ALBERT

Description: Recent geophysical surveys were designed to investigate the breakup process between India and East Antarctica and the effect of igneous activity on the formation of the Antarctic passive margin and the crust between the Kerguelen Plateau and Antarctica in the Princess Elizabeth Trough (PET). The Kerguelen Plateau marks one of the two most voluminous Large Igneous Provinces (LIP) in an oceanic setting and is attributed to a mantle hotspot emplaced at 120 Ma ago, about 15 m.y. after the previously suggested onset of seafloor spreading between India and Antarctica. Geophysical data analyses and modeling reveal a wide zone of highly extended continental crust on the Antarctic margin of Mac.Robertson Land. The partial continental affinity of the Southern Kerguelen Plateau, as indicated by earlier seismic data and ODP drill samples further north, continues to the southernmost limit of the plateau. Here, the continental crust must have been enormously thinned and fragmented as part of the rifting process between India and Antarctica. Ocean-bottom seismograph data indicate a narrow corridor of oceanic-type crust beneath the PET. Magmatic accretion to the crust is widely observed on both the plateau and the PET region.

Description: The Fram Strait between Svalbard and Greenland is the only deep water connection between the Arctic Ocean and the northern North Atlantic. A detailed understanding of this region, however, is difficult due to the absence of clear marine magnetic and other geophysical data. Within the last years the Alfred-Wegener-Institute conducted several geophysical data sets in order to solve some of the remaining problems in the Fram Strait and the adjacent basins (Molloy and Boreas Basin).In this contribution we present a new aeromagnetic data grid, new seismic reflection data and existing gravimetric data that provide new insights into the geodynamic evolution of this area. These data are the basis for estimations of initial opening scenarios, and palaeobathymetric maps. Seismic reflection lines crossing the entire Molloy and Boreas basins show rough basement topography and a deep axial valley. Roughness calculations also indicate ultra-slow spreading rates in the whole area. Using the age information of the aeromagnetic data, the thermal subsidence for oceanic crust corrected for the sediment load fits the observed basement depth reasonably well in the Boreas and Molloy basins. A compilation of additional seismic lines in this area contributes the basement depth and sediment distribution. Combining all information of the seismic data, the aeromagnetic data and the gravity data, a model of the evolution of the northern North Atlantic is created. The latest results of this palaeobathymetric study for the Fram Strait and its subsequent basins are shown.

Description: The Fram Strait between Greenland and Spitsbergen connects the Arctic Ocean and the northern North Atlantic. Today this gateway is about 450 km wide and in average 2500 m deep. It is the only connection between the Arctic Ocean and the world oceans, where dense oxygen rich water is exchanged. Such an exchange has important influences on the climate. A detailed knowledge of the timing of the Fram Strait opening provides a basis for a correlation with past climate changes.Due to the absence of clear marine magnetic and other geophysical data, a detailed understanding of this region has been difficult until now. Within the last years, the Alfred Wegener Institute conducted several geophysical data sets in order to solve some remaining problems in the Fram Strait and adjacent basins (Molloy, Boreas and Greenland Basin). In this contribution we present a new aeromagnetic data grid, new seismic reflection data and existing gravimetric data that provide new insights into the geodynamic evolution of this area. These data are the basis for estimations of initial opening scenarios, and palaeobathymetric maps. New seismic reflection lines crossing the entire Molloy and Boreas basins show rough basement topography and a deep axial valley. Roughness calculations also indicate ultra-slow spreading rates in the whole area. Using the age information of the aeromagnetic data, the thermal subsidence for oceanic crust corrected for the sediment load fits the observed basement depth reasonably well in the basins.A compilation of additional seismic reflection and refraction lines in the northern North Atlantic provide information on the crust thickness, the basement depth and sediment distribution. Based on this information, a model of the evolution of the northern North Atlantic is created. The latest results of this palaeobathymetric study for the Fram Strait and its subsequent basins are shown.

