The range and the meaning of the effective elastic thickness (EET) in continental
areas have been subject to controversy over the last two decades. Here we take advantage
of the new data set from the Hi-CLIMB seismological experiment to re-estimate the
EET of the India Plate along a south-north profile extending from the Ganges basin
to central Tibet. Receiver functions give a high-resolution image of the base of the
foreland basin at similar to 5 km depth and constrain the crustal thickness, which
increases northwards from similar to 35 km beneath the indo-gangetic plain to similar
to 70 km in southern Tibet. Together with available data sets including seismic profiles,
seismological images from both INDEPTH and HIMNT experiments, deep well measurements
and Bouguer anomaly profiles, we interpret this new image with 2-D thermomechanical
modelling solutions, using different type of crustal and mantle rheologies. We find
that (1) the EET of the India Plate decreases northwards from 60-80 to 20-30 km as
it is flexed down
beneath Himalaya and Tibet, due to thermal and flexural weakening; (2) the only resistant
layer of the India Plate beneath southern Tibet is the upper mantle, which serves
as a support for the topographic load and (3) the most abrupt drop in the EET, located
around 200 km south of the MFT, is associated with a gradual decoupling between the
crust and the mantle. We show that our geometrical constraints do not allow to determine
if the upper and lower crust are coupled or not. Our results clearly reveal that a
rheology with a weak mantle is unable to explain the geometry of the lithosphere in
this region, and they are in favour of a rheology in which the mantle is strong.
