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Interpretation seismischer und gravimetrischer Daten des Weddellmeeres, Antarktis = Interpretation of seismic and gravimetric data of the Weddell Sea, Antarctica
Rogenhagen, J. (2000). Interpretation seismischer und gravimetrischer Daten des Weddellmeeres, Antarktis = Interpretation of seismic and gravimetric data of the Weddell Sea, Antarctica. Ber. Polarforsch. Meeresforsch. 369: 1-135
In: Berichte zur Polar- und Meeresforschung = Reports on Polar and Marine Research. Alfred-Wegener-Institut für Polar- und Meeresforschung: Bremerhaven. ISSN 1618-3193, more
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  • Rogenhagen, J.

    The present day Weddell Sea, located between East Antarctica and the Antarctic Peninsula, is the region where the break-up of the supercontinent Gondwana initiated. The early geodynamic evolution of the opening of the Weddell Sea is still controversial due to a lack of geophysical data and safe datings. Perennial ice coverage makes it difficult to carry out systematic marine geophysical investigations. Nowadays, large scale potential field maps are available for this region. They provide an important tool for the investigation of tectonic structures. The relevance of some main tectonic structures resolved in the potential field data for the geodynamic evolution is still under debate. Hints for a more secure interpretation can be found with the aid of regional concentrated marine geophysical investigations. In austral summer 1997 the Weddell Sea was the target area for the expedition ANT XIV /3 carried out by the Alfred Wegener Institute with a focus on geophysical survey. Three regions were examined in detail with seismic reflection and refraction and gravimetric field work. The goal of this study is the interpretation of that data set. One target of the expedition has been the so-called Herringbone Pattern, a series of curvilinear gravity anomalies. The integrated analysis of the seismic and gravimetric measurements shows the Herringbone Pattern to be caused by fracture zones. The main clue for this interpretation is the modelled variation of crustal thickness. Along the gravity minima the gravity models show a decrease in crustal thickness to values around 4 km to 2 km. South of the Herringbone Pattern the Anomaly-T, a prominent East-West striking gravity anomaly is found. Its importance and relevance for the geodynamic evolution is controversial. This study presents a consistent picture of that gravity anomaly. Anomaly-T marks the border between two areas of oceanic crust with different spreading rates. The anomaly itself is caused by a region of increased basement roughness. North of Anomaly-T the half spreading rate is 6 mm a-1, south of Anomaly-T the rate is 15mm a-1. These estimates of spreading rates inferred from crustal roughness are in good agreement with modelled spreading rates of plate tectonic reconstructions. In contrast to previous reconstructions this study reveals a trend in spreading rates, that indicates another position of the pole of rotation for the plate movement during the generation of Anomaly-T. The trend shows an increase in spreading rate from east to west in the Weddell Sea. Four wide angle seismic measurements at locations between 66° S and 72° S in the western Weddell Sea were undertaken to obtain information on the sedimentary structure and the sediment thickness. The ascertained sediment thicknesses are between 5 km and 7 km. The sediments show a homogeneous structure with an typical depth velocity function. The sediment cover of the western Weddell Sea is divided into two distinct layers with comparable thickness but with different velocity gradients. A transition zone of around 1 km thickness and an increased velocity gradient separates these two layers.

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