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Continental areas affected by mantle plume dynamics are characterised by extensive high-elevated regions drained by large radial river networks. Despite successive isostatic adjustments and rifting events, several studies demonstrated that the persistence of these drainage systems for tens of millions of years is possible. In these geodynamic contexts rivers are precious sources of knowledge because, propagating the signals of tectonic and climatic changes across landscape, they shape the topography and allow to recognise the first-order imprint imposed by mantle plume. The Horn of Africa, characterised by the coexistence of a continental rift system, a large igneous province (continental flood basalts), and a wide uplifted plateau, is an ideal test site to investigate the interrelations between surface and deep processes. Studies demonstrated the long-term persistence of some river networks draining the region and the strong influence of dome-like uplift on their evolution. However a regional-scale quantitative river network analysis is missing, as well as, a complete evolutionary scenario of the Horn of Africa drainage system. In this study we quantitatively investigated the topographic configuration of the Horn of Africa and analysed the four principal drainage systems (Blue Nile, Tekeze, Omo, Wabe Shebele basins), extracting the river longitudinal profiles and the main topographic and hydrologic parameters. In order to reconstruct the evolution of the region, we elaborated the pre−/syn- and post-flood basalts topographies and calculated the elevation gain and loss with respect to the present configuration. Finally, we delineated a possible future drainage system evolution by analysing the present drainage divides stability. The results allowed to reconstruct the evolutionary scenario of the Horn of Africa river network since Oligocene and to investigate the mutual influence between surface and deep processes in shaping the landscape, providing new constraints to understand the formation and evolution of a drainage system in a context of a topography supported by a mantle plume.

A common feature of tectonic reconstructions is the migration of subduction zones and their interactions, resulting in complex tectonic patterns. Reduced migration rates, uplift, strong rotations, and slab break-off are all tectonics features commonly associated with convergent margin interactions, showing that while subduction zones' motions fundamentally shape tectonics settings, their interactions hold the key to their complexities. Fundamental properties such as slab buoyancy, dip direction, and coupled mantle flow determine the motions of single hinge zones. When these zones approach, stress transfers between the slabs through the lithosphere and the mantle, thereby altering the subduction force balance, favoring, opposing, or diverting further motions. We illustrate the range of configurations reported in tectonic reconstructions and address their dynamics through the results of analog and numerical models of subduction dynamics in the upper mantle. The Cenozoic evolution of the Mediterranean provides relevant examples of such interactions, where the coeval activity of several subduction zones during the Africa-Europe convergence has strongly overprinted the current tectonics. A comparison of new analog models with the deep dynamics of the Mediterranean shows how the interactions among slabs and mantle may have shaped the distribution of basins and mountain belts, their uplift, and volcanism in this tectonic province.

Tectonics and erosion–sedimentation are the main processes responsible for shaping the Earth's surface. The link between these processes has a strong influence on the evolution of landscapes. One of the tools we have for investigating coupled process models is analog modeling. Here we contribute to the utility of this tool by presenting laboratory-scaled analog models of erosion. We explore the erosional response of different materials to imposed boundary conditions, trying to find the composite material that best mimics the behavior of the natural prototype. The models recreate conditions in which tectonic uplift is no longer active, but there is an imposed fixed slope. On this slope the erosion is triggered by precipitation and gravity, with the formation of channels in valleys and diffusion on hillslope that are functions of the analog material. Using digital elevation models (DEMs) and a laser scan correlation technique, we show model evolution and measure sediment discharge rates. We propose three main components of our analog material (silica powder, glass microbeads and PVC powder; PVC: polyvinyl chloride), and we investigate how different proportions of these components affect the model evolution and the development of landscapes. We find that silica powder is mainly responsible for creating a realistic landscape in the laboratory. Furthermore, we find that varying the concentration of silica powder between 40 wt % and 50 wt % (with glass microbeads and PVC powder in the range 35 wt %–40 wt % and 15 wt %–20 wt %, respectively) results in metrics and morphologies that are comparable with those from natural prototypes., Earth Surface Dynamics, 8 (4), ISSN:2196-632X, ISSN:2196-6311

The study of slab-slab interactions has come to the front of geodynamics researches to explain geological and geophysical observations from tectonically complex areas. Here we aim to better understand the geodynamics of the Central Mediterranean, where the Adria plate subducts on its two opposite sides. Additionally, the slab below the Central South Apennines has been progressively breaking off during the last 3 Myr. The role of a slab window in a single slab or in an outward dipping double-sided subduction system is addressed by analog models at the scale of the upper mantle, realized using glucose syrup and silicone putty, to model the interaction between the Earth's mantle and the lithosphere. Our results show that the presence of a slab window modifies the pattern of mantle circulation, as well as the trench geometry and kinematics. In particular, the opening of the slab window induces the formation of two arcs flanking the window, while the mantle flows through it and turns toward the arcs, creating a small-scale toroidal flow. The effect of a slab window is more pronounced on double subduction systems, as the outflow through the window is amplified, while internal deformation is induced in the plate by the opposite slab pull force. These experimental results suggest that the origin of the Apenninic and the Calabrian arcs is the result of the formation of a slab window, providing a new interpretation of the surface deformation and the SKS shear wave splitting pattern of the Adria microplate.Plain Language Summary The Adria microplate in the Central Mediterranean is an important part of the tectonic puzzle between the converging Africa and Eurasia plates. The heavy lithosphere sinks into the underlying mantle on two sides of the Adria plate, under the Apennines in the west and under the Dinarides in the east. During the most recent few millions of years, the lithosphere started to detach from the surface in the Central South Apennines while sinking into the mantle. This opened a slab window, an additional escape route for the mantle, which is squeezed by the two subducting lithospheres. We scaled down and simplified this setting in order to model and investigate the role of the dual subduction and the opening slab window in the evolution of the Central Mediterranean by means of analog models. Our results show that the two opposite subduction zones have a regional tectonics effect via the complex subduction-induced mantle circulation. Furthermore, the detaching lithosphere modifies the geometry of the subduction zone, which results in a double-arc geometry resembling the Northern Apennines and Calabria.

The importance of slab–slab interactions is manifested in the kinematics and geometry of the Philippine Sea Plate and western Pacific subduction zones, and such interactions offer a dynamic basis for the first-order observations in this complex subduction setting. The westward subduction of the Pacific Sea Plate changes, along-strike, from single slab subduction beneath Japan, to a double-subduction setting where Pacific subduction beneath the Philippine Sea Plate occurs in tandem with westward subduction of the Philippine Sea Plate beneath Eurasia. Our 3-D numerical models show that there are fundamental differences between single slab systems and double slab systems where both subduction systems have the same vergence. We find that the observed kinematics and slab geometry of the Pacific–Philippine subduction can be understood by considering an along-strike transition from single to double subduction, and is largely independent from the detailed geometry of the Philippine Sea Plate. Important first order features include the relatively shallow slab dip, retreating/stationary trenches, and rapid subduction for single slab systems (Pacific Plate subducting under Japan), and front slabs within a double slab system (Philippine Sea Plate subducting at Ryukyu). In contrast, steep to overturned slab dips, advancing trench motion, and slower subduction occurs for rear slabs in a double slab setting (Pacific subducting at the Izu–Bonin–Mariana). This happens because of a relative build-up of pressure in the asthenosphere beneath the Philippine Sea Plate, where the asthenosphere is constrained between the converging Ryukyu and Izu–Bonin–Mariana slabs. When weak back-arc regions are included, slab–slab convergence rates slow and the middle (Philippine) plate extends, which leads to reduced pressure build up and reduced slab–slab coupling. Models without back-arcs, or with back-arc viscosities that are reduced by a factor of five, produce kinematics compatible with present-day observations.

