Kinematic evolution of the eastern Tethyan Himalaya: constraints from magnetic fabric and structural properties of the Triassic flysch in SE Tibet

Abstract

Anisotropy of magnetic susceptibility (AMS) combined with structural analysis are used in this work with the aim to characterize the tectonic evolution of the Triassic flysch within the eastern Tethyan Himalaya Thrust Belt in SE Tibet. The attitude of the magnetic foliation and lineation are concordant with the planar and linear structures of tectonic origin defined by the preferred orientation of the iron-bearing silicates. Two different tectonic domains can be defined: (a) the southern domain is controlled by the Eohimalayan tectonic foliation (S1) recorded in the magnetic foliation which trends east–west and dips to the north; (b) the northern domain is dominated by the Neohimalayan magnetic foliation with WNW–ESE strike and dips to the south opposite to the vergence of the main structures. A slightly prolate magnetic ellipsoid has been found in between the two domains recording the intersection of S1 and the subtle development of the S2 tectonic foliation. Hinterland propagation of the deformation lead to the Great Counter backthrust generation, pointed out by the SSW steeply plunging magnetic lineation. Furthermore different orientations of magnetic foliation may indicate an Early Miocene c. 20° clockwise vertical-axis rotation.

Metamorphic evolution of the Tethyan Himalayan flysch in SE Tibet

“…During the subsequent Neohimalayan (Hodges 2000) tectonic phase, north-facing folds with a related axial plane cleavage were developed (e.g. Carosi et al 2007;Montomoli et al 2008;Kellett & Godin 2009, Antolin et al 2011. In the study area these two deformation phases are well developed.…”

“…KT, Kakhtang thrust, position of STDS from Grujic et al (2002), McQuarrie et al (2008). Structures in the northern Tethyan Himalaya from Antolin et al (2011).…”

“…It is characterized by top-to-the-south thrust faults and south-facing folds (e.g. Burg & Chen 1984;Ratschbacher et al 1994;Carosi et al 2007;Aikman et al 2008;Montomoli et al 2008, Antolin et al 2011. During the subsequent Neohimalayan (Hodges 2000) tectonic phase, north-facing folds with a related axial plane cleavage were developed (e.g.…”

“…The first one is widespread in the southern sector, whereas the second one is well-developed in the northern portion. Consequently, two structural domains have been distinguished by Montomoli et al (2008) and Antolin et al (2011).…”

Kinematic evolution and structural styles of fold-and-thrust belts

“…Antolín et al 2011). Thus, folds verge usually towards the foreland in the case of foreland FAT belts (Figs 1-3 & 8b1), towards the trench in the case of accretionary wedges (Fig.…”