No abstract

Vector magnetic anomaly maps are derived at satellite altitude from Magsat data over the Caribbean and Middle America. To minimize smoothing of the anomaly field caused by averaging the data over the whole altitude range of Magsat measurements, two maps are derived in two nonoverlapping altitude ranges: 350–420 and 420–550 km. A composite map of the vertical component of the anomaly field is then computed at ground level. This map displays large positive anomalies associated with fast subduction zones. These anomalies define discontinuities in the downgoing slab associated with seismic gaps. Positive anomalies are also consistently observed above allochthonous blocks of continental origin in the Caribbean area and suggest that the average magnetization is larger in the continental lithosphere. Elongated magnetic lows are observed above transform boundaries of the Caribbean plate. The Cayman Trough anomaly is consistent with magnetization of the order of 1 A/m in the upper mantle. Demagnetization of the lithosphere along the Bocono‐El Pilar fault system which bounds the Caribbean plate to the south may be accounted for by frictional heating along shear zones. The pattern of anomalies along the southern margin of the United States is related to its accretionary tectonic history. Various estimates of the vertically integrated magnetization of both oceanic and continental lithospheres are computed using these anomalies and provide constraints on the vertical distribution of lithospheric sources of Magsat anomalies.

International audienceThe elucidation of key questions in astrophysics, in particular those related to black hole physics and census, and to particle acceleration mechanisms, necessitates to develop new observational capabilities in the hard X-ray domain with performances several orders of magnitude better than presently available. Relying on two spacecrafts in a formation flying configuration, Simbol-X will provide the world-wide astrophysics community with a single optics long focal length telescope. This observatory will have unrivaled performances in the hard X-ray domain, up to ~80 keV, as well as very good characteristics in the soft X-ray domain, down to ~0.5 keV. The Simbol-X mission has successfully passed a phase A study, jointly conducted by CNES and ASI, with the participation of German laboratories. It is now entering phase B studies with the participation of new international partners, for a launch in 2015. We give in this paper a general overview of the mission, as consolidated at the start of phase B

Vector magnetic anomaly maps derived at sea‐level from Magsat data show a large positive anomaly above the Middle America Trench Relative highs and lows correlate with variations in the seismicity of the subducted Cocos plate. These anomalies can only be modelled assuming complete demagnetization of the slab near seismic discontinuities. We propose that demagnetization is necessarily associated with tearing of the plate. Magnetic anomalies indicate tearing of the Cocos plate beneath Mexico and near Panama but further east than previously proposed on the basis of seismic data. Although the demagnetization process is likely to be related to the temperature increase, it is shown that thermal diffusion is not sufficient to produce the observed anomaly and that the slab must be heavily fractured in the vicinity of teared zones.

No abstract