6 March 2015
Reader Mike Pendergrass contributes this Friday’s fold:
I found your blog a couple years ago and I share your love of structural geology. I did my Master’s Thesis while at Northern Arizona University in the early 80’s and mapped an area on the Mazatzal Mountains of central Arizona. The Mazatzals in my field area contain metasedimentary rocks that were deformed in the Mazatzal Orogeny (~1.6-1.7 billion years ago). The stratigraphy includes older to younger, the Deadman Quartzite, Maverick Shale, and Mazatzal Quartzite. Together they may be approximately 3,000-5,000 feet thick. My field area was a large plunging syncline. The Maverick Shale has many classic structures associated with structurally deformed rocks, especially in the upper part where there are isolated quartzite layers that were folded and faulted into classic structures.
I visited last summer for the first time in 20 years and therefore the first time with a digital camera.
Here’s an overview shot:
Now, let’s zoom in!
The first is a photo of an entire canyon wall covered in chevron folds. This is the upper part of the Maverick Shale with the quartzite layers surrounded by the shale, so you have ductile and brittle deformation at the same time. The height of this outcrop is about 200-300 feet.
Spectacular! I love it.
This photo is the same outcrop as the first photo, but lower on the wall. The quartzite layer is probably 2-3 feet thick and you can see a few agave plants for scale. You can see that shorting that the shale was able to withstand made the quartzite layer turn into a series of thrust faults and folds.
Thanks, Mike. These are great.
Other readers who want to send me candidates for the Friday fold series, please do!
Happy Friday, everyone.