An outlier consists of an area of younger rocks surrounded by older ones. Its formation is mainly related to the erosion of surrounding rocks which causes the interruption of the original continuity of the rocks. Because of its origin, an outlier is an important witness of the paleogeography of a region and, therefore, essential to understand its topographic and geological evolution. The Mekele Outlier (N Ethiopia) is characterized by poorly incised Mesozoic marine sediments and dolerites (∼2000 m in elevation), surrounded by strongly eroded Precambrian and Paleozoic rocks and Tertiary volcanic deposits in a context of a mantle supported topography. In the past, studies about the Mekele outlier focused mainly in the mere description of the stratigraphic and tectonic settings without taking into account the feedback between surface and deep processes in shaping such peculiar feature. In this study we present the geological and geomorphometric analyses of the Mekele Outlier taking into account the general topographic features (slope map, swath profiles, local relief), the river network and the principal tectonic lineaments of the outlier. The results trace the evolution of the study area as related not only to the mere erosion of the surrounding rocks but to a complex interaction between surface and deep processes where the lithology played a crucial role.

The central Apennines, an accretionary wedge overlying an area of slab detachment, are characterized by prominent topography, active normal faulting, and high uplift rates. However, previous studies have failed to resolve the surface uplift history, complicating efforts to link the topographic evolution with underlying geodynamic processes. We aim to better quantify orographic changes by using stable oxygen isotope paleoaltimetry. Modern surface water δ 18 O are 5‰ lower at high elevation than at sea level, reflecting orographic rainout over the Apennines. We present 262 new lacustrine and paleosol carbonate δ 18 O measurements collected from ten extensional intermontane basins—spanning both high and low elevations—and combine these with 1,166 published δ 18 O data, permitting us to constrain changes in δ 18 O both spatially and temporally. Since the Pliocene, δ 18 O in present-day high-elevation basins has continuously decreased, even as δ 18 O in lowland basins has remained constant over time. We attribute this continuous 5‰ shift to increased orographic rainout as the central Apennines were uplifted. We estimate an increase in mean elevation of approximately 1–2 km since the late Pliocene, and these estimates match the suggested timing and expected amplitude of slab break-off related uplift. This supports the hypothesis that the opening of the Adriatic slab window and associated mantle flow contributed significantly to building topography in the central Apennines.

A fundamental scientific question is, what controls the Earth's topography? Although the theoretical principles of isostasy, flexure, and dynamic topography are widely discussed, the parameters needed to apply these principles are frequently not available. Isostatic factors controlling lithospheric buoyancy are frequently uncertain and non-isostatic factors, such as lithospheric bending towards subduction zones and dynamic topography, are hard to distinguish. The question discussed here is whether a set of simple rules that relate topography to lithospheric structure in various tectonic environments can be deduced in a way that missing parameters can be approximated; or does each area behave differently, making generalizations problematic. We contribute to this issue analyzing the Asia–Africa–Arabia–Europe domain following a top-down strategy. We compile a new crustal thickness map and remove the contribution of the crust from the observed elevation. Then, the challenge is to interpret the residual topography in terms of mantle lithosphere buoyancy and dynamics. Based on systematic relationships between tectonic environments and factors controlling topography, we argue that crustal buoyancy and mantle lithospheric density can be approximated from available geological data and that regions near mantle upwelling or downwelling are easily identified by their extreme residual topography. Yet, even for other areas, calculating lithospheric thickness from residual topography is problematic, because distinguishing variations in mantle lithosphere thickness from sub-lithospheric dynamics is difficult. Fortunately, the area studied here provides an opportunity to examine this issue. Based on the conjunction between the Afar Plume and the mid-ocean ridge in the nearby Gulf of Aden and southern Red Sea, we constrain the maximal amplitude of dynamic topography to ~ 1 km. This estimate is based on a narrow definition of dynamic topography that only includes sub-lithospheric processes and using mid-ocean ridges as reference, where mantle lithosphere buoyancy is zero.

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.

Recent measurements of surface vertical displacements of the European Alps show a correlation between vertical velocities and topographic features, with widespread uplift at rates of up to ~2–2.5 mm/a in the North-Western and Central Alps, and ~1 mm/a across a continuous region from the Eastern to the South-Western Alps. Such a rock uplift rate pattern is at odds with the horizontal velocity field, characterized by shortening and crustal thickening in the Eastern Alps and very limited deformation in the Central and Western Alps. Proposed mechanisms of rock uplift rate include isostatic response to the last deglaciation, long-term erosion, detachment of the Western Alpine slab, as well as lithospheric and surface deflection due to mantle convection. Here, we assess previous work and present new estimates of the contributions from these mechanisms. Given the large range of model estimates, the isostatic adjustment to deglaciation and erosion are sufficient to explain the full observed rate of uplift in the Eastern Alps, which, if correct, would preclude a contribution from horizontal shortening and crustal thickening. Alternatively, uplift is a partitioned response to a range of mechanisms. In the Central and Western Alps, the lithospheric adjustment to deglaciation and erosion likely accounts for roughly half of the rock uplift rate, which points to a noticeable contribution by mantle-related processes such as detachment of the European slab and/or asthenospheric upwelling. While it is difficult to independently constrain the patterns and magnitude of mantle contributions to ongoing Alpine vertical displacements at present, future data should provide additional insights. Regardless, interacting tectonic and surface mass redistribution processes, rather than an individual forcing, best explain ongoing Alpine elevation changes.

A better understanding of intraplate deformation requires the knowledge of the space–time scales involved in its development and to decipher possible links with the dynamic evolution of the plate boundaries. Central Iran provides an ideal test site to approach this scientific issue, since it is characterised by a prolonged history of Mesozoic–Cenozoic intraplate deformation that has been interfering with the spatio-temporal re-organization of the Zagros convergence zone along the Eurasia plate boundary. This study focus on the Doruneh Fault (DF) region that is considered as the northern mechanical boundary of the Central East Iranian Microcontinent. By combining field investigations with apatite low-temperature thermochronology, we present a revised tectono-stratigraphic scenario for the DF region, typified by a punctuated history of fault-related exhumation, burial and cooling history back to the Upper Cretaceous. When framed at regional scale, these results attest that the Zagros convergence zone, and its hinterland domain were fully mechanically coupled since ca. 40–35 Ma, a time lapse that is here referred as to the onset of continental collision along the Arabia–Eurasia plate boundary. In this scenario, the DF region operated throughout the Cenozoic as a major zone of residual stress accommodation and transfer in the hinterland domain of the Zagros convergence zone. Results of this study also suggest that the tectonic evolution along the Arabia–Eurasia plate boundary was modulated by the plate-boundary dynamics and by the modes of tectonic reactivation of the intracontinental weak zones of Central Iran and at its tectonic boundaries.

International audience; Unravelling the evolution of supradetachment basins developed in the hanging wall of low‐angle detachment faults may be an invaluable tool in reconstructing the tectonic evolution of highly extended terrains. These basins may record major regional tectonic events related to the exhumation of metamorphic core complexes, and the reconstruction of their evolution helps to quantify the amount of extension accommodated by such processes. Here we present stratigraphic and structural field evidence and micropaleontological constraints to the Neogene‐to‐Quaternary evolution of the supradetachment Gediz Graben that developed on top of the exhuming Central Menderes Massif (SW Turkey). This basin displays three different structural styles during its evolution: (i) it initiated as a ramp basin following the activation of the Gediz Detachment in the Middle Miocene; (ii) evolved as a half graben during the Late Miocene following the activation of high‐angle brittle faults at its southern margin; and (iii) reached its final symmetric graben configuration in Late Pliocene (?) – Quaternary times following the activation of its northern margin. New micropaleontological data document a short‐lived upper Tortonian marine episode in the basin, and major along‐strike variations in exhumation are documented on its southern margin. Our reconstruction shows how sedimentary basins originally formed in the hanging‐wall of detachment faults may eventually end up in tectonic contact with the mylonitic footwall. Finally, we highlight the importance of magmatism in localizing the deformation in highly extended terrains and in controlling the evolution of supradetachment systems.

