The production of intermediate magmas through magma mixing and commingling: Evidence from the Hoover Dam Volcanics, Mohave County, Arizona and Clark County, Nevada
- Univ. of Nevada, Las Vegas, NV (United States). Dept. of Geoscience
The Hoover Dam Volcanic section ([approximately]14 Ma) is composed of the reversely-zoned dacitic tuff of Hoover Dam, Switchyard basaltic andesite, Sugarloaf dacite, Black Canyon dacite and Kingman Wash basaltic andesite (Mills, 1985). The origin of this suite is best explained by the commingling and mixing of end-member mafic and felsic magmas. These end-member magmas were most likely formed by partial melting of the mantle and subsequent advective heating and melting of the crust respectively. Textural evidence for these processes is observed in the Black Canyon dacite which contains enclaves of basaltic andesite, and, in the Paint Pots pluton which contains commingled basaltic andesite and monzonite. The Black Canyon dacite is a biotite (4%), homblende (1%) and plagioclase 10% phyric dacite flow which contains up to 5% enclaves of basaltic andesite. The enclaves contain 54 wt% SiO[sub 2], 7.22 ppm Tl, 65 ppm Rb, 1,274 ppm Sr and 1,810 ppm Ba. The gray to purplish-red enclaves have crenulate margins, are commonly vesiculated and contain phenocrysts of biotite (< 1%), hornblende ([much lt]1%), plagioclase (1%) and clinopyroxene( ) (2%). Chemically, the enclaves are distinct from the Switchyard and Kingman Wash basaltic andesites. The enclaves most likely represent a more primitive magma from which the Switchyard and Kingman Wash basaltic andesites were derived. These two units were subsequently chemically modified by mixing with crustal melt and/or crystal fractionation. The presence of a small, clinopyroxenite xenolith (clinopyroxene 90%, garnet 5%, plagioclase 4%) within one of the enclaves indicates an upper mantle source for the enclave magma.
- OSTI ID:
- 5095747
- 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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