Javier Fullea

FA2BOUG-A FORTRAN 90 code to compute Bouguer gravity anomalies from gridded free-air anomalies: Application to the Atlantic-Mediterranean transition zone

In this paper we present a computer program written in FORTRAN 90 specifically designed to determine the Bouguer anomaly from publicly available global gridded free-air anomaly and elevation database sets. FA2BOUG computes the complete Bouguer correction (i.e. Bullard A, B and C corrections) for both land and sea points in several spatial domains according to the distance between the topography and the calculation point. In each zone a different algorithm is used. In a distant zone we consider the harmonic spherical expansion of the potential of each right rectangular prism representing an elevation grid point. In an intermediate zone we compute the gravitational attraction produced by each prism using the analytic formula. Finally, an inner zone contribution is divided into two parts: a flat-topped prism with a height equal to the elevation of the calculation point, and four quadrants of a conic prism sloping continuously from each square of the inner zone to the calculation point. The program has been applied to the Atlantic-Mediterranean transition zone to obtain a complete Bouguer anomaly map of the area, integrating available onshore Bouguer anomaly with satellite-derived free-air anomaly data. Positive Bouguer anomalies are found in the Atlantic oceanic domain (240-300mGal), central and eastern Alboran Basin (40-160mGal) and SW Iberian Peninsula (>40mGal). Major negative Bouguer anomalies are located beneath the west Alboran Basin (<-40mGal), the Rif, the Rharb Basin and the Atlas Mountains (<-120mGal). An isostatic residual anomaly map of the study area has been computed and compared with the crustal and lithospheric structure inferred from previous work.

Lithospheric structure in the Baikal–central Mongolia region from integrated geophysical‐petrological inversion of surface‐wave data and topographic elevation

[1] Recent advances in computational petrological modeling provide accurate methods for computing seismic velocities and density within the lithospheric and sub-lithospheric mantle, given the bulk composition, temperature, and pressure within them. Here, we test an integrated geophysical-petrological inversion of Rayleigh- and Love-wave phase-velocity curves for fine-scale lithospheric structure. The main parameters of the grid-search inversion are the lithospheric and crustal thicknesses, mantle composition, and bulk density and seismic velocities within the crust. Conductive lithospheric geotherms are computed using P-T-dependent thermal conductivity. Radial anisotropy and seismic attenuation have a substantial effect on the results and are modeled explicitly. Surface topography provides information on the integrated density of the crust, poorly constrained by surface waves alone. Investigating parameter inter-dependencies, we show that accurate surface-wave data and topography can constrain robust lithospheric models. We apply the inversion to central Mongolia, south of the Baikal Rift Zone, a key area of deformation in Asia with debated lithosphere-asthenosphere structure and rifting mechanism, and detect an 80–90 km thick lithosphere with a dense, mafic lower crust and a relatively fertile mantle composition (Mg# < 90.2). Published measurements on crustal and mantle Miocene and Pleistocene xenoliths are consistent with both the geotherms and the crustal and lithospheric mantle composition derived from our inversion. Topography can be fully accounted for by local isostasy, with no dynamic support required. The mantle structure constrained by the inversion indicates no major thermal anomalies in the shallow sub-lithospheric mantle, consistent with passive rifting in the Baikal Rift Zone.

Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

We undertake a petrologically driven approach to jointly model magnetotelluric (MT) and seismic surface wave dispersion (SW) data from central Tibet, constrained by topographic height. The approach derives realistic temperature and pressure distributions within the upper mantle and characterizes mineral assemblages of given bulk chemical compositions as well as water content. This allows us to define a bulk geophysical model of the upper mantle based on laboratory and xenolith data for the most relevant mantle mineral assemblages and to derive corresponding predicted geophysical observables. One-dimensional deep resistivity models were derived for two groups of MT stations. One group, located in the Lhasa Terrane, shows the existence of an electrically conductive upper mantle layer and shallower conductive upper mantle layer for the other group, located in the Qiangtang Terrane. The subsequent one-dimensional integrated petrological-geophysical modeling suggests a lithosphere-asthenosphere boundary (LAB) at a depth of 80–120 km with a dry lithosphere for the Qiangtang Terrane. In contrast, for the Lhasa Terrane the LAB is located at about 180 km but the presence of a small amount of water in the lithospheric mantle (<0.02 wt%) is required to fit the longest period MT responses. Our results suggest two different lithospheric configurations beneath the southern and central Tibetan Plateau. The model for the Lhasa Terrane implies underthrusting of a moderately wet Indian plate. The model for the Qiangtang Terrane shows relatively thick and conductive crust and implies thin and dry Tibetan lithosphere.

3-D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western-Central U.S.

