HR: 1330h
AN: T53A-07    [Abstracts]
TI: Deep Crustal Strucure of the Southern Morrocan Margin from Reflection and Wide-angle Seismic Data
AU: * Klingelhoefer, F
EM: fklingel@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Labails, C
EM: cinthia.labails@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Cosquer, E
EM: ecosquer@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Rouzo, S
EM: srouzo@univ-brest.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Tzimeas, C
EM: ctzimeas@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Nouze, H
EM: hnouze@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Geli, L
EM: geli@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Aslanian, D
EM: daniel.aslanian@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AU: Olivet, J
EM: jean.louis.olivet@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29180
AB: During the DAKHLA cruise, a joint project of Ifremer, the University of Brest, the University of Lisbon and Total, a total 1500 km of seismic reflection and wide-angle profiles were acquired off the southern Morrocan margin. Two profiles parallel to the margin and two profiles perpendicular to the margin were equipped with ocean-bottom seismometers (OBS). Both profiles perpendicular to the margin were additionally equipped with landstations in the prolongation of the marine profiles. A vibroseis study was carried out on land to determine the shallow structure underneath the landstations. The main aims of the cruise were to image the deep structure of the margin and to characterize the nature of the transition zone between the continental and oceanic crust. A profile perpendicular to the margin extended 200 km out onto oceanic crust and reveals a change in the roughness of the oceanic crust around anomaly M25. Modeling of the reflection and wide-angle seismic data reveals a 10 km deep sedimentary basin including two high velocity carbonate layers. The crustal thinning from 30 km at the continental part to 7 km in the oceanic part occurs over a 100 km wide zone. The continental crust is divided into two distinct layers of 12 and 18 km thickness. Oceanic crust east of the M25 magnetic anomaly displays higher velocities in layer 3 than west of the magnetic anomaly. No layer of anomalously high velocities between 7.2 and 8.0 km/s, which could be interpreted as underplate or serpentinized upper mantle material, has been detected at the ocean continent transition. The change in velocity suggests a possible link to changes in accretionary processes of the oceanic crust. A comparison with wide-angle models (SISMAR cruise) from the northern Morrocan margin shows similar crustal thickness but a wider ocean - continent transition zone. As in the DAKHLA velocity models no high velocity layer corresponding to either serpentinized upper mantle or underplating has been imaged in the SISMAR velocity model.
DE: 3025 Marine seismics (0935)
DE: 8105 Continental margins and sedimentary basins
DE: 9305 Africa
SC: Tectonophysics [T]
MN: 2005 Joint Assembly