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Sample Y-58441
NavDat sample number 2916 · TRACHYANDESITE
Sample
| Sample ID | Y-58441 |
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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 rock microporphyritic to aphyric, with texture varying from markedly trachytic to intergranular. The microphenocrysts, when present, are up to 1 mm in size and constitute less than 5% of the rock. They are of plagioclase An55, intensely iddingsitized olivine, clear diopside, and magnetite. The groundmass consists of microlites of the same plagioclase 60% of the groundmass, iddingsitized olivine 20%, diopside in clear laths 10%, and clouds of magnetite grains, plus occasional flakes of phlogopite and grains of apatite. All the plagioclase is slightly altered to clay along fractures and, in some crystals, in the cores. Blackcap Mountain is a small butte in the Goldfield volcano-tectonic depression in Nye County, 1/2 mile east of the Esmeralda County line. The butte has been preserved from erosion by a capping consisting of two flows which Ransome et al 1909, p. 73 and pl. 2 identified with the Malpais Basalt. The dates obtained for these flows, 11.8 and 12.9 m.y., correspond to the Barstovian-Clarendonian boundary Evernden and others, 1964; correlation with the Malpais Basalt is ruled out. The date for sample Y-5813 from a petrographically similar rock four miles northwest of Blackcap Mountain is consistent with the interpretation that it could be a part of the Blackcap Mountain flows. Likewise, the trachyandesite flow that supplied sample Y-58441 is probably part of the same volcanic episode, although not one of the other flows dated. |
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Location
| Latitude | 37.8708 |
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| Longitude | -117.296 |
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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 | Olivine trachyandesite flow overlying dacite vitrophyre equivalent to Y-58N260; low ridge about 4 mi SW of Mud Lake |
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Age
| Age (Ma) | Error | Min | Max | Geologic age | Dated by |
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| 12.3 |
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11.8 |
12.8 |
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Analyses
No chemical analyses are stored for this sample.
