Journal of Geology & Geophysics
Open Access

Strain partitioning and heterogeneous sub-simple shearing in the hinterland-dipping mid-crustal gneissic channel flow nappes of the Zagrosorogensis, Southwestern Iran

International Conference on Geology

June 22-23, 2015 Florida, USA

Khalil Sarkarinejad and Abdolreza Partabian

Posters-Accepted Abstracts: J Geol Geosci

Abstract :

Systematic field measurements of foliation and lineation of the metamorphosed cover sequences and the sheared quartzofeldspathic gneiss nappes in the Ghouri area reveal three gneissic ductile extrusions nappes with elongated semi-elliptical shapes parallel to the thrusts of the Zagros Thrust System of the Zagros orogenesis. These extrusions cored by the sheared quartzo-feldspathic gneiss, orthogneiss, garnet amphibolite, eclogite, blue schist and covered with the sequences of phyllite, phyllonite, muscovite schist and deformed conglomerate. The ductile extrusions are called ChahSabz, ChahGoni and Kuh-e- Zard nappes. The hinterland-dipping gniessic ductile extrusion nappes resulted from the interaction of the lower to middle hinterland involved-basement at 651º±90º C and hot subducting deformed Tethyan oceanic crust. Gneissic nappes flow were squeezed between the Zagros transpression curved boundary zones that is inclined at an angle α=25°. The estimated mean kinematic vorticity numbers of these three nappes are 0.65±0.6, 0.81±0.1 and 0.73±0.17, respectively. The mean kinematic vorticity (Wm) and finite strain (Rs) measurements of the ChahSabz, ChahGoni and Kuh-e-Zard ductile extrusion nappes indicate that the component of simple shear relative to pure shear component are ~45-(55% pure shear), 60%-(40% pure shear) and ~52%-(48%pure shear). This show concentration and localizations of high strain is highly heterogeneous in each nappe during ductile flow. Constructed finite strain ellipsoid based on deformed markers in the cover sequences show that the X-axis of the strain ellipsoid plunges with an angle Ï?=61° relative to the boundary zone. The steeply plunging stretching lineations were primarily controlled by ductilel flow. Basement detachment flow of the middle to lower crust source was progressively led to hinterland-dipping ductile extrusion. The X-, and Y- axes of the strain ellipsoid during this progressive deformation, rotated clockwise whilst the Z-axis rotated counterclockwise relative to the N55ºW thrust sheets, defining deformation with triclinic symmetry.