Regional crustal and lithospheric thickness model for Alaska, the Chukchi shelf, and the inner and outer bering shelves

SUMMARY This study presents for the first time an integrated image of the crust and lithospheric mantle of Alaska and its adjacent western shelves of the Chukchi and Bering seas based on joint modelling of potential field data constrained by thermal analysis and seismic data. We also perform 3-D forward modelling and inversion of Bouguer anomalies to analyse density heterogeneities at the crustal level. The obtained crustal model shows northwest-directed long wavelength thickening (32–36 km), with additional localized trends of thicker crust in the Brooks Range (40 km) and in the Alaska and St Elias ranges (50 km). Offshore, 28–30-km-thick crust is predicted near the Bearing slope break and 36–38 km in the northern Chukchi Shelf. In interior Alaska, the crustal thickness changes abruptly across the Denali fault, from 34–36 to the north to above 30 km to the south. This sharp crustal thickness gradient agrees with the presence of a crustal tectonic buttress guiding block motion west and south towards the subduction zone. The average crustal density is 2810 kg m−3. The denser crust, up to 2910 kg m−3, is found south of the Denali Fault likely related to the oceanic nature of the Wrangellia Composite Terrane rocks. Offshore, less dense crust (<2800 kg m−3) is found along the sedimentary basins of the Chukchi and Beaufort shelves. At LAB levels, there is a regional SE–NW trend that coincides with the current Pacific Plate motion, with a lithospheric root underneath the Brooks Range, Northern Slope, and Chuckchi Sea, that may correspond to a relic of the Chukotka-Artic Alaska microplate. The obtained lithospheric root (above 180 km) agrees with the presence of a boundary of cold, strong lithosphere that deflects the strain towards the South. South of the Denali Fault the LAB topography is quite complex. East of 150°W, below Wrangellia and the eastern side of Chugach terranes, the LAB is much shallower than it is west of this meridian. The NW trending limit separating thinner lithosphere in the east and thicker in the west agrees with the two-tiered slab shape of the subducting Pacific Plate.

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Scaling laws for stagnant-lid convection with a buoyant crust

Geophysical Journal International ◽

10.1093/gji/ggab366 ◽

2021 ◽

Vol 228 (1) ◽

pp. 631-663

Author(s):

Kyle Batra ◽

Bradford Foley

Keyword(s):

Heat Flux ◽

Scaling Laws ◽

Thermal Evolution ◽

Crustal Thickness ◽

Plate Motion ◽

Crustal Layer ◽

Lithospheric Thickness ◽

Thin Crust ◽

Mantle Temperature ◽

Thick Crust

SUMMARY Stagnant-lid convection, where subduction and surface plate motion is absent, is common among the rocky planets and moons in our solar system, and likely among rocky exoplanets as well. How stagnant-lid planets thermally evolve is an important issue, dictating not just their interior evolution but also the evolution of their atmospheres via volcanic degassing. On stagnant-lid planets, the crust is not recycled by subduction and can potentially grow thick enough to significantly impact convection beneath the stagnant lid. We perform numerical models of stagnant-lid convection to determine new scaling laws for convective heat flux that specifically account for the presence of a buoyant crustal layer. We systematically vary the crustal layer thickness, crustal layer density, Rayleigh number and Frank–Kamenetskii parameter for viscosity to map out system behaviour and determine the new scaling laws. We find two end-member regimes of behaviour: a ‘thin crust limit’, where convection is largely unaffected by the presence of the crust, and the thickness of the lithosphere is approximately the same as it would be if the crust were absent; and a ‘thick crust limit’, where the crustal thickness itself determines the lithospheric thickness and heat flux. Scaling laws for both limits are developed and fit the numerical model results well. Applying these scaling laws to rocky stagnant-lid planets, we find that the crustal thickness needed for convection to enter the thick crust limit decreases with increasing mantle temperature and decreasing mantle reference viscosity. Moreover, if crustal thickness is limited by the formation of dense eclogite, and foundering of this dense lower crust, then smaller planets are more likely to enter the thick crust limit because their crusts can grow thicker before reaching the pressure where eclogite forms. When convection is in the thick crust limit, mantle heat flux is suppressed. As a result, mantle temperatures can be elevated by 100 s of degrees K for up to a few Gyr in comparison to a planet with a thin crust. Whether convection enters the thick crust limit during a planet’s thermal evolution also depends on the initial mantle temperature, so a thick, buoyant crust additionally acts to preserve the influence of initial conditions on stagnant-lid planets for far longer than previous thermal evolution models, which ignore the effects of a thick crust, have found.

