From Open Energy Information
|Isotopic Analysis- Rock|
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"The hydrothermal fluids circulating in a …
"The hydrothermal fluids circulating in a geothermal system have a unique signature that can be used to determine where that water came from, how old it is, whether it has mixed with other fluids, and which direction it is moving in. Fractionating elements (H, C, O, and N) are useful for identifying recharge, water/rock ratios, and chemical equilibrium temperatures.'"`UNIQ--ref-00000003-QINU`"' Chemical interaction with host rocks will impart a unique isotopic signature similar to that of the reservoir fluid. Isotope ratios in hydrothermal alteration and vein minerals can yield important information regarding modern and fossil hydrothermal systems. At The Geysers vapor-dominated hydrothermal system in California, quartz and calcite veins cutting reservoir rocks showed Δ18O values that record the temperatures and isotopic compositions of fluids present during at least two distinct episodes of rock-fluid interaction.'"`UNIQ--ref-00000005-QINU`"' The first episode was recorded by veins of quartz and calcite cutting the host rock that showed Δ18O values around +19 and +16%, respectively. The Δ18O values of greenstones metamorphosed from spilitic basalts during (post-Cretaceous?) burial showed a similar isotopic shift. The D/H ratios of actinolite, chlorite, and micas in host rocks were also strongly altered during this episode. These isotopic results suggest that the vein and alteration minerals formed through interaction of marine silica and carbonate with ocean water entrapped in sediments at about 200°C. The Δ18O-depth distributions of vein minerals was also used to deduce that a paleogeothermal gradient of about 53°C/km existed during the first episode of fluid-rock interaction. The second episode was recorded by vein quartz with Δ18O values of +4 to +6% and cogenetic vein calcite with Δ18O values of +1 to +3%.'"`UNIQ--ref-00000007-QINU`"' This episode began in response to the start of the Pliocene-Pleistocene Clear Lake magmatism, during which time large quantities of meteoric water with temperatures of 160-180°C circulated through fractured host rocks. As temperatures rose and circulation of fluids was restricted, the ancestral hot-water system evolved into the existing active vapor-dominated system. According to the Δ18O values of cogenetic vein quartz and calcite, the modern geothermal system has experienced temperatures as high as 320°C." cannot be used as a page name in this wiki. The given value was not understood.wiki. The given value was not understood. +
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