Continuous GPS and broad-scale deformation across the Rhine Graben and the Alps

In order to study the ongoing tectonic deformation in the Rhine Graben area, we reconstruct the local crustal velocity and the strain rate field from GPS array solutions. Following the aim of this work, we compile the velocities of permanent GPS stations belonging to various networks (EUREF, AGNES, REGAL and RGP) in central western Europe. Moreover, the strain rate field is displayed in terms of principal axes and values, while the normal and the shear components of the strain tensor are calculated perpendicular and parallel to the strike of major faults. The results are compared with the fault plane solutions of earthquakes, which have occurred in this area. A broad-scale kinematic deformation model across the Rhine Graben is provided on the basis of tectonics and velocity results of the GPS permanent stations. The area of study is divided into four rigid blocks, between which there might be relative motions. The velocity and the strain rate fields are reconstructed along their borders, by estimating a uniform rotation for each block. The tectonic behaviour is well represented by the four-block model in the Rhine Graben area, while a more detailed model will be needed for a better reconstruction of the strain field in the Alpine regio

Glacial isostatic uplift of the European Alps

Following the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth's viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions

Mantle Flow and Deforming Continents: From India-Asia Convergence to Pacific Subduction

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

Coupled surface to deep Earth processes: Perspectives from TOPO-EUROPE with an emphasis on climate- and energy-related societal challenges

Understanding the interactions between surface and deep Earth processes is important for research in many diverse scientific areas including climate, environment, energy, georesources and biosphere. The TOPO-EUROPE initiative of the International Lithosphere Program serves as a pan-European platform for integrated surface and deep Earth sciences, synergizing observational studies of the Earth structure and fluxes on all spatial and temporal scales with modelling of Earth processes. This review provides a survey of scientific developments in our quantitative understanding of coupled surface-deep Earth processes achieved through TOPO-EUROPE. The most notable innovations include (1) a process-based understanding of the connection of upper mantle dynamics and absolute plate motion frames; (2) integrated models for sediment source-to-sink dynamics, demonstrating the importance of mass transfer from mountains to basins and from basin to basin; (3) demonstration of the key role of polyphase evolution of sedimentary basins, the impact of pre-rift and pre-orogenic structures, and the evolution of subsequent lithosphere and landscape dynamics; (4) improved conceptual understanding of the temporal evolution from back-arc extension to tectonic inversion and onset of subduction; (5) models to explain the integrated strength of Europe's lithosphere; (6) concepts governing the interplay between thermal upper mantle processes and stress-induced intraplate deformation; (7) constraints on the record of vertical motions from high-resolution data sets obtained from geo-thermochronology for Europe's topographic evolution; (8) recognition and quantifications of the forcing by erosional and/or glacial-interglacial surface mass transfer on the regional magmatism, with major implications for our understanding of the carbon cycle on geological timescales and the emerging field of biogeodynamics; and (9) the transfer of insights obtained on the coupling of deep Earth and surface processes to the domain of geothermal energy exploration. Concerning the future research agenda of TOPO-EUROPE, we also discuss the rich potential for further advances, multidisciplinary research and community building across many scientific frontiers, including research on the biosphere, climate and energy. These will focus on obtaining a better insight into the initiation and evolution of subduction systems, the role of mantle plumes in continental rifting and (super)continent break-up, and the deformation and tectonic reactivation of cratons; the interaction between geodynamic, surface and climate processes, such as interactions between glaciation, sea level change and deep Earth processes; the sensitivity, tipping points, and spatio-temporal evolution of the interactions between climate and tectonics as well as the role of rock melting and outgassing in affecting such interactions; the emerging field of biogeodynamics, that is the impact of coupled deep Earth – surface processes on the evolution of life on Earth; and tightening the connection between societal challenges regarding renewable georesources, climate change, natural geohazards, and novel process-understanding of the Earth system

Tectonic evolution of the Congo Basin using geophysical data and 3D numerical simulations

