Lithospheric Model Research Articles

Inferences on the lithospheric structure of Campi Flegrei District (southern Italy) from seismic noise cross-correlation

Lithospheric VS models are defined in the Campi Flegrei District (southern Italy) through the non-linear inversion of the group velocity dispersion curves of fundamental-mode Rayleigh waves extracted from ambient noise cross-correlations between two receivers, and the regional group and phase velocities of the Italian cellular lithospheric model (1°×1°cells). Four paths are investigated, of which one (ISCHIA-MIS) across two adjoining cells.The distribution of VS shows a pyroclastic covering with VS increasing from 0.3–0.7km/s to 2.1km/s. It rests on a lava or carbonate basement, about 5–6km thick, with VS increasing from 2.1km/s to 3.1km/s at about 2km of depth and rising to ∼0.6km towards the island of Procida. A metamorphic layer is detected at an average depth of 7.7km with VS of 3.8–3.9km/s, about 5km thick, overlying a low velocity layer (VS of 3.5km/s) at about 11–12km of depth. The VS model along the ISCHIA-MIS path, as average of the models obtained by combining local and regional dispersion data of the two adjoining cells, is well consistent with the other paths. The Moho discontinuity is retrieved at about 23km of depth with VS of 4.2km/s.

Seismic evidence of the lithosphere-asthenosphere boundary beneath Izu-Bonin area

The lithosphere-asthenosphere boundary (LAB) is the seismic discontinuity with the negative velocity contrast in the upper mantle. The plate tectonic theory describes that the rigid lithosphere translate coherently over the ductile asthenosphere, and the LAB implies the decoupling between the two layers. The seismic velocity, viscosity, electrical resistivity and other physical parameters change with the depths across the boundary. The LAB has become a focus of seismology studies for its significance in understanding the plate motions, the mantle convection and the lithospheric evolution processes. Seismic detections on the LAB in subduction zone areas are helpful to understand the interactions between the lithosphere and asthenosphere layers and the geodynamic processes related with the slab subductions. For the dense permanent networks and transportable arrays of the USArray, the abundant waveforms of the deep earthquake events beneath the Izu-Bonin area can be recorded and retrieved. In this study, the vertical broadband waveforms are collected from three earthquake events occurring from 2002 to 2014 with the focal depths of 400–600 km. The source parameters are taken from the Preliminary Determinations of Epicenters catalog of US Geological Survey, and the focal fault solutions are taken from the global Centroid-Moment-Tensor project. The seismic waveforms are manually selected with two criteria: (1) simple sP arrivals with clear peaks, and (2) high signal-to-noise ratios and without abnormal spikes. In order to enhance the weak unknown precursors, the linear slant stack method, which is the special form of the N -th root slant stack method and phase-weighted stack method, is applied to scan the differential slowness and stack the seismograms in the domain of differential travel-time and differential slowness. The selected waveform data is processed to obtain the vespagrams and the stacked waveforms. The sP precursors reflected on the LAB ( s LAB P ), which have the opposite polarities with the amplitude ratios of 0.17–0.21 relative to the sP phases, are successfully extracted in our results. To reduce the possible effects of the crustal structures on the propagations of sP phases, the one-dimensional modified velocity model (IASP91-IB) is established by replacing the crust part of the IASP91 model with the CRUST1.0 model. On the basis of the modified model, we obtain the distributions for six reflected points of the s LAB P phases near the source area. Our results reveal that the LAB depths range between 58 and 65 km beneath the Izu-Bonin Arc, with the average depth of 62 km and the small topography of 7 km. Based on the half-space cooling model for the oceanic lithosphere, the lithosphere beneath the Izu-Bonin Arc is about located at the isotherm of 950°C, and the lithosphere beneath the West Philippine Basin (WPB) and Parece Vela Basin (PVB) is about located at the isotherm of 1100°C. Compared with the results of the tectonic stable areas (WPB and PVB) in the Philippine Sea, the lithosphere beneath the Izu-Bonin Arc shows the obvious thinning phenomenon. The numerical modeling experiments have revealed the strong erosions of the convecting asthenosphere in the mantle wedge, resulting in the destruction of the craton. We infer that the lithospheric thinning beneath the Izu-Bonin Arc is closely related with the partial melting, which is caused by the volatiles continuously released from the subducted western Pacific slab, and the strong erosions of the small-scale mantle convections in the back-arc mantle wedge.

Remnants of a Late Triassic ocean island in the Gufeng area, northern Tibet: Implications for the opening and early evolution of the Bangong–Nujiang Tethyan Ocean

In this paper we present new major and trace element compositions of basaltic rocks in the Gufeng ocean island (GFOI) area in the western segment of the Bangong–Nujiang Suture Zone, northern Tibet. Our aim was to assess the genesis of these rocks and discuss the implications of this new dataset for the evolution of the Bangong–Nujiang Tethyan Ocean. An ocean-island-type double-layer structure comprising a basaltic basement and an oceanic sedimentary cover sequence found within the GFOI provides direct evidence for the interpretation that the assemblage is a typical ocean island. The basalts in the GFOI can be divided into three types (named G1, G2 and G3 basalts), and these basalts range in composition from MORB to OIB types, which is typical of ocean islands. The G1 basalts have MORB-type affinities, possibly indicating the existence of MORB oceanic crust under the GFOI. The G2 basalts represent the early stage of formation of the GFOI, and are produced by the interaction of rising OIB-type basaltic magma and the existing MORB oceanic crust. The G3 basalts are typical OIB basalts and they are the products of the direct eruption of OIB-type basaltic magmas. The G3 basalts have high (La/Yb)N (12.3–14.4), (Ce/Yb)N (10.8–11.8), (La/Sm)N (2.39–2.76), and (Sm/Yb)N (4.89–5.23) ratios, indicating the presence of oceanic lithosphere below the GFOI with a thickness of 50–60km. Geochemical analyses of the GFOI cherts show that they contain terrigenous material, indicating the GFOI formed close to a continental margin. Norian conodont fossils within the GFOI limestones indicate the GFOI formed during the Late Triassic. These data, combined with geological evidence and a half-space model of lithosphere cooling, where the thickness of the oceanic lithosphere is determined from the age of the lithosphere, indicate that the western segment of the Bangong–Nujiang Tethyan Ocean opened initially in the late Permian, expanded rapidly during the Early–Middle Triassic, and was a mature ocean during the Late Triassic.

Descending lithosphere slab beneath the Northwest Dinarides from teleseismic tomography

The area of study covers the marginal zone between the Adriatic microplate (African plate) and the Pannonian segment (Eurasian plate). We present a tomography model for this area, with special emphasis on the northwest Dinarides. A dense distribution of temporary seismic stations in the area of the Northern Dinarides along with permanent seismic stations located in the area, allowed us to construct this P-wave tomographic model. We assembled our travel-time dataset based on 26 seismic stations were used to collect the dataset. Teleseismic events were recorded for a period of 18 months and a set of 76 distant earthquakes were used to calculate the P-wave travel-time residuals. We calculated relative rather than absolute arrival-time residuals in the inversion to obtain depths of 0–400km.We imaged a pronounced fast velocity anomaly below the NW Dinarides which directly indicates a lithosphere slab downgoing beneath the Dinarides. This fast anomaly extends towards the NW direction to at least 250km depth, and we interpreted it as a descending lithosphere slab. The thrusting of the Adriatic microplate may be brought about by sub-lithosphere rising movement beneath the Pannonian region, along with a push from African plate. In our interpretation, the Adriatic lower lithosphere has been detached from the crust, and steeply sinks beneath the Dinarides. A lithosphere model of the contact between the Adriatic microplate and Pannonian tectonic segment was constructed based on the tomographic velocity model and results of previous crustal studies.

Imaging the lithospheric structure beneath the Indian continent

AbstractWe present a high‐resolution 3‐D lithospheric model of the Indian plate region down to 300 km depth, obtained by inverting a new massive database of surface wave observations, using classical tomographic methods. Data are collected from more than 550 seismic broadband stations spanning the Indian subcontinent and surrounding regions. The Rayleigh wave dispersion measurements along ~14,000 paths are made in a broad frequency range (16–250 s). Our regionalized surface wave (group and phase) dispersion data are inverted at depth in two steps: first an isotropic inversion and next an anisotropic inversion of the phase velocity including the SV wave velocity and azimuthal anisotropy, based on the perturbation theory. We are able to recover most of the known geological structures in the region, such as the slow velocities associated with the thick crust in the Himalaya and Tibetan plateau and the fast velocities associated with the Indian Precambrian shield. Our estimates of the depth to the Lithosphere‐Asthenosphere boundary (LAB) derived from seismic velocity Vsv reductions at depth reveal large variations (120–250 km) beneath the different cratonic blocks. The lithospheric thickness is ~120 km in the eastern Dharwar, ~160 km in the western Dharwar, ~140–200 km in Bastar, and ~160–200 km in the Singhbhum Craton. The thickest (200–250 km) cratonic roots are present beneath central India. A low velocity layer associated with the midlithospheric discontinuity is present when the root of the lithosphere is deep.

