Late Middle Eocence Nanny Creek calc-alkaline volcanic field, NE Nevada and NW Utah: Age, extent, and implications for Eocene tectonics
- Geological Survey, Denver, CO (United States)
Eighteen new [sup 40]Ar/[sup 39]Ar dates indicate that widespread rhyolitic to andesitic calc-alkaline volcanic rocks in NE Nevada and NW Utah are part of a distinct eruptive sequence that is late Middle Eocene in age, considerably older than previously believed. Most of the rocks were erupted at 41--39 Ma. The presently recognized extent of the field spans 11 ranges from near Elko on the west to the Silver Island Mts on the east and from 20 miles north of Wells to the southern Deep Creek Range. The authors informally designate this the Nanny Creek volcanic field, the type area being Nanny Creek, in the northern Pequop Mts, where compositional and stratigraphic features of the field are clearly displayed. Typically, the base of the sequence includes one or more rhyolite ash-flow tuffs and (or) dacite flows; sources for the tuffs probably were outside the study area as they all appear to be outflow-facies rocks. The similarities in age, chemistry, and mode of occurrence of these rocks throughout their extent indicate that they are all part of the same eruptive sequence. The widespread occurrence of ash-flows in the lower part of the eruptive cycle suggests that the region initially was one of moderate to low relief. The central part of the field rests with angular discordance on Devonian to Triassic rocks, whereas the western and eastern parts rest with angular discordance on lower Eocene rocks (Elko and White Sage basinal rocks, respectively). Ostracode-bearing limestones at several localities in the central part of the field are parallel to the overlying volcanics rocks; the authors interpret the limestones to be correlative with the Elko and White Sage and the limestone/volcanic contact to be a disconformity that is correlative with the angular unconformities to the east and west. These relationships identify a widespread pre-late Middle Eocene deformational event during which the Elko and White Sage basins, but not the intervening area, were deformed.
- OSTI ID:
- 5097758
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GEOLOGIC DEPOSITS
GEOLOGY
ISOTOPE DATING
NEVADA
UTAH
VOLCANIC ROCKS
ARGON 39
ARGON 40
EOCENE EPOCH
GEOLOGIC HISTORY
TECTONICS
VOLCANIC REGIONS
VOLCANOES
AGE ESTIMATION
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CENOZOIC ERA
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
IGNEOUS ROCKS
ISOTOPES
LIGHT NUCLEI
NORTH AMERICA
NUCLEI
RADIOISOTOPES
ROCKS
STABLE ISOTOPES
TERTIARY PERIOD
USA
YEARS LIVING RADIOISOTOPES
580000* - Geosciences