The reinterpretation of Leone lake sediments as a pyroclastic surge deposit and its tectonic significance

William F. McDonough, Albert F. Waibel, Marshall W. Gannett

研究成果: Article査読

3 被引用数 (Scopus)

抄録

A series of Miocene to Pliocene bedded pyroclastic units in the Western Cascades of Oregon, previously interpreted as being of fluvial and lacustrine origin, are described and reinterpreted as subaerial pyroclastic surge and palagonite tuff cone deposits. The pyroclastic surge units are characterized by (1) an abundance of transparent unaltered, blocky sideromelane fragments with low vesicularity; (2) a constant relative proportion of minerals; (3) limited plagioclase composition; (4) trace quantities of palagonite and secondary minerals; (5) a lack of accidental rock fragments not enveloped in sideromelane; and (6) absence of subaqueous sediments and fossils. The palagonite tuffs are characterized by: (1) massive lower portions that grade upward to finely laminated tops in each sequence of tuff beds; (2) the presence of vesicles; (3) the presence of angular, unaltered, vesicular basalt clasts; (4) an apparent quaquaversal structure displayed by the palagonite tuff bed attitudes; and (5) interstratification with the pyroclastic surge beds. Because these beds are primary volcanic features, the bedding angles are not useful in interpreting post-depositional tectonic flexuring or tilting, and cannot be used as evidence for a down-drop to the east structure in this part of the Cascades as has been proposed by earlier workers.

本文言語English
ページ(範囲)101-115
ページ数15
ジャーナルJournal of Volcanology and Geothermal Research
20
1-2
DOI
出版ステータスPublished - 1984 3月
外部発表はい

ASJC Scopus subject areas

  • 地球物理学
  • 地球化学および岩石学

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