Evidence for serpentinization of the Ionian upper mantle from simultaneous inversion of P- and S-wave arrival times

Simultaneous inversion of P- and S-wave arrival times, collected during a 3-years Ocean Bottom Seismometer with Hydrophone (OBS/H) monitoring campaign, yields 1D P- and S-wave velocity models for the Ionian lithosphere (Central Mediterranean). The 1D model highlights the presence, in the Ionian upper mantle, of two layers characterized by high seismic P-wave velocity (S1 and S2, 6.3–6.7 and 7.5km/s, respectively). These two layers, with thicknesses of about 3.3km and 5km, respectively, and ranging from ∼8 to ∼16km in depth, are characterized by low S-wave velocity (S1=3.05–3.2km/s, S2=3.85km/s) and high values of VP/VS (S1=2.06–2.09, S2=1.95). This is a characteristic feature, often encountered in passive margins and is generally interpreted as partly serpentinized peridotite. The VP, VS and VP/VS values of S1 are consistent with 55–65% of serpentinization of the upper mantle, while the S2 ones are consistent with 15–25% of serpentinization. This research provides a crucial hint about the debated nature of the Ionian crust, suggesting its oceanic structure.

Lithospheric deformation in the Africa‐Iberia plate boundary: Improved neotectonic modeling testing a basal‐driven Alboran plate

AbstractWe present an improved neotectonic numerical model of the complex NW Africa‐SW Eurasia plate boundary segment that runs from west to east along the Gloria Fault up to the northern Algerian margin. We model the surface velocity field and the ongoing lithospheric deformation using the most recent version of the thin‐shell code SHELLS and updated lithospheric model and fault map of the region. To check the presence versus the absence of an independently driven Alboran domain, we develop two alternative plate models: one does not include an Alboran plate; another includes it and determines the basal shear tractions necessary to drive it with known velocities. We also compare two alternative sets of Africa‐Eurasia velocity boundary conditions, corresponding to geodetic and geological‐scale averages of plate motion. Finally, we perform an extensive parametric study of fault friction coefficient, trench resistance, and velocities imposed in Alboran nodes. The final run comprises 5240 experiments, each scored to geodetic velocities (estimated for 250 stations and here provided), stress direction data, and seismic strain rates. The model with the least discrepancy to the data includes the Alboran plate driven by a basal WSW directed shear traction, slightly oblique to the westward direction of Alboran motion. We provide estimates of long‐term strain rates and slip rates for the modeled faults, which can be useful for further hazard studies. Our results support that a mechanism additional to the Africa‐Eurasia convergence is required to drive the Alboran domain, which can be related to subduction processes occurring within the mantle.

Flexure and gravity anomalies of the oceanic lithosphere beneath the Louisville seamount

We have calculated the elastic thickness (Te), flexural deflection, and gravity anomaly of the oceanic crust beneath the Louisville seamount (LSC-03), near the Kermadec trench. A regional-residual separation of the bathymetry was performed to remove the effect of other geologic features (e.g., the trench). We used the uniform density and dense core models to approximate the total mass of the seamount, which was defined as the surface load required for flexural deformation. From the flexure modeling results, we found that more flexural depression was predicted by the uniform density model than by the dense core model. However, the uniform density model predicted a significantly smaller gravity anomaly than observed, whereas the dense core model minimized the prediction misfits reasonably. The best flexure model was found with a Te of 16km for the uniform density model and 6km for the dense core model. The flexure computed with the dense core model was consistent with the seismically detected Moho. The flexure modeling for LSC-03, thus, indicates that the dense core model better approximates the inner structure of the LSC-03. Based on the crustal age and geochronology of the given seamount, the age of the oceanic crust at the time of seamount formation (Δt) is 20Ma. If this is the case, however, the Te estimates from both flexure models require some degree of lithospheric reheating by Louisville hotspot activity. Alternatively, considering the tectonic plate motion of the Osbourn Trough, Δt becomes approximately 4Ma. This younger lithosphere model is more consistent with the observed flexural deformation and the Te estimate from the dense core model. Therefore, the time that the seamount-induced lithospheric deformation occurred may be far earlier than the age-dated volcanism.

