12 November 2010
Friday fold: blueschist
Posted by Callan Bentley
Lately, this blog has been focusing a lot on a subduction zone complex in Turkey, the Tavşanlı Zone. Much of the geologic appeal of that complex is its profusion of high-pressure, low-temperature metamorphic rocks, those in the blueschist metamorphic facies. From the last location visited on the Tavşanlı Zone field trip, I collected this fine sample:
The penny is to provide a sense of scale. You’re looking at an oblique section through the fold, as revealed along a joint face which does not intersect the fold axis at a perfect 90° angle, and hence is not a true “profile” view of the fold. As you can see, this is a fold hinge region adorned with many parasitic folds of shorter wavelengths and amplitudes. The inside of the master fold’s curve shows these smaller folds expressed in three dimensions, as the blueschist is more likely to break along the plane of foliation (even if it is contorted) than across it.
Here’s a brief video, to give you a sense of its three-dimensional form:
Happy Friday! Have a good weekend.