Pacific Northwest NAGT Field Trip #2

I began writing about the 2011 Pacific Northwest NAGT field meeting here. On Friday we circumnavigated Steens Mountain. The final stop was in Colony Canyon south of Fields, Oregon near the Oregon Nevada Boarder. The area was postulated to be accreted terrain that was originally near the continental craton, but has been moved hundereds of kilometers east by the extension of the Basin and Range Province. There were numerous outcrops of highly metamorphic rock, and not enough time to thoroughly explore.

Andy and Turk debate the Metamorphic grade of the outcrop

I am not strong on metamorphic rocks, but I know a nicely folded schist when I see one, and it makes a nice folded structure for a Friday.

The schist was actually folded by three separate events, the first forming the shist planes, the second altering the foliated planes into wavey folds, and finally a large tilting of the whole block to dip towards the north east. The layer on the right that appears to be intruding into the schist was interpreted by Turk and Andy to be Ultra-mylonite. The area was also full of granitic intrusions with lots of trace minerals, many of which I could not identify.



A great stop, but it would take a field season to really get a feel for all of the geology.