Abstract: Fission-Track Ages of Hoh Diapirs and the Olympic Mountains, Olympic Peninsula, WA

CHRISFIELD, REBECCA 

The Olympic peninsula, Washington is a geologically complex region. This research project will investigate two related problems in the Olympic peninsula using similar analysis techniques. The first goal is to analyze several diapirs in the Hoh rock assemblage (western Olympic peninsula), confirmed to have hydrocarbon potential. Use of fission-track methods will determine accurate ages for the diapiric sediment and for diapiric emplacement. Diapirs to be dated include the offshore diapir penetrated by Pan Am well P-0141, and several coastal diapirs. Dates obtained will better constrain the regional structural and stratigraphic picture. This picture in turn can provide an increased under standing of the hydrocarbon migration path, and one might then infer where hydrocarbon traps occur in the western Olympic peninsula.

The second aim of this project is to date the uplift of the Olympic mountains. Past attempts to date the Olympics directly have failed because fossils are lacking, and all fission-track ages within the Olympic mountain core rocks are too young due to thermal resetting. Previous research has postulated that the Olympic mountain range is a very large diapir, formed when the "Hoh" diapirs were emplaced. This suggestion can be confirmed by dating the Montesano Formation (southwest Washington) which contains early eroded sediments from the Olympics. Assuming Montesano sediments were not buried deeply prior to uplift, and that the time between uplift and erosion is negligible, the fission-track ages of the Montesano sediment should match the ages of the Hoh diapirs and therefore confirm the age of the Olympic mountains.  

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid