Plumose joint, arrest hackles, slickensides and veins are found at the same plane....any help in interpretation to understand what and how happened this...
Thank you Zampieri for your valuable comments and the attached figures which will help in the interpretation....
Abdullah,
The slickenlines and steps along the slickensided surface suggest left-lateral or sinistral shear along the affected fault surface, but I can see no veins. I confess to having no knowledge at all of the structure enclosed in the blue ellipse, but it does suggest the possibility of having been created by some sort of impact. Whatever it is, It does not, however, seem to me that it is cogenetic with the faulting.
Sorry, but I see the slickenlines and steps along the slickensides surfaces in a dextral strike-slip context! Brittle deformation in limestones. Lower pictures emphasizes a road cut oblique to a dextral sub-vertical fault. The lack of extensional calcite fibres argues for compression on these stopovers and thus dextral from the view you give. changing fracture system or "brittle schistosity" may indicate refraction due to changing mechanical behavior of one limestone bed to the other... open to objections and discussion
Dear Abdullah,
as Helmut mentioned the secondary structures in the fault plane to the left are consistent with a dextral strike-slip movement. This shear zone is the best indicator for the orientation of the "paleo?" stress tensor.
If you are looking for a good paper about shear sense indicators on fault planes, check this one out:
Petit, J. P. (1987). "Criteria for the sense of movement on fault surfaces in brittle rocks." Journal of Structural Geology 9(5-6): 597-608.
Here, you will find the features explained, Helmut was refering to.
The fracture in the forefront with the nicely developed hackle fringe could very well be a wing crack (mode 1 fracture) as D. Zampieri explained. I would not suggest to use the wing crack orientation for stress tensor analysis because wing cracks form at the tip of fractures/faults characterised by stress amplification and strong rotation of the local stress field.
In general, all the nice features on fracture surfaces like feather structures, plumrose structures, arrest line and ridges provide only information about the fracture propagation but not the stress field causing the fracture. It is discussed that fracture propagation happens with the speed of sound and for example the hackle fringes are highly oblique minor shear fractures along the tip line of the main fracturer controlled by rotationof the local stress tensor along the fringes during high-speed fracture propagation.
Hope this helps.
Thanks Adam, Are these structures formed during the same tectonic event or more than one tectonic event?? the main structure is a dextral strike- slip fault but the plomose structure is considered as a tensional joint........
Dear Abdullah, the wing crack with the Plumrose structure is related to the development of the strike-slip fault. The wing cracks on the fault tips are the result of the local stress concentration during fault slip and fault growth. The wing cracks form first as tensile fractures in the fault tip process zone. In the next stage, small secondary shear fractures will form and link up with the mode1 wing cracks to larger fractures. This will allow the main fault to grow along-strike into this deformed zone.
The attached photo does show wing cracks (calcite veins) in the damage zone of a small scale normal fault in Lias limestones of the Bristol Channel Basin in Somerset, SW England. My pen is positioned at the fault tip. To the left you see the normal fault (vertical surface with calcite fibres, note displacement variation to "zero" fault tip. Highly oblique thin calcite veins in strike direction to the right of the pen are wing cracks. The thicker vein with zick-zack trace in strike-projection of the normal fault are linked hybrid fractures. In the next stage, the fault will grow laterally into the linked fracture system.
Gentlemen,
This is not an answer, but is a question. I am the only one who suggested sinistral rather than dextral slip in the fault zone that Abdullah has been working on. Would any of the three of you, if not all, be willing to point to some indicator that I am undoubtedly missing? I would really appreciate that. Thank you.
Joe
From the kinematic indicators the fault is of dextral sense, because the occurrence of rock surface (not mineral) steps on the fault surface in addition to the facets.......and the Riedle shear fractures with acute angle with the main fault......
One year later, but I am told that geologists have no sense of timing. Anyway concerning the sense of movement that created the slicks, I stand corrected. I blew that, and apologize. I guess I would like to state that I do not know what I was thinking, but it would be much more appropriate to declare that I was not thinking.
- Badges
- Science topic
- Similar topics
- Geoscience
- Cartography
- Mapping
- Maps