International audience; Trench motions represent the surface expression of the interaction between subducting plates and the underlyingmantle, but the inherent dynamics are not fully understood. One interesting case is the migration of the Izu-Bonin Marianas trench (IBM) that accommodates the subduction of the Pacific beneath the Philippine Sea Plate (PSP), which is in turn subducting beneath the Eurasian plate along the Ryukyu trench. The history of the IBM trench is dominated by fast, episodic retreat from 40 to 15 Ma. However, around 10–5 Ma, the IBM trenchreversed its motion from retreat to advance. The switch in trench motion occurred soon after the breakoff of thePSP slab along the Ryukyu trench and the onset of new subduction, and represents a fundamental change in thedynamics of the western Pacific subduction zones. Here, Following the modelling study of Čížková and Bina(2015), which suggested a link between IBM trench advance and Ryukyu subduction, we run 2-D numericalexperiments to test the influence of a newly formed Ryukyu slab on the established IBM subduction zone, we runtwo-dimensional numerical experiments to test the influence of this newly formed Ryukyu slab on the IBMsubduction zone. The results from our geodynamic model compare favourably with the reconstructed trend, indicating that the switch in trench motion along the IBM trench may indeed be related to the onset of a new subduction zone along the Ryukyu trench. Our analysis substantiates the idea that advancing trench motions in the western Pacific are due to the establishment of a double subduction system. Further analysis of such dynamics provides insights for the mechanisms controlling subducting plate and trench motions and mantle force transmission.

Active and fossil subduction systems consisting of two adjacent plates with opposite retreating directions occur in several areas on Earth, as the Mediterranean or Western Pacific. The goal of this work is to better understand the first-order plate dynamics of these systems using the results of experimental models. The laboratory model is composed of two separate plates made of silicon putty representing the lithosphere, on top of a tank filled with glucose syrup representing the mantle. The set of experiments is designed to test the influence of the width of plates and the initial separation between them on the resulting trench velocities, deformation of plates, and mantle flow. Results show that the mantle flow induced by both plates is asymmetric relative to the axis of each plate causing a progressive merging of the toroidal cells that prevents a steady state phase of the subduction process and generates a net outward drag perpendicular to the plates. Trench velocities increase when trenches approach each other and decrease when they separate after their intersection. The trench curvature of both plates increases linearly with time during the entire evolution of the process regardless their width and initial separation. The interaction between the return flows associated with each retreating plate, particularly in the interplate region, is stronger for near plate configurations and correlates with variations of rollback velocities. We propose that the inferred first-order dynamics of the presented analog models can provide relevant clues to understand natural complex subduction systems. ©2018. American Geophysical Union. All Rights Reserved., The work of M. P., M. F., and J. V. is part of the projects ALPIMED (PIE-CSIC- 201530E082) and MITE (CGL2014- 59516-P) and partly financed by the Generalitat de Catalunya (2014-SGR-1471 and 2017-SGR-847). The work of S. Z. is funded by the Spanish Ministry of Economy and Competitiveness through grant CICYT DPI2017-85139-C2-2-R and Generalitat de Catalunya (2017-SGR-1278).

The Late Cenozoic tectonic evolution of the Mediterranean region, which is sandwiched between the converging African and European continents, is dominated by the process of subduction orogeny. Subduction orogeny occurs where localized subduction, driven by negative slab buoyancy, is more rapid than the convergence rate of the bounding plates; it is commonly developed in zones of early or incomplete continental collision. Subduction orogens can be distinguished from collisional orogens on the basis of driving mechanism, tectonic setting, and geologic expression. Three distinct Late Cenozoic subduction orogens can be identified in the Mediterranean region, making up the Western Mediterranean (Apennine, external Betic, Maghebride, Rif), Central Mediterranean (Carpathian), and Eastern Mediterranean (southern Dinaride, external Hellenide, external Tauride) Arcs. The Late Cenozoic evolution of these orogens, described in this article, is best understood in light of the processes that govern subduction orogeny and depends strongly on the buoyancy of the locally subducting lithosphere; it is thus strongly related to paleogeography. Because the slow (4–10 mm/yr) convergence rate between Africa and Eurasia has preserved the early collisional environment, and associated tectonism, for tens of millions of years, the Mediterranean region provides an excellent opportunity to elucidate the dynamic and kinematic processes of subduction orogeny and to better understand how these processes operate in other orogenic systems.

International audience; The Menderes Massif is a Tertiary metamorphic core complex tectonically exhumed in the late Oligocene – Miocene during coeval development of a series of E-W trending basins. This study analyzes the source-to-sink evolution of the Gediz Graben and the exhumation pattern of the Central Menderes Massif at the footwall and hanging wall of the Gediz Detachment Fault. We use a comprehensive approach to detrital apatite fission-track dating combining analysis of modern river sediments, analysis of fossil sedimentary successions, and mineral fertility determinations. This approach allowed us to: i) define the modern short-term erosion pattern of the study area, ii) unravel the long-term exhumation history, iii) identify major exhumation events recorded in the sedimentary basin fill and iv) constrain the maximum depositional age of the sedimentary succession. Three main exhumation events are recorded in the analyzed detrital samples: i) a late Oligocene/early Miocene exhumation event involving the whole Menderes Massif; ii) a late Miocene event involving the northern edge of the Central Menderes Massif; iii) a Plio-Quaternary more localized event involving only the western part of the southern margin of the basin (Salihli area) and bringing to the surface the Gediz Detachment and its intrusive footwall (Salihli granodiorite). The modern short-term erosion pattern closely reflects this latter Plio-Quaternary event. Single grain-age distributions in the sedimentary basin fill highlight drainage pattern reorganizations in correspondence of the transition between different stratigraphic units, and allowed to better constrain the depositional age of the sedimentary units of the basin pointing to a possible onset of sedimentation in the basin during the middle Miocene.

Since several decades, the processes allowing for the subduction of the continental lithosphere less dense than the mantle in a collision context have been widely explored, but models that are based upon the premise that slab pull is the prominent driver of plate tectonics fail. The India–Asia collision, where several episodes of continental subduction have been documented, constitute a case study for alternative views. One of these episodes occurred in the early collision time within the Asian plate where continental lithosphere not attached to any oceanic lithosphere subducted southward in front of the Indian lithosphere during its northward subduction that followed the oceanic subduction of the Tethys ocean. This process, known as collisional subduction, has a counter-intuitive behavior since the subduction is not driven by slab pull. It has been speculated that the mantle circulation can play an important role in triggering collisional subduction but a detailed, qualitative analysis of it is not available, yet. In this work we explore the southward subduction dynamics of the Asian lithosphere below Tibet by means of analogue experiments with the aim to highlight how the mantle circulation induces or responds to collisional subduction. We found that during the northward oceanic subduction (analogue of Tethys subduction) attached to the indenter (Indian analogue), the main component of slab motion is driven vertically by its negative buoyancy, while the trench rolls back. In the mantle the convective pattern consists in a pair of wide convective cells on both sides of the slab. But when the indenter starts to bend and plunge in the mantle, trench motion reverses. Its advance transmits the far field forces to two upper plates (Asian analogues). The more viscous frontal plate thickens, and the less viscous hinterland plate, which is attached to the back wall of the box, subducts. During this transition, a pair of sub-lithospheric convective cells is observed on both sides of the Asian analogue slab, driven by the shortening of the frontal plate. It favors the initiation of the backwall plate subduction. Such subduction is maintained during the entire collision by a wide cell with a mostly horizontal mantle flow below Tibet, passively advecting the Asian analogue slab. Experimental results suggest that once the tectonic far-field force related to the forward horizontal motion becomes dominant upon the buoyancy forces, trench advancing and the transmission of the tectonic force to the upper and backwall plates are promoted. This peculiar condition triggers the subduction of the backwall plate, despite it is light and buoyant.

Slab‐slab interaction is a characteristic feature of tectonically complex areas. Outward dipping double‐sided subduction is one of these complex cases, which has several examples on Earth, most notably the Molucca Sea and Adriatic Sea. This study focuses on developing a framework for linking plate kinematics and slab interactions in an outward dipping subduction geometry. We used analog and numerical models to better understand the underlying subduction dynamics. Compared to a single subduction model, double‐sided subduction exhibits more time‐dependent and vigorous toroidal flow cells that are elongated (i.e., not circular). Because both the Molucca and Adriatic Sea exhibit an asymmetric subduction configuration, we also examine the role that asymmetry plays in the dynamics of outward dipping double‐sided subduction. We introduce asymmetry in two ways; with variable initial depths for the two slabs (“geometric” asymmetry), and with variable buoyancy within the subducting plate (“mechanical” asymmetry). Relative to the symmetric case, we probe how asymmetry affects the overall slab kinematics, whether asymmetric behavior intensifies or equilibrates as subduction proceeds. While initial geometric asymmetry disappears once the slabs are anchored to the 660 km discontinuity, the mechanical asymmetry can cause more permanent differences between the two subduction zones. In the most extreme case, the partly continental slab stops subducting due to the unequal slab pull force. The results show that the slab‐slab interaction is most effective when the two trenches are closer than 10–8 cm in the laboratory, which is 600–480 km when scaled to the Earth.

The Middle East region represents a key site within the Tethyan domain where continental break-up, collision, backarc extension and escape tectonics are kinematically linked together. We perform global mantle circulation computations to test the role of slab pull and mantle upwellings as driving forces for the kinematics of the Arabia-Anatolia-Aegean (AAA) system, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Model results are compared with geodetically inferred crustal motions, residual topography, and shear wave splitting measurements. The AAA velocity field with respect to Eurasia shows an anti-clockwise toroidal pattern, with increasing velocities toward the Aegean trench. The best match to these crustal motions can be obtained by combining the effect of slab pull exerted in the Aegean with a mantle upwelling underneath Afar and, more generally, with the large-scale flow associated with a whole mantle, Tethyan convection cell. Neogene volcanism for AAA is widespread, not only in the extensional or subduction settings, but also within plates, such as in Syria-Jordan-Israel and in Turkey, with geochemical fingerprints similar of those of the Afar lava. In addition, morphological features show large uplifting domains far from plate boundaries. We speculate that the tectonic evolution of AAA is related to the progressive northward entrainment of upwelling mantle material, which is itself associated with the establishment of the downwelling part of a convection cell through the segmented Tethyan slab below the northern Zagros and Bitlis collision zone. The recently established westward flow dragged Anatolia and pushed the Aegean slab south-westward, thus accelerating backarc extension. Our model reconciles Afar plume volcanism, the collision in the Bitlis mountains and northern Zagros, and the rapid increase of Aegean trench rollback in a single coherent frame of large scale mantle convection, initiated during the last similar to 40 Ma. (C) 2013 Elsevier B.V. All rights reserved.

The Cordillera of the Andes is a double-vergent orogenic belt built up by thickening of South American plate crust. Several models provide plausible explanations for the evolution of the Andes, but the reason why shortening started at ∼50 Ma is still unclear. We explore the evolution of the subduction zone through time by restoring the position of the Nazca trench in an absolute reference frame, comparing its position with seismic tomography models and balancing the evolution of the subducting slab. Reconstructions show that the slab enters into the lower mantle at ∼ 50 ± 10 Ma , and then progressed, moving horizontally at shallow lower mantle depth while thickening and folding in the transition zone. We test this evolutionary scenario by numerical models, which illustrate that compression in the upper plate intensifies once the slab is anchored in the lower mantle. We conclude that onset of significant shortening and crustal thickening in the Andes and its sustained action over tens of million years is related to the penetration of the slab into the lower mantle, producing a slowdown of lateral slab migration, and dragging the upper plate against the subduction zone by large-scale return flow.

The environmental recovery of quarried areas is increasingly a landscaping first-order issue in many countries and relevant lessons can be learned from each case history, depending upon factors such as the terrain nature and landscape consolidation over time. The case of the Tivoli travertine quarries near Rome (Acque Albule Basin, Italy) is addressed with a multidisciplinary approach and analytic data indicating sustainable and resilient future solutions. Geological data are analyzed to know the resources and natural hazards of this territory. Historical landscape analyses are next accomplished to know the cultural heritage and evolution of man-nature interactions. Eventually, the present land use and 3D landscape are considered to know the current setting. This territory is characterized by natural hazards including earthquakes, degassing, subsidence, and river flooding, and by resources such as abundant thermal waters. Historical analyses show the occurrence of a significant cultural heritage including two UNESCO world heritage sites. The present landscape is characterized by deep quarries and unplanned urbanization. The integration of geological data with historical information provides a new knowledge forming a geocultural database that must be taken into consideration for future planning. Based on these results, general landscape and urban guidelines are proposed for the future recovery of this intensively-quarried and -urbanized territory. The main lesson learned from the Tivoli case history is twofold: (1) the integration and feedback between multiple disciplines and professionals (architects and geologists) working together on environmental improvements and (2) the careful view of the past territory and meticulous analysis of existing buildings and urban landscapes are the key to sustainably interpret the future landscape. The main novelty of this lesson is the improvement of the concept of cultural landscape (UNESCO: http://whc.unesco.org/en/culturallandscape/) and its expansion toward geological issues and man-geology/nature interactions. In an urban-saturated territory that is also geologically-worn by human activities (e.g., Acque Albule Basin), restoring guidelines must comply with the partly-new concept of geocultural landscaping, which consists of a sustainable and resilient planning based on the study and understanding of natural-geological hazards, natural and cultural resources, and man-nature relationships over large spaces and long terms (4D). A general conceptual framework for geocultural landscaping is eventually proposed.

International audience; The Sila Massif is a small part of an orogenic wedge that sits on top of the narrow and active Calabrian subduction zone. The topography of the Sila Massif is characterized by a plateau region whose age and origin has been long debated. Here we integrate new apatite (U-Th)/He data from the eastern flank of the massif with existing apatite fission-track (AFT) data, to constrain the topographic evolution of the massif. The new AHe ages range from 9.7 Ma to 49.8 Ma and overlap the AFT ages indicating that a phase of rapid Cenozoic exhumation was followed by an abrupt decrease of the exhumation rate. A steep/inverse AFT age-elevation relationship from a vertical profile on top of the summit area of the north-eastern Sila may records post-exhumation relief degradation, which is consistent with the low-relief upland topography. To test this hypothesis we performed inverse numerical modeling using Pecube code. Integrating the new AHe ages and the numerical modelling results with the geological constraints we propose a new model for the regional topographic evolution from 30 Ma to the present.

Density anomalies beneath the lithosphere are expected to generate dynamic topography at the Earth's surface due to the induced mantle flow stresses which scale linearly with density anomalies, while the viscosity of the upper mantle is expected to control uplift rates. However, limited attention has been given to the role of the lithosphere. Here we present results from analogue modeling of the interactions between a density anomaly rising in the mantle and the lithosphere in a Newtonian system. We find that, for instabilities with wavelengths of the same order of magnitude as lithosphere thickness, the uplift rate and the geometry of the surface bulge are inversely correlated to the lithosphere thickness. We also show that a layered lithosphere may modulate the topographic signal. With respect to previous approaches our models represent a novel attempt to unravel the way normal stresses generated by mantle flow are transmitted through a rheologically stratified lithosphere and the resulting topographic signal. © 2017. American Geophysical Union. All Rights Reserved., T.W.B. was partially supported through NASA OSP 201601412-001.

Subduction-induced mantle circulation plays an important role in the dynamics of convergent margins. Different components of the flow, i.e. toroidal and poloidal, provide relevant driving forces for back-arc basin formation, overriding plate deformation, curvature of subduction zones and volcanic activity. Here, we investigate on the emergence and controls on the toroidal component of the subduction–induced mantle flow by means of numerical modeling. To characterize the toroidal cell's three-dimensional flow, size and length-scales and its disposing factors, we test separately a series of lithospheric and mantle parameters, such as the density difference and viscosity ratio between the slab and the mantle, the width of the slab, as opposed to the size, the stratification and the rheology of the mantle. Out of the tested parameters, the numerical results show that the strength of the flow depends on the mantle viscosity and the magnitude of the slab pull force, that is slab-mantle density difference and the mantle thickness, however the characteristic length, axis and the shape of the toroidal cell are almost independent of the slab's properties and mainly depend on the thickness of the convecting mantle.

International audience; The Menderes Massif of western Turkey is a key area to study feedback relationships between magma generation/emplacement and activation of extensional detachment tectonics. Here, we present new textural analysis and in situ U-(Th)-Pb titanite dating from selected samples collected in the transition from the undeformed to the mylonitized zones of the Salihli granodiorite at the footwall of the Neogene, ductile-to-brittle, top-to-the-NNE Gediz-Alaşheir (GDF) detachment fault. Ductile shearing was accompanied by the fluid-mediated sub-solidus transformation of the granodiorite to orthogneiss, which occurred at shallower crustal levels and temperatures compatible with the upper greenschist-to-amphibolite facies metamorphic conditions (530-580 °C and P < 2 GPa). The syn-tectonic metamorphic overgrowth of REE-poor titanite on pristine REE-rich igneous titanite offers the possibility to constrain the timing of magma crystallisation and solid-state shearing at the footwall of the Gediz detachment. The common Pb corrected 206Pb/238U (206Pb*/238U) ages and the REE re-distribution in titanite that spatially correlates with the Th/U zoning suggests that titanite predominantly preserve open-system ages during fluid-assisted syn-tectonic re-crystallisation in the transition from magma crystallization and emplacement (at ~ 16-17 Ma) to the syn-tectonic, solid-state shearing (at ~ 14 Ma). A minimum time lapse of ca. 1-2 Ma is then inferred between the crustal emplacement of the Salihli granodiorite and nucleation of the ductile extensional shearing along the Gediz detachment. The reconstruction of the cooling history of the Salihli granodiorite documents a punctuated evolution dominated by two episodes of rapid cooling, between ~ 14 Ma and ~ 12 Ma (~ 100 °C/Ma) and between ~ 3 and ~ 2 Ma (~ 105 °C/Ma). We relate the first episode to nucleation and development of post-emplacement of ductile shearing along the GDF and the second to brittle high-angle faulting, respectively. Our dataset suggests that in the Menderes Massif the activation of ductile extension was a consequence, rather than the cause, of magma emplacement in the extending crust.

International audience; The tectonic and topographic evolution of southeast Asia is attributed to the indentation of India into Eurasia, gravitational collapse of the uplifted terrains and the dynamics of the Sunda and other western Pacific subduction zones, but their relative contributions remain elusive. Here, we analyse 3D numerical geodynamic modeling results involving a collision-subduction system and show that vigorous asthenospheric flow due to differential along-strike slab kinematics may contribute to the surface strain and elevations at collision-subduction transition zones. We argue that protracted northward migration of the collisional front and Indian slab during south to south-westward rollback subduction along the Sunda margin might have produced a similar asthenospheric flow. This flow could have contributed to the southeast Asia extrusion tectonics and uplift of the terrains around the eastern Himalayan syntaxis and protruding from southeast Tibet. Therefore, we suggest that the tectonics and topographic growth east and southeast of Tibet are controlled not only by crustal and lithospheric deformation but also by asthenospheric dynamics.

The interaction of neighboring subducting lithospheres is a characteristic feature of many tectonically complex areas. Here we use numerical modeling to study the interactions between two oppositely dipping, adjacent subducting lithospheres and to understand their impact on the subduction evolution, mantle flow, and stress propagation through the mantle. As slabs subduct, rollback, and approach, they strongly affect each other if plate edges are at distances

International audience; Since the Mesozoic, Africa has been under extension with shorter periods of compression associated with obductionof ophiolites on its northern margin. Less frequent than “normal” subduction, obduction is a first order process that remainsenigmatic. The closure of the Neo-Tethys Ocean, by the Upper Cretaceous, is characterized by a major obduction event, from theMediterranean region to the Himalayas, best represented around the Arabian Plate, from Cyprus to Oman. These ophiolites wereall emplaced in a short time window in the Late Cretaceous, from 100 to 75 Ma, on the northern margin of Africa, in a contextof compression over large parts of Africa and Europe, across the convergence zone. The scale of this process requires anexplanation at the scale of several thousands of kilometres along strike, thus probably involving a large part of the convectingmantle. We suggest that alternating extension and compression in Africa could be explained by switching convection regimes.The extensional situation would correspond to steady-state whole-mantle convection, Africa being carried northward by alarge-scale conveyor belt, while compression and obduction would occur when the African slab penetrates the upper–lowermantle transition zone and the African plate accelerates due to increasing plume activity, until full penetration of the Tethys slabin the lower mantle across the 660 km transition zone during a 25 Myr long period. The long-term geological archives on whichsuch scenarios are founded can provide independent time constraints for testing numerical models of mantle convection andslab–plume interactions.; Depuis le Mésozoïque, l’Afrique a été en extension avec de courtes périodes de compression associées a`l’obduction d’ophiolites sur sa marge nord. Moins fréquente que la subduction, l’obduction est néanmoins un phénomènede premier ordre qui reste énigmatique. La fermeture de la Neo-Téthys au Crétacé supérieur est caractérisée par un épisodemajeur d’obduction, depuis la Méditerranée jusqu’a` l’Himalaya, en particulier sur la marge de l’Arabie, de Chypre a` l’Oman.Ces ophiolites furent toutes mises en place dans un court laps de temps pendant le Crétacé supérieur, de 100 a` 75 Ma, dansun contexte de compression enregistré en de larges portions de l’Afrique et de l’Europe, au travers de la zone de convergence.L’échelle de ce processus requiert une explication a` l’échelle de plusieurs milliers de kilomètres et donc impliquantvraisemblablement l’ensemble du manteau convectif. Nous suggérons que l’alternance de périodes extensives et compressivesen Afrique résulte de changements du régime convectif. Les périodes extensives correspondraient a` la convectionimpliquant tout le manteau, l’Afrique étant portée par une grande cellule de type tapis-roulant, tandis que la compressionet l’obduction se produiraient quand le panneau plongeant africain pénètre la transition entre le manteau supérieur et lemanteau inférieur et quand la plaque Afrique accélère en conséquence d’une plus grande activité du panache, jusqu’a`pénétration complète, durant une période d’environ 25 Myr. Les archives géologiques sur lesquelles ce type de scenarios estfondé peuvent fournir des contraintes temporelles indépendantes pour tester les modèles numériques de convectionmantellique et les interactions panache–panneau plongeant.

Back-arc extension in the Aegean, which was driven by slab rollback since 45 Ma, is described here for the first time in two stages. From Middle Eocene to Middle Miocene, deformation was localized leading to (i) the exhumation of high-pressure metamorphic rocks to crustal depths, (ii) the exhumation of high-temperature metamorphic rocks in core complexes, and (iii) the deposition of sedimentary basins. Since Middle Miocene, extension distributed over the whole Aegean domain controlled the deposition of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D and four steps at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry, and kinematics of ductile deformation, paleomagnetic data, and available tomographic models. The restoration model shows that the rate of trench retreat was around 0.6 cm/year during the first 30 My and then accelerated up to 3.2 cm/year during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, in Middle Miocene correlates with the acceleration of trench retreat and is likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral northeast–southwest strike-slip faults, since Middle Miocene, is illustrated by the 450 km long fault zone, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in Western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene, almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean.

Using silicone slabs as a model analogue for lithospheric plates subducting into a box of glucose syrup, as an analogue of the mantle, we explore the subduction of continental lithosphere in a context of intercontinental collision. The continental indenter pushed by a piston, reproducing the collision, attached to a dense oceanic plate, subducts to two-thirds of the depth of the mantle box. We show that, surprisingly, the continental plate attached to the back wall of the box subducts, even if not attached to a dense oceanic slab. The engine of this subduction is not the weight of the slab, because the slab is lighter than the mantle, but the motion of the piston, which generates horizontal tectonic forces. These are transmitted to the back wall plate through the indenter and the upper plate at the surface, and by the advancing indenter slab through the mantle at shallow depth. We define this process as collisional subduction occurring in a compressional context. The collisional subduction absorbs between 14% and 20% of the convergence, and represents an unexplored component of collisional mass balance. The transmission of tectonic forces far from the collision front favors the formation of a wide plateau. Our experiments reproduce adequately the amount and geometry of the Asian lithosphere subduction episodes inferred during the collision, leading us to conclude that it reproduces adequately the physics of such process.

The combination of analytical and analogue models gives new opportunities to better understand the kinematic parameters controlling the evolution of transpression zones. In this work, we carried out a set of analogue models using the kinematic parameters of transpressional deformation obtained by applying a general triclinic transpression analytical model to a tabular-shaped shear zone in the external Betic Chain (Torcal de Antequera massif). According to the results of the analytical model, we used two oblique convergence angles to reproduce the main structural and kinematic features of structural domains observed within the Torcal de Antequera massif (α = 15° for the outer domains and α = 30° for the inner domain). Two parallel inclined backstops (one fixed and the other mobile) reproduce the geometry of the shear zone walls of the natural case. Additionally, we applied digital particle image velocimetry (PIV) method to calculate the velocity field of the incremental deformation. Our results suggest that the spatial distribution of the main structures observed in the Torcal de Antequera massif reflects different modes of strain partitioning and strain localization between two domain types, which are related to the variation in the oblique convergence angle and the presence of steep planar velocity – and rheological – discontinuities (the shear zone walls in the natural case). In the 15° model, strain partitioning is simple and strain localization is high: a single narrow shear zone is developed close and parallel to the fixed backstop, bounded by strike-slip faults and internally deformed by R and P shears. In the 30° model, strain partitioning is strong, generating regularly spaced oblique-to-the backstops thrusts and strike-slip faults. At final stages of the 30° experiment, deformation affects the entire model box. Our results show that the application of analytical modelling to natural transpressive zones related to upper crustal deformation facilitates to constrain the geometrical parameters of analogue models.

Ethiopia offers an excellent opportunity to study the effects and linkage between mantle dynamics and surface processes on landscape evolution. The Ethiopian Highlands (NW Ethiopia), characterized by a huge basaltic plateau, is part of the African Superswell, a wide region of dynamically-supported anomalously high topography related to the rising of the Afar plume. The initiation and steadiness of dynamic support beneath Ethiopia has been explored in several studies. However the presence, role, and timing of dynamic support beneath Ethiopia and its relationship with continental flood basalts volcanism and surface processes are poorly defined. Here, we present a geomorphological analysis of the Ethiopian Highlands supplying new constraints on the evolution of river network. We investigated the general topographic features (filtered topography, swath profiles, local relief) and the river network (river longitudinal profiles) of the study area. We also apply a knickpoint celerity model in order to provide a chronological framework to the evolution of the river network. The results trace the long-term progressive capture of the Ethiopian Highlands drainage system and confirm the long-term dynamic support of the area, documenting its impact on the contrasting development of the Blue Nile and Tekeze basins.

Sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works. Acque Albule, the study area of this work, is a Plio-Pleistocene basin near Rome, central Italy, superficially filled by a large and thick deposit of late Pleistocene thermogene travertine. Human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes. To contribute to the proper assessment of these hazards, a geomorphologic study of the basin was performed using digital elevation models (DEMs), recent aerial photographs, and field surveys. Historical material such as old aerial photographs and past geomorphologic studies both pre-dating the most part of quarrying and village building was also used together with memories of the elderly population. This preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding. Where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings, a detailed subsurface study was performed using properly-calibrated electrical resistivity tomography (ERT) and dynamic penetration measurements (DPSH), together with some borehole logs made available from the local municipality. This second study highlighted the presence of sinkholes and caves that are, this time, substantially hidden to the resolution of standard methods and materials such as aerial photographs, DEMs, and field surveys. Active sinkhole subsidence in the Acque Albule Basin may explain, at least in part, the frequent damages that affect numerous buildings in the area. The main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of (hidden) sinkholes that can be masked by the Anthropocenic molding and blanketing of the territory. For these purposes, data from historical (pre-Anthropocene) documents as well as, where possible, subsurface investigations are fundamental.

International audience; Central Iran provides an ideal region in which to study the long-term morphotectonic response to the nucleation and propagation of intraplate faulting. In this study, a multidisciplinary approach that inte-grates structural and stratigraphic field investigations with apatite (U + Th)/He (AHe) thermochronometry is used to reconstruct the spatio-temporal evolution of the Kuh-e-Faghan Fault in northeastern central Iran. The Kuh-e-Faghan Fault is a narrow, similar to 80-km-long, deformation zone that consists of three main broadly left-stepping, E-W-trending, dextral fault strands that cut through the Mesozoic-Paleozoic substratum and the Neogene-Quaternary sedimentary cover. The AHe thermochronometry results indicate that the intrafault blocks along the Kuh-e-Faghan Fault experienced two major episodes of fault-related exhumation at ca. 18 Ma and ca. 4 Ma. The ca. 18 Ma faulting/exhumation episode is chiefly recorded by the structure and depositional architecture of the Neogene deposits along the Kuh-eFaghan Fault. A source-to-sink scenario can be reconstructed for this time frame, where topographic growth caused the synchronous erosion/exhumation of the pre-Neogene units and deposition of the eroded material in the surrounding fault-bounded continental depo-centers. Successively, the Kuh-eFaghan Fault gradually entered a period of relative tectonic quiescence and, probably, of regional subsidence, during which a thick pile of fine-grained onlapping sediments was deposited. This may have caused resetting of the He ages of apatite in the pre-Neogene and the basal Neogene successions. The ca. 4 Ma faulting episode caused the final exhumation of the fault system, resulting in the current fault zone and topography. The two faultrelated exhumation episodes fit with regional early Miocene collision-enhanced uplift/exhumation, and the late Miocene-early Pliocene widespread tectonic reorganization of the Iranian Plateau. The reconstructed longterm, spatially and temporally punctuated fault system evolution in intraplate central Iran during Neogene-Quaternary times may reflect states of far-field stress changes at the collisional boundaries.

Highlights • Plate boundary re-organization in the central Mediterranean Sea • Segmentation of the subduction complex along lithospheric transverse faults • STEP faults in the Ionian Sea • Pleistocene active faulting and Mt. Etna formation Abstract The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic Tethyan domain which acted as thrust faults during the Messinian and Pliocene; 3) the IF and the AEF, and locally the Malta escarpment, accommodate a recent tectonic event coeval and possibly linked to the Mt. Etna formation. Regional geodynamic models show that, whereas AEF and IF are neighboring fault systems, their individual roles are different. Faulting primarily resulting from the ESE retreat of the Ionian slab is expressed in the northwestern part of the IF. The AEF, on the other hand, is part of the overall dextral shear deformation, resulting from differences in Africa-Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments, which results in rifting processes within the Western Lobe of the Calabrian Arc accretionary wedge. As such, it is primarily associated with Africa-Eurasia relative motion.

Obduction is an odd geodynamic process characterized by the emplacement of dense oceanic “ophiolites” atop light continental plates in convergent settings. We herein present analog models specifically designed to explore the conditions (i.e., sharp increase of plate velocities — herein coined as ‘acceleration’, slab interaction with the 660 km discontinuity, ridge subduction) under which obduction may develop as a result of subduction initiation. The experimental setup comprises an upper mantle modeled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and high-viscosity silicone plates. Convergence is simulated by pushing a piston with plate tectonics like velocities (1–10 cm/yr) onto a model comprising a continental margin, a weakness zone with variable resistance and dip ( W ), an oceanic plate (with or without a spreading ridge), a preexisting subduction zone ( S ) dipping away from the piston and an upper active continental margin, below which the oceanic plate is being subducted at the start of the model (as for the Neotethyan natural example). Several configurations were tested over thirty-five parametric models, with special emphasis on comparing different types of weakness zone and the degree of mechanical coupling across them. Measurements of displacements and internal deformation allow for a precise and reproducible tracking of deformation. Models consistently demonstrate that once conditions to initiate subduction are reached, obduction may develop further depending on the effective strength of W .Results(1)constrainthe range of physical conditions required for obduction to develop/nucleate and (2) underline the key role of such perturbations for triggering obduction, particularly plate ‘acceleration’. They provide an explanation to the short-lived Peri-Arabic obduction, which took place along thousands of km almost synchronously (within ∼ 50–10 Myr), from Turkey to Oman, while the subduction zone beneath Eurasia became temporarily jammed. They also demonstrate that the emplacement of dense, oceanic material on continental lithosphere is not a mysterious process requiring extraordinary boundary conditions but results from large-scale, normal (oceanic then continental) subduction processes.

We present analogue models simulating the subduction of a buoyant ridge oriented perpendicularly or obliquely with respect to the trench, beneath an advancing overriding plate. The convergence velocity is imposed by lateral boundary conditions in this experimental set. We analyze the three-dimensional geometry of the slab, the deformation and topography of the overriding plate. Experiments suggest that ridge subduction diminishes the dip of the slab, eventually leading to the appearance of a horizontal slab segment in case boundary conditions impose a rapid convergence. This result contrasts with that obtained in free subduction experiments, in which ridge subduction diminishes the convergence velocity which, in turn, increases the dip of the slab beneath the ridge. The slab dip decrease is accompanied by the indentation of the overriding plate by the ridge, resulting in arc curvature. Experiments suggest that indentation is larger for small convergence velocity and large slab dip. Ridge subduction also uplifts the overriding plate. Uplift first occurs close to the trench (~ fore-arc area) and is accompanied by the flexural subsidence of the overriding plate behind the uplifted area (~ back-arc subsidence). The uplifted area migrates within the overriding plate interiors following the appearance of a horizontal slab segment. These results are compared with natural examples of ridge subduction in the circum-Pacific area. They explain why ridge subduction may have contrasted effects on the overriding plate dynamics depending on the global conditions that constrain the converging system.

We designed three-dimensional dynamically self-consistent laboratory models of subduction to analyse the relationships between overriding plate deformation and subduction dynamics in the upper mantle. We investigated the effects of the subduction of a lithosphere of laterally variable buoyancy on the temporal evolution of trench kinematics and shape, horizontal flow at the top of the asthenosphere, dynamic topography and deformation of the overriding plate. Two subducting units, which correspond to a negatively buoyant oceanic plate and positively buoyant continental one, are juxtaposed via a trench-perpendicular interface (analogue to a tear fault) that is either fully-coupled or shear-stress free. Differential rates of trench retreat, in excess of 6 cm yr−1 between the two units, trigger a more vigorous mantle flow above the oceanic slab unit than above the continental slab unit. The resulting asymmetrical sublithospheric flow shears the overriding plate in front of the tear fault, and deformation gradually switches from extension to transtension through time. The consistency between our models results and geological observations suggests that the Late Cenozoic deformation of the Aegean domain, including the formation of the North Aegean Trough and Central Hellenic Shear zone, results from the spatial variations in the buoyancy of the subducting lithosphere. In particular, the lateral changes of the subduction regime caused by the Early Pliocene subduction of the old oceanic Ionian plate redesigned mantle flow and excited an increasingly vigorous dextral shear underneath the overriding plate. The models suggest that it is the inception of the Kefalonia Fault that caused the transition between an extension dominated tectonic regime to transtension, in the North Aegean, Mainland Greece and Peloponnese. The subduction of the tear fault may also have helped the propagation of the North Anatolian Fault into the Aegean domain.

International audience; The geometric and kinematic evolution of the Andes provides insight onto the nature of the force balance beneath the South American plate. While the Andean load is opposed on its western edge by the force induced by subduction of the Nazca plate, its more elusive eastern counterpart, which we explore herein, requires some contribution from the mantle beneath the South Atlantic. Using a mantle flow model, we show that the Andes owe their existence to basal drag beneath South America caused by a cylindrical convection cell under the South Atlantic. We find that the observed Andean uplift requires both westward push fromactive upwelling beneath Africa andwestward drag toward the downgoing Nazca slab. These mutually-reinforcing downwellings and upwellings amount to 38% and 23% of the total driving force, respectively. Further decomposition reveals that the South Atlantic cell is most vigorous near its center, rendering the net drag force higher where the Andes also reach their highest elevation. Kinematic reconstructions suggest that the South Atlantic cell could have grown owing to the migration of the Nazca slab until ~50 Ma. We propose that from 50 Ma onwards, the cell may have ceased growing westward because (i) it had reached an optimal aspect ratio and (ii) the Nazca slab became anchored into the lower mantle. Continued westward motion of the plates, however, moved the surface expressions of spreading and convergence away from the upwelling and downwelling arms of this cell. Evidence for this scenario comes from the coeval tectonic, morphologic, and magmatic events in Africa and South America during the Tertiary.

""The relief around subduction zones results from the interplay of dynamic processes that may locally exceed the (iso)static contributions. The viscous dissipation of the energy in and around subduction zones is capable of generating kilometer scale vertical ground movements. In order to evaluate dynamic topography in a self-consistent subduction system, we carried out a set of laboratory experiments, wherein the lithosphere and mantle are simulated by means of Newtonian viscous materials, namely silicone putty and glucose syrup. Models are kept in their most simple form and are made of negative buoyancy plates, of variable width and thickness, freely plunging into the syrup. The surface of the model and the top of the slab are scanned in three dimensions. A forebulge systematically emerges from the bending of the viscous plate, adjacent to the trench. With a large wavelength, dynamic pressure offsets the foreside and backside of the slab by similar to 500 m on average. The suction, that accompanies the vertical descent of the slab depresses the surface on both sides. At a distance equal to the half-width of the slab, the topographic depression amounts to similar to 500 m on average and becomes negligible at a distance that equals the width of the slab. In order to explore the impact of slab rollback on the topography, the trailing edge of the plates is alternatively fixed to (fixed mode) and freed from (free mode) the end wall of the tank. Both the pressure and suction components of the topography are similar to 30% lower in the free mode, indicating that slab rollback fosters the dynamic subsidence of upper plates. Our models are compatible with first order observations of the topography around the East Scotia, Tonga, Kermadec and Banda subduction zones, which exhibit anomalous depths of nearly 1 km as compared to adjacent sea floor of comparable age. (C) 2011 Elsevier B.V. All rights reserved. RI Guillaume, Benjamin\\\/D-6570-2012""

Key-words. - Western Mediterranean, Convergent boundary, Tectonic reorganization, subduction, Back-arc basin, Basin inversion. Abstract. - In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian (W-Africa) northward subduction beneath Eurasia, subduction has almost ceased, as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic re- flection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the conver- gent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two back-arc oceanic bas- ins (Algerian-Liguro-Provencal and Tyrrhenian basins) and it is now mainly active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provencal, Algerian, and Alboran (partly) margins. Onset of compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins fol- lowing a similar propagation of the cessation of the subduction, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced on the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to really start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. Part of the contractional deformation may have shifted toward the north in the Liguro-Provencal basin possibly because of its weak rheological properties compared with those of the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are strongly heterogeneous along the boundary. These fea- tures prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred to follow a Wilson Cycle (at a small scale) with the following main steps : (1) northward Nubian subduction with Mediterranean back-arc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive onset of compression, from west to east, in the former back-arc domain and consequent basin inversion (since ~8-10 Ma); (4) possible future subduction of former back-arc basins.

No abstract has been provided

International audience; Recent global kinematic studies reveal that most of the trenches roll back but a significant number of them advance toward the upper plate. Those advancing trenches are mostly located in the Western Pacific and correspond to the subduction of very old, Mesozoic oceanic lithosphere. While retreating trenches are commonly explained by the slab pull action of the descending lithosphere, the origin of advancing trenches is still debated. Since this relationship is dependent upon the adopted reference frame, we select region where geological studies show the variability of trench migration style with time. The Izu-Bonin-Mariana (IBM) region represents a key example. The detailed reconstruction of the trench migration of the IBM subducting system reveals that after a long episode of asymmetric rollback, the IBM trench recently started advancing. We propose that this change from retreating to advancing trench mode results from the subduction of progressively older and stiffer lithospheric material. We test this hypothesis by means of two-dimensional (2-D) numerical models, reproducing the effects of the lithospheric aging during subduction. The result of our numerical tests shows that the entrance of old and stiff lithosphere forces the trench to advance because the increasing stiffness of the slab prevents the slab to unbend once it has subducted. We adapt this physical result to the IBM evolution, showing that the switch from trench retreat to trench advance can reconcile the shape of IBM slab as previously suggested. Finally we discuss the possibility that the subduction of the Cretaceous lithosphere might have triggered the change of the motion of the Pacific plate around 5 Ma.

Geophysical Journal International, 179 (3), ISSN:0956-540X, ISSN:1365-246X

International audience; The deep-sea trenches that circumscribe the Pacific basin are moving westward relative to the deep mantle by a few cm/yr, together with the Pacific seafloor. While the westward drift of the Pacific basin dominates the observed net westward rotation of Earth's tectonic plates relative to the deep mantle source of the Pacific hotspots, its cause remains uncertain. We demonstrate that the source of this westward drift is tectonic in origin: the westward push of the high Andean topography along the eastern Pacific margin is large enough to shear the entire Pacific upper mantle with a surface velocity of ~30 mm/yr. In addition, because the Pacific upper mantle is confined between vertically coherent slabs of subducted lithosphere on both sides of the Pacific, slabs in the western Pacific are forced to advance toward upper plates because the eastern Pacific slabs are pushed westward. This cross-Pacific interaction provides an explanation for trench advance, which is observed in the western Pacific and is not easily explained by the local dynamics of subduction in which dense sinking slabs essentially tend to retreat from overriding plates. Thus, the basic asymmetry of the Pacific system, which has been noted for almost all tectonic features including slab dips, trench motions, and upper plate tectonics, is the result of one-sided Andean forcing on the volume of Pacific upper mantle. The net rotation of the lithosphere is then the result of surface tectonics: westward motion is an accident resulting from the current distribution of tectonic plates, and was triggered by the mid-Cenozoic closure of the Tethys Ocean, via a westward expansion of the Atlantic and Andean cordilleran building.

International audience; Rocks metamorphosed under high-pressure (HP) and ultra high-pressure (UHP) conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities. In the Mediterranean realm, their occurrence in several belts related to a single subduction event shows that the burial­exhumation cycle is a recurrent transient process. Using the Calabria­Apennine and Aegean belts as examples, we show that the exhumation of HP rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback, creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before. The buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab. It then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate. Heated from below by the asthenosphere that flows into the opening mantle wedge, the exhumed crust weakens and undergoes core-complex-type extension, responsible for a second stage of exhumation at a lower rate. The full sequence of events that characterizes this model (crust­mantle delamination, slab rollback and trench retreat, HP rock exhumation, asthenosphere heating and core-complex formation) arises entirely from the initial condition imposed by the subduction of a small continental block. No specific condition is required regarding the rheology and erosion rate of HP rocks. The burial­exhumation cycle is transient and can recur every time a small continental block is subducted.

The motion of oceanic plates is commonly related to the subduction of cold and dense oceanic material into the mantle. These models predict plate velocities from subduction velocities but the trench motion is not directly included in the computation. Here, using a recent compilation of a global data set, we found that the motion of trenches (either advancing or retreating with respect to upper plates) scales with their corresponding subducting plates motion. Based on simple experimental tests, we found that subduction of strong slabs inside the upper mantle correctly predicts these kinematic relationships. We deduce that the motion of the trenches represent the surface manifestation of the resistance encountered by the subducting lithosphere to bend and penetrate within the upper mantle.

International audience; In this paper, we discuss the possibility that the North Anatolian fault (NAF) results from the deep deformation of the slab beneath the Bitlis Hellenic subduction zone. We described the tectonic evolution of the Anatolia Aegean area in three main steps, before, during and after the formation of the NAF. We remark that the tectonic conditions that are assumed to have triggered the formation of the NAF, i.e. collision to the east and extension to the west, was already achieved before the onset of that strike-slip fault system. We also highlight that the formation of the NAF was accompanied by the uplift of the Turkish Iranian plateau and by a surge of volcanism in the eastern Anatolia collisional area and probably by the acceleration of the Aegean trench retreat. We show tomographic images from global P-wave model of Piromallo and Morelli [C. Piromallo, A. Morelli, P wave tomography of the mantle under the Alpine Mediterranean area, J. Geophys. Res. 108 (2003) doi: 10.1029/2002JB001757.] showing that the slab beneath the Bitlis collisional belt is not continuous and that its possible rupture pursues to the west at least up to Cyprus and possibly up to the eastern end of the Hellenic trench. All these observations suggest that the plate tectonic re-organization occurred in the Late Miocene Early Pliocene in the region results from slab break-off in the Bitlis area and from its lateral propagation to the West. This idea is tested in analogue laboratory experiments, which confirm that the break of the slab under the collisional belt may trigger, (1) the acceleration of slab retreat to the west due to the increase in slab pull force, (2) the indentation of the continent in the collisional area and (3) produce the conditions that permit the lateral escape of material towards the west and the formation of the NAF.

International audience; We investigate, using 3D laboratory experiments, how the dynamics of indentation process are affected by the evolution at depth of the oceanic and continental subductions. Lithospheric plates are modelled by sand silicone plates floating on glucose syrup, and the density contrast between oceanic and continental lithospheric plates and asthenosphere is reproduced. Analogue experiments model the convergence between two lithospheric plates, a small continent indenting a large continental plate. We show that the surface deformation in front of the indenter and above the oceanic subduction zone depends on the behaviour of the slab below the collision zone. Slab break-off following the subduction of the small continent favours the indentation process, because it results in an increasing compression in front of the indenter, and extension above the neighbouring oceanic subduction, both of them being responsible for the appearance of the indenter-like geometry of the plate boundary. When the slab does not deform significantly at depth, in contrast, the closure of the oceanic domain in front of the indenter is followed by a longer period of continental subduction, during which the tectonic regime within the wide continent remains quite homogeneous. Comparing the presented analogue experiments with the subductions both part of the Arabian indenter within Eurasia, our results suggest that the different tectonic regime on both sides of the Arabia indenter may partly result from the probable occurrence of a detachment at depth under eastern Anatolia.

International audience; Three-dimensional laboratory experiments have been designed to investigate the way slab-bearing plates move during subduction inside the mantle. In our experiments a viscous plate of silicone (lithosphere) subducts under its negative buoyancy in a viscous layer of pure honey (mantle). Varying thickness, width, viscosity, and density of the plate and mantle, three characteristic modes of subduction are observed: a retreating trench mode (mode I), a retreating trench mode following a transient period of advancing trench (mode II), and an advancing trench mode (mode III). These modes are characterized by different partitioning of the amount of subduction into plate and trench motion. Our experiments show that the velocity of subduction can be modeled by the dynamic interaction between acting and resisting forces, where lithospheric bending represents 75-95% of the total resisting forces. However, our experimental results also show the impossibility to predict a priori the plate velocity only from the velocity of subduction without considering trench migrations. We find experimentally that the lithospheric radius of curvature, which depends upon plate characteristics (stiffness and thickness) and the mantle thickness, exerts a primary control on the trench behavior. Our results suggest that the complexity of the style of subduction could be controlled by geometrical rules of a plate bending inside a stratified mantle. The Earth system is in the crucial range for the interplay between the rigidity of the plate and the mantle stratification: this setting may be the responsible for the complexity of the past and present tectonic styles.