Utilizing thermal isostasy to estimate sub-lithospheric heat flow and anomalous crustal radioactivity

While surface heat flow relates to the heat loss through the lithosphere, it can be difficult to quantify and separate the heat produced internally through radiogenic decay from the heat transferred across the base of the lithosphere by mantle convection. In this study, we apply a thermo-isostatic analysis to Australia and estimate the sub-lithospheric and radiogenic heat flow components by employing a simple 1-D conservation of energy model. We estimate an anomalous radiogenic heat production across much of eastern Australia generally accounting for >50 mW m−2, while western Australia appears to have high crustal compositionally corrected elevation, possibly related to chemical buoyancy of the mantle lithosphere. A moderately high sub-lithospheric heat flow (∼40 mW m−2) along the eastern and southeastern coast, including Tasmania, is coincident with locations of Cenozoic volcanism and supports an edge-driven convection hypothesis. However, the pattern of sub-lithospheric heat flow along the margin does not support the existence of hotspot tracks. Thermo-isostatic models such as these improve our ability to identify and quantify crustal from mantle sources of heat loss and add valuable constraints on tectonic and geodynamic models of the continental lithosphere's physical state and evolution.

Macroscopic strength of oceanic lithosphere revealed by ubiquitous fracture-zone instabilities

The origin of plate tectonics is one of the most fundamental issues in earth and planetary sciences. Laboratory experiments indicate that the viscosity of silicate rocks is so strongly temperature-dependent that the entire surface of the Earth should be one immobile rigid plate. The rheology of oceanic lithosphere is, however, still poorly understood, and there exist few constraints on the temperature dependency of viscosity on the field scale. Here we report a new kind of observational constraint based on the geoid along oceanic fracture zones. We identify a large number of conspicuous small-scale geoid anomalies, which cannot be explained by the standard evolution model of oceanic lithosphere, and estimate their source density perturbations using a new Bayesian inversion method. Our results suggest that they are caused most likely by small-scale convection involving temperature perturbations of ∼300 K±100 K. Such thermal contrast requires the activation energy of mantle viscosity to be as low as 100±50 kJmol−1 in case of diffusion creep, and 225±112 kJmol−1 in case of dislocation creep, substantially reducing the thickness of the stiffest part of oceanic lithosphere. Oceanic lithosphere may thus be broken and bent much more easily than previously thought, facilitating the operation of plate tectonics.

Constraining lithosphere deformation modes during continental breakup for the Iberia–Newfoundland conjugate rifted margins

A kinematic model of lithosphere and asthenosphere deformation has been used to investigate lithosphere stretching and thinning modes during continental rifting leading to breakup and seafloor spreading. The model has been applied to two conjugate profiles across the Iberia–Newfoundland rifted margins and quantitatively calibrated using observed present-day water loaded subsidence and crustal thickness, together with observed mantle exhumation, subsidence and melting generation histories. The kinematic model uses an evolving prescribed flow-field to deform the lithosphere and asthenosphere leading to lithospheric breakup from which continental crustal thinning, lithosphere thermal evolution, decompression melt initiation and subsidence are predicted. We explore the sensitivity of model predictions to extension rate history, deformation migration and buoyancy induced upwelling. The best fit calibrated models of lithosphere deformation evolution for the Iberia–Newfoundland conjugate margins require; (1) an initial broad region of lithosphere deformation with passive upwelling, (2) lateral migration of deformation, (3) an increase in extension rate with time, (4) focussing of the deformation and (5) buoyancy induced upwelling. The model prediction of exhumed mantle at the Iberia–Newfoundland margins, as observed, requires a critical threshold of melting to be exceeded before melt extraction. The preferred calibrated models predict faster extension rates and earlier continental crustal separation and mantle exhumation for the Iberia Abyssal Plain–Flemish Pass conjugate margin profile than for the Galicia Bank–Flemish Cap profile to the north. The predicted N–S differences in the deformation evolution give insights into the 3D evolution of Iberia–Newfoundland margin crustal separation.

