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We explore the connections between crustal shortening, volcanism, and mantle dynamics in the Atlas of Morocco. In response to compressional forces and strain localization, this intraplate orogen has evolved far from convergent plate margins. Convective effects, such as lithospheric weakening and plume-related volcanism, contributed in important ways to the building of high topography. We seek to better understand how crustal and mantle processes interacted during the Atlas' orogeny by combining multiple strands of observations, including new and published data. Constraints on crustal and thermal evolution are combined with new analyses of topographic evolution, petrological, and geochemical data from the Anti-Atlas volcanic fields, and a simple numerical model of the interactions among crustal deformation, a mantle plume, and volcanism. Our findings substantiate that: (a) crustal deformation and exhumation accelerated during the middle/late Miocene, contemporaneous with the onset of volcanism; (b) volcanism has an anorogenic signature with a deep source; (c) a dynamic mantle upwelling supports the high topography. We propose that a mantle plume and the related volcanism weakened the lithosphere beneath the Atlas and that this favored the localization of crustal shortening along pre-existing structures during plate convergence. This convective-tectonic sequence may represent a general mechanism for the modification of continental plates throughout the thermo-chemical evolution of the supercontinental cycle., Geochemistry, Geophysics, Geosystems, 24 (6), ISSN:1525-2027

Transient topography represents an opportunity for extracting information on the combined effect of tectonics, mantle-driven processes, lithology and climate across different temporal and spatial scales. The geomorphic signature of transient conditions can be used to unravel the landscape evolution and to assess perturbations in uplift rates, especially in areas devoid of stratigraphic constraints. The Atlas-Meseta system experienced a large scale topographic rejuvenation during the Cenozoic through a combination of different processes. Despite the uplift, the Western Moroccan Meseta (WMM) represents a quiescent tectonic domain with deeply incised valleys and high-standing erosional surfaces (relict landscape). This topography is characterized by elevated non-lithological knickpoints, that delimit an uplifted relict landscape, implying a transient response to a change in uplift rates. Here, we determine denudation rates of selected watersheds and bedrock outcrops from cosmogenic nuclides and perform stream profile, regional and basin-scale geomorphic analysis. Denudation rates of the relict and the rejuvenated landscape range from 15 to 20 m/Myr and from 30 to 40 m/Myr, respectively. These results allow estimating the erodibility parameter for performing river-profile inversions and hence extracting rock uplift rates through time. Inverted rock uplift rates are 10-25 m/Myr from 45 to 22 Ma and 30-55 m/Myr from 22 to 10 Ma. Despite the different time scales, the inverted rates are consistent with 10Be averaged denudation rates (15-20 and 30-40 m/Myr) and river incision values from Pleistocene lava flows (

We investigate the processes driving spatial-temporal patterns of Cenozoic exhumation in the Mediterranean and the Middle East by compiling >7300 published low-temperature thermochronometric ages and converting them into exhumation rates through a formal inversion process based on thermal modeling and closure temperature kinetics. Exhumation rates are resolved using piecewise-continuous spatial variability and timesteps of five million years. The spatial variability of the inferred rates is constrained by a plate tectonic reconstruction based on the integration of available kinematic data. In this model we recognize different tectonic blocks with a relative homogenous tectono-sedimentary and tectono-magmatic history. The inverted erosion rates for each block are then compared with regional and local geodynamic rates, eustatic curves, and climatic forcing to decipher common patterns and possible teleconnections among different blocks. The results document asynchronous exhumation across different tectonic blocks indicating local (i.e., at the scale of a single orogen) rather than regional (i.e., at the scale of multiple orogens) control on erosion rates. The main processes driving exhumation include collisions of Arabia, Adria, and Iberia with Eurasia, and subduction and retreat of the various Neo-Tethys slabs and back-arc basins. Specifically, we recognize two tectonic domains: collisional deformation zones where exhumation is controlled by surface uplift and erosion, and back-arcs areas where exhumation is controlled by tectonic denudation. In both cases we observe an increase in mean rates and rate variance during tectonic activity, followed by a decrease in each metric as tectonic activity wanes. Finally, we note (with a few exceptions) an overall increase in exhumation rates over most of the Mediterranean and Middle East in the last 5 Ma. This increase is more evident in areas of active tectonics and/or high topographic relief. Although we cannot exclude a tectonic contribution to some of these higher rates, the occurrence of higher exhumation rates, even in regions that did not experience enhanced tectonic activity, indicates that such an increase occurred most likely in response to the late Cenozoic global cooling and the Pleistocene increase in climate cyclicity

The evolution of the Sicily Channel Rift Zone (SCRZ), located south of the Central Mediterranean, is thought to accommodate the regional tectonic stresses of the Calabrian subduction system. It is unclear whether the rifting of the SCRZ is passive from far-field extensional stresses or active from mantle upwelling beneath. To map the structure and dynamics of the region, we measure Rayleigh- and Love-wave phase velocities from ambient seismic noise and invert for an isotropic 3-D shear-velocity and radial anisotropic model. Variations of crustal S-velocities coincide with topographic and tectonic features: slow under high elevation, fast beneath deep sea. The Tyrrhenian Sea has a VSV); areas experiencing compression and subduction-related volcanism have negative anisotropy (VSH