We apply a novel 3-D multiobservable probabilistic tomography method that we have recently developed and benchmarked, to directly image the thermochemical structure of the Colorado Plateau and surrounding areas by jointly inverting P wave and S wave teleseismic arrival times, Rayleigh wave dispersion data, Bouguer anomalies, satellite-derived gravity gradients, geoid height, absolute (local and dynamic) elevation, and surface heat flow data. The temperature and compositional structures recovered by our inversion reveal a high level of correlation between recent basaltic magmatism and zones of high temperature and low Mg# (i.e., refertilized mantle) in the lithosphere, consistent with independent geochemical data. However, the lithospheric mantle is overall characterized by a highly heterogeneous thermochemical structure, with only some features correlating well with either Proterozoic and/or Cenozoic crustal structures. This suggests that most of the present-day deep lithospheric architecture reflects the superposition of numerous geodynamic events of different scale and nature to those that created major crustal structures. This is consistent with the complex lithosphere-asthenosphere system that we image, which exhibits a variety of multiscale feedback mechanisms (e.g., small-scale convection, magmatic intrusion, delamination, etc.) driving surface processes. Our results also suggest that most of the present-day elevation in the Colorado Plateau and surrounding regions is the result of thermochemical buoyancy sources within the lithosphere, with dynamic effects (from sublithospheric mantle flow) contributing only locally up to ∼15–35%. ©2016. American Geophysical Union. All Rights Reserved.

Comment on “Deep resistivity cross section of the intraplate Atlas Mountains (NW Africa): New evidence of anomalous mantle and related Quaternary volcanism”

Citation: Jones, A. G., D. Kiyan, J. Fullea, J. Ledo, P. Queralt, A. Marcuello, A. Siniscalchi, and G. Romano (2012), Commenton “Deep resistivity cross section of the intraplate Atlas Mountains (NW Africa): New evidence of anomalous mantle and relatedQuaternary volcanism,” Tectonics, 31, TC5011, doi:10.1029/2011TC003051.

Geochemical and geophysical constrains on the dynamic topography of the Southern African Plateau

The deep mantle African Superswell is considered to contribute to the topographic uplift of the Southern African Plateau, but dynamic support estimates vary wildly depending on the approach and data used. One reason for these large disparities is that the role of lithospheric structure, key in modulating deep dynamic contributions to elevation, is commonly ignored or oversimplified in convection studies. We use multiple high-quality geophysical data coupled with xenolith-based geochemical constraints to compute the isostatic lithospheric contribution to the elevation of the Plateau, facilitating isolation of the current dynamic component from the total observed elevation. We employ a multi-observable stochastic algorithm to invert geoid anomaly, surface-wave dispersion data, magnetotelluric data and surface heat flow to predict elevation in a fully thermodynamically and internally-consistent manner. We find that a compositionally-layered 230 ±7 km thick lithosphere is required to simultaneously fit all four data types, in agreement with abundant independent xenolith evidence. Our stochastic modelling indicates a lithospheric contribution to elevation of the order of 670 m, which implies dynamic support arising from the convecting sub-lithospheric mantle of ∼650 m. Our results have important implications for the understanding of lithospheric-deep mantle feedback mechanisms and for calibrating dynamic topography estimates from global convection studies.

Lithospheric structure of Central Europe: Puzzle pieces from Pannonian Basin to Trans‐European Suture Zone resolved by geophysical‐petrological modeling

We have analyzed the thermochemical structure of the mantle in Central Europe, a complex area with a highly heterogeneous lithospheric structure reflecting the interplay of contraction, strike slip, subduction, and extension tectonics. Our modeling is based on an integrative 3-D approach (LitMod) that combines in a self-consistent manner concepts and data from thermodynamics, mineral physics, geochemistry, petrology, and solid Earth geophysics. This approach minimizes uncertainties of the estimates derived from modeling of various data sets separately. To further constrain our 3-D model we have made use of the vast geophysical and geological data (2-D and 3-D, shallow/crustal versus deep lithospheric experiments) based on experiments performed in Central Europe in the past decades. Given the amount and the different nature/resolution of the available constraints, one of the most challenging tasks of this study was to consistently combine them, finding a trade-off between all local and regional data sets available in a way that (i) preserves as many structural details as possible and (ii) summarizes those data sets into a single robust regional model. The resulting P/T-dependent mantle densities are in LitMod 3-D calculated based on a given mineralogical composition. They therefore provide more reliable estimates compared to pure gravity models, which enhance modeling of the crustal structures. Our results clearly indicate presence of several lithospheric domains characterized by distinct features, Pannonian Basin being one of the most outstanding ones. It has the thinnest crust and lithosphere in the area modeled, characterized by relatively fertile composition.

