Microthermometry of Fluid Inclusions from the VC-1 Core Hole in Valles Caldera, New Mexico

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Journal Article: Microthermometry of Fluid Inclusions from the VC-1 Core Hole in Valles Caldera, New Mexico

Abstract
Fluid inclusions in vein quartz and calcite from core samples of the VC-1 hole were studied with microscope heating/freezing and crushing stages. All samples originate from hydrothermally altered Paleozoic rocks predating formation of the Jemez Mountains volcanic field and Valles caldera. Most homogenization temperatures (Th) of the liquid-rich inclusions are above the present well temperature, but some Th of primary inclusions from 515 m and those of secondary inclusions from 723 m fit the present well temperature curve measured 10 months after completion of the well. The maximum temperature recorded by the primary inclusions is 275°C from hydrothermal quartz in the Sandia Formation at 811-m depth. The total range of Th for samples from several depths (90°C) indicates cooling from the maximum temperature. The salinity of fluid inclusions in hydrothermal quartz and calcite is generally low, <1 wt % NaCl eq. High-salinity fluid, up to 5 wt % NaCl eq, has been found in several calcite veins from the lower part of the Madera Limestone. The salinity decreases with decrease of Th of the secondary inclusions, and that with lowest Th at the lower part of the Madera Limestone is similar to those from the other depths. These data show that early hot water circulation system involved several types of fluid, whereas the later one was a homogeneous fluid. The salinity of fluid inclusions in detrital quartz (presumably inherited inclusions) is higher than that in hydrothermal minerals. Some of these inclusions show extraordinary low temperatures of final melting point of ice (about −40°C), suggesting that a CaCl2 component is present. CO2 contents in fluid inclusions were estimated by the bubble behavior on crushing. Crushing results indicate that CO2 content of the early fluid is ≧0.35 wt %, and that of the later fluid is ∼0.2–0.3 wt %. Geothermal fluid trapped in the fluid inclusions representing the present temperature regime is comparable in composition to those from the Baca geothermal field inside the caldera and to those from hot springs in San Diego Canyon.

Author 
Masakatsu Sasada








Published Journal 
Journal of Geophysical Research, 06/1988





DOI 
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Citation

Masakatsu Sasada. 06/1988. Microthermometry of Fluid Inclusions from the VC-1 Core Hole in Valles Caldera, New Mexico. Journal of Geophysical Research. 93(B6):6091-6096.


Related Geothermal Exploration Activities
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Areas (1)
  1. Valles Caldera - Redondo Geothermal Area
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