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The dynamics of subduction zones is linked to the rise and demise of forearc and backarc sedimentary basins in the overriding plate. Subsidence and uplift rates of these distinct basins are controlled by variations in plate convergence and subduction velocities and determined by the rheological and thermal structure of the lithosphere. In this study we conducted a series of high-resolution 2D numerical models of oceanic subduction and subsequent continental collision. The numerical code 2DELVIS involves erosion, sedimentation, and hydration processes. The models show the evolution of wedge-top basins overlying the accretionary wedge and retro-forearc basins in the continental overriding plate, separated by a forearc high. These forearc regions are affected by repeated compression and extension phases. Higher subsidence rates are recorded in the syncline structure of the retro-forearc basin when the slab dip angle is higher and the subduction interface is stronger. This implies the importance of the slab suction force as the main forcing factor creating up to 3-4 km negative residual topographic signals. Extensional back-arc basins are either localized along inherited weak zones at large distance from the forearc region or are initiated just above the hydrated mantle wedge. Back-arc subsidence is primarily governed by crustal and lithospheric thinning controlled by slab roll-back. Our results are compared with the evolution of the Mediterranean and we classify the Western and Eastern Alboran, Paola and Tyrrhenian, Transylvanian and Pannonian Basins to be genetically similar forearc–backarc basins, respectively.

The Sicily Channel, located on the north-central African plate foreland between Sicily, Tunis and Libya, is characterised by a seismically and volcanically active rift zone. This rift extends for more than 600 km in length offshore from the south of Sardinia to the south-east of Malta. Much of the observations we have today are either limited to the surface and the upper crust, or are broader and deeper from regional seismic tomography, missing important details about the lithospheric structure and dynamics. The project GEOMED (https://geomed-msca.eu) addresses this issue by processing all the seismic data available in the region in order to understand better the geodynamics of the Central Mediterranean. A recently compiled earthquake catalogue for the eastern part of the Sicily Channel Rift Zone (SCRZ) will be presented highlighting offshore active faults in the region, and new results from seismic tomography give an insight of what lies beneath. We measure seismic velocities from across the region using ambient seismic noise recorded on more than 50 stations located on Algeria, Italy (Lampedusa, Linosa, Pantelleria, Sardinia, Sicily), Libya, Malta, and Tunisia. The phase-velocity dispersion curves have periods ranging from 5 to 100 seconds and sample through the entire lithosphere. We find that slow and fast seismic velocities coincide with regional tectonic and topographic features. At short periods, Africa and Italy have slower velocities indicating these areas have thick continental crust in contrast to areas beneath Tyrrhenian and Ionian basins. The central area of the SCRZ has relatively faster velocities suggesting that there is a thinner crust. At longer periods the central area of SCRZ is characterised by slower velocities indicative of warmer temperatures than the surrounding. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 843696., peer-reviewed

The formation of mountain belts or rift zones is commonly attributed to interactions between plates along their boundaries, but the widely distributed deformation of Asia from Himalaya to the Japan Sea and other back‐arc basins is difficult to reconcile with this notion. Through comparison of the tectonic and kinematic records of the last 50 Ma with seismic tomography and anisotropy models, we show that the closure of the former Tethys Ocean and the extensional deformation of East Asia can be best explained if the asthenospheric mantle transporting India northward, forming the Himalaya and the Tibetan Plateau, reaches East Asia where it overrides the westward flowing Pacific mantle and contributes to subduction dynamics, distributing extensional deformation over a 3,000‐km wide region. This deep asthenospheric flow partly controls the compressional stresses transmitted through the continent‐continent collision, driving crustal thickening below the Himalayas and Tibet and the propagation of strike‐slip faults across Asian lithosphere further north and east, as well as with the lithospheric and crustal flow powered by slab retreat east of the collision zone below East and SE Asia. The main shortening direction in the deforming continent between the collision zone and the Pacific subduction zones may in this case be a proxy for the direction of flow in the asthenosphere underneath, which may become a useful tool for studying mantle flow in the distant past. Our model of the India‐Asia collision emphasizes the role of asthenospheric flow underneath continents and may offer alternative ways of understanding tectonic processes., Key Points Coeval India‐Asia collision and Pacific back‐arc extension explained by asthenospheric flowMantle flow correlates with long‐term kinematics from India to Pacific borderIndian mantle reaches Pacific border and Asian lithosphere spreads above ponding slabs

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International audience; We present here a number of geological observations in extensional contexts, either continental rifts or back-arcs, that show different situations of potential coupling between asthenospheric flow and crustal deformation. Several of these examples show a deformation distributed over hectometre to kilometre thick shear zones, accommodated by shallow dipping shear zones with a constant asymmetry over large distances. This is the case of the Mediterranean back-arc basins, such as the Aegean Sea, the northern Tyrrhenian Sea, the Alboran domain or the Gulf of Lion passive margin. Similar types of observation can be made on some of the South Atlantic volcanic passive margins and the Afar region, which were formed above a mantle plume. In all these examples the lithosphere is hot and the lithospheric mantle thin or possibly absent. We discuss these contexts and the main controlling parameters for this asymmetrical distributed deformation that implies a simple shear component at the scale of the lithosphere. These parameters include an original heterogeneity of the crust and lithosphere (tectonic heritage), lateral density gradients and contribution of the underlying asthenospheric flow through basal drag or basal push. We discuss the relations between the observed asymmetry and the direction and sense of the mantle flow underneath. The chosen examples suggest that two main mechanisms can explain the observed asymmetry: (1) shearing parallel to the Moho in the necking zone during rifting and (2) viscous coupling of asthenospheric flow and crustal deformation in back-arc basins and above plumes. Slipping along pre-existing heterogeneities seems a second-order phenomenon at lithospheric or crustal scale.

