Strain and vorticity analyses using rotated porphyroclasts in the Tanbour metamorphic rocks: Evidence of transpressional deformation along the Sanandaj-Sirjan metamorphic belt, SW Iran

Abstract

The Tanbour Metamorphic Complex (TMC) is located within the Sanandaj-Sirjan Metamorphic Belt, SW Iran, along the northeastern margin of the Afro-Arabian plate. Detailed kinematic and strain analyses were combined with vorticity estimates on rocks from the TMC to document patterns and geometry of deformation. The strain parameter measurements including strain ratio in the XZ principal plane of strain ellipsoid (RXZ), strain ellipsoid shape (K) and strain intensity (D), highlight the deformed gneissic rocks in the TMC exhibit constrictional to approximately plane-strain shape of the strain ellipsoids. Several kinematic shear sense indicators including S/C fabrics, mantled porphyroclasts, oblique grain shape, micro-shears with bookshelf geometry and mineral fish show top-to-the-SE sense of shear. The quantitative kinematic analyses highlight that Wk varies between 0.64 and 0.78, implying a general shear flow with 44% < simple shear <58% and 42% < pure shear <57%. The exhumation of TMC is attributed to the exhumation-controlled transpressive tectonic process during oblique convergence between the Afro-Arabian continent and the Central-Iranian microcontinent which started since Upper Cretaceous.