Figure 3 - uploaded by Bhuban Mohan Behera
Content may be subject to copyright.
(a) Field photograph of granite mylonite showing foliation, feldspar porphyroclasts and S-C fabric suggesting NW vergence shear, vertical section, pencil (right) length 14 cm, (b) down-dip stretching lineations, deBned by stretched quartz grains, vertical section, hammer is 12 inch, (c) mylonitic foliation deBned by quartz ribbons (Qtz), biotitic rich layers (Bt) and feldspar layers (Fsp), and (d) sigma type feldspar porphyroclasts showing NW vergence.
Source publication
The Terrane Boundary Shear Zones provide important information regarding tectonics of juxtaposition between different terranes. In this paper, we have studied the Lakhna shear zone, between the Eastern Ghats Mobile Belt and the Bastar Craton. Detailed structural study, sampling and strain analysis through measurement of size and orientation of dyna...
Citations
... Ductile shear zones record non-coaxial strain evidence in planar or curviplanar collisional belts (Regenauer-Lieb and Yuen, 2003;Xypolias and Kokkalas, 2006;Mukherjee, 2012;Biswas, 2014, 2015). These shear zones, in diverse scales from microscopic shear bands to intensely deformed zone with tens of kilometers width, take place in the various tectonic settings, such as the Cap de Creus shear zones in the eastern most Pyrenees (Carreras, 2001), shear zones in the Aravalli-Delhi mobile belt, NW India (Tiwari et al., 2020), the Lakhna shear zone between the Eastern Ghats Mobile Belt and the Bastar Craton, NW Odisha (Meher et al., 2020) and Comeglians-Paularo shear zone in the Southern Alps (Bartel et al., 2014). ...
Quantitative microstructural investigations involving finite strain and vorticity analyses of quartz-rich mylonites provide significant information regarding the kinematic characteristics of the Samen shear zone (SSZ) within the Sanandaj–Sirjan Metamorphic Belt, Zagros Mountain of Iran. A dominant top-to-the-SE sense shear in the study area is recognized by several kinematic indicators. The results of the finite strain analyses indicate approximately plane strain deformation conditions (Rxz = 2.46–3.53). The mylonitic granitoid rocks record general-shear deformation (Wm = 0.37–0.94) associated with a spatial increase in simple-shear component (23%–78%) from W to E. In the study area, kinematic analyses indicate spatial variations of finite strain, deformation temperature, and the kinematic vorticity numbers resulted in partitioned progressive deformation. These spatial variations reveal an increase of all values towards the Samen thrust sheet. Ductile SSZ developed under greenschist-amphibolite facies metamorphic conditions (464–619 °C), as indicated by the presence of quartz, feldspar, biotite, muscovite, hornblende mineral assemblages, opening angles (OAs) of quartz c-axis fabrics and recrystallization regimes. The dynamic and kinematic characteristics of the study area were generally controlled by ongoing oblique convergence of the Afro-Arabian plate and the Iranian plateau with estimation of a horizontal shortening of ∼20–38% measured perpendicular to the boundaries of the SSZ.
... The main kinematic shear sense indicators including σ and δ-type of rotated porphyroclasts (Hanmer and Passchier 1991) (Fig. 4a and b), mica fish, (Hanmer, 1986;Passchier and Trouw, 2005) (Fig. 4c), S/C shear band (Passchier and Trouw, 2005;Mukherjee, 2013;Meher et al., 2020) (Fig. 4d) and rotated garnet were selected from oriented thin sections cut on the XZ-plane of strain ellipsoid (Fig. 4e). Feldspar grains indicate undulatory extinction and brittle microfracturing, and incipient dynamic recrystallization is rare. ...
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.