The formation and evolution of a backarc basin are linked to the dynamics of the subduction system. The opening of the central Mediterranean basins is a well-documented example of backarc extension characterized by short-lived episodes of spreading. The underlying reasons for this episodicity are obscured by the complexity of this subduction system, in which multiple continental blocks enter the subduction zone. We present results from three-dimensional numerical models of laterally varying subduction to explain the mechanism of backarc basin opening and the episodic style of spreading. Our results show that efficient backarc extension can be obtained with an along-trench variation in slab buoyancy that produces localized deformation within the overriding plate. We observe peaks in the trench retreating velocity corresponding first to the opening of the backarc basin, and later to the formation of slab windows. We suggest that the observed episodic trench retreat behavior in the central Mediterranean is caused by the formation of slab windows.

Previous AFT, ZFT, AHe and ZHe data used in this study

Supplementary text

Table S3 (Dated Fish Canyon Tuff zircons) and S4 (Dated Durango apatites).

Table S5: Age2edot inversion of previous and new thermochronologic ages

International audience; 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.

We present new crust and lithosphere thickness maps of the African mainland based on integrated modeling of elevation and geoid data and thermal analysis. The approach assumes local isostasy, thermal steady state, and linear density increase with depth in the crust and temperature-dependent density in the lithospheric mantle. Results are constrained by a new comprehensive compilation of seismic Moho depth data consisting of 551 data points and by published tomography models relative to LAB depth. The crustal thickness map shows a N-S bimodal distribution with higher thickness values in the cratonic domains of southern Africa (38–44 km) relative to those beneath northern Africa (33–39 km). The most striking result is the crustal thinning (28–30 km thickness) imaged along the Mesozoic West and Central African Rift Systems. Our crustal model shows noticeable differences compared to previous models. After excluding the Afar plume region, where the modeling assumptions are not fulfilled, our model better fits the available seismic data (76.3% fitting; root mean square error = 4.3 km). The LAB depth map shows large spatial variability (90 to 230 km), with deeper LAB related to cratonic domains and shallower LAB related to Mesozoic and Cenozoic rifting domains, in agreement with tomography models. Though crustal and lithosphere thickness maps show similar regional patterns, major differences are found in the Atlas Mountains, the West African Rift System, and the intracratonic basins. The effects of lateral variations in crustal density as well as the nonisostatic contribution to elevation in the Afar plume region, which we estimate to be ~1.8 km, are also discussed., The project and the author J. Globig were funded by the European Commission grant Marie Curie Actions (264517-TOPOMOD-FP7-PEOPLE-2010-ITN).

The evolution of the Gibraltar Arc and the whole western Mediterranean region is still highly debated by geologists and geophysicists. This work is based on a recent geodynamic model proposing a lateral change in subduction polarity of the Ligurian Tethys oceanic domain to explain its formation and evolution since 46 Myr. The aim of this study is to reproduce and analyze the curvature evolution of the Rif-Gibraltar-Betic slab in such tectonic scenario by means of numerical modelling. The 3D numerical model is carried out via the Underworld framework that solves the Stokes flow equations using Finite Elements combined with a particle-in-cell approach, thus the discretization combines a standard Eulerian Finite Element mesh with Lagrangian particles. The model setup consists of two oceanic plates with a visco-plastic rheology subducting into the viscous upper mantle in opposite directions. In the present-day Alboran Basin region, the plate dips to the southeast with the trailing edge fixed to the Iberian margin, whereas in the present Algerian Basin region the plate dips to the northwest and the trailing edge is fixed to the African margin. To initiate subduction a small slab perturbation is initially imposed. In addition, we include a continental African plate segment west of the present Alboran Basin region, with different shear strength values. We study the influence of the lateral side plates on the trench curvature and the geodynamic consequences in terms of trench velocities, stress distribution, mantle flow, and plate deformation produced by the proximity between the opposite retreating slabs., This work is part of the projects ALPIMED (PIE-CSIC-201530E082) and MITE (CGL2014-59516-P). We also thank to the project AECT-2017-3-0008 of the Barcelona Supercomputing center (BSC-CNS).

