Physical Sciences and Mathematics Commons^™

The Geology Of Southwestern Fidalgo Island, Daryl Gusey

WWU Graduate School Collection

Detailed geologic mapping of rocks in the upper stratigraphic levels of the Fidalgo ophiolite Indicates that keratophyres and spilites are interbedded with tuffaceous sediments, sedimentary breccias, and graywacke. Sedimentary breccias containing plutonlc rock fragments as well as volcanic rock fragments are common. The graywackes were derived from a volcanic source area. Radiolaria In the tuffaceous sediments indicate a depositional age of Lower Kimmeridgian to Upper Valanginian.

Compared to the stratigraphy and petrology of other ophiolites and present-day tectonic environments, the Fidalgo Complex most closely resembles that of ancient and modern island-arc sequences.