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3D geological modelling of the South Orkney Microcontinent (southern Scotia Arc, Antarctica) from seismic and potential field data

10.5194/egusphere-egu21-10699 ◽

2021 ◽

Author(s):

Cecilia Morales-Ocaña ◽

Fernando Bohoyo ◽

Carlota Escutia ◽

Carlos Marín-Lechado ◽

María Druet ◽

...

Keyword(s):

Drake Passage ◽

Sedimentary Basins ◽

Weddell Sea ◽

Magnetic Data ◽

The South ◽

Seismic Profiles ◽

Potential Field Data ◽

Continental Block ◽

Scotia Arc ◽

Free Air Gravity

The South Orkney Microcontinent (SOM) is located in the central sector of the South Scotia Arc, at the Weddell Sea northern edge. The SOM is the largest continental block in the southern Scotia Arc with a surface of more than 70.000 km2. Its current location is the result of the continental break-up from the Antarctic Peninsula related to the Powell Basin opening, considered one of the first steps in the formation of the Drake Passage during the Eocene-Oligocene.In this work we present a 3D geological model of the SOM built with Geomodeller&#174; using free-air gravity anomaly data from Topex and magnetic data from WDMAM. To obtain a reliable result, some constrains have been taken into account: (1) GEBCO data are used to establish the bathymetric level, (2) basement depth and geometry is calculated from multi-channel seismic profiles over the study area obtained from the Seismic Data Library System (SDLS), and (3) the analytic signal of total field magnetic anomalies has been used to limit the extension of the bodies that cause the PMA (Pacific Margin Anomaly).All these data, together with additional geological and geophysical interpretation, have allowed to build the 3D model. The characterization of the sedimentary basins shape, the deep crust structure and Moho geometry, the volume of the magnetic bodies and the nature and geometry of the SOM margins will provide a better understanding of the complex SOM structure resulting from different tectonic phases since the Mesozoic and related to the Scotia-Drake opening.The preliminary result shows a good fit between the observed and calculated gravimetric anomaly. We are currently working on the gravimetric inversion to obtain an optimal adjustment.

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Distribution and volume of rocks in sedimentary basins – unusual case of the South Caspian basin

Proceedings of OilGasScientificResearchProjects Institute SOCAR ◽

10.5510/ogp20200300439 ◽

2020 ◽

pp. 7-13

Author(s):

I.S. Guliyev ◽

◽

N.R. Abdullayev ◽

Sh.M. Huseynova ◽

◽

...

Keyword(s):

Unusual Case ◽

Sedimentary Cover ◽

Sedimentary Basins ◽

Caspian Basin ◽

The South ◽

South Caspian Basin ◽

Lithospheric Thickness ◽

The Earth ◽

Unique Nature ◽

Sedimentary Layer

The article gives a brief overview of the sedimentary cover of the Earth and summarizes volumes and mass of sediments contained in the Earth sedimentary layer (stratisphere). Using available data authors show unique nature of the South Caspian Basin and other rapidly subsiding basins with large amount of sediments and attenuated crust. Sedimentary, crustal and lithospheric thickness correlations are discussed.

