Oğuz H. Göğüş

Mantle lithosphere delamination driving plateau uplift and synconvergent extension in eastern Anatolia

Eastern Anatolia is the site of lithospheric thinning, plateau uplift, heating, and synconvergent extension. Using numerical geodynamic experiments, we test the hypothesis that these tectonic anomalies are all related and the consequence of delamination of the mantle lithosphere. Our findings indicate that delamination during plate convergence results in ~2-km-high plateau uplift. The removal of mantle lithosphere induces distinct regions of contraction and thickening, as well as extension and thinning of the crust. The latter occurs even within a regime of plate shortening, although it is muted with increasing plate convergence. Detachment of the delaminating slab results in minor surface topographic perturbation, but only above the delamination hinge. The plateau uplift and pattern of surface contraction and/or extension are consistent with a topographic profile at 42°E and geologically interpreted zone of synconvergent extension at eastern Anatolia.

Near‐surface diagnostics of dripping or delaminating lithosphere

[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.

The surface tectonics of mantle lithosphere delamination following ocean lithosphere subduction: Insights from physical‐scaled analogue experiments

Many postulated lithospheric removal events occur in regions with an earlier history of subduction, but the relationship between the two processes has not been explored. In this work, we use physical-scaled analogue experiments to investigate the evolution from ocean lithosphere subduction to collision and possible delamination of the mantle lithosphere from the crust. We test how varying the magnitude of plate convergence alters the behavior of the subduction-delamination model. Our experiments show that a retreating ocean proplate can evolve to continental mantle lithosphere delamination. Negative surface topography is supported at the delamination hinge, and this migrates back with the peeling lithosphere. With high plate convergence, delamination is suppressed. Rather, the crust and mantle lithosphere split at the collision zone in a form of flake tectonics as oncoming procrust is accreted on top of the retroplate and the promantle lithosphere subducts below. Localized high topography develops at this zone of crustal accretion and thickening. The results suggest that delamination may be a continental continuation of plate retreat and that lithospheric removal is triggered by the transition from one process to another.

Insights from geodynamical modeling on possible fates of continental mantle lithosphere: collision, removal, and overturn

Geodynamic modeling demonstrates various modes of behaviour of the tectonically active continental mantle lithosphere. At continental collision, mantle lithosphere below thickening crust can be accommodated by mixed subduction-like consumption and viscous drip-like instability, depending on the material rheology, temperature, and convergence velocity. Late-stage slab steepening, dual-sided and ablative consumption, and breakoff can occur as the buoyant crust resists subduction. Removal of accreted crust by erosion can modify how even the deepest portions of the mantle lithosphere evolves during contraction. When gravitational forcing rather than plate shortening dominates, mantle lithosphere may be removed through viscous dripping-like instability or delamination. The removal induces crustal heating, modified topography, and deformation, but distinctive styles of these develop depending on whether mantle lithosphere delaminates or drips. With a modified density stratification postulated for the Archean, r...

Rifting and subsidence following lithospheric removal in continental back arcs

It has been suggested that post-orogenic lithospheric removal in continental back arcs promotes extension and surface subsidence. However, the surface response of this process and its primary difference from “classical” back-arc opening have remained uncertain. Here, the back-arc extension process with varying continental mantle lithosphere thickness and thermal heterogeneities is studied by using thermomechanical subduction experiments. The experiments illustrate that models with only slab retreat result in minor surface subsidence and extension in the back-arc region. Alternatively, there is notable extension due to the slab retreat and a localized high-temperature zone in the back arc with uniform lithospheric thickness. Models with advecting mantle (after lithospheric removal) in the extending back arc predict rifting (stretching factor b > 2) and surface subsidence (>1.5 km) in the center of the basin. The results of this work suggest that lithospheric removal may be an important trigger for continental back-arc development rather than slab retreat alone causing lithospheric extension and subsidence. The findings help explain rift formation and subsidence in the Aegean Sea–west Anatolia, and possibly other Mediterranean back arcs, such as the Alboran Sea and the Pannonian Basin.

Drip tectonics and the enigmatic uplift of the Central Anatolian Plateau

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.The recycling of continental lithosphere and rapid plateau uplift is believed to be the result of lithospheric drips, but natural examples are missing. Here, the authors use geodynamic models to suggest that the folding and thickening of the Central Anatolian arc caused lithospheric dripping of the arc root.

Postcollisional lithospheric evolution of the Southeast Carpathians: Comparison of geodynamical models and observations

Seismic evidence and thermal and topographic transients have led to the interpretation of lithospheric removal beneath the Southeast Carpathians region. A series of numerical geodynamic experiments in the context of the tectonic evolution of the region are conducted to test the surface-crustal response to lithosphere delamination and slab break-off. The results show that a delamination-type removal (“plate-like” migrating instability) causes a characteristic pattern of surface uplift/subsidence and crustal extension/shortening to occur due to the lithospheric deformation and dynamic/thermal forcing of the sublithospheric mantle. These features migrate with the progressive removal of the underlying lithosphere. Model results for delamination are comparable with observables related to the geodynamic evolution of the Southeast Carpathians since 10 Ma: the mantle structure inferred by seismic tomography, migrating patterns of uplift (>1.5 km) and subsidence (>2 km) in the region, crustal thinning in the Carpathian hinterland and thickening at the Focsani depression, and regional extension in the Carpathian corner (e.g., opening of Brasov basin) correlating with volcanism (e.g., Harghita and Persani volcanics) in the last 3 Myr.

Mantle Lithosphere Rheology, Vertical Tectonics, and the Exhumation of (U)HP Rocks

Numerical modeling results indicate that mantle lithosphere rheology can influence the pressure-temperature-time (P-T-t) trajectories of continental crust subducted and exhumed during the onset of continental collision. Exhumation of ultrahigh-pressure (~35 kbar)/high-temperature (~750°C) metamorphic rocks is more prevalent in models with stronger continental mantle lithosphere (e.g., dry), whereas high-pressure (~9–22 kbar)/low-temperature (350°C–630°C) metamorphic rocks occur in models with weaker rheology (e.g., hydrated) for the same layer. In the latter case, the buried crustal rocks can remain encased in ablatively subducting mantle lithosphere, reach only moderate temperatures, and exhume by dripping/detachment of the lithospheric root. In this transition from subduction to a dripping style of “vertical tectonics,” burial and exhumation of crustal rocks are driven without imposed far-field plate convergence. The model results are compared against thermobarometric P-T estimates from major (ultra) high-pressure metamorphic terranes. We propose that the exhumation of high-pressure/low-temperature metamorphic rocks in Tavşanlı and Afyon zones in western Anatolia may be caused by viscous dripping of mantle lithosphere suggesting a weaker continental mantle lithosphere, whereas (ultra)high-pressure exhumation (e.g., Dabie Shan-eastern China and Dora Maira-western Alps) may be associated with plate-like subduction. In the latter case, the slab is much stronger and deformation is localized to the subduction interface along which rocks are buried to >100 km depth before they are exhumed to the near surface.