Usage of strain and vorticity analyses to interpret large-scale fold mechanisms along the Sanandaj-Sirjan HP-LT metamorphic belt, SW Iran

摘要

3D finite strain analyses and kinematic vorticity measurements were carried out on the Loghon Anticline within the HP-LT Sanandaj-Sirjan metamorphic belt (Neyriz area, SW Iran). Rf{hook}/φ and Fry methods were used on the strain markers (e.g. deformed fossils) to interpret geometric relationships between the fold axis, strain ellipsoid axes and shear zone boundaries. The results indicate the predominance of prolate strain in the anticline. Quantitative kinematic analyses show that the W _k parameter is 0. 67±0. 06 (i.e. pure-shear dominated non-coaxial flow). This study quantitatively supports the establishment of a dextral transpressive system, which is responsible for the development of the large-scale right-lateral shear zones that strike sub-parallel to the major folds. Flexural shear combined with regional dextral-shear is suggested to be the most common mechanism of folding in this area.