Subduction trench curvature is generally attributed to the Earth's sphericity. Although, observed trench curvature in Nature are usually larger than those imposed by Earth radius. Other factors potentially influencing curvature are the mantle flow (produced by some other geodynamic process), internal heterogeneities in the subducting plate (e.g. variations in plate age and consequently in its thickness), the presence of crustal features (e.g. seamounts or plateaus), the orientation of the main plate structures (parallel/perpendicular to the trench) and the geometry of the upper plate. The role of a weak lithosphere on a lateral side perpendicular to the strike of the retreating subduction, e.g. continent/transfer zones, is unexplored. We study the influence of this boundary condition in a retreating subduction setting by varying its kinematic nature using analog modelling. A continental block is considered in one side of the plate, and the kinematic nature of the contact with the oceanic plate is varied considering: 1) fully attached, 2) half attached, and 3) completely free. To first order, lateral boundary perpendicular to the trench introduces an asymmetry in the trench curvature. The magnitude of this asymmetry is proportional to the resistance of the transfer zone. This kinematic resistance slows down the subduction of the oceanic plate near the contact and enhances the subduction in the free lateral side, thus affecting the retreat velocities along the trench. This work has implications for present and geologic past subduction zones where asymmetric trench and laterally varying retreat velocities have been observed/postulated. This is a SUBITOP (674899-SUBITOP-H2020-MSCA-ITN-2015) contribution., This is a SUBITOP (674899-SUBITOP-H2020-MSCA-ITN-2015) contribution.

In this study we present the results of numerical and analogue experiments of a double subduction system characterized by two adjacent slabs retreating in opposite directions. Such a tectonic scenario has been proposed to occur in several regions of the Earth, most recently in the Westernmost Mediterranean. The basic setup consists of two oceanic plates with a linear viscous rheology descending into the upper mantle. Both plates are fixed at their trailing edge to enforce roll-back behavior during subduction driven by a Rayleigh-Taylor instability. The two retreating plates interact with each other as a result of subduction-induced mantle counter-flow. Previous laboratory experiments, based on viscous syrup (representing the mantle) and silicone putty (representing the plates), show that the mantle flow induced by both plates is asymmetrical producing variations of rollback velocities and lateral separation between plates. Additionally, a high-resolution finite difference 3D numerical model (I3ELVIS code) is carried out with the identical material parameters and geometry as for the analogue model. The combination of both experiments allows us to numerically quantify the physical parameters that characterize the evolution of the system such as trench velocities, strain rates, and stresses. We also study how boundary conditions and scaling for analogue modelling may affect the numerical results., This work is part of the projects ALPIMED (PIE-CSIC-201530E082) and MITE (CGL2014-59516-P). We also thank to the project AECT-2017-3-0008 of the Barcelona Supercomputing center (BSC-CNS).

Opposite subduction retreating in adjacent plate segments has been proposed in several regions of the Earth and particularly in the Westernmost Mediterranean (Verg´es et al., 2012; Casciello et al., 2015). Recent numerical experiments show a strong interaction between the induced mantle flows of each retreating plate (Kir´aly et al., 2016). In this work we show the result of a series of analogue models based on viscous syrup (representing the mantle) and silicone putty (representing the subducting plate), which have been designed to simulate the evolution of a double subduction system. The basic setup contains a pair of plates subducting in opposite directions. The plates are fixed at their trailing edge to enforce slab rollback behaviour and subduction is started by deflecting manually the leading edge of the plate (i.e., initial slab pull, phase 1). Different setups were designed to test the influence of two variables on the system: i) the width of the plates, that varies from 10 cm to 30 cm (1 cm in model corresponds to 60 km in nature) and ii) the lateral distance between the two subducting plates, that varies from 10 to 0.5 cm. Our results show that trench velocities increase during the stage of approaching trenches (phase 2) and then decrease after trenches pass each other (phase 3). On the other hand, the trench curvature increases linearly during the entire evolution whereas the lateral distance increases along time, indicating that effective lateral stresses are produced associates with the asymmetry of toroidal flows. This behaviour indicates a strong interaction between the stresses produced by the two retreating slabs that propagate through the mantle flow, which in turn depends on the initial plate separation.

International audience; In passive margins or back-arc regions, extensional deformation is often asymmetric, i.e. normal faults or extensional ductile shear zones dip in the same direction over large distances. We examine a number of geological examples in convergent or divergent contexts suggesting that this asymmetry results from a coupling between asthenospheric flow and crustal deformation. This is the case of the Mediterranean back-arc basins, such as the Aegean Sea, the northern Tyrrhenian Sea, the Alboran domain or the Gulf of Lion passive margin. Similar types of observation can be made on some of the Atlantic volcanic passive margins and the Afar region, which were all formed above a mantle plume. We discuss these contexts and search for the main controlling parameters for this asymmetric distributed deformation that imply a simple shear component at the scale of the lithosphere. The different geodynamic settings and tectonic histories of these different examples provide natural case-studies of the different controlling parameters, including a pre-existing heterogeneity of the crust and lithosphere (tectonic heritage) and the possible contribution of the underlying asthenospheric flow through basal drag or basal push. We show that mantle flow can induce deformation in the overlying crust in case of high heat flow and thin lithosphere. In back-arc regions, the cause of asymmetry resides in the relative motion between the asthenosphere below the overriding plate and the crust. When convergence and slab retreat work concurrently the asthenosphere flows faster than the crust toward the trench and the sense of shear is toward the upper plate. When slab retreat is the only cause of subduction, the sense of shear is opposite. In both cases, mantle flow is mostly the consequence of slab retreat and convergence. Mantle flow can however result also from larger-scale convection, controlling rifting dynamics prior to the formation of oceanic crust. In volcanic passive margins, in most cases normal faults dip toward the continent. This asymmetry may either result from the mantle flowing underneath regions evolving above a migrating plume, such as the Afar, when an asymmetry is observed at the scale of the rift, or from necking of the lithosphere when the conjugate margins show an opposite asymmetry. We summarize the various observed situations with normal faults dipping toward the continent ("hot" margins) or toward the ocean ("cold" margins) and discuss whether mantle flow is responsible for the observed asymmetry of deformation or not. Slipping along pre-existing heterogeneities seems a second-order phenomenon at lithospheric or crustal scale, except at the initiation of rifting.

