Origins of dacite and rhyodacite of the South Sister magmatic system, central high Cascades, Oregon
- Baylor Univ., Waco, TX (United States)
A gap from 66 to 72 weight percent silica (48--62 ppm Rb) separates dacite from rhyodacite of the South Sister system. The authors results indicate that rhyodacite can not be produced by fractional crystallization from dacite. Variation among rhyodacite and associated rhyolite is, however, most likely the result of fractional crystallization, in agreement with previous studies. Dacite in the South Sister system probably had multiple origins, as suggested by trace element plots for Y, Nb and Zr. Some dacite was produced by fractional crystallization from andesitic magmas, while others were largely the result of mixing between andesite and rhyodacite. Mafic enclaves occurring in dacite are compositional similar to Holocene basalt, and their mixing with dacitic magma may have triggered eruptions, but they are probably not directly related genetically to their host rocks. The rhyodacites are probably crustal melts. Previous workers have suggested high-level melting of hypabyssal silicic plutons or amphibolite sources for the rhyodacites. The authors suggest melting of granitic plutonic sources, similar to those exposed in the Klamath Mountains, for the origin of the rhyodacites.
- OSTI ID:
- 5025379
- Report Number(s):
- CONF-9305259--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:5; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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