Determination of the Sense of Shear Using the Orientation of Shear Band Foliation in Mylonites: Field Evidence from the Keban Complex, Eastern Turkey

Year 1986, Volume: 105-106 Issue: 105-106, 1 - 14, 01.10.1986

Gültekin Savcı

Abstract

The structural features of the northern part of the Bitlis suture zone of the Alpine-Himalayan orogenic
belt (Turkey) show intense internal deformations. The variable lithology and microstructural features of the high strain
zones commonly found in the Keban complex are characterized by mylonitic texture. The Keban complex were formed in
ancient continental margin sedimentary sequences of the northern branch of the Neo-Tethys. Single sets of shear band
foliations occur within mylonite zones composed of strongly foliated phyllitic psammites. Two well defined microscopic
criteria, the tails of the augen structures and smaller scale shear zones which were formed between the relatively undeformed
pod shaped aggregates, are used to deduce the sense of shear in a lithologically inhomogeneous brittle-ductile
shear zone of the Keban complex. The sense of shear determined in this way from the anastomosing part of the shear
zone is then applied to the orientation of shear band foliation in the same shear zone. This microscopic evaluation of the
structures suggests that the acute angle between the shear band foliation and the mylonitic foliation points in the shear
direction as proposed by earlier research which were based on experimental studies. Therefore, the determination of
sense the of shearing in the field using the orientation of shear band foliations in mylonites is suggested.

Keywords

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