Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)

This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300 km in the north-western limb of the Western Moroccan Meseta

Geofísica-SMART: Simples experiMentos de enseñanza apRendizaje en entoRnos digiTales

La Geofísica es una disciplina asociada a la Física experimental con gran desarrollo en multitud de ámbitos que van desde la arqueología a diferentes areas de la ingeniería como la geotécnia, ingeniería de minas o ingeniería geológica o bien el ámbito académico. Precisa de un conocimiento Físico de las leyes de la naturaleza pero también una destreza asociada a la Física más aplicada con multitud de experimentos en campo. Éstos son a veces difíciles de encontrar en libros de texto que se centran en los aspectos teóricos de la disciplina. Por eso, este proyecto pretende hacer ver a los estudiantes el diseño, desarrollo y procesado de experiencias de Geofísica Aplicada o prospectiva dentro de su desarrollo curricular

Development of numerical methods to determine the litospheic structure combining geopetential, litosthatic and heat transport equations. Application to the Gibraltar arc system.

Detailed modelling of the present-day lithospheric structure is of paramount importance to understand the evolution of the Earth in the context of plate tectonics. The objectives of this thesis are twofold: the development of numerical methods to determine the lithospheric structure combining geopotential, lithostatic and heat transport equations, and the application of these methods to the study area, the Gibraltar Arc System region (GAS). The final product should be a useful 3D tool to analyse the lithosphere integrating, in a consistent manner, the thermal field, elevation, geoid and gravity anomalies, and SHF. In this sense, four main goals are: 1) Development of a numerical code to compute Bouguer anomalies from publicly available satellite-derived free air data in both continental and marine areas. 2) Development of a 1D method to calculate a first order lithospheric structure using elevation and geoid anomaly as input data. 3) Development of a 3D interactive code to perform lithospheric forward modelling, integrating SHF, gravity and geoid anomalies, and elevation. 4) Obtain a 3D image of the lithosphere geometry over the study region independent from seismic tomography in order to improve our knowledge of the deep, present day, lithospheric structure of the GAS region, and discuss the different geodynamic models proposed to explain its origin. FA2BOUG is a FORTRAN 90 code to compute Bouguer anomaly specially intended to work with global elevation and free air data bases (Chapter 3). The program is designed to calculate in both continental and oceanic areas. Chapter 4 deals with a method based on the combination of elevation and geoid anomaly data that allows for a rapid calculation of the crustal and lithospheric thickness over large regions under the assumption of local isostasy, thermal steady state, linear vertical density gradient for the crust, and temperature dependent mantle density. Chapter 5 presents GEO3Dmod, a computer program intended to perform interactive 3D lithospheric forward modelling, integrating SHF, elevation, gravity anomaly and geoid anomaly. The program consists of two modules. The first one (GEO3Dmod) resolves the direct problem, i.e. given a lithospheric model (a set of layers with different properties), it calculates the 3D thermal and density structure of the lithosphere and the associated geophysical observables. The second one (GEO3Dmod_INTF) is a graphical interface designed to visualize and modify the lithospheric structure according to the differences between calculated and measured geophysical observables. To test the program, we used a number of synthetic models composed of crust, lithospheric mantle, sea water and asthenosphere. In Chapter 6 we applied GEO3Dmod to the Gibraltar Arc System region using as initial geometry of the Moho and the LAB the 1D model obtained using elevation and geoid anomaly (Chapter 4). The application of the model to the GAS region yields a crustal and lithospheric structure that coincides fairly well with previous works. The whole Atlas Mountains seem to be affected by lithospheric thinning (60-90 km), but this feature is more conspicuous in its southern part, the Anti Atlas Variscan domain, and to the north, in the Middle Atlas. The eastern branch of the Atlas does not seem to be much affected by this lithospheric thinning. The strongest LAB topography gradients are present in the northern, southern and eastern limits of the thick lithosphere imaged beneath the Gulf of Cadiz, the Betics and the Rif (170-210 km). These regions coincide with the contact between the Iberian Variscan Massif and the Betic chain in the north, the contact between the Middle Atlas and the external Rif domain to the south, and the contact between the Betic-Rif orogen and the Alboran Basin to the east. The rough topography of the LAB suggests that the mantle contribution to the isostatic balance is not negligible, as confirmed by the isostatic residual anomaly map calculated for the GAS region. The presence of the SW-NE oriented zone of lithospheric thinning affecting the High, Anti and Middle Atlas and extending to the eastern Alboran Basin, as well as the parallel thick lithosphere zone extending along the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz, put severe constraints on the proposed geodynamic models. Slab tear and asymmetric roll-back could be a plausible mechanism to explain the lithospheric thickening, whereas lateral asthenospheric flow would cause the lithosphere thinning. An alternative mechanism responsible for the lithospheric thinning could be the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe.

