Title

The Structure Stratigraphy And Geochemistry Of The Mount Tebo Area, Southeastern Olympic Mountains, Northwest Washington State, Usa

Document Type

Article

Publication Date

4-1-2000

Publication Title

Abstracts With Programs - Geological Society Of America

Department

Geology

Abstract

The Crescent basalt formation is a horseshoe shaped, 15-16 km thick, basaltic formation surrounding the core of the Olympic Mountains. The origin of this 50-58 Ma formation remains unclear due to its chaotic structure, inconsistent geochemistry and poor exposure. In order to better describe the Crescent formation and perhaps discover its origin, three weeks were spent in the Mount Tebo area of the Olympic Mountain mapping and sampling outcrops of the Crescent basalt formation. A comprehensive map of the area was created along with a stratigraphic column of a well-exposed section of the mapped area. Mapping revealed that the area north of the Skokomish river is mainly submarine pillow flows and sills from a shallow marine environment. No dikes were found in this area; thus, it is believed that the mapped area was some distance from an eruptive center. Consistent structural information, striking approximately NE-SW and dipping 40 to 70 degrees, suggests that the mapped area may have undergone some post-eruptive tectonic history different than the better understood and structurally variable region to the southwest. Thin section analyses on 30 samples reveals that rocks in the area have been significantly altered, mainly alteration to calcium carbonate minerals. Pillows and columns are significantly coarser grained than sills, and typical basalt mineral assemblages were found. Geochemical analysis, including spectrometry, is in progress.

Volume

32

Issue

66

pp.

14-14

ISSN

0016-7592

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