River network evolution as a major control for orogenic exhumation: case study from the western Tibetan plateau
Gourbet Loraine, Gweltaz Mahéo, David L. Shuster, Alka Tripathy-Lang, P. H. Leloup, Jean-Louis Paquette
The
westernmost Tibetan plateau, despite being internally drained, has a
high topographic relief. Here, using apatite (U–Th–Sm)/He and 4He/3He
thermochronometry, we reconstruct the exhumation history of the Rutog
batholith during the Neogene. Thermal modeling in 1D using the QTQt
program indicates that relatively slow cooling occurred from 30 Ma to
19 Ma, which we interpret as an exhumation rate of ∼10m/Ma. This was
followed by two pulses of moderate cooling from 19 to 17 Ma and ∼11 to
9Ma that correspond to a total exhumation of about 1500 m. Cooling
since 9 Ma has been negligible. This differs from exhumation patterns
in central Tibet but reveals timing similarities with externally
drained portions of southern Tibet. We interpret our cooling
constraints as recording two different transitions in western Tibet
from an externally to an internally drained system since the Oligocene.
External drainage allowed this part of the Tibetan plateau, unlike
internally drained portions of central Tibet, to record regional-scale
processes. The first cooling event, at about 20 Ma, was likely related
to a major geodynamic event such as slab breakoff that induced
contemporaneous potassic and ultrapotassic magmatism. The second rapid
cooling pulse from ∼11 Ma to 9 Ma and subsequent negligible cooling was
most likely controlled by a local factor such as Indus and Shyok river
network reorganization caused by dextral motion of the Karakorum fault.
We discuss these interpretations and their limitations in this
contribution.
Earth
and Planetary Science Letters Volume: 456 Issue 1, 2016. ISSN:
0012-821X Online ISSN: 1385-013X ; DOI :
10.1016/j.epsl.2016.09.037