Quaternary rhyolite from the Mineral Mountains, Utah, USA. Final report, Volume 77-10

Technical Report · Wed Mar 01 04:00:00 EST 1978

DOI:https://doi.org/10.2172/5696814· OSTI ID:5696814

Evans, Jr, S H; Nash, W P

A suite of silicic volcanic rocks is associated with the Roosevelt Hot Springs geothermal area in southwestern Utah. The volcanic sequence includes Tertiary rhyolite 8 My old and obsidian, ash and rhyolite of Quaternary age. The Quaternary lavas are characterized by high silica content (76.5% Si0/sub 2/) and total alkalies in excess of 9 percent. Obsidians commonly contain greater amounts of fluorine than water. Two older flows (0.8 My) can be distinguished from younger dome and pyroclastic material (approximately 0.5 My) by subtle differences in their chemistry. The mineralogy of the rhyolites consists of alkali feldspar, plagioclase, and small amounts of Fe-Ti oxides, biotite, hornblende and rare allanite. Fe-Ti oxide temperatures are 740 to 785/sup 0/C for the flows and 635 to 665/sup 0/C for the domes; two feldspar temperatures give similar results. The phase relationships of bulk rock, glass and feldspar compositions demonstrate that the younger Quaternary rhyolites could have been derived from the earlier magma type, represented by the obsidian flows, by a process of crystal fractionation. The major phases which must fractionate are alkali feldspar, plagioclase and quartz with minor amounts of biotite, magnetite and ilmenite participating also. Trace element patterns support this scheme as well. The Tertiary lavas cannot be related to the Quaternary rhyolites and are thought to represent a separate event.

• Research Organization: Utah Univ., Salt Lake City (USA)
• OSTI ID: 5696814
• Report Number(s): IDO-1601-T7
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150201* -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
AMPHIBOLE
BIOTITE
CENOZOIC ERA
CHEMICAL ANALYSIS
CHEMISTRY
CRYSTALLIZATION
ELECTRON MICROPROBE ANALYSIS
FELDSPARS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGY
GEOTHERMOMETRY
Geothermal Legacy
HORNBLENDE
IGNEOUS ROCKS
MICA
MICROANALYSIS
MINERALOGY
MINERALS
NORTH AMERICA
PETROGENESIS
PETROGRAPHY
PHASE TRANSFORMATIONS
QUATERNARY PERIOD
RHYOLITES
ROCKS
ROCKY MOUNTAIN REGION
USA
UTAH
VOLCANIC ROCKS