Description: While evolution of the Eurasian Basin and North Atlantic starting at ~55 Ma are well known, this holds not true for the Fram Strait. The Lena Trough, a mid-ocean ridge in the centre of the Fram Strait, is the only deep water connection of the Arctic Ocean. The lack of geophysical data prevented any detailed model for the geodynamic history of this gateway so far. New multi-channel seismic and aeromagnetic data show the straits opening as far south as 81°N at ~16 Ma. Before, intermediate-depth water exchange might have existed through deep grabens of the recent Yermak Plateau. Its basement topography is very rough and the plateau-like bathymetry is a young feature. Large drift deposits on oceanic crust younger than 10 Ma indicate strong current activity and erosion of the surrounding shelves after opening of the gateway. Furthermore, the data show that the Fram Strait was in place long before the high frequency glacial/interglacial cycles started in the northern hemisphere at ~3 Ma. Though the gateway might have played an important role in the long-term cooling of the northern hemisphere, it is unlikely to have been solely responsible for the intensification of the northern hemisphere glaciations in the Late Pliocene/Pleistocene.

Description: The ocean region of the Fram Strait between Svalbard and Greenland is the only deep water connection between the Arctic Ocean and the North Atlantic. A detailed understanding of this region, however, is difficult due to the absence of clear marine magnetic and other geophysical data. Within the last years the Alfred Wegener Institute conducted several geophysical surveys to achieve a more systematic geophysical data set in order to solve some of the remaining problem in the Fram Strait and the subsequent basins (Molloy and Boreas basins). Typical for the magnetic signature of the Boreas Basin is the complete absence of continuous sea floor spreading anomalies. Furthermore, the spreading in this basin seemed to be asymmetric and/or a ridge jump occurred. Similar problems exist in the Molloy Basin and the Fram Strait.In this contribution we present new aeromagnetic data grid, seismic reflection data and existing gravimetric data that provide new insights into the geodynamic evolution of this area. Seismic reflection lines crossing the entire Molloy and Boreas basins show a deep axial valley and very rough basement topography. Combining the depth information of the seismic reflection data with the age information of the aeromagnetic data, the thermal subsidence for oceanic crust corrected for the sediment load fits the observed basement depth reasonably well. A subsequent roughness analysis of the basement topography show that the values fall into the same class as the ultra-slow spreading Gakkel Ridge. Furthermore, the spreading rates, which are typical for the calculated roughness, are applied to constrain the spreading history of these basins. The latest results of this analysis for the Fram Strait and its subsequent basins are shown.

Description: The northern branch of the worlds mid-ocean ridge system is located in the northern Norwegian-Greenland Sea (Fram Strait) and the central Arctic Ocean (Gakkel Ridge). The initial phase of the opening of the North Atlantic and the Arctic Ocean started some 55 Ma. While the timing and geometry of the opening of the Arctic Ocean and North Atlantic are well known, this is not true for the Fram Strait. The Lena Trough, a mid-ocean ridge in the centre of the Fram Strait, is the only deep water connection of the Arctic Ocean, and believed to have played a critical role in the development of global climate. The lack of seismic and magnetic data in this critical area prevented any detailed model for the geodynamic history of this gateway.We present new geophysical data, which provides an enhanced model of the timing and geometry of the Fram Strait opening. Seismic data, together with new aeromagnetic information, show that the strait had opened already around 16 Ma as far south as 81°N. Then, the rift slowly propagated southwards, allowing the development of a shallow water connection between the Arctic and the North Atlantic. Large drift deposits are found on oceanic crust younger than 10 Ma, indicating the starting and continuous strong erosion of the surrounding shelves and those south of the gateway (e.g. Barents Sea, Svalbard). The new data show that the Fram Strait was in place long before the high frequency glacial/interglacial cycles started in the northern hemisphere at around 3 Ma. Furthermore, they indicate that although the gateway most likely played an important role in the long-term cooling of the northern hemisphere, it is unlikely to have been solely responsible for the intensification of the northern hemisphere glaciations in the Late Pliocene/Pleistocene.