The structure of the 1985 Tibet Geotraverse, Lhasa to Golmud

Abstract

The structures of Tibet were generated during the accretion on to the Asian plate, firstly of the Qiangtang Terrane during the Triassic, then the Lhasa Terrane during the Jurassic -Cretaceous and finally the Indian continent during the Palaeogene. The southern Kunlun mountains show intense deformation associated with the accretion of deep water sediments on to an active plate margin .The deformation was essentially by footwall propagation of thrusts, though there was pronounced out-of sequence thrusting with the deformation of basins above the main thrust zone, and the back steepening and back thrusting of earlier structures. The Jinsha Suture probably represents the southern edge of this zone. The Banggong Suture between the Qiangtang and Lhasa Terranes is characterized by pre-collisional ophiolite obduction for over 100 km to the south across the Lhasa T errane, plus local intense intracratonic deformation of parts of the Lhasa Terrane. However, for this collision there is now very little evidence for intense deformation along the line of the suture and the Qiangtang Terrane itself remained only weakly deformed throughout. Post—Middle Cretaceous, pre-Tertiary deformation of the Lhasa region produced upright- to north-verging folds which decrease in in tensity north wards. They may have been formed at the margin of the Gangdise batholith, or they may have originated from early collisional phases along the line of the Indus-Zangbo Suture. However this deformation is approximately synchronous with the more intense deformation of the Xigatse flysch on the accretionary prism and is therefore probably subduction-related, predating collision. Tertiary deformation is relatively widespread across Tibet, producing SSE-directed thrusts across the Fenghuo Shan region of the Qiangtang Terrane and across the northern part of the Lhasa Terrane. Several hundred kilometres shortening can be estimated to have occurred during this deformation, probably reworking older Mesozoic structures. How ever this shortening is insufficient to provide all of that estimated from palaeo magnetic work or from a study of displacement rates of the Indian plate, and much of the displacement of India into Asia during the Tertiary must be taken up on strike-slip faults in Tibet or on thrusts an d strike-slip faults in central Asia north o the Tibetan Plateau. The Tertiary shortening cannot account for all the thickening o f the Tibetan crust.

Constraints on the early uplift history of the Tibetan Plateau

“…3) indicate that FG and YG strata were strongly deformed before deposition of the WG (30). Structural cross sections suggest that crustal shortening in the Fenghuo Shan region is Ϸ43% (30,33), with the majority of this shortening complete by the end of the Oligocene. These structural relationships are similar to those observed in the Nanqian-Yushu region to the east (27,34).…”

Reconstructing the Late Palaeozoic – Mesozoic topographic evolution of the Chinese Tian Shan: available data and remaining uncertainties

“…Hendrix et al, 1992;Gu, 1996;Fang et al, 2006a;De Grave et al, 2007). However, the absence of Late Jurassic -Early Cretaceous cooling episode in the SongpanGarze area (East Tibet), immediately north of the Bangong -Nujiang suture Zone between the Lhasa and Qiangtang blocks suggests that this accretion generated only a very limited deformation (Coward et al, 1988;Roger et al, 2008Roger et al, , 2010Roger et al, , 2011. Nonetheless, further to the north, between the Kunlun Ranges and the Tarim Basin, low temperature thermochronology and sediment analysis do indicate some small-scale Cretaceous vertical movements potentially linked to the Lhasa collision (e.g.…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…Much of the Lhasa block shows relatively undeformed granites of the Gangdese-Ladakh and other related Transhimalayan batholiths with flat-lying or gently folded Linzizong volcanic rocks. Although the Lhasa and Qiangtang blocks appear not to have undergone much shortening following the India-Asia collision, major Palaeocene to Miocene shortening has been documented in northern Tibet along the Fenghuo Shan-Nanqian thrust belts (Coward et al 1988;Horton et al 2002;Spurlin et al 2005).…”