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View Full Version : Shear zones, (Photo`s)



Lady
09-14-2012, 06:32 PM
Wikipedia is going to take some thought processing on the different types of shears zones. I am posting some photos I have taken in our area.
1st, Map of our area.
2nd, gold zone,
3rd, this is really interesting. The out crop has several layers of free gold and gold on the quartz. You could see how it rolled out of the mountain and folded in.
4th, this is also interesting. We had cleaned this out and if he had not had a hold of the pry bar it would have gone all the way threw. A gap about 3" wide. Really red dirt and it is carrying gold. Down the hill from the Spain s Vein.

A shear zone is a zone of strong deformation (with a high strain rate) surrounded by rocks with a lower state of finite strain. It is characterised by a length to width ratio of more than 5:1.[1]

Shear zones form a continuum of geological structures, ranging from brittle shear zones (or faults) via brittle–ductile shear zones (or semibrittle shear zones), ductile–brittle to ductile shear zones. In brittle shear zones, the deformation is concentrated in a narrow fracture surface separating the wall rocks, whereas in a ductile shear zone the deformation is spread out through a wider zone, the deformation state varying continuously from wall to wall. Between these end-members, there are intermediate types of brittle–ductile (semibrittle) and ductile–brittle shear zones that can combine these geometric features in different proportions.

This continuum found in the structural geometries of shear zones reflects the different deformation mechanisms reigning in the crust, i.e. the changeover from brittle (fracturing) at or near the surface to ductile (flow) deformation with increasing depth. By passing through the brittle–semibrittle transition the ductile response to deformation is starting to set in. This transition is not tied to a specific depth, but rather occurs over a certain depth range - the so-called alternating zone, where brittle fracturing and plastic flow coexist. The main reason for this is found in the usually heteromineral composition of rocks, with different minerals showing different responses to applied stresses (for instance, under stress quartz reacts plastically long before feldspars do). Thus differences in lithology, grain size, and preexisting fabrics determine a different rheological response.