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Oxygen And Carbon Isotope Ratios Of Hydrothermal Minerals From Yellowstone Drill Cores
Abstract Oxygen and carbon isotope ratios were meas
Oxygen and carbon isotope ratios were measured for hydrothermal minerals (silica, clay and calcite) from fractures and vugs in altered rhyolite, located between 28 and 129 m below surface (in situ temperatures ranging from 81 to 199°C) in Yellowstone drill holes. The purpose of this study was to investigate the mechanism of formation of these minerals. The Δ18O values of the thirty-two analyzed silica samples (quartz, chalcedony, α-cristobalite, and β-cristobalite) range from -7.5 to +2.8‰. About one third of the silica 7samples have Δ18O values that are consistent with isotopic equilibrium with present thermal waters; most of the other silica samples appear to have precipitated from water enriched in 18O (up to 4.7‰) relative to present thermal water, assuming precipitation at present in situ temperatures. Available data on fluid-inclusion homogenization temperatures in hydrothermal quartz indicate that silica precipitation occurred mostly at temperatures above those measured during drilling and imply that 15O enrichments in water during silica precipitation were generally larger than those estimated from present conditions. Similarly, clay minerals (celadonite and smectite) have Δ18O values higher (by 3.5 to 7.9‰) than equilibrium values under present conditions. In contrast, all eight analyzed calcite samples are close to isotopic equilibrium with present thermal waters. The frequent incidence of apparent 18O enrichment in thermal water from which the hydrothermal minerals precipitated may indicate that a higher proportion of strongly 18O-enriched deep hydrothermal fluid once circulated through shallow portions of the Yellowstone system, or that a recurring transient 18O-enrichment effect occurs at shallow depths and is caused either by sudden decompressional boiling or by isotopic exchange at low water/rock ratios in new fractures. The mineralogy and apparent 18O enrichments of hydrothermal fracture-filling minerals are consistent with deposition during transient boiling or rock-water exchange (fracturing) events.
r rock-water exchange (fracturing) events.  +
Author N. C. Sturchio  + , T. E. C. Keith  + , K. Muehlenbachs  +
Citation N. C. Sturchio,T. E. C. Keith,K. Muehlenba
N. C. Sturchio,T. E. C. Keith,K. Muehlenbachs. 1990. [[Oxygen And Carbon Isotope Ratios Of Hydrothermal Minerals From Yellowstone Drill Cores]]. Journal of Volcanology and Geothermal Research. <span title="Missing required info" style="font-weight:bold;color:red;">(!)[[Category:Missing Required Information]]</span> .
sing Required Information]]</span> .  +
Document type Journal Article  +
Name Oxygen And Carbon Isotope Ratios Of Hydrothermal Minerals From Yellowstone Drill Cores  +
PublicationDate 1990  +
Publisher Journal of Volcanology and Geothermal Research  +
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Core Analysis At Yellowstone Region (Sturchio, Et Al., 1990) + , Fluid Inclusion Analysis At Yellowstone Region (Sturchio, Et Al., 1990) + , Isotopic Analysis At Yellowstone Region (Sturchio, Et Al., 1990) + Reference material
 
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