[1] In various geological regions, it has been postulated that the mantle lithosphere has been thinned or completely removed. Two of the primary removal mechanisms that have been put forward include: (1) delamination, a wholesale peeling away of a coherent block of the mantle lithosphere, and (2) lithospheric ''dripping,'' viscous Rayleigh-Taylor instability of the mantle lithosphere. Using computational models, we investigate several near-surface observables to determine if these may be diagnostic of either (often ambiguous) removal mechanism. Surface topography associated with delamination has a broad region of uplift above the lithospheric gap and a localized and mobile zone of subsidence at the delaminating hinge. With dripping lithosphere, the topographic expression is symmetric and fixed above the downwelling. Delamination of mantle lithosphere is more efficient than dripping for thermal heating of the crust; the onset is more rapid and the elevated temperatures persist longer. The resultant crustal P-T-t paths show modest pressure variations and high temperature increases with large-scale delamination or dripping. Delamination also causes contraction directly above the (migrating) hinge and distal extension. Dripping lithosphere induces superimposed contraction and extension above and symmetric about the viscous instability. For all the observables, if only a portion of the mantle lithosphere is removed by viscous instability (delamination inherently removes all of the mantle lithosphere), the differences between the two removal mechanisms are even more pronounced. With only partial removal of the mantle lithosphere, uppermost mantle lithosphere remains well coupled to the crust, leading to lower surface temperature variations and broad zones of crustal deformation/thickening.

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Lithospheric drips have been interpreted for various regions around the globe to account for the recycling of the continental lithosphere and rapid plateau uplift. However, the validity of such hypothesis is not well documented in the context of geological, geophysical and petrological observations that are tested against geodynamical models. Here we propose that the folding of the Central Anatolian (Kırşehir) arc led to thickening of the lithosphere and onset of “dripping” of the arc root. Our geodynamic model explains the seismic data showing missing lithosphere and a remnant structure characteristic of a dripping arc root, as well as enigmatic >1 km uplift over the entire plateau, Cappadocia and Galatia volcanism at the southern and northern plateau margins since ~10 Ma, respectively. Models show that arc root removal yields initial surface subsidence that inverts >1 km of uplift as the vertical loading and crustal deformation change during drip evolution.

[1] The nature of lithospheric deformation during continental plate collision still remains unresolved. While it has often been proposed that the mantle lithosphere is accommodated by distributed thickening of a viscous root, an alternate hypothesis suggests that significant portions of convergent mantle lithosphere essentially undergo underthrusting or subduction. To further consider this issue, we model the thermochemical evolution of the lithospheremantle system using arbitrary Lagrangian-Eulerian finite element techniques. We incorporate a mix of viscous (thermally activated power law creep) and plastic (frictional Coulomb with strain softening) rheologies in the numerical experiments to treat disparate composition in the crust and mantle. A range of rheological and mechanical parameters is explored to determine controls on the style of lithospheric deformation. The models suggest that during the initial stages of plate collision the mantle lithosphere is characterized by plate-like behavior and underthrusting/subduction of the upper region in conjunction with distributed thickening and Rayleigh-Taylor type viscous instability of the lower portion. Depending on the material rheology, temperature regime, and imposed convergence velocity, the deforming mantle lithosphere demonstrates various combinations of these ''end-member'' behavioral modes. The modeling results are interpreted in the context of observed lithospheric deformation across South Island, New Zealand. A combined style of underthrusting and distributed thickening is consistent with the observed crustal structure in the young collisional orogen as well as seismic imaging of the geometry of the underlying lithosphere.

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