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Fluid inclusion and isotopic systematics of an evolving magmatic-hydrothermal system

The Geysers, California, is the site of a long-lived hydrothermal system that initially developed 1.5–2 m.y. ago in response to the intrusion of a hypabyssal granitic pluton. Although wells drilled into The Geysers produce only dry steam, fluid inclusion, isotopic, and mineralogic data demonstrate t...

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Bibliographic Details
Published in:Geochimica et cosmochimica acta 1995-10, Vol.59 (19), p.3887-3907
Main Authors: Moore, Joseph N., Gunderson, Richard P.
Format: Article
Language:English
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Summary:The Geysers, California, is the site of a long-lived hydrothermal system that initially developed 1.5–2 m.y. ago in response to the intrusion of a hypabyssal granitic pluton. Although wells drilled into The Geysers produce only dry steam, fluid inclusion, isotopic, and mineralogic data demonstrate that the present vapor-dominated regime evolved from an earlier and more extensive, liquid-dominated hydrothermal system. Circulation of these early fluids produced veins characterized by tourmaline ± biotite ± actinolite ± clinopyroxene within the pluton and adjacent biotite-rich hornfels, actinolite ± ferroaxinite ± epidote and epidote ± chlorite within the intermediate parts of the thermal system and calcite in the outer parts. Potassium feldspar and quartz are present in all assemblages. Pressure-corrected homogenization temperatures and apparent salinities of fluid inclusions trapped in vein minerals range from 440°C and 44 wt% NaCl equivalent within the hornfels (
ISSN:0016-7037
1872-9533
DOI:10.1016/0016-7037(95)00289-C