Orogen‐parallel ductile extension and extrusion of the Greater Himalaya in the late Oligocene and Miocene

Abstract

[1] Predominant stretching structures in the Greater Himalayan Crystalline Complex (GHC) trend perpendicular to the belt and are linked to the southward exhumation or emplacement of the GHC between the South Tibet Detachment (STD) and the Main Central Thrust. However, our field investigations in southern Tibet reveal the widespread presence of gently dipping shear zones with a penetrative orogen-parallel stretching lineation, which separates the Tethyan Himalayan Sequence and the underlying GHC. The shear zones are well preserved in the upper part of the GHC, south to and structurally lower than the STD. Field criteria, microstructures, and quartz fabrics indicate top-to-the-east shearing in the Yadong shear zone (eastern GHC), coexistence of top-to-the-east and topto-the-west shearing in the Nyalam shear zone (central GHC), but top-to-the-west shearing in the Pulan shear zone (western GHC). Characteristic microstructures and slip systems of quartz in the high-grade GHC rocks resulted from the lateral flow under upper amphibolite (up to 650-700 C) to greenschist facies conditions. U-Pb ages of metamorphic zircon rims by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation multi-collector inductively coupled plasma mass spectrometry ( Ar cooling ages of biotite and muscovite suggest cessation of ductile sharing at 13-11 Ma on the Yadong shear zone, which is coeval with the activation of the STD. Combined with previous studies, we propose that initiation of orogen-parallel extension marks the transition from burial/crustal thickening to exhumation of the GHC. Due to lateral crustal thickness gradients in a thickened crust, orogen-parallel gravitational collapse occurred within the convergent Himalayan orogen in the late Oligocene-Miocene. This tectonic denudation triggered and enhanced partial melting and ductile extrusion of the GHC in the Miocene.

Thermochronological constraints on the late Paleozoic tectonic evolution of the southern Chinese Altai

“…6) (Li and Sun, 2014). The extensional orogenic collapse has been widely recognized in the modern collisional zones such as the Himalayas and Alps (Dewey, 1988;Frisch et al, 2000;Xu et al, 2013), and may play a crucial role during the collision of the Chinese Altai with the East Junggar. The following convergence was characterized by the development of the sinistral Erqis Shear Zone with reversed components (Qu and Zhang, 1994), which may have led to the regional uplift and cooling of the southern Chinese Altai.…”

Varying Indian crustal front in the southern Tibetan Plateau as revealed by magnetotelluric data

“…The GHC and LHS are structurally defined by the STD and the Main Central Thrust (MCT) from top to bottom. The Neoarchean to early Paleozoic amphibolite to granulite facies gneisses, amphibolites, granulites, and widely intruded early to middle Miocene leucogranites are detected in the GHC (Streule et al 2010;Xu et al 2013). …”

Paleo-Tethyan evolution of Tibet as recorded in the East Cimmerides and West Cathaysides

“…10; Xu et al, 1986Xu et al, , 1992Xu et al, , 2012Xu et al, , 2013. The only significant difference between the two is that the Songpan Ganze terrane represents a high-temperature collisional orogen, whereas the South Qinling orogenic belt is mainly a low-temperature mountain belt.…”

“…Brittle thrust faults with top-to-the-south sense of shearing are superimposed on these previously formed ductile structures ( example of such an orogenic collage, extending nearly 5200 km along its E-W length and 2500 km across its N-S width, and it is thus an excellent natural laboratory to study the processes of an accretionary orogen buildup (Xu et al, , 2013. The…”

“…The curvilinear Longmu Tso-Shuanghu-Changning Menglian Suture Zone extends from the E-W striking Longmu Tso-Shuanghu suture zone in central Tibet to the N-S striking Changning Menglian suture zone in SE Tibet between the East Cimmerides and West Cathaysides (Li et al, 1995Zhong, 1998;Metcalfe, 2006Metcalfe, , 2013Xu et al, 2013). The Changning Menglian suture zone connects with the Inthanon and Sara Kaeo suture zones in the south ( Fig.…”