skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Petrogenesis of the Fifes Peak volcanics, south-central Cascades Range, Washington

Abstract

During the late Oligocene (ca. 27--23 Ma.), a voluminous section of subduction-related basalt to rhyolite flows and interbedded pyroclastics, comprising the Fifes Peak Formation, were extruded in the south-central Cascades Range of Washington State. Microprobe analyses reveal that basalts and basaltic andesites contain megacrysts of aluminous clinopyroxene and spinel (hercynite) that may be xenocrysts derived from an upper mantle source zone or early, high pressure magmatic phases. Mass balance calculations indicate that the compositional variation of the Fifes Peak basalt and andesite was controlled mainly by high-pressure clinopyroxene-dominated fractionation, coupled with lower pressure fractionation of plagioclase + orthopyroxene + magnetite/ilmenite. Trace element data and mass balances also show that the more silicic lavas must contain a significant crustal component (such as a high Ba/Nb pelagic sediment). The dacites and rhyolites were probably formed mainly by crustal melting, rather than contamination of mantle-derived magmas. The Fifes Peak volcanics have a typical arc-type trace-element distribution with distinct depletions in Ta, Nb, and Ti and enrichment in Th and large-ion-lithophile elements. All of the analyzed Fifes Peak flows are light-rare-earth-element enrichment, with a mean La/Yb ratio of 7.6. There is no indication of an OIB mantle source array, nor the low fluid-flux subductionmore » conditions that characterize magmas generated in the southwest Cascades. Apparently the anomalous nature of the subduction zone in that region of the Cascades arc does not extend northward to the south-central Cascades.« less

Authors:
;  [1]
  1. (Western Washington Univ., Bellingham, WA (United States). Geology Dept.)
Publication Date:
OSTI Identifier:
5292067
Alternate Identifier(s):
OSTI ID: 5292067
Report Number(s):
CONF-9305259--
Journal ID: ISSN 0016-7592; CODEN: GAAPBC
Resource Type:
Conference
Journal Name:
Geological Society of America, Abstracts with Programs; (United States)
Additional Journal Information:
Journal Volume: 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; Journal ID: ISSN 0016-7592
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GEOLOGIC FORMATIONS; PETROCHEMISTRY; PETROGENESIS; VOLCANIC ROCKS; WASHINGTON; CASCADE MOUNTAINS; CHEMICAL COMPOSITION; GEOCHEMISTRY; MICROANALYSIS; SUBDUCTION ZONES; TERTIARY PERIOD; TRACE AMOUNTS; CENOZOIC ERA; CHEMISTRY; DEVELOPED COUNTRIES; GEOLOGIC AGES; GEOLOGY; IGNEOUS ROCKS; MOUNTAINS; NORTH AMERICA; PETROLOGY; ROCKS; USA 580000* -- Geosciences

Citation Formats

Babcock, R.S., and Thompson, J.M.S. Petrogenesis of the Fifes Peak volcanics, south-central Cascades Range, Washington. United States: N. p., 1993. Web.
Babcock, R.S., & Thompson, J.M.S. Petrogenesis of the Fifes Peak volcanics, south-central Cascades Range, Washington. United States.
Babcock, R.S., and Thompson, J.M.S. Thu . "Petrogenesis of the Fifes Peak volcanics, south-central Cascades Range, Washington". United States.
@article{osti_5292067,
title = {Petrogenesis of the Fifes Peak volcanics, south-central Cascades Range, Washington},
author = {Babcock, R.S. and Thompson, J.M.S.},
abstractNote = {During the late Oligocene (ca. 27--23 Ma.), a voluminous section of subduction-related basalt to rhyolite flows and interbedded pyroclastics, comprising the Fifes Peak Formation, were extruded in the south-central Cascades Range of Washington State. Microprobe analyses reveal that basalts and basaltic andesites contain megacrysts of aluminous clinopyroxene and spinel (hercynite) that may be xenocrysts derived from an upper mantle source zone or early, high pressure magmatic phases. Mass balance calculations indicate that the compositional variation of the Fifes Peak basalt and andesite was controlled mainly by high-pressure clinopyroxene-dominated fractionation, coupled with lower pressure fractionation of plagioclase + orthopyroxene + magnetite/ilmenite. Trace element data and mass balances also show that the more silicic lavas must contain a significant crustal component (such as a high Ba/Nb pelagic sediment). The dacites and rhyolites were probably formed mainly by crustal melting, rather than contamination of mantle-derived magmas. The Fifes Peak volcanics have a typical arc-type trace-element distribution with distinct depletions in Ta, Nb, and Ti and enrichment in Th and large-ion-lithophile elements. All of the analyzed Fifes Peak flows are light-rare-earth-element enrichment, with a mean La/Yb ratio of 7.6. There is no indication of an OIB mantle source array, nor the low fluid-flux subduction conditions that characterize magmas generated in the southwest Cascades. Apparently the anomalous nature of the subduction zone in that region of the Cascades arc does not extend northward to the south-central Cascades.},
doi = {},
journal = {Geological Society of America, Abstracts with Programs; (United States)},
issn = {0016-7592},
number = ,
volume = 25:5,
place = {United States},
year = {1993},
month = {4}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share: