HR: 1330h
AN: T53A-01    [Abstracts]
TI: A New Starting Point for the History of the Central Atlantic
AU: Sahabi, M
EM: msahabi@ucd.ac.ma
AF: Faculte des Sciences d'El Jadida, BP 20, El Jadida, 24000 Morocco
AU: * Aslanian, D
EM: daslanian@ifremer.fr
AF: Ifremer, BP 70, PLOUZANE, 29280 France
AU: Labails, C
EM: clabails@ifremer.fr
AF: Ifremer, BP 70, PLOUZANE, 29280 France
AU: Moulin, M
EM: mmoulin@ifremer.fr
AF: Ifremer, BP 70, PLOUZANE, 29280 France
AU: Rabineau, M
EM: marina.rabineau@univ-brest.fr
AF: CNRS - UMR6538, Place Nicolas Copernic, PLOUZANE, 29280 France
AU: Olivet, J
EM: jlolivet@ifremer.fr
AF: Ifremer, BP 70, PLOUZANE, 29280 France
AB: The African and American margins of the central Atlantic Ocean have a major historical and geological importance: 1- American margins were the place of the most intense geological and geophysical exploration and synthesis related to continental margins (most concepts were defined or tested there); 2- in contrast to the North Atlantic which has a complex rifting history, breakup in the central Atlantic seems to occur in a single phase, at the Trias-Lias boundary, allowing for much easier modelling; 3- contrary to the South and North Atlantic, intracontinental deformation is not so crucial and does not complicate the initial reconstruction; 4- the Central Atlantic is the very place (with the exception of the Alpes) to "read" the breakup history of Pangea and the beginning of the closure of the Thetys Ocean. Since 1986, the breakup story of this region has been largely based on the interpretation of Klitgord & Schouten, which did not take into account the African margin and its magnetic anomalies and salt basins. We propose here a new reconstruction with a new interpretation of these African data. The American margin is characterised by the strong, continuous East Coast Magnetic Anomaly (ECMA) and the Blake Spur Magnetic Anomaly (BSMA). The ECMA, fringed throughout by a salt basin, is thought to represent the continental-oceanic boundary. In the north nevertheless, the salt runs largely over the ECMA. The West African Coast Magnetic Anomaly (WACMA), homologue of the ECMA, is not so well defined due to its weaker amplitude and to a lack of data. Our interpretation is based on all available magnetic data and the following two important points : the similarity in shape of both magnetic anomalies and the position of the Mauritanian salt basin. In contrary to Klitgord & Schouten, who considered the anomaly S in the Morocco Basin as the homologue of the BSMA, this anomaly represents the northern part of the WACMA in our interpretation. This modification has important consequences on the age of the fit which had been supposed to be 175 Ma, by simple extrapolation of the spreading rate between the anomalies M25 and BS to the fit. Our reconstruction at 195 Ma (top Sinemurian) of the Central juxtaposes the ECMA and the WACMA and places side by side the large salt basins of Morocco and Nova Scotia, as well as those of Mauritania and Carolina. The outflowing salt, in the northern part of the area, is interpreted as a large post-rifting slide. Both the ECMA and WACMA coincide with the limit of the salt basin. This fit of the two magnetic anomalies is therefore the paleo-reconstruction of the lower-liasic salt basin, at its maximum extension. Their age is connected to the end of salt deposition, i.e 195 Ma, 20 Ma older than previously thought but in good agreement with the age of the volcanic activity on both sides of the Atlantic ocean (Lower Lias).
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 8122 Dynamics, gravity and tectonics
DE: 8130 Heat generation and transport
DE: 8159 Rheology--crust and lithosphere
SC: Tectonophysics [T]
MN: 2005 Joint Assembly