Role of the Early Miocene Jinhe-Qinghe Thrust Belt in the building of
the Southeastern Tibetan Plateau topography
Abstract
Understanding the development of key thrust faults in southeastern Tibet
is significant to reconstructing the geodynamic and topographic
processes. Detailed structure analysis along the ~400 km
long Jinhe-Qinghe thrust belt (JQTB) indicate thrust motion with a minor
left-lateral component. The exhumation history of the Baishagou granite,
based on apatite (U-Th)/He and fission-track thermochronology and
thermal modeling, suggest an accelerated exhumation rate
(~0.42 km/Myr) between 20 and 15 Ma. We interpret that
fast exhumation due to the activation of the Nibi thrust, a northern
branch of the JQTB. The ~1.5-2.2 km of exhumation that
occurred corresponds to the present topographic difference across the
thrust belt. In the Early Miocene, significant relief along JQTB was
generated by thrusting. When compared with previous studies it appears
that Cenozoic exhumation and relief creation in southeastern Tibet
cannot be explained by a single mechanism. Rather, at least three stages
of relief creation should be invoked. The first phase is an Eocene NE-SW
compression partly coeval with Eocene sedimentation. During the Late
Oligocene to Early Miocene the second thrusting phase occurred along the
Yulong and Longmenshan thrust belts, and then migrated to the JQTB
further to the southeast during 20-15 Ma. A third phase involved the
activation of the Xianshuihe fault and the re-activation of the
Longmenshan thrust belts and the Muli thrust. The interaction between
thrusting and fast river erosion triggered by climate change is not
certain but thrusting along thrust belts appears to explain most of the
present-day relief in the southeastern Tibetan Plateau.