On joint modelling of electrical conductivity and other geophysical and petrological observables to infer the structure of the lithosphere and underlying upper mantle

El texto completo de este trabajo no se encuentra disponible por no haber sido facilitado aún por su autor, por restricciones de copyright, o por no existir una versión digitalThis review paper focuses on joint modelling and interpretation of electromagnetic data and other geophysical and petrological observables. In particular, integrated geophysical-petrological modelling approaches, where the electrical conductivity and other physical properties of rocks are required to be linked by the common subsurface thermochemical conditions within a self-consistent thermodynamic framework, are reviewed. The paper gives an overview of the main geophysical electromagnetic techniques/data sets employed in lithospheric and mantle imaging including recent advances using satellite data, and an up-to-date summary of the most relevant laboratory experiments regarding the electrical conductivity of upper mantle minerals for various temperature-pressure-water conditions. The sensitivity of electrical conductivity and other geophysical parameters (density, seismic velocities) of mantle rocks to changes in temperature and composition are presented based on a Monte Carlo method parameter exploration. Finally, a case study in Central Tibet is presented where both seismological (long-period surface wave phase velocities) and electromagnetic (magnetotelluric) data-simultaneously including the constraints offered by topography, surface heat flow and mantle xenoliths-have been integrated. The modelling is based on a self-consistent petrological-geophysical thermodynamic framework where mantle properties are calculated as a function of temperature, pressure, and composition. The Tibetan case study offers an excellent opportunity to illustrate the different and complementary sensitivities of the various data sets used and to show how integrated thermochemical models of the lithosphere can help understand settings with a complex tectonic evolution.Marie Curie ActionsScience Foundation IrelandDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu

Constraining the geotherm beneath the British Isles from Bayesian inversion of Curie depth: integrated modelling of magnetic, geothermal, and seismic data

Curie depth offers a valuable constraint on the thermal structure of the lithosphere, based on its interpretation as the depth to 580 degrees C, but current methods underestimate the range of uncertainty. We formulate the estimation of Curie depth within a Bayesian framework to quantify its uncertainty across the British Isles. Uncertainty increases exponentially with Curie depth but this can be moderated by increasing the size of the spatial window taken from the magnetic anomaly. The choice of window size needed to resolve the magnetic thickness is often ambiguous but, based on our chosen spectral method, we determine that significant gains in precision can be obtained with window sizes 15-30 times larger than the deepest magnetic source. Our Curie depth map of the British Isles includes a combination of window sizes: smaller windows are used where the magnetic base is shallow to resolve small-scale features, and larger window sizes are used where the magnetic base is deep in order to improve precision. On average, the Curie depth increases from Laurentian crust (22.2 +/- 5.3 km) to Avalonian crust (31.2 +/- 9.2 km). The temperature distribution in the crust, and associated uncertainty, was simulated from the ensemble of Curie depth realizations assigned to a lower thermal boundary condition of a crustal model (sedimentary thickness, Moho depth, heat production, thermal conductivity), constructed from various geophysical and geochemical datasets. The uncertainty in the simulated heat flow field substantially increases from +/- 10 mW m(-2) for shallow Curie depths at similar to 15 km to +/- 80 mW m(-2) for Curie depths > 40 km. Surface heat flow observations are concordant with the simulated heat flow field except in regions that contain igneous bodies. Heat flow data within large batholiths in the British Isles exceed the simulated heat flow by similar to 25 mW m(-2) as result of their high rates of heat production (4-6 mu W m(-3)). Conversely, heat refraction around thermally resistive mafic volcanics and thick sedimentary layers induce a negative heat flow misfit of a similar magnitude. A northward thinning of the lithosphere is supported by shallower Curie depths on the northern side of the Iapetus Suture, which separates Laurentian and Avalonian terranes. Cenozoic volcanism in Northern Britain and Ireland has previously been attributed to a lateral branch of the proto-Icelandic mantle plume. Our results show that high surface heat flow (> 90 mW m(-2)) and shallow Curie depth (similar to 15 km) occur within the same region, which supports the hypothesis that lithospheric thinning occurred due to the influence of a mantle plume. The fact that the uncertainty is only +/- 3-8 km in this region demonstrates that Curie depths are more reliable in hotter regions of the crust where the magnetic base is shallow.Irish Research Council for Science, Engineering and TechnologyH2020 Marie Sklodowska-Curie ActionsDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu

3-D thermochemical structure of lithospheric mantle beneath the Iranian plateau and surrounding areas from geophysical–petrological modelling

