By only looking at that picture I would assume dextral. Don't you have thin sections or different images of that outcrop?

As Tim said, dextral shear can be seen, what I marked on your photo.

You have to be careful about where you set the boundaries of a shear zone and also pay attention to evidence of partitioning of deformation inside the shear zone.  Seems to me that the "adjacent areas" actually belong to a single partitioned zone, which has a consistent dextral sense of slip as Tim and Mirka pointed out.

Dear, Tim, Mirka, Felipe thank you for your replies.

In this particular outcrop, the sence of shear seems to be dextral indeed. In kinematic terms for this area, means a NE escape of a sedimentary cover. The point is, every other outcrop shows opposite sence of shearing (SSW escape) determined by several microcinematic indicators. So, I was searched for an oppinion matching in any other outcrop observation derived by this specific brittle shear zone. Now I have to re-consider re-evaluate the whole thinking. In any case, thank you!

Dear Alexandrides,

do you have thins section images?

Tim

I would say dextral as well. But a couple of pictures at a different scale (one bigger one smaller) would make it more clear.

In my opinion, this is a fragment of thrust mélange zone

I agree with you Victor in the part of beeing melange, although we could use the term "melange" for any brittle-ductile mixture of rocks inside a shear zone. I think "melange" also shows the absence of foliation, but in this case I think it's safer to talk about "laminated-foliated cataclasites" or "cataclastic flow", due to lack of  evidence of thrust movement. Your suggestion puts me in thoughts.

Also thank you, Telemaco and Haider.

Dear Alexandrides,

by looking at this picture the sense of shear is definitively dextral. To puzzle this picture in Your regional framework , I guess You should consider if it could be related to secondary fault zones having different sense of shear respect to main fault zones. In strike-slipe regimes for instances, secondary fauts can do that....

With best regards,

Emiliano

By close looking to the picture, specifically at the head of the pen, it seems that a dextral sense prevail in the photograph. Exact answer is possible only based on: i)  the field alingment of the photographs, ii) large scale photograph of the exposure, and iii) thin section in area of small cross-cutting fractures/veins.

In my opinion it is not as obvious at it looks at first glance. The material is probably very heterogeneous to start with and the sigmoidal shape might be inherited, especially if it really is some sort of mélange. I can see no clear drag of a schistosity around that large 'clast'! I would look for small-scale structures such as a crenulation or C' fabrics in the more foliated zones. The foliation in the upper left part appears to be slightly folded/crenulated, which would rather indicate a sinistral movement in that image. Is a lineation visible and is it perpendicular to the viewing direction? Cheers, Daniel

Dear Daniel,

Unfortunately, lination is the most difficult structure to observe in this brittle sh. zone, I believe due to absolute pulverization (ultracataclasite, clay-sized particles) of the footwall and hanging wall rocks.

Your suggestion for folded surfaces it seems interesting. For example, the lower plane of the "clast" seems to be folded indeed, in a pattern which does not support the dextral sence of shear. The same curvature can be also observed in other places of the outcrop, as you correctly suggested.

Kind regards,

Ioannis Alexandrides

Ok, so I think you don't have thin sections? 

NEAR THE HEAD OF THE PEN , THE '' CLAST' SEEMS TO HAVE TAILING WITH 'S' TYPE GENTLE LOOP THAT PROBABLY REPRSENT SINISTRAL SENSE.  THE BOUDINS AT THE BOTTOM ALSO BOUND BY SINISTRAL SLIP PLANE

This has a sigmodal, asymmetrical winged shape and would indicate a dextral sense of movement.

Nice answer Dani.

It looks like  a clast with a tail of sigma- type complex indicates a dextral shear...for further information you can see structural geology texts e,g EARTH STRUCTURES by DER VAN PLUIJM & MARSHAK , 2004........etc.

Please have a look at the following for all possibilities:

"Dutta D, Mukherjee S. in press. Opposite shear senses: Geneses, global occurrences, numerical simulations and a case study from the Indian western Himalaya. Journal of Structural Geology."

It is not obvious (and I suspect the picture is not taken in the best orientation), but my guess is that is is dextral.

Dear Soumyajit Mukherjee thank you for the suggestion.

Dear Telemaco Tesei thank you for the comment. Concerning the orientation you mentioned, I always shoot photos horizontally. I believe all of us. What do you exactly mean?

Regards

Ioannis A

Dear Ioannis,

I mean that it may be possible (I obviously don't know for sure) that the picture is not taken on a plane perpendicular to the fault plane and on a section parallel to tectonic transport. Obviously the outcrop does not always allows such a point of view. In general it might be worth looking at different angles as well. But I am sure that you already did it.

In this specific case, also a sligtly larger view would help, I think.

best

Telemaco

Dear Telemaco Tesei , I see what you mean. Maybe it is as you say, I took this photo 7 years ago. Though, it is more or less a proper caption. Even if you are correct, I can't see how this could affect a judgement about the sence of shear. One step back and view of the "forest" instead of a "tree" always helps, I agree to that.

Cheers, Ioannis

Dear Ioannis T. Alexandridis ,

I agree with the others. This picture appears a bit problematic. At first glance, the yellowish 'clast' points to a dextral shear, but I can't see any other S-C structures, kinematic indicators and foliation deflection in this image. Moreover, this 'clast' does not appear clearly wrapped by a foliation, as it should be in a nice shear zone. One possibility could be that this shape is inherited (as Daniel Egli said), or that you are not looking at the right section (in agreement with Telemaco Tesei ). To my experience, sometimes you may also have some fluid-rock interaction in brittle shear zones and produce areas that are severely altered by fluids. I am telling you this because I see many other yellowish domains in your picture that could be simply be a result of fluid circulation in the shear zone.

Best,

Samuele

Dear Samuele Papeschi,

thank you for your comment. You are right about the fluid circulation. I have a better understanding for the zone now, than 6 years ago when I had these questions. you can take a look here:Research Foliated gouge architecture and kinematics of a low-angle no...

Best regards

Ioannis

At first glance, not focusing on the oxidized "clast" and not knowing the details, I´d say it´s dextral. See picture attached.

thank you Tomas Correa , i agree!

Dextral shear, however, in the image I draw just the structures that I Could follow really well... Regards