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Identification of Dacitic Tephra by Activation Analysis of their Primary Mineral Phenocrysts1

Published online by Cambridge University Press:  20 January 2017

M.J. Dudas ,
M.E. Harward  and
R.A. Schmitt
M.J. Dudas
Affiliation:
Department of Soil Science, Oregon State University, Corvallis
M.E. Harward
Affiliation:
Department of Soil Science, Oregon State University, Corvallis
R.A. Schmitt
Affiliation:
Department of Chemistry and the Radiation Center, Oregon State University, Corvallis, Oregon 97331 USA
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Abstract

Primary mineral phenocrysts from eight different late Quaternary pyroclastic deposits were fractionated for neutron-activation analysis with the purpose of characterizing each of the deposits on the basis of trace and minor element compositions. In hornblende separates, contents of several rare earth and transition elements were found to be distinctive for the Mazama, Glacier Peak, and several St. Helens deposits. In magnetites, abundances of transition elements are characteristic and serve as good discriminants for the pyroclastic deposits examined in this investigation. Contents of transition and rare earth elements in hyperthenes also appear useful in distinguishing volcanic ash deposits. Trace and minor element abundances in plagioclase phenocrysts did not appear adequate for identification of pyroclastics due to elemental depletion and similarity of contents for feldspar separates. It was found that contents of Sm and Yb in hornblende phenocrysts would serve to distinguish between several pyroclastic deposits from the Pacific Northwest.

Type
Original Articles
Information
Quaternary Research , Volume 3 , Issue 2 , August 1973 , pp. 307 - 315
Copyright
University of Washington

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