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Sample Y-B3-13
NavDat sample number 2919 · TRACHYANDESITE
Sample
| Sample ID | Y-B3-13 |
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| Rock name | TRACHYANDESITE |
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| Rock type | VOLCANIC |
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| Composition | INTERMEDIATE |
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| Material | IGNEOUS |
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| Collected by | Charles J. Vitaliano |
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| Comment | A black, fine-grained slightly vesicular rock. Under the microscope it is seen to be microporphyritic, with small <1 mm microphenocrysts of zoned plagioclase An45-51 constituting 20% of the rock, iddingsitized olivine 10%, augite 10%, hornblende rimmed with iron oxide about 5%, and magnetite about 5%. The groundmass 50% consists of microlites of the above minerals with a small amount about 3% of the groundmass of brown glass. Less than 0.1% of the vesicles are lined with carbonate. The trachyandesites represented by samples Y-5780, Y-57233, and Y-B3-13 are Miocene and definitely older than the Black Cap Mountain and related flows. A consistent decrease in age of capping mafic lavas southeastward from central Nevada was shown by Armstrong 1970. The mafic capping lavas in the Tonopah-Goldfield region show a similar southward decrease in age. The southward decrease in initial Sr87/Sr86 ratios from central Nevada that was observed by Scott and others 1971 is paralleled by the two results we report here samples Y-B2-7 and Y-B3-13. |
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Location
| Latitude | 38.1708 |
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| Longitude | -117.039 |
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| Location | Nye County, NV |
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| State / province | Nevada |
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| Volcanic field | Goldfield-Tonopah region, West-Central Nevada |
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| Location comment | Uppermost olivine trachyandesite flow of the series forming Thunder Mountain, 322 feet above the base of the series; NE of Tonopah |
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Age
| Age (Ma) | Error | Min | Max | Geologic age | Dated by |
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| 19.4 |
|
17.9 |
20.9 |
|
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Analyses
Whole rock
| Item | Value | Std. dev. | Unit | Method |
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| SR87_SR86 | 0.7052 | | | MS |
