In ductile shear zones, we expect to find a single major sense of movement. However, it is not as simple as that. For your case study, there are multiple solutions:

1. Multiple ductile deformation in progressive deformation: Folding accompanying shear movement in simple shear/ simple+pure shear. So, you can get sinistral sense (reverse) in one limb and dextral sense (normal) on the other in case of tight-isoclinal fold, provided there are folds with axial planes subparallel to shear zone. (for reverse faults)

2. Relative displacement within a single shear zone: The shear zone may show an overall shear sense with slivers of opposite sense of movement. It may generate due to accommodating space (accommodation structure). (for strike-slip faults). Or, simply flower kind of structures.

3. Remnant of earlier fabric: may be a case. Reorientation of earlier fabric.

If you get oblique slip movement according to the stretching lineation, all of the above are possible. I hope that field data will solve your case-specific problem.

Thank you!

Please find attached a photo of a cross section through a foliated epidote amphibolite. Location of this specimen is the emerald deposit Habachtal, Austria. The dark band in the middle is shifted diagonally. Deformation phenomena (interlocking) along that diagonal joint indicate a renewed (third) reverse foliation subparallel to the dark band.

The reason for the third foliation in the reverse direction is that the first ductile foliation and the third ductile foliation are separated by cooling (brittle deformational event).

For further details please see my papers:

G. Grundmann & G. Morteani (1989):

Emerald Mineralization during Regional Metamorphism: The Habachtal (Austria) and Leydsdorp (Transvaal, South Africa) Deposits. In Economic Geology, Vol. 84, 1989, pp. 1835-1849.

R.B. Trumbull, M.S. Krienitz, G. Grundmann & M. Wiedenbeck (2009):

Tourmaline geochemistry and delta11B variations as a guide to fluid-rock interaction in the Habachtal emerald deposit, Tauern Window, Austria. In Contrib Mineral Petrol (2009) 157:411-427.

Best regards,

Guenter Grundmann

@ Guenter Grundmann Thanks for sharing your research.

Dear Proloy,

Can you please send me one picture of XZ thin section?

As you have a specific problem, it will be better to see a thin section image rather than answering straight forward.

Thanks!

@ Abhijit Patra Please find the attached images of both dextral and sinistral asymmetry in XZ sections. Both samples are looked from east.

In ductile shear zones, we expect to find a single major sense of movement. However, it is not as simple as that. For your case study, there are multiple solutions:

1. Multiple ductile deformation in progressive deformation: Folding accompanying shear movement in simple shear/ simple+pure shear. So, you can get sinistral sense (reverse) in one limb and dextral sense (normal) on the other in case of tight-isoclinal fold, provided there are folds with axial planes subparallel to shear zone. (for reverse faults)

2. Relative displacement within a single shear zone: The shear zone may show an overall shear sense with slivers of opposite sense of movement. It may generate due to accommodating space (accommodation structure). (for strike-slip faults). Or, simply flower kind of structures.

3. Remnant of earlier fabric: may be a case. Reorientation of earlier fabric.

If you get oblique slip movement according to the stretching lineation, all of the above are possible. I hope that field data will solve your case-specific problem.

Thank you!

Thank you for the two meaningful pictures. I have summarized my interpretation in two sketches (attached) showing the contours of quartz grains of the same crystallographic orientation. I would like to comment on three features: 1. Both thin sections show distinct features of isoclinal folding of the quartz grains (marked with red ovals). 2. Both thin sections show distinct features of flattening and extensional deformation (marked with blue ovals). 3. The "Dextral" thin section show blocky subgrain pattern of high quartz "chessboard pattern" in the later strongly flattened and folded quartz grains.

Overall, a multi-stage crystallization and deformation history can be seen with a cooling stage and brittle deformation (transverse fractures, which are subsequently healed again, dashed lines in my sketches). In addition, I essentially agree with the comments made by Abhijit Patra.

Best regards, Guenter Grundmann

Thanks to @Abhijit Patra and @Guenther Grundmann for your valuable comments. However it would be highly appreciated if you please share any references in support of your logic.

May I recommend the world class book of Ron H. Vernon (see cover and back cover attached):

A practical guide to Rock Microstructure

In this book you will find everything that is important for your interpretations.

However, I have already shared with you two references that support my interpretation (see my answer above).

Best regards,

Guenter Grundmann

@ Guenter Grundmann Many thanks for your help.

Have a look at the paper Dutta and Mukherjee 2019 in J Struct Geology where in detail we discussed opposite shear sense.

@ Soumyajit Mukherjee I shall go through the paper. Thanks for your reply.

Please Soumayajit Can you sent the paper of Dutta and Mukherje 2019 from Structural Geology where in détails we discuss opposite shear sense? Thanks