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Sample USGSM-BH20
NavDat sample number 2906 · RHYODACITE
Sample
| Sample ID | USGSM-BH20 |
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| Rock name | RHYODACITE |
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| Rock type | PLUTONIC |
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| Composition | FELSIC |
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| Material | IGNEOUS |
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| Comment | Light- to medium-gray porphyritic rock with phenocrysts of biotite, quartz, plagioclase, and hornblende in a glassy, partly devitrified groundmass. This plug is one of several that intrude the walls and central portion of a volcanic collapse structure termed the Big Alkali Caldera by Chesterman 1968. The walls of the caldera are underlain by dacite flows and are intruded by rhyodacite to rhyolite plugs and irregular dikes along the boundary fault. Tuff breccias and lava flows of the Willow Springs Formation see no. USGSM-BH19A of approximately 8 m.y. were erupted from this feature. The magma continued to differentiate and to erupt the rhyodacite to rhyolite intrusives in the caldera rim zone and center. USGSM-BH6 and -BH20 represent the youngest volcanic rocks of the Bodie Hills field and postdate the mineralization at Bodie by at least 1 m.y. Chesterman, 1968, p. 63-65. |
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Location
| Latitude | 38.2198 |
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| Longitude | -119.148 |
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| Location | Mono County, CA |
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| State / province | California |
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| Volcanic field | Bodie Mining District and Bodie Hills Volcanic Field |
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| Location comment | 300 ft NW of top of 7599' hill, 7 1/2 mi W of Bodie townsite |
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Age
| Age (Ma) | Error | Min | Max | Geologic age | Dated by |
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| 5.3 |
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5 |
5.6 |
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Analyses
No chemical analyses are stored for this sample.