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Constraining Basin Parameters Using a Known Subsidence History

Geosciences ◽

10.3390/geosciences10070263 ◽

2020 ◽

Vol 10 (7) ◽

pp. 263 ◽

Cited By ~ 2

Author(s):

Mohit Tunwal ◽

Kieran F. Mulchrone ◽

Patrick A. Meere

Keyword(s):

Thermal History ◽

Sedimentary Basins ◽

Crustal Thickness ◽

Temperature History ◽

Physical Parameters ◽

Lithospheric Thickness ◽

Campos Basin ◽

Subsidence History ◽

Stretching Factor ◽

Subsidence Curve

Temperature history is one of the most important factors driving subsidence and the overall tectono-stratigraphic evolution of a sedimentary basin. The McKenzie model has been widely applied for subsidence modelling and stretching factor estimation for sedimentary basins formed in an extensional tectonic environment. Subsidence modelling requires values of physical parameters (e.g., crustal thickness, lithospheric thickness, stretching factor) that may not always be available. With a given subsidence history of a basin estimated using a stratigraphic backstripping method, these parameters can be estimated by quantitatively comparing the known subsidence curve with modelled subsidence curves. In this contribution, a method to compare known and modelled subsidence curves is presented, aiming to constrain valid combinations of the stretching factor, crustal thickness, and lithospheric thickness of a basin. Furthermore, a numerical model is presented that takes into account the effect of sedimentary cover on thermal history and subsidence modelling of a basin. The parameter fitting method presented here is first applied to synthetically generated subsidence curves. Next, a case study using a known subsidence curve from the Campos Basin, offshore Brazil, is considered. The range of stretching factors estimated for the Campos basin from this study is in accordance with previous work, with an additional estimate of corresponding lithospheric thickness. This study provides insight into the dependence of thermal history and subsidence modelling methods on assumptions regarding model input parameters. This methodology also allows for the estimation of valid combinations of physical lithospheric parameters, where the subsidence history is known.

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Anomalous azimuthal variations with 360° periodicity of Rayleigh phase velocities observed in Scandinavia

Geophysical Journal International ◽

10.1093/gji/ggaa553 ◽

2020 ◽

Vol 224 (3) ◽

pp. 1684-1704

Author(s):

Alexandra Mauerberger ◽

Valérie Maupin ◽

Ólafur Gudmundsson ◽

Frederik Tilmann

Keyword(s):

Seismic Anisotropy ◽

Broad Band ◽

Shear Velocity ◽

Velocity Variation ◽

The South ◽

Study Region ◽

Lithospheric Thickness ◽

Phase Velocities ◽

The North ◽

Southern Norway

SUMMARY We use the recently deployed ScanArray network of broad-band stations covering most of Norway and Sweden as well as parts of Finland to analyse the propagation of Rayleigh waves in Scandinavia. Applying an array beamforming technique to teleseismic records from ScanArray and permanent stations in the study region, in total 159 stations with a typical station distance of about 70 km, we obtain phase velocities for three subregions, which collectively cover most of Scandinavia (excluding southern Norway). The average phase dispersion curves are similar for all three subregions. They resemble the dispersion previously observed for the South Baltic craton and are about 1 per cent slower than the North Baltic shield phase velocities for periods between 40 and 80 s. However, a remarkable sin(1θ) phase velocity variation with azimuth is observed for periods >35 s with a 5 per cent deviation between the maximum and minimum velocities, more than the overall lateral variation in average velocity. Such a variation, which is incompatible with seismic anisotropy, occurs in northern Scandinavia and southern Norway/Sweden but not in the central study area. The maximum and minimum velocities were measured for backazimuths of 120° and 300°, respectively. These directions are perpendicular to a step in the lithosphere–asthenosphere boundary (LAB) inferred by previous studies in southern Norway/Sweden, suggesting a relation to large lithospheric heterogeneity. In order to test this hypothesis, we carried out 2-D full-waveform modeling of Rayleigh wave propagation in synthetic models which incorporate a steep gradient in the LAB in combination with a pronounced reduction in the shear velocity below the LAB. This setup reproduces the observations qualitatively, and results in higher phase velocities for propagation in the direction of shallowing LAB, and lower ones for propagation in the direction of deepening LAB, probably due to the interference of forward scattered and reflected surface wave energy with the fundamental mode. Therefore, the reduction in lithospheric thickness towards southern Norway in the south, and towards the Atlantic ocean in the north provide a plausible explanation for the observed azimuthal variations.

