Wednesday, May 5, 2010

Ophiolites and being a Grunt Geologist

I sometimes refer to myself as a grunt geologist. Grunt geologist do not have as much time to pursue geologic observations as much as they would sometimes like. Lately I have been doing a fair bit of small field site visits and I just completed a report that I would once describe as a thesis. I now can describe in detail the aggregate resources in Clallam and Jefferson County. But outside of a narrow self interested group, I would likely put anyone asleep with stories about sand and gravel deposits.

Field work the past two weeks has been damp and chilly. The field work has been followed up with lots of writing including the aggregate study. Below is a view looking north from Fidlago Island to Cypress Island, one of the Jan Juan Islands. I took the picture during a small project assessing a slope on a chilly wet late April afternoon. Cypress is one of the San Juan Islands that is actually not in San Juan County. It is in Skagit County. Most of Cypress is protected as a Natural Resources Conservation Area and as a Natural Area Preserve.  

The shoreline along Fidalgo Island I was traversing involved technical crawling. Lots of sharp boulders covered with very slippery oak leaf seaweed.

The boulders consist of ultamafic rocks of the Fidalgo ophiolite. Ultramafic refers to the fact that these rocks are very high in iron and magnesium content relative to most rocks. An ophiolite is a section ocean crust. These rocks are part of an ocean basement that somehow got thrust up and accreted to the edge of North America. The Fidalgo ophiolite is part of a complex assemblage of rocks making up parts of the San Juan Islands and the Northwest Cascades that is referred to as the San Juan - North Cascades Complex. The complex is well very complicated and not necessarily for the understanding of a grunt geologist like me just trying to figure out if a slope is stable. But it was fun to use the term ophiolite in a report. And I enjoyed observing the mineralogy and layering that only a metamorphic petrologist or a student of deep ocean crust can fully appreciate. And besides I once spent a fair bit of time helping try to sort out some the pieces of the puzzle explaining how these rocks ended up here as a graduate student.

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