The Congo basin (CB) is an intracratonic basin that occupies a large part of the Congo Craton (1.2 million km2) covering approximately 10% of the continent [1]. It contains up to 9 km of sedimentary rocks from the Mesoproterozoic until Cenozoic age. The formation of the CB started with a rifting phase during Mesoproterozoic with the amalgamation of the Rodinia supercontinent (1.2 Gyr). Afterwards, the main episodes of subsidence occurred during the subsequent Neoproterozoic post-rift phases, which were followed by phases of compression at the end of the Permian and during the Early Jurassic age and other sedimentation episodes during Upper Cretaceous and Cenozoic [2]. We reconstruct the stratigraphy and tectonic evolution of the basin by analyzing seismic reflection profiles. Furthermore, we estimated the velocity, density, and thickness of the sedimentary layers in order to calculate their gravity effect. Afterwards, we calculate the gravity disturbance and Bouguer anomalies using a combined satellite and terrestrial data gravity model. The gravity disturbance obtained from the EIGEN-6C4 gravity model [3] shows two types of anomalies. One with a long wavelength (~50 mGal) that covers the entire area of the Congo basin and a second one with a short wavelength (~130 mGal), having a NW-SE trend, which corresponds to the main depocenters of sediments detected by the interpretation of seismic reflection profiles. These results have been used as input parameters for 3D numerical simulations to test the main mechanisms of formation and evolution of the CB. For this aim, we used the thermomechanical I3ELVIS code [4] to simulate the initial rift phase. The numerical tests have been conducted considering a sub-circular weak zone in the central part of the cratonic lithosphere [2] and applying a velocity of 2.5 cm/yr in two orthogonal directions (NS and EW), to test the hypothesis of the formation of a multi extensional rift in a cratonic area. We repeated these numerical tests by increasing the size of the weak zone and varying its lithospheric thickness. The results of these first numerical experiments show the formation of a circular basin in the central part of the cratonic lithosphere, in response to extensional stress, inducing the uplift of the asthenosphere. [1] Kadima, et al. (2011), Structure and geological history of the Congo Basin: an integrated interpretation of gravity, magnetic and reflection seismic data, doi:10.1111/j.1365-2117.2011.00500.x. [2] De Wit, et al. (2008), Restoring Pan-African-Brasiliano connections: more Gondwana control, less Trans-Atlantic corruption, doi:10.1144/SP294.20 [3] F\uf6rste et al. (2014) EIGEN-6C4 The latest combined global gravity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and GRGS Toulouse; doi: 10.5880/ICGEM.2015.1, 2014 [4] Gerya (2009), Introduction to numerical geodynamic modelling, Cambridge University Pres

Contrasts of seismic velocity, density and strength across the Moho

We provide an overviewof contrast of elastomechanical parameters across the Moho, basically contrasts in seismicwave velocities, density and yield strength. These can be regarded as dynamic and quasi-static endmembers of elastomechanical parameters of the crust\u2013mantle transition. With respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models. We address both average global Moho models and petrophysical and structural factors that cause deviations from the global averages, such as variations in Moho depth, temperature and rock composition, fabric (anisotropy) and macro-scale heterogeneity. Besides principle considerations these factors are put in a regional context in order to demonstrate howthey are related to past and present tectonic processes. Seismic velocity and density contrasts are found between 0 and 25% whereas strength or viscosity contrastsmay be orders of magnitude higher, but may vanish as well or showa discontinuity of higher order only. Especially, oceanic and old cratonic crust and near-Mohomantlemay appear as a rheological unit although they are seismically well distinguishable. In terms of seismic velocities the Moho may \u201cvanish\u201d mainly under the influence of serpentinization or eclogitization. Originally defined as a first-order discontinuity in seismic velocity, the Moho has turned out to be an interface across which other seismic properties, such as seismic velocity gradients, anisotropy and heterogeneity scale parameters, can change strongly, too. However, knowledge of these parameters, as well as their relation to the rheology of the crust\u2013mantle transition, is still restricted to local or regional examples so no global conclusions can be drawn

NACr14: A 3D model for the crustal structure of the North American Continent

Based on the large number of crustal seismic experiments carried out in the last decadeswe create NACr14, a 3D crustal model of the North American continent at a resolution of 1° × 1°. We present maps of thickness and average velocities of the main layers that comprise the North American crystalline crust, obtained from the most recent seismic crustalmodelswithin the USGS crustal structure database. However, the crustal data are unevenly distributed and in some cases discrepancies exist between published models. In order to construct a consistent 3D crustal model with three layers in the crystalline crust, we refrained from a direct interpolation of the crustal seismic parameters in the database. Instead, weimplemented the following sequence of steps: 1. Definition of the geometry of the main tectonic provinces of North America; 2. Selection and evaluation of the reliability of seismic crustal models in the database; 3. Estimation of the P-wave seismic velocity and thickness of the upper, middle and lower crust for each tectonic province; 4. Estimation of the interpolated Pn velocity distribution. The resulting average velocity of the crystalline crust ismostly consistent with that of the seismic points. The main variations of the structure of the crystalline crust of North America displayed in the model can be related to its tectonic evolution. The model, available in a digital form, can be used in various geophysical applications, such as the correction for the crustal effects in gravity and seismic tomography and models of dynamic topography, in order to detect heterogeneities characterizing the underlying upper mantl

Revisiting the geodynamics of the Middle East region from an integrated geophysical perspective

