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Potassium-Argon Ages of Volcanic Rocks in Nye and Esmeralda Counties, Nevada

By
Ronald W. Kistler
Ronald W. Kistler
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Published:
January 01, 1968

Potassium-argon ages of minerals are reported for 29 specimens of flows and tuffs from volcanic rocks that crop out in Nye and Esmeralda Counties, Nevada.

Formation or group  Epoch  Range of K/Ar ages (m.y.)  Range of K concentration (wt. percent)
 
Biotite  Alkali feldspar 
Thirsty Canyon Tuff  Pliocene  6.2 to 7.5  absent  5.14 to 5.49 
Piapi Canyon Group and Indian Trail Formation  Pliocene t o Miocene  10.5 to 16  6.19 to 6.76  4.86 to 5.97 
Older volcanic rocks  Miocene  18 to 26  6.76 to 7.21  8.80 
Formation or group  Epoch  Range of K/Ar ages (m.y.)  Range of K concentration (wt. percent)
 
Biotite  Alkali feldspar 
Thirsty Canyon Tuff  Pliocene  6.2 to 7.5  absent  5.14 to 5.49 
Piapi Canyon Group and Indian Trail Formation  Pliocene t o Miocene  10.5 to 16  6.19 to 6.76  4.86 to 5.97 
Older volcanic rocks  Miocene  18 to 26  6.76 to 7.21  8.80 

Precision of the age determinations on biotite and sanidine from these rocks is estimated by three sets of data

  1. (1) Duplicate analysis for argon and potassium; σ = 0.9 to 3.6 percent.

  2. (2) Age determinations of mineral pairs from seven specimens; σ = 1.2 to 3.0 percent.

  3. (3) Age determinations from 5, 4, and 2 widely separated localities in three welded tuffs; σ = 2.3 to 6.5 percent, (σ = population standard deviation at 95 percent confidence level.)

For purposes of stratigraphie correlation, the precision estimates indicate that in order to be able to distinguish between two rocks at the 95 percent confidence level, their ages must differ by 3.4 to 8.5 percent if each rock is dated by a mineral pair.

In contrast to the diversity reported for chemical compositions of the volcanic rocks dated, the potassium concentrations in biotite and sanidine from pyroclastic units in each of the three sequences appear to be remarkably consistent. A check of the published K/Ar ages in Nevada and Utah suggests that this characteristic of minerals in pyroclastic rocks is widespread.

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GSA Memoirs

Nevada Test Site

Edwin B. Eckel
Edwin B. Eckel
Editor
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Geological Society of America
Volume
110
ISBN print:
9780813711102
Publication date:
January 01, 1968

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