Recent works documented Neogene to Quaternary dextral strike-slip tectonics along the Kuh-e-Sarhangi and Kuh-e-Faghan intraplate strike-slip faults at the northern edge of the Lut Block of Central Iran, previously thought to be dominated by sinistral strike-slip deformation. This work focuses on the evidence of Quaternary activity of one of these fault systems, in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario. Through geomorphological and structural investigation, integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces (at ~53, ~25, and ~6 ka), this study documents (i) the topographic inheritance of the long-term (Myr) punctuated history of fault nucleation, propagation, and exhumation along the northern edge of Lut Block; (ii) the tectonic control on drainage network evolution, pediment formation, fluvial terraces, and alluvial fan architecture; (iii) the minimum Holocene age of Quaternary dextral strike-slip faulting; and (iv) the evidence of Late Quaternary fault-related uplift localized along the different fault strands. The documented spatial and temporal constraints on the active dextral strike-slip tectonics at the northern edge of Lut Block provide new insights on the kinematic model for active faulting in Central Iran, which has been reinterpreted in an escape tectonic scenario.

The goal of this work is to understand the dynamics of a subduction system characterized by two adjacent subducting plates with opposite retreating directions as recently proposed for the Westernmost Mediterranean. A series of analogue models based on viscous syrup (representing the mantle) and silicone putty (representing the subducting plate) have been designed to simulate the evolution of a double subduction system. The basic setup contains a pair of plates subducting in opposite directions. The plates are fixed at their back edge to enforce a slab rollback behavior and subduction is started by deflecting manually the leading edge of the plate (i.e. initial slab pull, phase 1). Different setups were designed to test the influence of two variables on the system: i) the width of the plates, that varies from 10 cm to 30 cm (1 cm in model corresponds to 60 km in nature) and ii) the lateral distance between the two subducting plates, that varies from 10 to 0.5 cm. Our results show that trench velocities increase during the stage of approaching trenches (phase 2) and then decrease after trenches pass each other (phase 3). This behavior indicates an interaction of the mantle flows produced by the two retreating slabs. On the other hand, the trench curvature increases linearly during the entire evolution and the lateral distance between plates remains constant along time, indicating that no effective lateral stress is produced when the opposing plates have similar dimensions. In addition, we have reproduced numerically some of the laboratory experiments., This work is part of the projects WE-ME (PIE-CSIC-201330E111) and MITE (CGL2014-59516-P). We also thank to the project AECT-2016-1-0002 of the Barcelona Supercomputing center (BSC-CNS).

International audience; The Menderes Massif (Western Turkey) is a Tertiary continental metamorphic core complexexhumed in the upper Oligocene – Miocene time, during the deposition of a series of E-Wtrending basins. Several studies addressed the exhumation history of the massif, but the depositionalhistory of these basins is still poorly defined. Moreover, the full potential of supradetachmentbasins in recording major tectonic events is often unexploited. In this work, weuse the Gediz Graben supradetachment basin as a case study to illustrate the benefits of acomprehensive approach to detrital fission track dating that combines analysis of modern riversediments, analysis of fossil sedimentary successions, and mineral fertility determinations. Thisapproach allowed us i) to reconstruct the modern short-term erosion pattern, ii) to constrainthe long-term exhumation history of the margins of the basin highlighting relevant alongstrikevariations and deciphering the spatial relevance of the main exhumation events, iii) toidentify major exhumation event recorded in the sedimentary sequence of the basin and iv)to constrain the maximum age for the onset of sedimentation in the basin and for the mainsedimentary units. Here we illustrate how to reconcile our detrital apatite fission track datasetwith field evidences in order to build a coherent 4D model for the evolution of this supradetachmentbasin, which is eventually discussed within the framework of the Cenozoic evolutionof the Menderes Massif

