13-7 Knock-on Collision: A View of Cordilleran Tibet on the Cusp of Continental Collision

Session: Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains

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Even prior to the India-Asia collision, a protracted history of subduction and terrane accretion built a Cordilleran orogen featuring a high-elevation, low-relief landscape (“Lhasaplano”) comparable to the modern Andes. North of this Lhasaplano, paleoaltimetric evidence and fossil palm leaves suggest that tropical, low-lying basins persisted along a suture valley between two accreted terranes until at least ~39 Ma. What happens to such a Cordilleran mountain belt as it begins to collide with a continent, and compressive stresses are then transferred hundreds of kilometers outboard of collisional plate boundaries? Some geodynamic models predict out-of-sequence deformation, crustal thickening, and lithosphere removal at the earliest stages of collision far north of the India-Asia suture and the proto-Lhasaplano, as a consequence stress transfer via the stronger Lhasa terrane mantle lithosphere — but is this substantiated in the geologic record? A late Cretaceous to Eocene north-vergent thrust belt in northern Tibet associated with a >4-km thick flexural foreland basin imply an elevated central Tibet with thickened crust. However, the difficulty of accessing central Tibet (Qiangtang) has hindered documentation and dating of the numerous hinterland depocenters that could directly provide insights into the far-field tectonic activity around the onset of continental collision. In this talk I summarize new observations from recent field expeditions that provide direct evidence of crustal shortening, thickening and potential lithosphere removal >200 km north of the Indus-Yarlung suture by ~48-43 Ma.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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