Browsing by Author "Madureira, P."
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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.
- TRIDENT – Technology based impact assessment tool foR sustaInable, transparent Deep sEa miNing exploraTion and exploitation: A project overviewPublication . Silva, E.; Viegas, D.; Martins, A.; Almeida, J.; Almeida, C.; Neves, B.; Madureira, P.; Wheeler, A. J.; Salavasidis, G.; Phillips, A.; Schaap, A.; Murton, B.; Berry, A.; Weir, A.; Dooly, G.; Omerdic, E.; Toal, D.; Collins, P. C.; Miranda, M.; Petrioli, C.; Barrera Rodríguez, C.; Demoor, D.; Drouet, C.; Serafy, G. El; Jesus, Sergio; Dañobeitia, J.; Tegas, V.; Cusi, S.; Lopes, L.; Bodo, B.; Beguery, L.; VanDam, S.; Dumortier, J.; Neves, L.; Srivastava, V.; Dahlgren, T. G.; Thomassen Hestetun, J.; Eiras, R.; Caldeira, R.; Rossi, C.; Spearman, J.; Somoza, L.; González, F. J.; Bartolomé, R.; Bahurel, P.By creating a dependable, transparent, and cost-effective system for forecasting and ongoing environmental impact monitoring of exploration and exploitation activities in the deep sea, TRIDENT seeks to contribute to the sustainable exploitation of seabed mineral resources. In order to operate autonomously in remote locations under harsh conditions and send real-time data to authorities in charge of granting licenses and providing oversight, this system will create and integrate new technology and innovative solutions. The efficient monitoring and inspection system that will be created will abide by national and international legal frameworks. At the sea surface, mid-water, and the bottom, TRIDENT will identify all pertinent physical, chemical, geological, and biological characteristics that must be monitored. It will also look for data gaps and suggest procedures for addressing them. These are crucial actions to take in order to produce accurate indicators of excellent environmental status, statistically robust environmental baselines, and thresholds for significant impact, allowing for the standardization of methods and tools. In order to monitor environmental parameters on mining and reference areas at representative spatial and temporal scales, the project consortium will thereafter develop and test an integrated system of stationary and mobile observatory platforms outfitted with the most recent automatic sensors and samplers. The system will incorporate high-capacity data processing pipelines able to gather, transmit, process, and display monitoring data in close to real-time to facilitate prompt actions for preventing major harm to the environment. Last but not least, it will offer systemic and technological solutions for predicting probable impacts of applying the developed monitoring and mitigation techniques.
- Variation of magnetic properties in sedimentary rocks hosting the Foum Zguid dyke (southern Morocco): combined effects of re-crystallization and Fe-metasomatismPublication . Silva, P. F.; Henry, B.; Marques, F. O.; Mateus, A.; Madureira, P.; Lourenco, N.; Miranda, J. M.The effects of dyke intrusion on the magnetic properties of host sedimentary rocks are still poorly understood. Therefore, we have evaluated bulk magnetic parameters of standard palaeomagnetic samples collected along several sections across the sediments hosting the Foum Zguid dyke in southern Morocco. The study has been completed with the evaluation of the magnetic fabric after laboratory application of sequential heating experiments. The present study shows that: (1) close to Fourn Zguid dykes, the variations of the bulk magnetic parameters and of the magnetic fabric is strongly related with re-crystallization and Fe-metasomatism intensity. (2) The thermal experiments on AMS of samples collected farther from the dyke and, thus, less affected by heating during dyke emplacement, indicate that 300-400 degrees C is the minimum experimental temperature necessary to trigger appreciable transformations of the pre-existing magnetic fabrics. For temperatures higher than ca. 580 degrees C, the magnetic fabric transformations are fully realized, with complete transposition of the initial fabric to a fabric similar to that of samples collected close to the dyke. Therefore, measured variations of the magnetic fabric can be used to evaluate re-crystallization temperatures experienced by the host sedimentary rock during dyke emplacement. The distinct magnetic behaviour observed along the cross-sections strongly suggests that samples collected farther from the dyke margins did not experience thermal episodes with temperatures higher than 300 degrees C after dyke emplacement. (3) AMS data shows a gradual variation of the magnetic fabric with distance from the dyke margin, from sub-horizontal K-3 away from the dyke to vertical K3 close to the dyke. Experimental heating shows that heat alone can be responsible for this strong variation. Therefore, such orientation changes should not be unequivocally interpreted as the result of a stress field (resulting from the emplacement of the dyke, for instance). (4) Magnetic studies prove to be a very sensitive tool to assess rock magnetic transformations, thermally and chemically induced by dyke intrusion in hosting sediments. (c) 2005 Elsevier B.V. All rights reserved.