National audience; The Menderes Massif of Western Turkey in an outstandingexample of Tertiary continental metamorphic core complex exhumedduring upper Oligocene – Miocene times; its exhumationwas accompanied by the development of a series of continentalE-W trending basins. Several studies addressed the exhumationhistory of the massif, but the relative relevance of the identified exhumationevents and the depositional history of these basins is stillpoorly defined. In this study, we focused our investigations on theGediz Graben supradetachment basin, which has been used as acase history to illustrate the benefits of a comprehensive approachto detrital apatite fission track dating that combines analysis ofmodern river sediments, analysis of fossil sedimentary successions,and mineral fertility determinations. This approach allowed us (i)to constrain the maximum age for the beginning of sedimentationin the basin, after providing that post depositional annealing wasnegligible, (ii) to identify major exhumation events recorded in theNeogene-to-Quaternary sedimentary fill of the basin, (iii) to reconstructthe exhumation history of bedrock unit at the footwall andat the hanging wall of the Gediz detachment, and (iv) to reconstructthe modern short-term erosion pattern of the study area.Three main exhumation events with different spatial relevancehave been identified in the area, related to the main exhumationof the Menderes Massif, to a major structural reorganization inthe basin resulting in the exhumation of the margins of the CentralMenderes Massif, and to a localized event related to the finalexhumation of the Gediz detachment and its intrusive footwall.Our results, integrated with field evidences, allowed us to proposea coherent 4D reconstruction for the evolution of the GedizGraben. The implications of the proposed model for the Cenozoicevolution of the Menderes Massif and for the Aegean extensionalregion more in general are eventually discussed.

We report the paleomagnetic and magnetic fabric results of 58 sites from Cretaceous-Miocene marine and continental strata from the Eastern Cordillera (EC) and the Cucuta zone, at the junction between the Santander Massif and the Merida Andes of Colombia. The EC is an intracontinental doubly vergent range inverting a Triassic to Early Cretaceous rift zone. Twenty-three sites reveal nonsystematic tectonic rotations, including unrotated areas of the EC range with respect to stable South America. Our data show that the EC inverted a NNE oriented rift zone and that the orientation of the Mesozoic rift and the mountain chain roughly correspond. Interestingly, magnetic lineations from anisotropy of magnetic susceptibility analysis do not trend parallel to the chain but rather are oblique to the main orogenic trend. By also considering GPS evidence of a ~1 cm/yr ENE displacement of central western Colombia accommodated by the EC, we suggest that the Miocene-Recent deformation event of this belt arises from ENE oblique convergence reactivating a NNE oriented rift zone. Oblique shortening was likely partitioned into pure dip-slip shear characterizing thick-skinned frontal thrust sheets (well known along both chain fronts) and by range-parallel right-lateral strike-slip faults, which have not been identified yet, but likely exist in the axial part of the EC. Finally, the 35° ± 9° clockwise rotation observed in four post-Miocene magnetically overprinted sites from the Cucuta zone reflects late Cenozoic and ongoing right-lateral strike-slip displacement occurring along faults parallel to the Boconó fault system, possibly connected with the right-lateral faults inferred to exist along the axial part of the EC.

[1] We use 2.5 to 14 years long position time series from >800 continuous Global Positioning System (GPS) stations to study vertical deformation rates in the Euro-Mediterranean region. We estimate and remove common mode errors in position time series using a principal component analysis, obtaining a significant gain in the signal-to-noise ratio of the displacements data. Following the results of a maximum likelihood estimation analysis, which gives a mean spectral index ~ −0.7, we adopt a power law + white noise stochastic model in estimating the final vertical rates and find 95% of the velocities within ±2 mm/yr, with uncertainties from filtered time series ~40% smaller than from the unfiltered ones. We highlight the presence of statistically significant velocity gradients where the stations density is higher. We find undulations of the vertical velocity field at different spatial scales both in tectonically active regions, like eastern Alps, Apennines, and eastern Mediterranean, and in regions characterized by a low or negligible tectonic activity, like central Iberia and western Alps. A correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area. Glacial isostatic adjustment and weathering processes do not completely explain the measured rates, and a combination of active tectonics and deep-seated geodynamic processes must be invoked. Excluding areas where localized processes are likely, or where subduction processes may be active, mantle dynamics is the most likely process, but regional mantle modeling is required for a better understanding.

Integrating seismic reflection profiles, well logs, and field evidence with GPS velocities from a network installed in Calabria, southern Italy, we have discovered that the Crotone basin is gliding toward the Ionian Sea over a buried viscous salt layer. This previously unknown megaslide (~1000 km2) is characterized by an onshore updip extensional domain and an offshore downdip toe-thrust rim. The GPS velocity from the Crotone station is significantly higher than velocities from other stations in the region and differently oriented. We ascribe at least part of the anomalous GPS velocity from the Crotone station to the seaward motion of the megaslide or part of it. From the GPS velocity and other evidence, we obtain a viscosity of the buried salt layer within the known range of rock salt viscosity in nature.

International audience; Mountain building at convergent margins requires tectonic forces that can overcome frictional resistance along large-scale thrust faults and support the gravitational potential energy stored within the thickened crust of the orogen. A general, dynamic model for this process is still lacking. Here we propose that mountain belts can be classified between two end-members. First, those of "slab pull" type, where subduction is mainly confined to the upper mantle, and rollback trench motion lead to moderately thick crustal stacks, such as in the Mediterranean. Second, those of "slab suction" type, where whole-mantle convection cells ("conveyor belts") lead to the more extreme expressions of orogeny, such as the largely thickened crust and high plateaus of present-day Tibet and the Altiplano. For the slab suction type, deep mantle convection produces the unique conditions to drag plates toward each other, irrespective of their nature and other boundary conditions. We support this hypothesis by analyzing the orogenic, volcanic, and convective history associated with the Tertiary formation of the Andes after ~40 Ma and Himalayas after collision at ~55 Ma. Based on mantle circulation modeling and tectonic reconstructions, we surmise that the forces necessary to sustain slab-suction mountain building in those orogens derive, after transient slab ponding, from the mantle drag induced upon slab penetration into the lower mantle, and from an associated surge of mantle upwelling beneath Africa. This process started at ~65-55 Ma for Tibet-Himalaya, when the Tethyan slab penetrated into the lower mantle, and ~10 Myr later in the Andes, when the Nazca slab did. This surge of mantle convection drags plates against each other, generating the necessary compressional forces to create and sustain these two orogenic belts. If our model is correct, the available geological records of orogeny can be used to decipher time-dependent mantle convection, with implications for the supercontinental cycle.

