Rock magnetic investigation of possible sources of the Bangui magnetic anomaly

International audienceThe Bangui magnetic anomaly (BMA) is the largest lithospheric magnetic field anomaly on Earth at low latitudes. Previous studies investigated its geological source using constraints from satellite and ground magnetic field measurements, as well as from surface magnetic susceptibility measurements on rocks from the Panafrican Mobile Belt Zone (PMBZ). Here we combine magnetic field data modelling and rock magnetic property measurements (susceptibility and natural remanent magnetization, NRM) on many samples from this PMBZ and the surrounding formations. It reveals that NRM is a significant component of the total magnetization (Mt) of the BMA source, which reaches 4.3 A/m with maximum thicknesses of 38 and 54 km beneath the western and eastern parts of the BMA. Only the isolated and relatively thin banded iron formations and some migmatites show such Mt values. Thus we suggest that the thick BMA source may be composed either by overlapped slices of such metamorphic rocks, or by an iron-rich mafic source, or by a combination of these two geological structures

Magnetic field microscopy of rock samples using a giant magnetoresistance–based scanning magnetometer

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95412/1/ggge1634.pd

A Neolithic occupation at the bottom of the Monts de Vaucluse, the site of La Boudine in Saumane-de-Vaucluse

Le site de La Boudine est localisé sur la commune de Saumane-de-Vaucluse. Le mobilier archéologique découvert ensurface a pu être attribué au Néolithique moyen. Cette homogénéité et la proximité du site avec les gisements de silex bédoulien des monts de Vaucluse, ont motivé une opération de sondage. Des lambeaux d’occupation néolithique ont pu être découverts. Le site a été fortement érodé mais cette opération permet de documenter positivement l’occupation humaine dans les piémonts des monts de Vaucluse.The site of La Boudine is located on the municipality of Saumane-de-Vaucluse. The artefacts on surface can be attributed to middle Neolithic. This homogeneity and the proximity with the deposits of bedoulian flint of Monts de Vaucluse, have motivated an excavation. Remaining of Neolithic activity have been discovered. The site was strongly affected by erosion. However, this studies allows to document the human activity in piedmont of monts de Vaucluse

Making a Better Magnetic Map

A new version of the World Digital Magnetic Anomaly Map, released last summer, gives greater insight into the structure and history of Earth's crust and upper mantle.Published1A. Geomagnetismo e PaleomagnetismoN/A or not JC

Thermoremanence acquisition and demagnetization for titanomagnetite under lithospheric pressures

The geological sources of large-scale lithospheric magnetic field anomalies are poorly constrained. Understanding the magnetic behavior of rocks and minerals under the pressures and temperatures encountered at large crustal depths is particularly important in that task. The impact of lithospheric pressure is not well known and most of the time neglected in numerical models of the geological sources of magnetic anomalies. We present thermal remanent magnetization (TRM) acquisition and stepwise thermal demagnetization on synthetic titanomagnetite dispersed powder, within an amagnetic cell under hydrostatic pressure up to 1 GPa. TRM is measured after thermal cycling within a cryogenic magnetometer. Pressure-dependent increase in the Curie temperature (initially in the 50–70°C range) is observed, mostly between 0.3 and 0.6 GPa, on the order of 20 K/GPa. TRM intensity also increases with pressure up to 200% at 675 MPa, although the pressure variation with temperature inside the cell complicates the interpretation. ©2017. American Geophysical Union. All Rights Reserved

Crustal Thickness and Magnetization beneath Crisium and Moscoviense Lunar Impact Basins

International audienceGRAIL data recently confirmed that the Crisium and Moscoviense large impact basins have the thinnest (< 5 km) crust of the Moon. Crisium also shows two localized intense magnetic fields located nearby its North and South borders, while Moscoviense shows a relatively-intense central magnetic field anomaly. In details, these magnetic fields are exactly located where the thinnest (<1-3 km) crust within these basins is predicted by the crustal thickness models. Here we investigate this apparent anti-correlation by modeling the sources of these potential field data using several approaches in 2D and 3D. Our results show that, beneath the very thin Mare basalt layer, a strongly-magnetized layer with laterally-varying thickness-but still thin (~2-3 km)-and density can be present. This layer may correspond to an impact melt sheet with large magnetization due to accumulation of iron-rich fluids during the impact event and/or to post-impact processes

2D crustal models of the Chicxulub impact structure, constrained by potential field data

International audienc

Exemples terrestres et planétaires de modélisation contrainte par des données de champs potentiels

International audienc

Crustal Thickness and Magnetization beneath Crisium and Moscoviense Lunar Impact Basins

International audienceGRAIL data recently confirmed that the Crisium and Moscoviense large impact basins have the thinnest (< 5 km) crust of the Moon. Crisium also shows two localized intense magnetic fields located nearby its North and South borders, while Moscoviense shows a relatively-intense central magnetic field anomaly. In details, these magnetic fields are exactly located where the thinnest (<1-3 km) crust within these basins is predicted by the crustal thickness models. Here we investigate this apparent anti-correlation by modeling the sources of these potential field data using several approaches in 2D and 3D. Our results show that, beneath the very thin Mare basalt layer, a strongly-magnetized layer with laterally-varying thickness-but still thin (~2-3 km)-and density can be present. This layer may correspond to an impact melt sheet with large magnetization due to accumulation of iron-rich fluids during the impact event and/or to post-impact processes

Some magnetic field data processing: terrestrial and planetary cases

International audienceA workshop and a school will be held for 3 days on inverse problems in harmonic electromagneti and approximation, with applications mainly dedicated to geomagnetism and paleomagnetism. They will more precisely concern direct and inverse potential problems of source detection and non-destructive control, data extension, conductivity or permittivity estimation from boundary data, together with resolution algorithms. The techniques pertain to harmonic analysis, e.g. expansions in spherical harmonics or other families of special functions, Hodge decomposition principles, approximation theory and constrained optimization, Fourier analysis, ... Applications to geosciences and planetary sciences concern in particular geomagnetism, subsoil prospection, paleomagnetism, gravimetry, source imaging, processing of stellar signals, measure protocols and steering of instruments. The school and the workshop are open to Master or PhD students and of course to post-doctoral researchers, researchers, professors, engineers. Communications from young participants (PhD, post-doc., young researchers, engineers) are strongly encouraged