Abstract
We apply teleseismic P-wave tomography to reconstruct the velocity structure of the Longmenshan area. Our results show possible large-scale delamination beneath the Songpan-Ganzi and Qiangtang terranes, which induced upwelling asthenosphere. Upwelling asthenosphere might have led to lower crust heating, facilitating eastward extrusion of the Songpan Ganzi terrane resulting in localized deformation and uplift along the Longmenshan orogenic belt. We suggest that the eastward extrusion of the Songpan-Ganzi terrane against the rigid lithospheric root of the Sichuan Basin results in stress accumulation and release, leading to large earthquakes in the Longmenshan area.
Highlights
The Longmenshan thrust belt is approximately 500 km long and 30–50 km wide[1,2,3,4,5,6,7] with a relief of over 5 km[8]
These high-velocity structures are at almost the same depth of ca. 400–500 km, and we suggest that these high-velocity structures may be attributed to ancient lithosphere that could have been delaminated beneath the Songpan-Ganzi terrane, Ordos Basin and Sichuan Basin
We propose that asthenosphic upwelling heated the lower crust, facilitating the easy eastward extrusion of the Songpan-Ganzi terrane and resulting in uplift and deformation of the Longmenshan orogenic belt in the Cenozoic due to the Indian-Asian plate collision
Summary
The Longmenshan thrust (or orogenic) belt is approximately 500 km long and 30–50 km wide[1,2,3,4,5,6,7] with a relief of over 5 km[8]. The deformation and uplift mechanism for the Longmenshan orogenic belt remains controversial, and two end-member models have been proposed: (1) Crustal thickening through major slip along thrust faults rooted in the lithosphere[29,30,31] and (2) Channel flow or extrusion of partially molten middleto lower-crustal materials with extremely low viscosity outwards from the Tibetan Plateau since approximately 40 Ma4,10,14,25,32,33. These works do not take into account the effect of mantle dynamics. Correspondence and requests for materials should be addressed to C.H.
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