While the crustal structure across the Iranian plateau is fairly well constrained from controlled source and passive seismic data, the lithospheric mantle structure remains relatively poorly known, in particular in terms of lithology. Geodynamics rely on a robust image of the present-day thermochemical structure interpretations of the area. In this study, the 3-D crustal and upper mantle structure of the Iranian plateau is investigated, for the first time, through integrated geophysical-petrological modelling combining elevation, gravity and gravity gradient fields, seismic and petrological data. Our modelling approach allows us to simultaneously match complementary data sets with key mantle physical parameters (density and seismic velocities) being determined within a self-consistent thermodynamic framework. We first elaborate a new 3-D isostatically balanced crustal model constrained by available controlled source and passive seismic data, as well as complementary by gravity data. Next, we follow a progressively complex modelling strategy, starting from a laterally quasi chemically homogeneous model and then including structural, petrological and seismic tomography constraints. Distinct mantle compositions are tested in each of the tectonothermal terranes in our study region based on available local xenolith suites and global petrological data sets. Our preferred model matches the input geophysical observables (gravity field and elevation), includes local xenolith data, and qualitatively matches velocity anomalies from state of the art seismic tomography models. Beneath the Caspian and Oman seas (offshore areas) our model is defined by an average Phanerozoic fertile composition. The Arabian Plate and the Turan platform are characterized by a Proterozoic composition based on xenolith samples from eastern Arabia. In agreement with previous studies, our results also suggest a moderately refractory Proterozoic type composition in Zagros-Makran belt, extending to Alborz, Turan and Kopeh-Dagh terranes. In contrast, the mantle in our preferred model in Central Iran is defined by a fertile composition derived from a xenolith suite in northeast Iran. Our results indicate that the deepest Moho boundary is located beneath the high Zagros Mountains (similar to 65 km). The thinnest crust is found in the Oman Sea, Central Iran (Lut Block) and Talesh Mountains. A relatively deep Moho boundary is modelled in the Kopeh-Dagh Mountains, where Moho depth reaches to similar to 55 km. The lithosphere is similar to 280 km thick beneath the Persian Gulf (Arabian-Eurasian Plate boundary) and the Caspian Sea, thinning towards the Turan platform and the high Zagros. Beneath the Oman Sea, the base of the lithosphere is at similar to 150 km depth, rising to similar to 120 km beneath Central Iran, with the thinnest lithosphere (<100 km) being located beneath the northwest part of the Iranian plateau. We propose that the present-day lithosphere-asthenosphere topography is the result of the superposition of different geodynamic processes: (i) Arabia-Eurasia convergence lasting from mid Jurassic to recent and closure of Neo-Tethys ocean, (ii) reunification of Gondwanian fragments to form the Central Iran block and Iranian microcontinent, (iii) impingement of a small-scale convection and slab break-off beneath Central Iran commencing in the mid Eocene and (iv) refertilization of the lithospheric mantle beneath the Iranian microcontinent.Atraccion Talento senior fellowship - Comunidad Autonoma de Madrid (España)University of TehranChristian Albrechts University of KielDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu

WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data

We present a new global thermochemical model of the lithosphere and underlying upper mantle constrained by state of the art seismic waveform inversion, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data: WINTERC-G. The model is based upon an integrated geophysical–petrological approach where seismic velocities and density in the mantle are computed within a thermodynamically self-consistent framework, allowing for a direct parametrization in terms of the temperature and composition variables. The complementary sensitivities of the data sets allow us to constrain the geometry of the lithosphere–asthenosphere boundary, to separate thermal and compositional anomalies in the mantle, and to obtain a proxy for dynamic surface topography. At long spatial wavelengths, our model is generally consistent with previous seismic (or seismically derived) global models and earlier integrated studies incorporating surface wave data at lower lateral resolution. At finer scales, the temperature, composition and density distributions in WINTERC-G offer a new state of the art image at a high resolution globally (225 km average interknot spacing). Our model shows that the deepest lithosphere–asthenosphere boundary is associated with cratons and, also, some tectonically active areas (Andes, Persian Gulf). Among cratons we identify considerable differences in temperature and composition. The North American and Siberian Cratons are thick (&amp;gt;260 km) and compositionally refractory, whereas the Sino-Korean, Aldan and Tanzanian Cratons have a thinner, fertile lithosphere, similar to younger continental lithosphere elsewhere. WINTERC-G shows progressive thickening of oceanic lithosphere with age, but with significant regional differences: the lithospheric mantle beneath the Atlantic and Indian Oceans is, on average, colder, more fertile and denser than that beneath the Pacific Ocean. Our results suggest that the composition, temperature and density of the oceanic mantle lithosphere are related to the spreading rate for the rates up to 50–60 mm yr–1: the lower spreading rate, the higher the mantle fertility and density, and the lower the temperature. At greater spreading rates, the relationship disappears. The 1-D radial average of WINTERC-G displays a mantle geothermal gradient of 0.55–0.6 K km–1 and a potential temperature of 1300–1320 °C for depths &amp;gt;200 km. At the top of the mantle transition zone the amplitude of the maximum lateral temperature variations (cratons versus hotspots) is about 120 K. The isostatic residual topography values, a proxy for dynamic topography, are large (&amp;gt;1 km) mostly in active subduction settings. The residual isostatic bathymetry from WINTERC-G is remarkably similar to the pattern independently determined based on oceanic crustal data compilations. The amplitude of the continental residual topography is relatively large and positive (&amp;gt;600 m) in the East European Craton, Greenland, and the Andes and Himalayas. By contrast, central Asia, most of Antarctica, southern South America and, to a lesser extent, central Africa are characterized by negative residual topography values (&amp;gt;–400 m). Our results show that a substantial part of the topography signal previously identified as residual (or dynamic) is accounted for, isostatically, by lithospheric density variations.Atraccion de Talento senior fellowship - Comunidad Autonoma de Madrid (España)Agencia Espacial EuropeaScience Foundation IrelandGeological Survey of IrelandUnión Europea Horizonte 2020Marie Curie ActionsDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu

