Plumose marking or Plume Structure
A quick blog on
Plumose markings or Plume structure
Joint surfaces are sometimes have characteristic surface markings. They are of two types Hackle marks and Rib Marks. Plumose or Plume structure is the most common type of Hackle mark. They are feather like markings on the joint surface with a central axis from which the rays or barbs branch out into either side.
According to Parker 1942 plume structures are common on shear joints while they are rare in conjugate joints.
All these photos are taken by me and are from Lunavada, Gujarat, India. You can easily find many such outcrops on Ahmedabad zalod highways road cut sections.
Abhishek Tiwari,
GEOLOGY FREAK
Geologist at The Geological Survey of India and Administrator of GeologyFreak.com. A geologist by day and a blogger by night. I share my adventures and experiences through this blog. Follow me on facebook and Twitter.
Interesting. I’ll have to pay more attention to those markings. Never gave it any thought before. What’s the difference between shear joints and conjugate joints?
Well in simple terms, shear joints are not joints (no displacement) but they are microfaults. You should closely observe for displacement and if you find sliken sides then it’s confirmed shear joints.
Where as conjugate joints (seen in folds) are are two sets of joints crossing each other along the fold axis and the line formed due to intersection of two joints is always perpendicular to fold axis and parallel to axial plane .
Hope it helps.