Lithospheric strength and elastic thickness of the Barents Sea and Kara Sea region

Interpretation of tomography data indicates that the Barents Sea region has an asymmetric lithospheric structure characterized by a thin and hot lithosphere in the west and a thick and cold lithosphere in the east. This suggests that the lithosphere is stronger in the east than in the west. This asymmetric lithosphere strength structure may have a strong control on the lithosphere response to tectonic and surface processes. In this paper, we present computed strength and effective elastic thickness maps of the lithosphere of the Barents Sea and Kara Sea region. Those are estimated using physical parameters from a 3D lithospheric model of the Barents Sea and Kara Sea region. The lithospheric strength is computed assuming a temperature-dependent ductile and brittle rheology for sediments, crust and mantle lithosphere. Results show that lithospheric strength and elastic thickness are mostly controlled by the lithosphere thickness. The model generally predicts much larger lithospheric strength and elastic thickness for the Proterozoic parts of the East Barents Sea and Kara Sea. Locally, the thickness and lithology of the continental crust disturb this general trend. At last, the gravitational potential energy (GPE) is computed. Our results show that the difference in GPE between the Barents Sea and the Mid-Atlantic Ridge provides a net horizontal force large enough to cause contraction in the western and central Barents Sea.

3D crustal and lithospheric model of the Arabia–Eurasia collision zone

Three-dimensional joined inversion of topography, gravity and geoid data was carried out in the collision zone between the Eurasian and Arabian plates, comprising Central and Eastern Anatolia, the Black Sea Basin and the Caucasus region. The 3D algorithm, first introduced by Motavalli-Anbaran et al. (2013), is based on a Bayesian approach with Gaussian density functions in which the targeted area is divided into vertical columns, each comprised of four layers namely water (of known thickness i.e. bathymetry) if present, crust, lithospheric mantle, and asthenosphere. The inversion results are Moho depth, average crustal density and depth to the lithosphere–asthenosphere boundary, defined here as the 1350°C isotherm. Existing seismic Moho depths were used as a priori information in order to constrain crustal thicknesses. Thickest crust (up to 50km) was found underneath the Great Caucasus Mountains, thinnest crust (22–25km) underneath the Black Sea Basin. The East-Anatolian plateau is underlain by relatively thick crust (up to 45km), thinning to less than 40km towards the Central Anatolian Plateau. Eastern Anatolia and the eastern part of Central Anatolia are underlain by strongly thinned lithosphere (up to 100km). Thickest lithosphere (up to 200km) underlies the Caspian Basin and the Russian Platform.

Visualizing the Structure of the Earth’s Lithosphere on the Google Earth Virtual-Globe Platform

While many of the current methods for representing the existing global lithospheric models are suitable for academic investigators to conduct professional geological and geophysical research, they are not suited to visualize and disseminate the lithospheric information to non-geological users (such as atmospheric scientists, educators, policy-makers, and even the general public) as they rely on dedicated computer programs or systems to read and work with the models. This shortcoming has become more obvious as more and more people from both academic and non-academic institutions struggle to understand the structure and composition of the Earth’s lithosphere. Google Earth and the concomitant Keyhole Markup Language (KML) provide a universal and user-friendly platform to represent, disseminate, and visualize the existing lithospheric models. We present a systematic framework to visualize and disseminate the structure of the Earth’s lithosphere on Google Earth. A KML generator is developed to convert lithospheric information derived from the global lithospheric model LITHO1.0 into KML-formatted models, and a web application is deployed to disseminate and visualize those models on the Internet. The presented framework and associated implementations can be easily exported for application to support interactively integrating and visualizing the internal structure of the Earth with a global perspective.

Propagated rifting in the Southwest Sub-basin, South China Sea: Insights from analogue modelling

How the South China Sea rifted has long been a puzzling question that is still debated, particularly with reference to the Southwest Sub-basin (SWSB). Analogue modelling remains one of the most useful tools for testing rift models and processes. Here, we present and discuss a series of analogue modelling experiments designed to investigate the rifting process of the SWSB. Convincing geophysical results were compiled to provide realistic constraints to test the experimental results and interpretations. A heterogeneous lithosphere model with a varied lithospheric structure showed tectono-morphological features similar to the natural case of the SWSB, indicating that the initial thermal condition and rheological stratification of the lithosphere should have a dominant effect on the rifting process of the SWSB. Rigid tectonic blocks existed in the continental margin, such as the Macclesfield Bank and the Reed Bank, and they played important roles in both the shaping of the continent–ocean boundary and the coupling between the crust and mantle. The initial thermal condition and rheological stratification of the lithosphere under the South China Sea controlled the propagated rifting process of the SWSB. Extension was centred on the deep troughs between the rigid blocks, and the break-up occurred in these areas between them. The westward rifting propagation is best explained with a heterogeneous lithosphere model characterized by varied lithospheric structure, and it was responsible for producing the V-shaped configuration of the SWSB.

