Geochemical evolution of topaz rhyolites from the Thomas Range and Spor Mountain, Utah
Two sequences of rhyolite lava flows and associated pyroclastic deposits are exposed in the Thomas Range (6 m.y.) and at Spor Mountain (21 m.y.) in west-central Utah. Both contain topaz indicative of their F-enrichment (>0.2%) and aluminous nature. The rhyolites are part of the bimodal sequence of basalt and rhyolite typical of the region. Moderate changes in major elements coupled with large variations in trace elements in vitrophyres from the Thomas Range are generally consistent with fractionation of observed phenocrysts. Especially important roles for the trace minerals are suggested. Nonetheless, disagreement between major and trace element models regarding the degree of crystallization as well as improbably high anti D/sup Ta/ and anti D/sup Th/ suggest that some diffusive differentiation involving the migration of trace elements complexed with volatiles also occurred or that monazite, titanite or samarskite fractionation was important. Higher concentrations of F in the evolving Spor Mountain rhyolite drove residual melts to less silicic compositions with higher Na and Al and promoted extended differentiation yielding rhyolites extremely enriched in Be, Rb, Cs, U, Th, and other lithophile elements at moderate SiO/sub 2/ concentrations (74%).
- Research Organization:
- Arizona State Univ., Tempe
- OSTI ID:
- 6747494
- Journal Information:
- Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 69:3-4; ISSN AMMIA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580400* -- Geochemistry-- (-1989)
ACTINIDES
ALKALI METALS
ALKALINE EARTH METALS
ALUMINIUM
BERYLLIUM
CESIUM
CHEMISTRY
DIFFUSION
ECOLOGICAL CONCENTRATION
ELEMENTS
FEDERAL REGION VIII
FRACTIONATION
GEOCHEMISTRY
GEOLOGY
IGNEOUS ROCKS
IRON
METALS
MIGRATION
NORTH AMERICA
PETROLOGY
RHYOLITES
ROCKS
RUBIDIUM
SEPARATION PROCESSES
SODIUM
TANTALUM
THORIUM
TRANSITION ELEMENTS
URANIUM
USA
UTAH
VOLCANIC ROCKS