- Usage in publication:
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- Virginia Dale Quartz Monzonite*
- Modifications:
-
- Named
- Geochronologic dating
- Dominant lithology:
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- Quartz monzonite
- AAPG geologic province:
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- Mojave basin
Summary:
Unit is named the Virginia Dale Quartz Monzonite of the Bullion Mountains Intrusive Suite (new) for Virginia Dale mine in the eastern Pinto Mountains, San Bernardino Co., CA. Is widely exposed in the Pinto, Bullion, and Sheep Hole Mountains. Consists of medium-grained, porphyritic sphene-hornblende-biotite and sphene-biotite quartz monzonite and monzogranite. Alkali-feldspar phenocrysts 1-2 cm across and typically lavender and round. Subspherical mafic enclaves 5-15 cm across common. Recrystallized and foliated (in places an augen gneiss) where hear Cretaceous granitoids. Age is Jurassic based on isotopic (K-Ar [hornblende, 159 +/-5 Ma; biotite, 155 +/-5 Ma at Valley Mountain (Calzia and Morton, 1980)], [biotite, 167 +/-7 Ma near Marbolite mine in the Pinto Mountains (Bishop, 1964)]; preliminary U-Pb [zircon, about 165-160 Ma] from near Marbolite mine).
Source: GNU records (USGS DDS-6; Menlo GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).