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Sample Y-B1-1
NavDat sample number 2910 · BASALT
Sample
| Sample ID | Y-B1-1 |
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| Rock name | BASALT |
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| Rock type | VOLCANIC |
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| Composition | MAFIC |
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| Material | IGNEOUS |
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| Collected by | Charles J. Vitaliano |
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| Comment | A fine- to medium-grained, slightly vesicular, porphyritic rock with vesicles sparsely lined with calcite. Phenocrysts of labradorite An50, olivine, and diopside comprise 40% of the rock. The phenocrysts are mostly 98% plagioclase. The olivine is extensively iddingsitized and the pyroxene slightly altered to serpentine. Andesine, olivine, and pyroxene microlites plus accessory phlogopite, magnetite, and apatite can be identified in the groundmass, which is exceedingly fine-grained. A small amount of carbonate has been developed in the olivine, a small amount of palagonite and clay in the labradorite phenocrysts, and a notable quantity of clay in the labradorite microlites. Samples Y-B1-1, B1-2, B1-14, and B1-17 are from two flows of the 30 m thick Malpais Basalt Ransome et al, 1909, p. 72 which caps the mesa. The average date for the basalt approx 7.7 m.y. is greater than the more precise age of 6.7 .1 m.y. obtained for the underlying Spearhead Rhyolite. The errors are so large that the discrepancy is not significant; but the excess age suggests that the basalt may have been slightly contaminated with radiogenic argon at the time of eruption. It seems reasonable to assume that the flows constituting the Malpais Basalt were extruded not long after deposition of the Spearhead, and within a relatively brief time interval. |
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Location
| Latitude | 37.6958 |
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| Longitude | -117.244 |
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| Location | Esmeralda 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 | Malpais Basalt, basal flow; NW wall of Pozo Canyon |
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Age
| Age (Ma) | Error | Min | Max | Geologic age | Dated by |
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| 8.9 |
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7.4 |
10.4 |
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Analyses
No chemical analyses are stored for this sample.