""Data constraining the paleoenvironmental conditions during the Messinian evaporative drawdown of the. Mediterranean basin are still conflicting. Here we present a comprehensive paleoclimatic reconstruction. during Messinian halite deposition from several Italian sites. We performed fluid inclusion analyses to define. better both the composition of the Mediterranean water body and the paleotemperatures of the Messinian. brine during halite crystallization. We measured homogenization temperatures on 218 primary all-liquid fluid. inclusions in Messinian halite from the Volterra, Crotone, and Caltanissetta evaporite basins. These. measurements provided mean homogenization temperatures of 17–18C, with a range between 10–11C and. 28–29C, which should be close to the SST of the Mediterranean Sea during halite deposition. The occurrence. of major elements such as Cl, Na, Mg, S, Ca, and K within the halite fluid inclusions, together with the. presence of minerals such as pentahydrite, polyhalite, and Ca-, K-, and Mg-sulfates, indicates that these salt. bodies originated from mainly marine water. Taking into account both the present-day annual SST of the. Mediterranean Sea around the sampling sites, which ranges between 18 and 20C, and the lower latitude of. the Mediterranean Basin during the Messinian Salinity Crisis, our homogenization temperatures point to a. colder climate during the Messinian halite deposition compared to the present interglacial climate stage. This. conclusion is consistent with halite deposition during a Late Miocene glacial interval (TG12).""

We analyze the role of slab pull acting on the Pacific plate during its early Tertiary change in motion. Slab pull forces are estimated by integrating the negative buoyancy of a 700 km long slab along a revised subduction boundary model adopting the Muller et al. (2008) seafloor age reconstructions. Our results indicate that torques predicted from a simple slab pull model match the Pacific plate Euler vectors during the Tertiary fairly well. The change of the Pacific motion at similar to 50-40 Ma appears to be driven by the onset of the Izu-Bonin-Mariana system and, soon afterwards, by the Tonga-Kermadec subduction zones. Citation: Faccenna, C., T. W. Becker, S. Lallemand, and B. Steinberger (2012), On the role of slab pull in the Cenozoic motion of the Pacific plate, Geophys. Res. Lett., 39, L03305, doi: 10.1029/2011GL050155. RI Becker, Thorsten/A-6665-2010

""At oceanic margins, syn-convergent exhumation, subduction erosion, and inter-plate coupling are intimately related, but ample questions remain concerning their interaction and individual mechanisms. To analyze these interactions for a thick-skinned, visco-elastic wedge, we focus on properly modeling stresses, energies, and topographies at the inter-plate and wedge bounding interfaces using a Coulomb frictional contact algorithm. In this innovative plane-strain, free surface, Lagrangian finite element model, fault dynamics is modulated by retreating subduction. Subduction is dynamically driven by slab-pull due to a slab sinking in a semi-analytic, computationally favorable approximation of three-dimensional induced mantle flow. Nodal trajectories show that continuous underthrusting of a slab induces a steady state corner flow through forced underplating and subsequent trenchward extrusion due to gravitational spreading. This flow pattern confirms early-proposed models of syn-orogenic deep-seated rock exhumation propelled by coexisting extension and continuous shortening at depth. A distinct reduction in upward flowing material and accompanying decrease of exhumation velocities, to millimeters per year as observed in nature, is induced by a diversion of orogenic wedge material toward the mantle once a subduction channel is formed. The key parameter affecting model evolution and spontaneous formation of a subduction channel is basal friction, which modulates the amount of erosion. However, formation of a subduction channel entrance needs to be ensured through the deformability of the overriding plate, which is influenced by applied pressure at the overriding plate tip and material properties. The down dragging of the overriding plate is sufficient above a threshold inter-plate shear stress of about 2–7 MPa. ""

One of the major issues of the evolution of continental lithospheres is the detachment of the lithospheric mantle that may occur under certain conditions and its impact on the surface. In order to investigate the dynamics of continental delamination, we performed a parametric study using physically scaled laboratory models. The adopted setup is composed of a three-layers visco-elastic body (analog for upper crust, lower crust, lithospheric mantle) locally thickened/thinned to simulate a density anomaly (lithospheric root) and an adjacent weak zone, lying on a low viscosity material simulating the asthenosphere. The results emphasize the interplay between mantle flow, deformation, surface topography and plate motion during a three-phases process: (1) a slow initiation phase controlled by coupling and bending associated with contraction and dynamic subsidence, (2) lateral propagation of the delamination alongside with extension and a complex topographic signal controlled by coupling and buoyancy, while poloidal mantle flow develops around the tip of the delaminating lithospheric mantle, and (3) a late phase characterized by a counterflow that triggers retroward motion of the whole model. A semiquantitative study allows us to determine empirically two parameters: (1) an initiation parameter that constrains the propensity of the delamination to occur and correlates with the duration of the first stage, (2) a buoyancy parameter characterizing the delamination velocity during late stages and therefore its propensity to cease. Finally, we point out similarities and differences with the Sierra Nevada (California, USA) in terms of topography, deformation and timing of delamination.