Hot Upper Mantle Beneath the Tristan da Cunha Hotspot From Probabilistic Rayleigh‐Wave Inversion and Petrological Modeling

Understanding the enigmatic intraplate volcanism in the Tristan da Cunha region requires knowledge of the temperature of the lithosphere and asthenosphere beneath it. We measured phasevelocity curves of Rayleigh waves using cross-correlation of teleseismic seismograms from an array of ocean-bottom seismometers around Tristan, constrained a region-average, shear-velocity structure, and inferred the temperature of the lithosphere and asthenosphere beneath the hotspot. The ocean-bottom data set presented some challenges, which required data-processing and measurement approaches different from those tuned for land-based arrays of stations. Having derived a robust, phase-velocity curve for the Tristan area, we inverted it for a shear wave velocity profile using a probabilistic (Markov chain Monte Carlo) approach. The model shows a pronounced low-velocity anomaly from 70 to at least 120 km depth. VS in the low velocity zone is 4.1–4.2 km/s, not as low as reported for Hawaii (�4.0 km/s), which probably indicates a less pronounced thermal anomaly and, possibly, less partial melting. Petrological modeling shows that the seismic and bathymetry data are consistent with a moderately hot mantle (mantle potential temperature of 1,410–1,4308C, an excess of about 50–1208C compared to the global average) and a melt fraction smaller than 1%. Both purely seismic inversions and petrological modeling indicate a lithospheric thickness of 65–70 km, consistent with recent estimates from receiver functions. The presence of warmer-than-average asthenosphere beneath Tristan is consistent with a hot upwelling (plume) from the deep mantle. However, the excess temperature we determine is smaller than that reported for some other major hotspots, in particular Hawaii.

Shear‐Wave Velocity Structure of Southern Africa's Lithosphere: Variations in the Thickness and Composition of Cratons and Their Effect on Topography

Seismic-wave velocities offer essential constraints on the temperature, thickness, and composition of the lithosphere of cratons. We invert broadband, Rayleigh-wave phase and Love-wave phase velocities measured across the Kaapvaal Craton and Limpopo Belt for depth distributions of shear-wave velocity and radial anisotropy, from the upper-crust down to deep upper mantle. Our probabilistic, Bayesian inversion addresses model nonuniqueness by means of direct parameter-space sampling. An increase in Vs between the Moho and 100–150 km depths occurs across the region and can be explained by the gradual emergence of garnet below 80 km, due to the spinel peridotite-garnet peridotite transformation and due to the exsolution of garnet from mantle orthopyroxene. Lateral variations in this Vs gradient can provide new information on lateral compositional variations. Cold cratonic lithosphere is manifest in very high shear velocities, up to 4.8 km/s. The depth extent of the shear-velocity anomaly and the inferred lithospheric thickness increase from 200 km beneath the central and southwestern Kaapvaal to 300 km beneath the Limpopo Belt. Curiously, surface elevation decreases monotonically with the increasing lithospheric thickness. The relationship between the lithospheric thickness and topography depends on the lithospheric composition and, with the crustal structure taken into account, our results imply that the bottom part of the Limpopo lithosphere (200–300 km) is weakly-to-moderately depleted (Mg# 89.7–90.8). Our results also show that the central-southwestern Kaapvaal lithosphere is thinner than it was (according to kimberlites) 100–200 m.y. ago. It may have been thinned by the same mantle plume that, initially, triggered the kimberlite eruptions. Plain Language Summary Cratons, the ancient cores of continents, have an unusually thick lithosphere (the tectonic plate beneath them). At least 200 km thick, it has a highly anomalous composition, making it less dense than the surrounding mantle. Cratonic lithosphere can thus be cooled to much lower temperatures than elsewhere. Variations in this delicate buoyancy balance probably give rise to variations in the surface elevation across the Earth’s stable continents. Lithospheric thickness and composition are key parameters, but both are notoriously difficult to determine. Here we use very accurate measurements of seismic surface-wave velocities and determine deep structure beneath cratons in southern Africa. We discover an unexpectedly strong, gradual thickening of the lithosphere from the central Kaapvaal Craton to the neighboring Limpopo Belt (from 200 to 300 km thick). Curiously, surface elevation decreases monotonically with increasing lithospheric thickness. This demonstrates the effect of the deep lithosphere on topography and gives us new information on the composition of the deepest parts of lithosphere.

Integrating gravity and surface elevation with magnetic data: mapping the Curie temperature beneath the British Isles and surrounding areas

In this work, we study the lithospheric structure of the British Isles using a methodology that allows for forward modelling of the Curie temperature depth based on seismic, elevation and gravity observations within an integrated geophysical-petrological approach (LitMod3D). We compute 3D thermal models and self-consistently determine the density in the mantle based on temperature, pressure and bulk composition. Finally, we derive Curie temperature depth maps and forward calculate magnetic anomalies at the airborne level using a spherical magnetic modelling software (magnetic tesseroids) to estimate the geothermal magnetic signal. Our results show lateral lithospheric variations across the model domain, with Great Britain being characterized in general by thicker and colder lithosphere, especially in the south-east, and the thinnest and warmest lithosphere being located beneath west Scotland, Northern Ireland and in the north-west oceanic area. Our estimated Curie temperature depth map resembles the values obtained using other techniques (spectral method and surface heat flow inversion) in some areas, but discrepancies are notable in general. We determine that the effect of typical lateral temperature variations (i.e., Curie isotherm depth) accounts for 5-15%, on average, and up to 70% locally of the crustal magnetic signal at the airborne level (5 km altitude). Our lithospheric models are in general agreement with published tomography models as well as other geophysical studies.