Link to the original image: https://postimg.cc/v4bRqxxR

I believe this image represents two folds which are overturned and plunging. I would like to analyse these folds on a stereonet, but I am unsure how to split the data.

I have annotated the image (link below) to show my thoughts on splitting the data into domains. What I am finding confusing is the relation of the data in the "northern domain" to the "southern domain".

Link to annotated image: https://postimg.cc/Wtc7JBD3

Any advise on how to split the data into domains would be helpful and reassuring in my understanding.


1 Answer 1


I think you may have more than 2 domain based on satellite image. Maybe you have three limbs of folds (green) and a fault (red). Please consider this interpretation carefully, I don't know where your study area is, what are its geologic units and structures and plutonic intrusions may deform other rocks (sedimentary, metamorphic and vulcanic), which its satelite images will look like your area, specially in old terrain (Archean ones as part of Brazil, Australia, Canada, United States, Russia, Sweden, among others).

enter image description here

I recommend:

  1. Try to draw the morphostructural lineaments in the topographic raster of your area. You should use the shadow relief to help you in this task. Then, based on its directions, you can have a ideia about the spacial distribution of the domains.
  2. The relief texture (I don't know if these are right words) can also be used to define domains. The roughness of the mountain terrain is the highest in your area.
  3. The units with similar ages as Paleoproterozoic ones and Neoproterozoic ones define two domains, at least. It can also improve or subdivided your domains.
  4. Plot all data of a specific structure* in some stereogram program as Stereonet, OpenStereo or Georient. The Georient has an advantage, you can enter the data by clipboard. The similar structures will be plotted nearby. Based on the clustering, you may improve the domain boundaries.

*Please, do not plot foliation (Sn) and bedding (S0) in the same stereogram. Each structure should be interpretate individually.

About stereogram interpretation, you should see the book of Marshak & Mitra (1988) that show excelent description about this.

Marshak, S. & Mitra, G. 1988. Basic Methods of Structural Geology. Enlewwod Cliffs, Prentice Hall

However, the best way is observed the relationship between foliations of different order (Sn and Sn+1) and/or foliation and bedding (Sn X S0) in field. This relationship will indicate the vergence. And then, you must proceed to the interpretation of stereogram.

I don't think there are easy way to split. You should to do this manually. I commonly import the data to Excel and classify by domains following the dip direction (or strike), location and, more important, vergence.

And, please, read about the geology of your area before you start. This help a lot. I hope that I could help you. I have listen what I wrote to you several times from my teachers during my graduation :). Best luck in your studies.


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