Absolute plate motion models with respect to a deep mantle reference frame (e.g., hot spots) typically contain some net rotation (NR) of the lithosphere. Global mantle flow models for the present-day plate setting reproduce similarly oriented NRs but with amplitudes significantly smaller than those found in some high NR Pacific hot spot reference frames. It is therefore important to understand the mechanisms of NR excitation, which we attempt here with two-dimensional cylindrical models of an idealized Pacific domain. We study the influence of slab properties, oceanic ridge position, continental keels, and a weak asthenospheric layer on NR and trench migration. Fast slab return flow develops in models with stiff slabs and moderate slab dips. Rapid NRs, comparable to the high NR Pacific hot spot reference frames, are primarily induced by asymmetric slab dips, in particular a shallow slab beneath South America and a steep slab in the western Pacific. A scaling relationship links the amplitude of NR to plate size, slab dip angle, and slab viscosity. Asymmetric ridge positions also promote NR through asymmetric plate sizes. Continental keels have less impact, in contrast to what has been found in earlier global studies. Several models yield unidirectional Pacific trench motions, such as slab advance in the western Pacific and, simultaneously, slab retreat in the eastern Pacific. Our model provides a physical explanation for NR generation in the present-day Pacific setting and hints at mechanisms for the temporal evolution of the basin. RI Becker, Thorsten/A-6665-2010; Moresi, Louis/H-1390-2011

""High-energy seismicity is historically recorded in Tripolitania, Libya suggesting that. this area, far from Mediterranean convergent margin, is currently deforming. How this deformation. relates to surrounding tectonics of the Africa-Europe convergence is still poorly known. Here, we. use remote sensing image analysis and structural survey to show the recent deformation history that. affected Tripolitania and reactivated the western bordering structures of Sirte Basin. This tectonic. regime onset long after the Paleocene–Oligocene deformation correlated to the Hellenic subduction. evolution (Libyan tectonics have been quiescent since then) and is compatible with age and. trends of the Sicily Channel rift zone, a deformational belt that developed across the Maghrebian. chain. We show that the continuity of this belt reaches farther than that previously acknowledged,. as far as c. 1400 km from the collisional front. We speculate on the causes of deformation in this. remote area, suggesting that the extensional belt formed in response to the strong slab-pull gradients. at the central Mediterranean subduction margin which followed the progressive closure of the. oceanic basin.""

We describe the origin and evolution of a travertine deposit located 20 km east of Rome (Italy), near Tivoli. Borehole analysis reveals that the Tivoli travertine body was deposited in a 20-km2 basin, has an average thickness of 50 m and is thicker (more than 80 m) along a steeper base along the west north–south striking side. Structural analysis reveals that this north–south Q1 oriented margin is controlled by dextral strike–slip faults and associated N20–408E oblique and normal faults and joint system that serve as a preferential pathway for hydrothermal circulation, linked to mixing between a shallow fresh water table and deeper circuit. The age of the travertine was calculated by means of U-series disequilibrium, with the beginning and end of the deposition dated at c. 120 and 30 ka, respectively. Five unconformities within the travertine sequence may be linked to erosional episodes related to fluid discharge and low sea level. We conclude that the growth of the Roman thermogene travertine, and therefore the upwelling of hydrothermal fluid along the fault zone, was favoured by a warm and humid climate.

Recent geodetic data are compatible with NNE– SSW tectonic extension at a rate of ∼5 mm/yr in Sicily, southern Italy, within a broader region of net active compression along the Nubian plate margin (northern Africa). The structures that accommodate such extensional regime and its cause are still unknown. From field structural surveys and seismological analyses, the geometry, kinematics, structural architecture, and seismic potential of an extensional seismic zone linking Cefalù and Mount Etna in central eastern Sicily are defined. The zone includes high‐angle WNW striking normal and right‐lateral strike‐slip faults and subordinate north and NNE striking strike‐slip faults either right or left lateral. The occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage. The ongoing seismic activity possibly reactivates preexisting faults. Instrumentally and historically recorded earthquakes are lower than about 6 in magnitude, and destructive events are historically unknown since at least 1300 A.D. This apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms, which all together suggest a value between 6 and 6.5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area. Lateral extension on preexisting faults and upwelling of melt mantle material beneath Mount Etna are considered viable processes to explain, at least in part, the active extensional tectonics along the Cefalù‐Etna seismic zone. Strike‐slip seismic faulting beneath Mount Etna may be part of a previously proposed diffuse transfer zone affecting northeastern Sicily and including the Tindari Fault.