Casto Ring Zone: A 4,500-km2 fossil hydrothermal system in the Challis Volcanic Field, central Idaho
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Abstract
δ18O analyses of granitic and volcanic rocks reveal the largest hydrothermal system ever documented around a single granite pluton, occupying a 4,500-km2 area in central Idaho. The remains of this meteoric-hydrothermal system are principally preserved within a sharply bounded, 15-km-wide, 70-km-diameter annulus of low δ18O rock (+2.0 to −8.8‰) termed the Casto Ring Zone. The zone centered on a less depleted (+4.5) core zone consisting of granitic rocks of the Casto pluton. This 700-km2 Eocene subvolcanic batholith has intruded, domed, and hydrothermally metamorphosed a thick sequence of Challis Volcanics, the stratigraphically low rocks in the 2,000-km2 Van Horn Peak and the 1,000-km2 Thunder Mountain cauldron complexes being most strongly altered. Less extreme 18O depletions occur in the youngest major ash-flow sheets of these complexes, indicating a vertical 18O gradient. Water/rock ratios of geothermal systems are surprisingly insensitive to the circulation scale.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Casto Ring Zone: A 4,500-km2 fossil hydrothermal system in the Challis Volcanic Field, central Idaho |
| Series title | Geology |
| DOI | 10.1130/0091-7613(1984)12<331:CRZAKF>2.0.CO;2 |
| Volume | 12 |
| Issue | 6 |
| Year Published | 1984 |
| Language | English |
| Publisher | Geological Society of America |
| Description | 4 p. |
| First page | 331 |
| Last page | 334 |
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