The Geological Survey of Norway (NGU) has produced new aeromagnetic and gravity maps from Norway and adjacent areas, compiled from ground, airborne and satellite data. Petrophysical measurements on core samples, hand specimens and on in situ bedrock exposures are essential for the interpretation of these maps. Onshore, the most prominent gravity and magnetic anomalies are attributed to lower crustal rocks that have been brought closer to the surface. The asymmetry of the gravity anomalies along the Lapland Granulite Belt and Kongsberg–Bamble Complex, combined with the steep gradient, points to the overthrusted high-density granulites as being the main source of the observed anomalies. The Kongsberg–Bamble anomaly can be traced southwards through the Kattegat to southern Sweden. This concept of gravity field modelling can also be applied to the Mid-Norwegian continental shelf and could partially explain the observed high-density rocks occurring below the Møre and Vøring basins and in the Lofoten area. Extrapolations of Late-Caledonian detachment structures occurring on the mainland can be traced on aeromagnetic and gravimetric images towards the NW across the continental margin. Subcropping Late Palaeozoic to Cenozoic sedimentary units along the mid-Norwegian coast produce a conspicuous magnetic anomaly pattern. The asymmetry of the low-amplitude anomalies, with a steep gradient and a negative anomaly to the east and a gentler gradient to the west, relates the anomalies to gently westward dipping strata. Recent aeromagnetic surveys in the Barents Sea have revealed negative magnetic anomalies associated with shallow salt diapirs. Buried Quaternary channels partly filled with gravel and boulders of crystalline rocks generate magnetic anomalies in the North Sea. The new maps also show that the opening of the Norwegian–Greenland Sea occurred along stable continental margins without offsets across minor fracture zones, or involving jumps in the spreading axis. A triple junction formed at 48 Ma between the Lofoten and Norway Basins.

Eocene magmatic breakup along the mid‐Norway rifted margin was preceded by extreme Jurassic‐Cretaceous crustal thinning in a magma‐poor environment. Along the SE borders of the rift, “top basement” detachment faults with heaves on the order of 15–40 km evolved in at least two stages to become the boundaries between moderately thinned (20–30 km thick) crust and a 100–200 km wide, highly extended area with crustal thicknesses generally between 2 and 12 km under the present‐day Møre and Vøring basins. In the footwalls of the basin flank detachments, lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults. Under the most highly thinned areas, a more distal set of deep‐seated (basin floor) detachments incised and extended remnant crust and, probably, the upper mantle, leaving as little as <5 km of continental crust to be preserved under thick synrift and postrift deposits. We suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust. Thus, they prepare the ground for incision by the basin floor detachments, which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed.

No abstract

We present a new global model for the Earth's lithosphere and upper mantle (LithoRef18) obtained through a formal joint inversion of 3-D gravity anomalies, geoid height, satellite-derived gravity gradients and absolute elevation complemented with seismic, thermal and petrological prior information. The model includes crustal thickness, average crustal density, lithospheric thickness, depth-dependent density of the lithospheric mantle, lithospheric geotherms, and average density of the sublithospheric mantle down to 410 km depth with a surface discretization of 2 • × 2 •. Our results for lithospheric thickness and sublithospheric density structure are in excellent agreement with estimates from recent seismic tomography models. A comparison with higher resolution regional studies in a number of regions around the world indicates that our values of crustal thickness and density are an improvement over a number of previous global crustal models. Given the strong similarity with recent tomography models down to 410 km depth, LithoRef18 can be readily merged with these seismic models to include seismic velocities as part of the reference model. We include several analyses of robustness and reliability of input data, method and results. We also provide easy-to-use codes to interrogate the model and use its predictions for the development of higher-resolution models. Considering the model's features and data fitting statistics, LithoRef18 will be useful in a wide range of geophysical and geochemical applications by serving as a reference or initial lithospheric model for (i) higher-resolution gravity, seismological and/or integrated geophysical studies of the lithosphere and upper mantle, (ii) including far-field effects in gravity-based regional studies, (iii) global circulation/convection models that link the lithosphere with the deep Earth, (iv) estimating residual, static and dynamic topography, (v) thermal modelling of sedimentary basins and (vi) studying the links between the lithosphere and the deep Earth, among others. Several avenues for improving the reliability of LithoRef18's predictions are also discussed. Finally, the inversion methodology presented in this work can be applied in other planets for which potential field data sets are either the only or major constraints to their internal structures (e.g. Moon, Venus, etc.).

Active source seismology provides a critical constraint on the global crustal structure. However, the heterogeneous data coverage means that interpolation is necessary to fill the gap between seismic profiles. This has the potential to cause large uncertainties especially if the data are interpolated over a large distance. In previous models, geological intuition was often employed to ensure reasonable results. To investigate crustal model uncertainty, we apply geostatistical analysis to a database of active seismic investigations. Unlike previous models, our workflow in the construction of the crustal model is completely transparent. Apart from the points from the database, we only use an a priori separation in oceanic and continental domains. We calculate global maps of Moho depth and average P wave velocity in the crystalline crust. Additionally, we obtain the interpolation error and error covariance. Overall, our results agree with previous global crustal models such as Crust1.0. Our uncertainty estimates show that the Moho depth uncertainty in the most well studied areas such as North America and Europe is less than 4 km but can reach 10 km or more in frontier regions such as most of Africa. P wave velocity shows the same pattern, but is less accurate overall, due to more small‐scale variation. We demonstrate the benefit of having a numerical estimate of uncertainty by propagating the uncertainty to the residual topography. We see two main uses for our crustal model in the geophysical research community: (1) as a starting model for inversions focusing on the crust and upper mantle and (2) as a starting point for including other pointwise information about crustal structure, for example, from passive seismology.

No abstract

No abstract

The lithospheric structure of Antarctica is still underexplored. Moho depth estimate studies are in disagreement by more than 10 km in several regions, including, for example, the hinterland of the Transantarctic Mountains. Taking account the sparseness of seismological stations and the nonuniqueness of potential field methods, inversions of Moho depth are performed here based on satellite gravity data in combination with currently available seismically constrained Moho depth estimates. Our results confirm that a lower density contrast at the Moho is present under East Antarctica than beneath West Antarctica. A comparison between the Moho depth derived from our inversion and an Airy‐isostatic Moho model also reveals a spatially variable buoyancy contribution from the lithospheric mantle beneath contrasting sectors of East Antarctica. Finally, to test the plausibility of different Moho depths scenarios for the Transantarctic Mountains‐Wilkes Subglacial Basin system, we present 2‐D lithospheric models along the Trans‐Antarctic Mountain Seismic Experiment/Gamburtsev Mountain Seismic experiment seismic profile. Our models show that if a moderately depleted lithospheric mantle of inferred Proterozoic age underlies the region, then a shallower Moho is more likely beneath the Wilkes Subglacial Basin. If however, refertilization processes occurred in the upper mantle, for example, in response to Ross‐age subduction, then a deeper Moho scenario is preferred. We conclude that 3‐D lithospheric modeling, coupled with the availability of new seismic information in the hinterland of the Transantarctic Mountains, is required to help resolve this controversy, thereby also reducing the ambiguities in geothermal heat flux estimation beneath this key part of the East Antarctic Ice Sheet.