21 pages, 12 figures, supplementary material https://doi.org/10.1016/j.jog.2023.102005.-- Data Availability: All data can bedowloaded freely or requested to the authors (it is a synthesis paper) and the link to the tomography model is specified in the manuscriptA long-standing question in geodynamics is whether mantle flow is driven by the plate motion alone, or mantle upwelling makes a significant contribution to it. Subducting slabs and lateral variations of the continental lithosphere can further influence the asthenospheric flow and control its direction. The Middle East region (MER) is a complex continental setting where different processes such as rifting, break-up, plate collision, and tectonic escape kinematically interact with each other. In this context, the role that lithospheric structure, mantle flow, and active upwellings may play is debated. Tomographic images provide a snapshot of the current thermal conditions of a region and seismic anisotropy can also help resolve mantle convection. Here, we synthesize shear-wave splitting observations together with up-to-date tomography models of the mantle structure beneath the MER and other geophysical data. Low-velocity anomalies are seen at asthenospheric depths beneath W Arabia, NW Iran, and Anatolia, suggesting a spreading zone of warm mantle. Two deep low-velocity bodies in Afar and Levant –interpreted as hot mantle plumes– are the sources of this shallower mantle flow. Where low velocities are imaged, we observe predominantly NE–SW oriented anisotropy, anomalously high topography, and abundant basaltic volcanism. The integrated analysis suggests that a horizontal component associated with active upwelling is present in the upper-mantle flow field. The large-scale circulation flow fed by the Afar and Levant Plumes, aided by the subduction-induced forces, facilitates the lateral motion of the Anatolian microplate and affects the dynamic evolution of the Zagros orogen. The proposed scenario demonstrates that the interplay between plate-tectonic events and mantle dynamics controls the kinematics of the region and can explain the general patterns of deformation observed at the surfaceThis work was supported by the grant CEX2019-000928-S funded by AEI 10.13039/501100011033. C. C. acknowledges the Programma Per Giovani Ricercatori “Rita Levi Montalcini” (grant D86-RALMI23CIVIE_01 awarded by the Italian Ministry of University and Research). M. T. acknowledges funding from the Progress in Research of Interest (PRIN) project 2017: Intraplate deformation, magmatism andtopographic evolution of a diffuse collisional belt: Insights into the geodynamics of the Arabia-Eurasia collisional zones’Peer reviewe

Mantle flow and deforming continents, insights from the Tethys realm

International audienceContinent deformation is partly a consequence of plate motion along plate boundaries. Whether underlying asthenospheric flow can also deform continents through basal shear or push on topographic irregularities of the base of the lithosphere is an open question. Eurasia has been extending at different scales since 50 Ma, from the Mediterranean back-arc domains to extension of Asia between the India-Asia collision zone and the Pacific subduction zones. While compression at plate margins, in subduction or collision zones can propagate far within continents, the mechanism explaining extension distributed over thousands of kilometres is unclear. We use trajectories of continental plates and continental fragments since 50 Ma in different kinematic frames and compare them with various proxies of asthenospheric flow such as seismic anisotropy at various depths. These trajectories partly fit sub-lithospheric seismic anisotropy with two main circulations, one carrying Africa and Eurasia away from the large low velocity anomaly (LLSVP) underlying South and West Africa and one carrying the Pacific plate away from the LLSVP underlying the southern Pacific. Under eastern Eurasia the flow converges with the Pacific flow and distributed extension affects eastern Asia all the way to Western Pacific back-arc basins. We speculate that the flow carrying India northward and Eurasia eastward has invaded the Pacific domain and caused this widely distributed extension that interferes with the strike-slip faults issued from the Himalaya-Tibet collision zone. This model is in line with earlier propositions based on geochemical proxies. We discuss this model and compare it to other widely distributed extensional deformation episodes such as the Early Cretaceous extension of Africa and lastly propose a scheme of large-scale continental deformation in relation to underlying mantle convection at different scales

Density, temperature and composition of the North American lithosphere: new insights from a joint analysis of seismic, gravity and mineral physics data: 2. Thermal and compositional model of the upper mantle.

Temperature and compositional variations of the North American (NA) lithospheric mantle are estimated using a new inversion technique introduced in Part I, which allows us to jointly interpret seismic tomography and gravity data, taking into account depletion of the lithospheric mantle beneath the cratonic regions. The technique is tested using two tomography models (NA07 and SL2013sv) and different lithospheric density models. The first density model (Model I) reproduces the typical compositionally stratified lithospheric mantle, which is consistent with xenolith samples from the central Slave craton, while the second one (Model II) is based on the direct inversion of the residual gravity and residual topography. The results obtained, both in terms of temperature and composition, are more strongly influenced by the input models derived from seismic tomography, rather than by the choice of lithospheric density Model I versus Model II. The final temperatures estimated in the Archean lithospheric root are up to 150°C higher than in the initial thermal models obtained using a laterally and vertically uniform “fertile” compositional model and are in agreement with temperatures derived from xenolith data. Therefore, the effect of the compositional variations cannot be neglected when temperatures of the cratonic lithospheric mantle are estimated. Strong negative compositional density anomalies (92, characterize the lithospheric mantle of the northwestern part of the Superior craton and the central part of the Slave and Churchill craton, according to both tomographic models. The largest discrepancies between the results based on different tomography models are observed in the Proterozoic regions, such as the Trans Hudson Orogen (THO), Rocky Mountains, and Colorado Plateau, which appear weakly depleted (>−0.025 g/cm3 corresponding to Mg # ∼91) when model NA07 is used, or locally characterized by high-density bodies when model SL2013sv is used. The former results are in agreement with those based on the interpretation of xenolith data. The high-density bodies might be interpreted as fragments of subducted slabs or of the advection of the lithospheric mantle induced from the eastward-directed flat slab subduction. The selection of a seismic tomography model plays a significant role when estimating lithospheric density, temperature, and compositional heterogeneity. The consideration of the results of more than one model gives a more complete picture of the possible compositional variations within the NA lithospheric mantle