Quantitative kinematic analysis of the asymmetric boudins of the Zagros accretionary prism, Iran

摘要

Asymmetric boudins that are widespread in the Seh-Ghalatoun area in the Neyriz, southwestern Iran are good indicators to estimate the kinematic vorticity number (W-k) and sense of shear. This area is part of the Sanandaj-Sirjan HP-LT metamorphic belt located within the Zagros orogenic belt. Boudins have been analyzed on the meso- and micro-scales. Domino and shearband boudins are developed in deformed quartzitic layers associated with quartzo-feldspathic gneiss, amphibolite, mica-schist and marble. Shearband boudins with backward rotation and domino boudins with forward rotation, mantled porphyroclasts, drag folds, and asymmetric folds which all display a dextral sense of shear. The mean kinematic vorticity number was estimated by using the asymmetric boudin hyperbolic distribution method and quartz caxis patterns. The estimated mean kinematic vorticity number is W-k = W-m = 0.85 +/- 0.04, which indicates 34% pure shear and 66% simple shear components of deformation. The estimated mean deformation temperature based on the opening angle of the quartz c-axis fabrics is 530 +/- 50 A degrees C. These quantitative analyses suggest a sub-simple shear deformation developed at the epidote-amphibolite to amphibolite facies conditions at depth along the Sanandaj-Sirjan HP-LT metamorphic belt, which is associated with a transpressional flow regime with shortening perpendicular to the shear zone boundary.