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Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications

Marine Geophysical Research ◽

10.1007/s11001-013-9196-2 ◽

2013 ◽

Vol 35 (1) ◽

pp. 1-20 ◽

Cited By ~ 1

Author(s):

Neil C. Mitchell ◽

Nathalie Dubois

Keyword(s):

Pacific Plate ◽

Sediment Deposition ◽

Plate Motion

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The Congo basin: an example of failed rift

10.5194/egusphere-egu21-5950 ◽

2021 ◽

Author(s):

Francesca Maddaloni ◽

Damien Delvaux ◽

Magdala Tesauro ◽

Taras Gerya ◽

Carla Braitenberg

Keyword(s):

Congo Basin ◽

Gravity Inversion ◽

Inversion Method ◽

Formation Mechanisms ◽

Equatorial Position ◽

The South ◽

Weak Zone ◽

Lithospheric Thickness ◽

Numerical Tests ◽

History Of

The Congo basin (CB), considered as a typical intracratonic basin, due its slow and long-lived subsidence history and the largely unknown formation mechanisms, occupies a large part of the Congo craton, derived from the amalgamation of different cratonic pieces. It recorded the history of deposition of up to one billion years of sediments, one of the longest geological records on Earth above a metamorphic basement. The CB initiated very probably as a failed rift in late Mesoproterozoic and evolved during the Neoproterozoic and Phanerozoic under the influence of far-field compressional tectonic events, global climate fluctuation between icehouse and greenhouse conditions and drifting of Central Africa through the South Pole then towards its present-day equatorial position. Since Cretaceous, the CB has been subjected to an intraplate compressional setting due to ridge-push forces related to the spreading of the South Atlantic Ocean, where most of sediments are being eroded and accumulated only in the center of the basin.In this study, we first reconstructed the stratigraphy, the depths of the main seismic horizons, and the tectonic history of the CB, using geological and exploration geophysical data. In particular, we interpreted about 2600 km of seismic reflection profiles and well log data located inside the central area of the CB (Cuvette Centrale). We used the obtained results to constrain the gravity field data that we analyzed, in order to reconstruct the depth of the basement and investigate the shallow crustal structure of the basin. To this purpose, we used a gravity inversion method with two different density contrasts between the surface sediments and crystalline rocks.The results evidence NW-SE trending structures, also revealed by magnetic and seismic data, corresponding to the alternation of highs and sediments filled topographic depressions, related to rift structures, characterizing the first stage of evolution of the CB. They also show a general good consistency between the seismic and gravity basement along the seismic profiles and evidence the presence of possible high-density bodies in the shallow to deep crust. The identified structures are prevalently the product of an extensional tectonics, which likely acted in more than one direction.Therefore, we performed 3D numerical simulations to test the hypothesis of the formation of the CB as multi-extensional rift in a cratonic area, using the thermomechanical I3ELVIS code, based on a combination of a &#64257;nite di&#64256;erence method applied on a uniformly spaced Eulerian staggered grid with the marker-in-cell technique. To this purpose, the numerical tests have been conducted considering a sub-circular weak zone in the central part of the cratonic lithosphere and applying a velocity of 2.5 cm/yr in two orthogonal directions (N-S and E-W). We repeated these numerical tests by increasing the size of the weak zone and varying its lithospheric thickness. The results show the formation of a circular basin in the central part of the cratonic lithosphere, characterized by a series of highs and depressions, consistent with those obtained from geophysical/geological reconstructions.

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