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Sample USGSM-856-8
NavDat sample number 2890 · DACITE
Sample
| Sample ID | USGSM-856-8 |
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| Rock name | DACITE |
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| Rock type | VOLCANIC |
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| Composition | FELSIC |
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| Material | IGNEOUS |
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| Comment | Gray porphyritic dacite with phenocrysts of plagioclase and hornblende in a fine-grained groundmass. Hornblende is sparse, rimmed with iron oxide and partially chloritized. Groundmass shows development of some chlorite and addition of K-feldspar. Same intrusive as sample USGSM-B271. The discordant age relations are due to the effect of alteration. The K content is approximately double that of unaltered rock of similar mineralogy, and is due to the addition of adularia to the groundmass. Oxygen isotopic analyses of the whole rock sample USGSM-B271 and the plagioclase and hornblende of sample USGSM-856-8 J.R. O'Neil, written commun., 1971 indicate equilibration with hydrothermal fluids depleted in O^18. The hornblende of sample B271 shows normal O^18/16 for unaltered volcanic rock. The temperature during alteration of sample 856-8 probably did not reach the level required for equilibration of hornblende with the light hydrothermal fluid. Its age is probaby the closest to that of crystallization of the Bodie Bluff dacite; however, all ages for this plug should be considered suspect. |
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Location
| Latitude | 38.2152 |
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| Longitude | -119.002 |
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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 | lowest level of the Roseclip opencut Mine, S side of Standard Hill |
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Age
| Age (Ma) | Error | Min | Max | Geologic age | Dated by |
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| 8.4 |
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8.2 |
8.6 |
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Analyses
No chemical analyses are stored for this sample.
