Petrology and geochemistry of the Pelican Butte area, S. Oregon
- Beloit Coll., WI (United States)
The Cascade mountain range consists of a linear chain of composite volcanoes extending from British Columbia to northern California. The volcanic rocks of the Cascades range in age from Miocene to Holocene. They are believed to result from subduction of the Juan de Fuca plate beneath the North American plate. The area studied is located in the southeastern Oregon Cascades, near Fish Lake, Oregon. Little formal mapping of this area has been done. The purpose of the project was to describe the volcanic units in a seven square mile map area located on the southwestern flank of Pelican Butte. Pelican Butte is a large eruptive center northeast of Mt. McLoughlin. Its summit has been dated at 0.54 Ma + 0.05 Ma. The rocks range in composition from basalts to andesites. Outcrops are generally blocky flows, some of which are associated with pyroclastic material. The overall mineralogy consists of plagioclase feldspar, olivine, [+-] clinopyroxene, [+-] orthopyroxene. In order to investigate genetic relationships between basaltic and andesitic compositions, incompatible elements were plotted on a Cartesian coordinate system. On such a plot, ratios of incompatible elements remain constant among units whose source is the same. A La/Ba plot shows two distinct groups (andesites and basalts) which represent two distinct magmatic sources. The ratios of light REE's, CeN/LaN, however, are within error for all compositions. This suggests a similar mantle source for both basalts and andesites. The increase in Ba in the andesitic compositions may indicate crustal contamination of the mantle source. The trends within compositional groups probably result from crystal fractionation but no fractionation evidence exists between compositional groups.
- OSTI ID:
- 7141004
- Report Number(s):
- CONF-9404217-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 26:5; Conference: 27. annual conference of the North-Central Section of the Geological Society of America (GSA), Kalamazoo, MI (United States), 28-29 Apr 1994; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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