A) Tectonics & Geology:
In Tibet most of our knowledge on recent deformation is inferred from active faults and Cenozoic magmatism. Most simply, Tibet has thick-skinned thrusting and folding over broad areas due to Tertiary shortening. Active crustal shortening however occurs prodominantly along and the north of Kunlun range. On the northeastern side of the plateau, geological mapping indicates young sedimentary deposits formed synchronous with active fold and thrust belts (Yin & Harrison, 2000) (figure 6). Based on this, some authors claim that these thrust belts migrate towards north through time (Tapponier et al. 2001).
Figure 6. Geology map of the Himalayan-Tibetan orogen (different rock units indicate by various colors. Simply, lighter colors indicate younger unit and reddish colors symbolize
volcanic assemblages [Yin & Harrison, 2000].
In northern Tibet, slip partitioning also plays a major role and accommodates oblique convergence by series of sinistral strike-slip fault systems. Horizontal offsets along these faults indicates that strike-slip faulting started earlier in the south than in the north after the continental impact (~15 Ma) and propagated eastward (Tapponier et al. 2001). Long-term slip rates measured along the active left-lateral Kunlun fault located at the northern margin of the plateau indicate uniform slip rate of 12 mm/yr which is also consistent with the amount of shortening in this region (Van der Woerd et al. 1998). In southern Tibet and Yunnan, active ~N-S trending normal faults which postdate Miocene, indicates extension. The high topographic signature of these young rift basins implies gravitational collapse under large vertical stresses (figure 7).
Figure 7. Active faults of Himalayan-Tibetan orogen plotted over digital elevation map of the region. White arrows indicate plate motion
(Bold lines represents the most active faults with slip at 5 mm/year or more) [Tapponier et al; 2001].
Although, much of the geology of the plateau is still waiting to be explored, some significant work have been done on volcanic assemblages. According to these studies, early magmatism in Tibet was initiated due to post-collisional subduction (~60 Ma) along linear belts (Arnaud et al. 1992). Their geochemistry is characterized by high K-lavas (shoshonites, latites) and calc-alkaline dacites, trachytes and ryholites. The most recent volcanism which occurred in the past 20 Ma, is distributed south of Kunlun range (Arnaud et al. 1992). The origin of this volcanism was suggested to be southward subduction of Tarim and Qaidam basins under Tibet (Arnaud et al. 1992). However, absence of foreland basins and basaltic outcrops just over the trace of possible subduction, disagrees with this interpretation. In general, spatial distribution of volcanic ages indicates high variations but still one can argue that volcanism is younger towards the north.
A) Tectonics & Geology B) Seismicity C) GPS D) Seismic profiles & Tomography
E) Gravity F) Anisotropy G) Paleomagnetism H) Geochemistry I) MT studies
Home Introduction Paleotectonic Evolution Recent Deformation Models Discussion References