From orogenic range to orogenic plateau, what evolution along the Tethys subduction zone from the Alps to Tibet?

For long, the continental lithosphere considered less dense than the mantle, was not supposed to be able to subduct. Nevertheless, continental subduction has been proposed for decades as a key process occurring during the long-lasting collision between India and Asia since ~50 Ma, allowing the subduction of the continental lower crust attached to the lithospheric mantle while the upper crust thickens and forms the Tibetan plateau (e.g. Mattauer, 1986; Tapponnier et al., 2001). In this talk, I will present the available data and models of this key process for the India/Asia collision, which requires to go beyond the paradigm of slab pull as a unique driver of plate tectonics, then I will compare to the Alps.

First, the deep intracontinental seismicity of the Pamir and Hindu Kush at the western extremity of the collision system reveals two subduction zones of opposite vergence. Global P-waves tomography shows the maximum depth extent of the two distinct slabs and the maximum depth of seismicity has been modeled, compatible with continental lithosphere subduction (Negredo et al., 2007). Further regional seismic studies reveal the continental nature of the slab beneath Pamir (Schneider et al., 2013) and the underplating of the Indian lithosphere below Pamir (Mechie et al., 2012). Beneath the Himalaya, the Indian lower crust, attached to its lithospheric mantle, is bent and is underplated below southern Tibet (Nabelek et al., 2008), with eclogitization of the Indian lower crust during the bending, which density could be close to mantle density (Hetenyi et al., 2007). The Asian lithosphere in central Tibet is inferred to subduct southward down to 300 km, with no related seismicity (Kind et al., 2002; Replumaz et al., 2013). During the early Tibetan collision stage, a first episode of subduction of the Asian lithosphere likely occurred, recorded by Cenozoic volcanics (Roger et al., 2000).

However, a dynamic explanation of continental subduction is still lacking. A low-density contrast between the continental lithosphere and the mantle, as inferred during the Indian plate bending, facilitates the subduction of the continental lithosphere attached to a dense oceanic slab (Capitanio et al., 2010). At the mantle scale, analogue models show that the continental subduction could occur in a context of convergence, due to far field forces instead of subduction related forces (Replumaz et al., 2016; Pitard et al., 2018), which could be due to the long lasting oceanic subduction on both sides of the Indian continent (Bose et al., 2022).

Bose et al., 2023, doi:10.1016/j.tecto.2023.229727

Capitanio et al., 2010, doi:10.1038/NGEO725

Hetenyi et al., 2007, doi:10.1016/j.epst.2007.09.036

Kind et al., 2002, doi:10.1126/science.1078115

Kufner et al., 2016, doi:10.1016/j.epsl.2015.11.046

Mattauer, 1986, BSGF, 2

Mechie et al., 2012. doi:10.1111/j.1365-246X.2011.05278.x

Nábĕlek et al., 2009, doi:10.1126/science.1167719

Negredo et al., 2007, doi:10.1016/j.epsl.2007.04.043

Pitard et al., 2018, doi:10.1016/j.epsl.2018.08.050

Replumaz et al., 2013, doi:10.1016/j.gr.2012.07.019

Replumaz et al., 2016, doi:10.1130 /G38276 .1

Roger et al., TerraNova, 12

Schneider et al., 2013, doi:10.1016/j.epsl.2013.05.015

Tapponnier et al., 2001, Science, 294