A compilation of new airborne magnetic and gravity data across Dronning Maud Land, Antarctica.

The evolution of the South Atlantic region including the Weddell Sea and its adjacent areas is of crucialimportance for understanding the processes of the structure and tectonics of the Antarctic lithosphere, its relation to geodynamic processes, especially to the timing and geometry of the initial stages of the Mesozoic break-up between Africa, Antarctica and South America. For unravelling the geological evolution of Antarctica prior to the break-up of Gondwana, the sub-glacial geology is of utmost importance. Understanding the sub-ice geology allows reconstruction of ancient mountain chains (collision zones) across continents, which are separated by large ocean basins in the presentworld. Since only the peaks of the Dronning Maud Land (DML) mountains can be geologically sampled, geophysical methods are required to uncover the geological structure beneath the ice. Therefore, extensive airborne surveys were conducted across DML between 2001 to 2005 to close data gaps and to improve existing data sets

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

The Alfred Wegener Institute of Polar and Marine Research, the University of Bergenand the Hokkaido University acquired new seismic refraction data along a transect fromthe Knipovich Ridge to the inner Van Mijenfjorden in southern Svalbard. A close spacing ofon- and offshore receivers and a dense marine shot pattern provide the data for a high resolutionp-wave velocity model for geological interpretation. Additional new seismic reflection data(University of Bergen) yield structural information for a more reliable analysis.Crustal thickness along the Van Mijenfjorden is 33 to 34 km. Seismic velocities of 5.0 km/sare observed within the upper crustal section of the Tertiary Central Spitsbergen Basin.A Paleozoic sedimentary basin with a depth of 8 to 10 km is associated with the Nordfjorden Block.The seismic velocities are up to 6.0 km/s. Paleozoic sedimentary rocks are expected furtherto the west of the Hornsund Lineament since seismic velocities reveal a similar range here.West of the Bellsund the continental crust thins gradually over a 90 km wide rifted zone.The velocity structure within this section is very complex and comprises zones of decreasedvelocities below the West Spitsbergen Fold Belt (down to 20 km depth) and slightly elevatedvelocities (7.2 km/s) at the crust-mantle transition. The first structure is interpreted as intensivelyfractured rocks linked to post-Late Paleocene transpressive orogenic activity and subsequentlyaffected by transtension during break-up from Greenland. The faster deep-crustal velocities aresupposed to express magmatic intrusions of an unidentified origin. Melts could either be channelled by theSpitsbergen Shear Zone from more distant sources, or originate in magmatic interaction between the northern Knipovich Ridgeand the neighbouring young rifted crust.Oceanic crust each side of the Knipovich Ridge is thin (~3.5 km) and is characterised by theabsence of oceanic layer 3 (3.5/4.1 to 4.7 km/s). The oceanic section exhibits zones of verythin crust (~1 km) that are interpreted as fracture zones. Beneath these we observed decreasedmantle velocities (~7.3 km/s) indicating probable serpentinization of peridotites along thesefracture zones. Thickness variations further provide information about the segmentationand magma supply along the northern Knipovich Ridge

Paleo-Current Activity in the Eastern Arctic Ocean - Evidence from Seismic

Four stages of deposition regime have been detected on high-resolution seismic reflection profiles. First, in strata of Paleocene-Eocene age small vertical faults indicate differential compaction of probably anoxic sediments deposited in the still isolated Eurasian Basin. Than, a high-amplitude-reflector sequence indicates a time of widespread changes in deposition realm associated with the gradual opening of the Fram Strait and ongoing subsidence of the Lomonosov Ridge (LR) in Eocene and Oligocene. Episodical incursions of water masses from the North Atlantic were the consequences and led to the deposition of sediments of strongly different lithology. The third stage marks widespread and pelagic sedimentation since earliest Miocene. Sediment waves are evidence for paleo-bottom current activity and the onset of an ocean circulation system. The slope of the LR is structured into terraces, indicating fault-controlled sediment drifts arisen due to the onset and intensification of current circulation. Advanced deepening of the Fram Strait likely enabled an effective exchange of water masses between the North Atlantic and Arctic Ocean. Continuous sagging of the LR, reactivation of former faults and bottom currents passing along the ridge may shape the steep sediment free flanks of the terraces in addition. At least, a continuous regional drape of reflectors marks the transition to glaciation of the northern hemisphere in early Pliocene