I have tried looking at that feature many times, the only thing that I understood was that either it is a parallel-to-boundary opening or a dextral shear opening (figure attached). Some kind of very strong force with cherty liquid was responsible for the brecciation, that did not really cause relative movement but just opening up of the fracture (some type of hydraulic fracturing). I tried matching the boundaries of the vein, I got a dextral sense of opening for the crack.
In the opened up crack, I tried to asses the fragments that look like domino-type stacks but I could not think further than this.
Dear Raghav,
Do not complicate the situation.
Onto base of the photos it seems that you have a simple mechanical fracture in the rock mass which was formed by stress (tectonical gravitational) … It seems that the rock body have been moving very slightly. In time of this moving was produced flowing fracture. Parallel with this fracture in the nonfactured rock near the facture, you have to find sign of flowing. The fracture filling (fragments from rock, and hydrothermal fluid or fluid from outside… The before made statement can be well verified on the rock place (geomorphology) or with micro cut from rock….
My regards,
Laszlo
i
Dear Raghav,
This looks like brecciation in fractures, indeed probably by hydraulic fracturing. You do not need a "cherty fluid", just a fluid whose pressure reduces the effective pressure (lithostatic P minus fluid P) so that the rock can break. If you have quartz in the matrix and veins, this fluid was SiO2-bearing. If you find a consistent shear direction by matching the sides, this would indicate some tectonic formation of the structures, but it can also be purely by fluid overpressure (perfect hydraulic fracturing). You can find a number of papers on brecciation and the shape and patterns of breccia clasts in:
Weisheit, A., Bons, P.D., Elburg, M.A. 2013. Long-lived crustal-scale fluid-flow: The hydrothermal mega-breccia of Hidden Valley, Mt. Painter Inlier, South Australia. International Journal of Earth Sciences 102, 1219-1236. DOI: 10.1007/s00531-013-0875-7.
Useful papers may be:
Mort K, Woodcock NH (2008) Quantifying fault breccia geometry:
Dent Fault, NW England. J Struct Geol 30:701–709
Je´brak M (1997) Hydrothermal breccias in vein-type ore deposits: a
review of mechanisms, morphology and size distribution. Ore
Geol Rev 12:111–134
etc.
Best wishes, Paul.
Thank you sir Laszlo for your suggestions. I will look closely to the rocks.
Thank you Paul Bons sir. There is a brecciated zone about 50m wide next to these small fractures. The fragments are haphazardly oriented with lots of SiO2 deposition in them. I would read papers and again look at the rocks in the field.
Regards
Seems to be typical hydraulic breccia, formed by fluid overpressure as Paul Bons describes above.
Best wishes, Sonja
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