The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States.

E. H. Christiansen, M. F. Sheridan, Donald Burt

Research output: Chapter in Book/Report/Conference proceedingChapter

43 Citations (Scopus)

Abstract

High-silica, topaz-bearing rhyolites of Cainozoic age are widely distributed across the W USA and Mexico; they are characteristically rich in F (>0.2 wt.%) and contain topaz crystallized during post-magmatic vapour-phase alteration. Their emplacement followed or was contemporaneous with calc-alkaline and basaltic magmatism in the Basin and Range province, along the Rio Grande rift, and in Montana, and coincided with episodes of extensional tectonism in these regions. Analyses for major and trace elements and REE are tabulated and the petrography and mineralogy of these topaz rhyolites are described. Magmatic phenocrysts include sanidine (Or50), quartz, sodic plagioclase (usually oligoclase) and biotite rich in F and Fe; Fe-rich hornblende or clinopyroxene occur in a few lavas. Common accessory minerals include magnetite, ilmenite, zircon, apatite, allanite and fluorite; garnet, bixbyite, pseudobrookite and hematite occur with topaz in cavities or in devitrified groundmass. The REE patterns are almost flat but have strong negative Eu anomalies. The topaz rhyolites are intimately related to economic deposits of lithophile elements (Be, U, F, Li, Sn). In their age, tectonic setting, mineralogy, chemistry and style of replacement, the topaz-rhyolites resemble the rhyolitic stocks associated with Climax-type Mo deposits, and some may be surface manifestations of such deposits. The topaz rhyolites are distinct from both peralkaline rhyolites and calc-alkaline rhyolites, but are similar to other aluminous rhyolites erupted in bimodal associations with basalts in W USA; they may be the equivalent of the topaz-bearing ongonites of the USSR. They appear to have evolved from partial melts of a residual felsic granulite source in the lower or middle crust of the Precambrian continent.-R.A.H.

Original languageEnglish (US)
Title of host publicationThe Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States.
PublisherGeological Society of America: Special Paper 205
ISBN (Print)0813722055
StatePublished - 1800
Externally publishedYes

Fingerprint

topaz
geochemistry
geology
mineralogy
rare earth element
bimodal association
allanite
sanidine
accessory mineral
climax
fluorite
granulite
petrography
ilmenite
hornblende
tectonic setting
hematite
clinopyroxene
apatite
magnetite

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)
  • Environmental Science(all)

Cite this

Christiansen, E. H., Sheridan, M. F., & Burt, D. (1800). The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States. In The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States. Geological Society of America: Special Paper 205.

The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States. / Christiansen, E. H.; Sheridan, M. F.; Burt, Donald.

The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States.. Geological Society of America: Special Paper 205, 1800.

Research output: Chapter in Book/Report/Conference proceedingChapter

Christiansen, EH, Sheridan, MF & Burt, D 1800, The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States. in The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States.. Geological Society of America: Special Paper 205.
Christiansen EH, Sheridan MF, Burt D. The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States. In The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States.. Geological Society of America: Special Paper 205. 1800
Christiansen, E. H. ; Sheridan, M. F. ; Burt, Donald. / The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States. The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States.. Geological Society of America: Special Paper 205, 1800.
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