic replacement reactions. In addition, nano-size fluorite grains are aligned across the microtextures. The fluorite occurrence records the behavior of fluorine related to feldspar reactions.