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 notectonic origin, 2) GPS and
earthquake data do not support E–W left-lateral shear in south Tibet
and 3) there is no evidence for active left-lateral shearing so far in
the region west of the eastern Himalayan syntaxis.
Earth and Planetary Science Letters 285 (2009) 217–222
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