A comment on “Orogen-parallel, active left-slip faults in the eastern Himalaya: Implications for the growth mechanism of the Himalayan arc” by Li and Yin (Earth Planet Sci. Lett. 274 (2008) 258–267)

Abstract

Understanding how convergence is partitioned in the Himalayan arc and across the entire Tibetan plateau provides critical kinematic constraints on mechanical models of continental lithospheric deformation. Based on geomorphic evidence, Li and Yin (2008) recently claimed to have discovered several active E–W trending left-lateral faults in south Tibet. These faults, interpreted to be part of a ~100 km-wide and N500 km-long Dinggye–Chigu fault zone (DCFZ), would follow the Himalayan arc from ~88°E to the eastern syntaxis (95°E). The total slip-rate across this zone would be at least 4 to 8 mm/yr, and possibly up to 25 to 70 mm/yr (when summing given slip-rate on each fault). The rates are then compared with the right-lateral slip-rate along the Karakorum fault in western Tibet, inferred to be between 1 and 10 mm/yr from the literature. It is concluded that, since 4 Ma, oroclinal bending is the dominant process in Himalayan tectonics (Klootwijk et al., 1985). This article has major implications on the mechanics of the Himalayas and of the collision belts in general. Our fieldwork, geomorphic and geodetic analysis of the region studied by Li and Yin (2008) suggest that: 1) the geomorphic offsets interpreted by these authors are better explained by landform alignments with no Fig. 1. Simplified geological and active fault map of the Dinggye region (see inset for location within Indo-Asia collision framework). The Gongzuo and Comuzhelin basins are characterized by folds, trending on average EW, of the Tethysian sediments in the hanging wall of thenorthdipping southTibetandetachment system(e.g., Burgetal.,1984). Presentday active faults are NS trending normal faults (e.g. Armijo et al.,1986). Note the extension of high lake stands (at 4400 and 4460m asl) marked by clear shorelines (sand bars, steep cliffs, etc...). Arrow is location of Fig. 3. Rectangles are Figs 2, 4 and 5. r Woerd).