Browsing by Author "Adam, C."
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- Mantle dynamics and characteristics of the Azores plateauPublication . Adam, C.; Madureira, P.; Miranda, M; Lourenço, Nuno; Yoshida, M.; Fitzenz, D.Situated in the middle of the Atlantic Ocean, the Azores plateau is a region of elevated topography encompassing the triple junction between the Eurasian, Nubian and North American plates. The plateau is crossed by the Mid-Atlantic Ridge, and the Terceira Rift is generally thought of as its northern boundary. The origin of the plateau and of the Terceira Rift is still under debate. This region is associated with active volcanism. Geophysical data describe complex tectonic and seismic patterns. The mantle under this region is characterized by anomalously slow seismic velocities. However, this mantle structure has not yet been used to quantitatively assess the influence of the mantle dynamics on the surface tectonics. In this study, we use a highly resolved tomography model to model the convection occurring in the mantle beneath the Azores region. The convection pattern points out two distinct upwelling, thus proving that the volcanism emplacement is created by a buoyant mantle upwelling. The modeled dynamic topography recovers well the characteristics of the depth anomaly associated with the Azores plateau, except for the south-eastern most part, thus proving that most of the depth anomaly associated with the Azores plateau is created by the present-day mantle dynamics. The stresses induced by the mantle convection can account for the lifting regime observed over the Azores plateau and the Terceira Rift, and its consequences in terms of surface morphology and seismicity. (C) 2012 Elsevier B.V. All rights reserved.
- Nitroso group transfer from N-nitrososulfonamides to thiolate ions. Intrinsic reactivityPublication . Moreira, José; García-Río, Luís; Leis, J. R.; Adam, C.The nitroso group transfer from N-nitrososulfonamides to thiolate ions was studied. Based on the results, the reaction rate is strongly dependent on the nature of the leaving group (αlg≈−1.30)(αlg≈−1.30), but virtually independent of the basicity of the thiol (βnuc≈0.10)(βnuc≈0.10). This dependence is ascribed to the presence of a nucleophile desolvation equilibrium (βd)(βd) that is followed by the attack of the thiolate ion on the nitroso group (βnuc′) via a concerted mechanism. The equilibrium constants for the loss of a nitroso group from a nitrosothiol and an N-nitrososulfonamide were used to obtain the equilibrium constants for the different reactions involved. By using rate–equilibrium correlations, the parameters αlgnorm, βdβd, and βnuc′norm were obtained.