Mechanical versus kinematical shortening reconstructions of the Zagros High Folded Zone (Kurdistan region of Iraq)

Abstract

[1] This paper compares kinematical and mechanical techniques for the palinspastic reconstruction of folded cross sections in collision orogens. The studied area and the reconstructed NE-SW trending, 55.5 km long cross section is located in the High Folded Zone of the Zagros fold-and-thrust belt in the Kurdistan region of Iraq. The present-day geometry of the cross section has been constructed from field as well as remote sensing data. In a first step, the structures and the stratigraphy are simplified and summarized in eight units trying to identify the main geometric and mechanical parameters. In a second step, the shortening is kinematically estimated using the dip domain method to 11%-15%. Then the same cross section is used in a numerical finite element model to perform dynamical unfolding simulations taking various rheological parameters into account. The main factor allowing for an efficient dynamic unfolding is the presence of interfacial slip conditions between the mechanically strong units. Other factors, such as Newtonian versus power law viscous rheology or the presence of a basement, affect the numerical simulations much less strongly. If interfacial slip is accounted for, fold amplitudes are reduced efficiently during the dynamical unfolding simulations, while welded layer interfaces lead to unrealistic shortening estimates. It is suggested that interfacial slip and decoupling of the deformation along detachment horizons is an important mechanical parameter that controlled the folding processes in the Zagros High Folded Zone.

Furrow-and-Ridge Morphology on Rockglaciers Explained by Gravity-Driven Buckle Folding: A Case Study From the Murtèl Rockglacier (Switzerland)

“…For the Murtèl rockglacier, the 2D approximation is justified because of its straight tongue‐like geometry and unidirectional flow field (Kääb et al, ). Details of the numerical technique can be found in Frehner and Schmalholz (); Frehner () and Frehner et al (), who all applied variations of this model to simulate viscous buckle folding under kinematic layer‐parallel forcing. In the present model, the rockglacier flows solely under the effect of gravity.…”

Orogeny

“…However, recent studies have demonstrated that the characteristics and the wavelength of folding in fold-and-thrust belts are strongly influenced by rheological parameters and 2014 mechanical isotropies of the stratigraphic pile (Yamato et al, 2011;Ruh et al, 2012). Therefore, future research will focus on mechanical reconstructions of fold-and-thrust belts (Simpson, 2009;Frehner et al, 2012;Vidal-Royo et al, 2012) including three-dimensional mechanical interaction of fold and fault growth (Schmid et al, 2008a;Grasemann and Schmalholz, 2012). (iii) A crystalline core zone forms the central and highest part of a mountain belt, usually above the orogenic root, where the crust is the thickest.…”

Optimization of the outlet portal of Heybat Sultan twin tunnels based on the value engineering methodology

“…The study area is located in Zagros high folded zone from sedimentary-structural classification point of view [14]. Due to the specific tectonic conditions, this area consists of the crushed rock masses of gypsum, limestone, mudstone, sandstone, shale and marlstone.…”