Kinematic analysis of deformed structures in a tectonic mélange: a key unit for the manifestation of transpression along the Zagros Suture Zone, Iran

Abstract

<jats:title>Abstract</jats:title><jats:p>Kinematic analysis of mélange fabrics provides critical information concerning tectonic processes and evaluation of the kinematics of ancient relative plate motion. Systematic kinematic analysis of deformed structures within a tectonic mélange exposed along the Zagros Suture Zone elucidates that this zone is an ancient transpressional boundary. The mélange is composed of a greywacke and mudstone matrix surrounding various lenses, blocks and ribbons of radiolarian chert, limestone, sandstone, pillow lava, tuff, serpentinite, shale and marl. The deformation fabrics of the mélange suggest that the mélange units were tectonically accreted at shallow levels within a subduction complex, resulting in layer-parallel extension and shearing along a NW–SE-trending suture that juxtaposes the Afro-Arabian continent to the south and the Central Iranian microcontinents to the north. The tectonic mélange is characterized by subhorizontal layer-parallel extension and subsequent heterogeneous non-coaxial shear resulting in alternating asymmetric and layer-parallel extensional fabrics such as P–Y fabrics and boudinaged layers. Kinematic data suggest that the mélange formed during oblique subduction of the Neo-Tethys oceanic lithosphere in Late Cretaceous time. Kinematic shear sense indicators reveal that the slip direction (N9°E to N14°E) during accretion-related deformations reflects the relative plate motion between the Afro-Arabian continent and Central Iranian microcontinents during Late Cretaceous to Miocene times.</jats:p>

Mélange development in the Neyriz region of Zagros Orogen, Iran: Record of convergence and collision in the Neotethyan Realm

“…The provenance of mélanges, their formation processes and tectonic settings were surveyed in three scales of mapping, outcrop and microscopic studies. Tectonic mélange displays a lenticular block in scaly matrix fabric; which is similar to the structures in mylonitic shear zones (Faghih, Kusky, & Samani, 2012; Lister & Snoke, 1984). In this study, we used the S‐surfaces (the foliation in the matrix or shear surfaces) and C‐surfaces (the alignment of the long axes of the clasts) for the description of the mélange fabrics (Faghih, Kusky et al, 2012).…”

“…It is, therefore, likely to have been formed as a result of the progressive movement of the nappes and reverse faulting in the sheared zones after the Miocene (Ricou et al, 1977; Figures 2 and 5). The geometries of the blocks and boudins suggest a dextral shear sense and south‐westward–directed thrusting (Faghih, Kusky et al, 2012). The long axes of boudins in the scaly cleavage indicate layer parallel extension.…”

A Middle Permian Ophiolitic Mélange Belt in the Solonker Suture Zone, Western Inner Mongolia, China: Implications for the Evolution of the Paleo‐Asian Ocean

“…Here we document complex planar fabrics, stretching lineations, thrust faults, and asymmetric structures on macroscopic and microscopic scales. The structures in the mélange include both contractional and extensional fabrics, which are similar to those in other mélanges, such as the mélange in the Shimanto Belt of the Akaishi Mountains, central Japan (Kano et al, ; Kimura & Mukai, ), the McHugh Complex in the Kenai Peninsula of Alaska (Kusky et al, ; Kusky & Bradley, ), and the tectonic mélange along the Zagros Suture Zone (Faghih et al, ). The extensional fabrics were produced by stretching of coherent layers related to layer‐parallel shearing, while the contractional fabrics were produced by extruding the coherent layers (Kimura & Mukai, ; Kusky, Bradley, & Haeussler, ; Kusky, Bradley, Haeussler, & Karl, ).…”

“…In some strongly sheared outcrops, the mélange exhibits two foliations which are geometrically analogous to S and C foliations in mylonitic rocks (Passchier & Trouw, ). S‐C structure is the dominant asymmetric fabric developed within the mélange in Japan (Kano et al, ), Alaska (Kusky, Bradley, & Haeussler, ; Kusky, Bradley, Haeussler, & Karl, ; Kusky & Bradley, ), Costa Rica (Escuder‐Viruete & Baumgartner, ), and Iran (Faghih et al, ). Likewise, S‐C structure is well developed in the siliceous‐argillaceous matrix of the Solonker mélange, observable both in outcrop and microscope scales (Figures f–h).…”

“…Kinematic analysis of structures of the Solonker ophiolitic mélange, including scaly foliations, S‐C foliations, boudinage, asymmetric blocks, thrust faults, and isoclinal folds, provides important information for deciphering the previous plate motions and understanding subduction and accretion processes (Faghih et al, ; Hashimoto & Kimura, ; Kano et al, ; Kimura & Mukai, ; Kusky & Bradley, ; Onishi et al, ; Onishi & Kimura, ). Structural elements which can be used to indicate the kinematics include the following: (1) lineations developed on the foliation surface and the intersection of mesoscopic planar elements (S, C, R1, and P foliation; Kano et al, ; Onishi & Kimura, ; Shibata & Hashimoto, ); (2) asymmetric fabrics of boudinage, tails around blocks, strain shadows, folds, oblique grain‐shape quartz, and calcite aggregates (Cowan & Brandon, ; Kano et al, ; Kusky & Bradley, ); and (3) duplex structures in thrust belts (Hashimoto & Kimura, ; Sample & Fisher, ).…”