Major-element evidence for multiple magma batches in the evolution of Pleistocene and Holocene volcanic rocks of the Markagunt Plateau volcanic field, southwestern Utah
- Geological Survey, Denver, CO (United States)
Pearce element ratios (PER) provide an initial understanding of the evolution of Pleistocene and Holocene alkali basalt to trachyandesite magmas of the Markagunt Plateau. The magmas erupted from numerous cinder cones, shield-like centers, and dikes. Vent areas were controlled by structures (e.g., grabens) related to the tectonic evolution of the transition zone between the Basin and Range and Colorado Plateaus provinces. The cinder cone-fed basalt flows and a single dike-fed basalt flow are probably older than shield-fed basalt and trachyandesite flows. Chemically, cinder cone- and dike-fed basalt flows are more mafic than shield-fed basalt flows. Trachyandesite flows are latite and benmoreite (58.7--59.7 wt % SiO[sub 2]). PER analysis of flow chemistry indicates that the shield-fed flows represent at leas three cogenetic magma batches, that cinder cone-fed flows must be related to more than one magma batch, but that all andesite is genetically related to a common parent magma. The dike-fed basalt flow is not genetically related to any other magma type. Although several magma batches erupted, chemical variations in the magmatic series are consistent with the fractionation of the observed phenocryst phases: olivine, plagioclase, clinopyroxene, and spinel. This four-phase fractionation assemblage relates compositional differences within each basalt type better than it does the entire magmatic series. Fractionation of no single mineral phase can adequately explain chemical variations in the basaltic magmas of the Markagunt Plateau.
- OSTI ID:
- 5024774
- 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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