Subduction and slab detachment under moving trenches during ongoing
India- Asia convergence
Abstract
The dynamics of slab detachment and associated geological fingerprints
have been inferred from various numerical and analogue models. These
invariably use a setup with slab-pull-driven convergence in which a slab
detaches below a mantle-stationary trench after the arrest of plate
convergence due to arrival of continental lithosphere. In contrast,
geological reconstructions show that post-detachment plate convergence
is common and that trenches and sutures are rarely mantle-stationary
during detachment. Here, we identify the more realistic kinematic
context of slab detachment using the example of the India-Asia
convergent system. We first show that only the India and Himalayas slabs
(from India’s northern margin) and the Carlsberg slab (from the western
margin) unequivocally detached from Indian lithosphere. Several other
slabs below the Indian Ocean do not require a Neotethyan origin and may
be of Mesotethys and Paleotethys origin. Additionally, the
still-connected slabs are being dragged together with the Indian plate
forward (Hindu Kush) or sideways (Burma, Chaman) through the mantle. We
show that Indian slab detachment occurred at moving trenches during
ongoing plate convergence, providing more realistic geodynamic
conditions for use in future numerical and analogue experiments. We
identify that the actively detaching Hindu Kush slab is a type-example
of this setting, whilst a 25-13 Ma phase of shallow detachment of the
Himalayas slab, here reconstructed from plate kinematics and tomography,
agrees well with independent, published geological estimates from the
Himalayas orogen of slab detachment. The Sulaiman Ranges of Pakistan may
hold the geological signatures of detachment of the laterally dragged
Carlsberg slab.