Oxygen Isotopic Alteration of Nohi Rhyolites
スポンサーリンク
概要
- 論文の詳細を見る
About sixty Nohi rhyolites and several sedimentary rock specimens from the basement, were provided for whole-rock oxygen isotope measurement and major and minor element analyses. Deuterium isotopic composition of whole-rock rhyolite was also determined for several specimens. The studied rhyolites are completely devitrified, and contain some amounts of alteration minerals such as sericite, chlorite, epidote, calcite, smectite and smectite-vermiculite mixed-layer mineral. The rhyolites have δ<SUP>18</SUP>O values of -5.2 to +9.2 ‰ (SMOW), and δD values of -112 to -102 ‰ (SMOW). The hydrothermal alteration was brought by circulation of solutions of meteoric water origin. The circulation pervasively penetrated Nohi rhyolites down to underlying sedimentary rocks. In some parts, at least, of the rhyolites, hydrothermal alterations took place at temperatures higher than 300°C with very high water/rock ratios. Lack of rocks with <SUP>18</SUP>O-enrichment indicates that highly oxygen-shifted waters were rather rare, or inactive if any in respect of isotopic exchange reaction with rocks, and that fresh waters could reach to depth without appreciable oxygen shift. As to major element chemistry, depletion in Na and large variation of K contents are conspicuous. According to TAKENO'S (1989) simulation results, Na-depleted rhyolites could not be rocks of recharge zones, while some K-enriched rhyolites possibly represent discharge zones in the alteration processes.
- 資源地質学会の論文
資源地質学会 | 論文
- 資源情報 2008年度秋季講習会 西南北海道の中新世熱水活動と金属鉱化作用
- 飛騨帯の石灰岩類 -地質特性・構成鉱物・岩石組織とドロマイトの産状-
- 飛騨帯神岡鉱床周辺の変閃緑岩・変斑れい岩類
- 神岡鉱床周辺のいわゆる伊西ミグマタイトとスカルン鉱(杢地鉱)中の単斜輝石の組成変化
- 北部北上山地南東部, 大谷山鉱山北方地域に分布する層状マンガン鉱床の層位学的研究