Two end member models of how the high elevations in Tibet formed are (i) continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and (ii) time-dependent, localized shear between coherent lithospheric blocks. Recent studies of Cenozoic deformation, magmatism, and seismic structure lend support to the latter. Since India collided with Asia ∼55 million years ago, the rise of the high Tibetan plateau likely occurred in three main steps, by successive growth and uplift of 300- to 500-kilometer-wide crustal thrust-wedges. The crust thickened, while the mantle, decoupled beneath gently dipping shear zones, did not. Sediment infilling, bathtub-like, of dammed intermontane basins formed flat high plains at each step. The existence of magmatic belts younging northward implies that slabs of Asian mantle subducted one after another under ranges north of the Himalayas. Subduction was oblique and accompanied by extrusion along the left lateral strike-slip faults that slice Tibet's east side. These mechanisms, akin to plate tectonics hidden by thickening crust, with slip-partitioning, account for the dominant growth of the Tibet Plateau toward the east and northeast.

http://science.sciencemag.org/content/sci/294/5547/1671.full.pdf

Oblique Stepwise Rise and Growth of the Tibet Plateau

Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations

http://www2.ess.ucla.edu/~yin/05-Publications/papers/124-Yin-2010-Tectonophysics.pdf

Cenozoic tectonic evolution of Asia: A preliminary synthesis

New structural, petrographic, and 40Ar/39Ar data constrain the kinematics of the ASRR (Ailao Shan-Red River shear zone). In the XueLong Shan (XLS), geochronological data reveal Triassic, Early Tertiary, and Oligo-Miocene thermal events. The latter event (33–26 Ma) corresponds to cooling during left-lateral shear. In the FanSiPan (FSP) range, thrusting of the SaPa nappe, linked to left-lateral deformation, and cooling of the FSP granite occurred at ≈35 Ma. Rapid cooling resumed at 25–29 Ma as a result of uplift within the transtensive ASRR. In the DayNuiConVoi (DNCV), foliation trends NW-SE, but is deflected near large-scale shear planes. Stretching lineation is nearly horizontal. On steep foliations, shear criteria indicate left-lateral shear sense. Zones with flatter foliations show compatible shear senses. Petrographic data indicate decompression from ≈6.5 kbar during left-lateral shear (temperatures >700°C). 40Ar/39Ar data imply rapid cooling from above 350°C to below 150°C between 25 and 22 Ma without diachronism along strike. Along the whole ASRR cooling histories show two main episodes: (1) rapid cooling from peak metamorphism during left-lateral shear; (2) rapid cooling from greenschist conditions during right-lateral reactivation of the ASRR. In the NW part of the ASRR (XLS, Diancang Shan), we link rapid cooling 1 to local denudations in a transpressive environment. In the SW part (Ailao Shan and DNCV), cooling 1 resulted from regional denudation by zipper-like tectonics in a transtensive regime. The induced cooling diachronism observed in the Ailao Shan suggests left-lateral rates of 4 to 5 cm/yr from 27 Ma until ≈17 Ma. DNCV rocks always stayed in a transtensive regime and do not show cooling diachronism. The similarities of deformation kinematics along the ASRR and in the South China Sea confirms the causal link between continental strike-slip faulting and marginal basin opening.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JB900322

New constraints on the structure, thermochronology, and timing of the Ailao Shan-Red River shear zone, SE Asia

Parallel Tethyan sutures in mainland Southeast Asia: New insights for Palaeo-Tethys closure and implications for the Indosinian orogeny

The Wang Chao and Three Pagodas fault zones cut the western part of the Indochina block and run parallel to the Red River Fault. Evidence of intense ductile left-lateral shear is found in the Lansang gneisses, which form a 5 km wide elongated core along the Wang Chao fault zone. Dating by 40 Ar/ 39 Ar shows that such deformation probably terminated around 30.5 Ma. The Wang Chao and Three Pagodas faults offset the north striking lower Mesozoic metamorphic and magmatic belt of northern Thailand. 40 Ar/ 39 Ar results suggest that this belt suffered rapid cooling in the Tertiary, probably around 23 Ma. These results imply that the extrusion of the southwestern part of Indochina occurred in the upper Eocene-lower Oligocene. It probably induced rifting in some basins of the Gulf of Thailand and in the Malay and Mekong basins. In the Oligo-Miocene, the continuing penetration of India into Asia culminated with the extrusion of all of Indochina along the Ailao Shan - Red River fault. This occurred concurrently with the onset of E-W extension more to the south. Plotting in a geographical reference frame the diachronic time spans of movement on left-lateral faults east and southeast of Tibet implies that the northward movement of the Indian indenter successively initiated new strike-slip faults located farther and farther north along its path.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/96JB03831

Tertiary diachronic extrusion and deformation of western Indochina: Structural and 40Ar/39Ar evidence from NW Thailand

The Wang Chao and Three Pagodas fault zones cut the western part of the Indochina block and run parallel to the Red River Fault. Evidence of intense ductile left- lateral shear is found in the Lansang gneisses, which form a 5 km wide elongated core along the Wang Chao fault zone. Dating by 4oAr/39Ar shows that such deformation probably termi- nated around 30.5 Ma. The Wang Chao and Three Pagodas faults offset the north striking lower Mesozoic metamorphic and magmatic belt of northern Thailand. 4oAr/39Ar results sug- gest that this belt suffered rapid cooling in the Tertiary, probably around 23 Ma. These results imply that the extrusion of the southwestern part of Indochina occurred in the upper Eocene- lower Oligocene. It probably induced rifting in some basins of the Gulf of Thailand and in the Malay and Mekong basins. In the Oligo-Miocene, the continuing penetration of India into Asia culminated with the extrusion of all of Indochina along the Ailao Shan- Red River fault. This occurred concurrently with the onset of E-W extension more to the south. Plotting in a geographical reference frame the diachronic time spans of movement on left-lateral faults east and southeast of Tibet implies that the northward movement of the Indian indenter successively initiated new strike-slip faults located farther and farther north along its path.

/pdf/tertiary-diachronic-extrusion-and-deformation-of-western-xykr8strzb.pdf

Adul Charoenravat

Papers

Tertiary diachronic extrusion and deformation of western Indochina: Structural and 40Ar/39Ar evidence from NW Thailand

Tertiary diachronic extrusion and deformation of western Indochina: Structural and 4øAr/39Ar evidence