Satellite gravity gradient grids for geophysics.

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth’s mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets.

Lithosphere model of the Pannonian–Adriatic overthrusting

A gravity model has been established at the contact of the southern part of the Pannonian basin and central Dinarides. Two-dimensional gravity modelling was carried out by means of the calibrated density set, defined at the Alp07 profile (Šumanovac, 2010), which significantly improved the resolution of the method. Gravity attraction caused by the structure in the upper mantle was analyzed in detail, which enabled construction of complete lithosphere model at the contact of the Dinarides, as a part of the Adriatic microplate, and the Pannonian basin as a segment of the Eurasian plate.Geophysical models demonstrate that overthrusting structures need to be considered in the present geological model; notably, the thrusting of the Adriatic microplate under the European plate. However, overthrusting processes cannot provide a complete explanation of the processes in the Pannonian basin. Considering that the Pannonian basin area is in fact a large geothermal anomaly, it is necessary to introduce the asthenosphere upwelling into the model. The presence of this structure is confirmed by a change in densities and seismic velocities in the uppermost mantle. This process has led to a significant thinning of the crust in the Tisia block and to the homogenization of properties as a result of the rising of the asthenosphere, and the crust can therefore be considered as a single layer. The combined effect of the push exerted by the African plate, and the rising of the asthenosphere and the thinning of the crust in the Pannonian basin caused the underthrusting of the Adriatic microplate below the Pannonian segment, thickening of the crust and steeply sinking of the Adriatic upper mantle below the Dinarides. Seismicity of the area and earthquake hypocenters enable the construction of active faults, which correlate well with the main faults at the surface and boundaries of density blocks in the crust.

Constraining a mafic thick crust model in the Andean Precordillera of the Pampean flat slab subduction region

Elastic properties in twelve representative rock samples from Central and Western Precordillera in the Andean backarc region of Argentina between 30 and 31°S were estimated from detailed petrological analysis. Thus, P and S seismic-wave velocities (Vp, Vs) as well as Poisson's ratio (σ) among other parameters were derived for gabbros, leuco-gabbros and wehrlites, in greenschist and amphibolite metamorphic conditions using a framework of a wide variety of empirical observations from active continental margins. In addition, Vs lithosphere models along two west–east cross sections were obtained using a joint inversion of teleseismic Rayleigh waves and receiver functions. These models clearly delineate the upper-plate crustal structure and the flat-slab subduction of the Nazca plate at about 100 km depth in this region. The suggested seismic velocity structure shows a relatively low (<3.3 km/s) Vs layer located in the first 15–18 km depth, then an increase of it from 3.3 to 4 km/s between 20 and 55 km depth with a mayor change at 40 km depth beneath the Precordillera showing an increase in Vs from 3.3 to 3.8 km/s. The Moho discontinuity was identified at around 65 km depth beneath the Precordillera (Vs = 4.3 km/s) and shows a low shear-wave velocity contrast in comparison with the upper continental mantle's parameters. Using this seismological model, Vs estimations derived from the petrological analyses for the 12 collected samples can be projected at depths greater than 30 km. These geophysical and petrological results agree with the hypothesis of a mafic thickened and partially eclogitized lower crust beneath the Precordillera, which has been predicted previously on a base of seismological studies only. Our petrological and seismological results collectively support a thick crustal model of a mafic–ultramafic composition extending to middle-to-lower crustal levels beneath Central and Western Precordillera; this region correlates with a suture zone between the eastern Cuyania terrane and the western Chilenia terrane.

OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures

Abstract. We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

Seismic cycle is controlled by stress and displacement loading between crust and mantle: the Lithospheric Feedback model

Seismic cycle is controlled by stress and displacement loading between crust and mantle: the Lithospheric Feedback model