The lithosphere–asthenosphere system beneath Ireland from integrated geophysical–petrological modeling II: 3D thermal and compositional structure

El texto completo de este trabajo no se encuentra disponible por no haber sido facilitado aún por su autor, por restricciones de copyright, o por no existir una versión digitalThe lithosphere-asthenosphere boundary (LAB) depth represents a fundamental parameter in any quantitative lithospheric model, controlling to a large extent the temperature distribution within the crust and the uppermost mantle. The tectonic history of Ireland includes early Paleozoic closure of the Iapetus Ocean across the Iapetus Suture Zone (ISZ), and in northeastern Ireland late Paleozoic to early Mesozoic crustal extension, during which thick Permo-Triassic sedimentary successions were deposited, followed by early Cenozoic extrusion of large scale flood basalts. Although the crustal structure in Ireland and neighboring offshore areas is fairly well constrained, with the notable exception of the crust beneath Northern Ireland, the Irish uppermost mantle remains to date relatively unknown. In particular, the nature and extent of a hypothetical interaction between a putative proto Icelandic mantle plume and the Irish and Scottish lithosphere during the Tertiary opening of the North Atlantic has long been discussed in the literature with diverging conclusions. In this work, the present-day thermal and compositional structure of the lithosphere in Ireland is modeled based on a geophysical-petrological approach (LitMod3D) that combines comprehensively a large variety of data (namely elevation, surface heat flow, potential fields, xenoliths and seismic tomography models), reducing the inherent uncertainties and trade-offs associated with classical modeling of those individual data sets. The preferred 3D lithospheric models show moderate lateral density variations in Ireland characterized by a slightly thickened lithosphere along the SW-NE trending ISZ, and a progressive lithospheric thinning from southern Ireland towards the north. The mantle composition in the southern half of Ireland (East Avalonia) is relatively and uniformly fertile (i.e., typical Phanerozoic mantle), whereas the lithospheric composition in the northern half of Ireland (Laurentia) seems to vary from moderately depleted to fertile, in agreement with mantle xenoliths erupted in northwestern Ireland.JAE-DOC programme (CSIC-Spain)Ministerio de Economía y Competitividad (España)Science Foundation IrelandAustralian Research CouncilDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu

A rapid method to map the crustal and lithospheric thickness using elevation, geoid anomaly and thermal analysis. Application to the Gibraltar Arc System, Atlas Mountains and adjacent zones

We present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness. The main assumptions are local isostasy and a four-layered model composed of crust, lithospheric mantle, sea water and the asthenosphere. We consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle. We perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of RMS error of elevation and geoid anomaly databases. The application of this method to the Gibraltar Arc System, Atlas Mountains and adjacent zones reveals the presence of a lithospheric thinning zone, SW–NE oriented. This zone affects the High and Middle Atlas and extends from the Canary Islands to the eastern Alboran Basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz. A number of different, even mutually opposite, geodynamic models have been proposed to explain the origin and evolution of the study area. Our results suggest that a plausible slab-retreating model should incorporate tear and asymmetric roll-back of the subducting slab to fit the present-day observed lithosphere geometry. In this context, the lithospheric thinning would be caused by lateral asthenospheric flow. An alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe.Ministerio de Educación y Ciencia (España)Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu