The CASE projects (Circum-Arctic Structural Events) of the Federal Institute for Geosciences and Natural Resources
Report of the project:
From 1992 onwards, BGR has extended its successful approach of combined marine and terrestrial research activities from Antarctica to the High Arctic as well. In the marine sector, BGR had already been active with scientific cruises to the Arctic, e.g. the Labrador Sea, the Barents Shelf, and the East Greenland Shelf. It was therefore a logical step to include terrestrial geology in the northern Polar regions as well. From a practical viewpoint, it was easily possible to build on the logistics and polar experience gained during Antarctic expeditions.
Plate tectonic reconstruction for the Greenland/Nares Strait area 50 million years ago
Source: BGR
As an overall research focus, the geodynamics of continental margins around the Arctic Ocean were chosen (CASE: Circum-Arctic Structural Events). Methodologically, the focus lies on structural geology, the petrography and geochemistry of Arctic volcanic provinces, and aeromagnetic studies of areas covered by ice and water.
Thus the most remote and difficult areas of the Arctic, the ice covered shelf zones, can be assessed. Air-borne aeromagnetics can provide measurements equally from offshore, onshore, and ice covered areas and is therefore ideal to connect marine and terrestrial studies. So far, measurements have been carried out over the Lincoln Sea (PMAP-CASE 1997, 1998) and the North Greenland Shelf (NOGRAM 1998), in cooperation with Canadian institutions and Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven (AWI).
Projects CASE 1 and 2
The first research objects of CASE were the poorly understood Tertiary foldbelts on Spitsbergen and North Greenland. Here, compression paradoxically took place contemporaneously to the extension and opening of the adjacent Arctic Ocean.
The first land expedition (CASE 1) took place in 1992, to Spitsbergen. Helicopter supported field work was carried out to analyse the well exposed but rather inaccessible West Spitsbergen fold belt as a whole, cooperating with experts of different German and foreign universities. CASE 1 was followed by an expedition to the corresponding fold belt in North Greenland (Peary Land) in 1994 (CASE 2).
The results of the first two CASE projects can be summarized as follows:
The Tertiary West Spitsbergen and North Greenland fold belts display a very similar structural style. Greenland and Spitsbergen have been separated by a large strike slip fault, amounting to at least 300 km offset. CASE 1 and 2 were able to show, however, that the compressive structures are not cogenetic with this strike slip event. The compressive structures are the result of a uniform, north directed tectonic transport direction, and have then been torn apart by the strike slip fault. Because of the lack of metamorphism, syntectonic magmatism, and ocean crust relics, the fold belt cannot be considered a classic plate boundary orogen, but must have originated in an intra-plate position.
Two questions, however, had to remain unsolved: the exact age of deformation and the driving force for the compression. Due to the scarcity of marine fossils, the stratigraphic time bracket of the deformation remains ambiguous. Due to the lack of metamorphism, isotopic dating of the compressional event was not applicable either. Therefore, it remains difficult to correlate the geodynamic evolution onshore with basin and ocean crust formation offshore. As the strike slip event has been ruled out as "motor" for the compression, the search for the driving force had to continue.
CASE 4 to 6
For this reason, CASE was extended to include Arctic Canada, where relevant Tertiary deposits with compressional structures are present in large areas of the Arctic islands. Cooperation with the Geological Survey of Canada, Calgary, was possible through their mapping project on Ellesmere Island, where no official geological map exists to date. Coordinating the research interests of both partners, it was possible to combine logistics in a joint 3-year project. This cooperation project includes the expeditions CASE 4 (1998), CASE 5 (1999), and CASE 6 (2000). The field area was immediately adjacent to the Nares Strait, which is presumed to be a similar transform fault as the one between Spitsbergen and North Greenland. This made the field area ideal for examining the relationships between compression and strike slip, which was one of the central problems on Spitsbergen.
During Tertiary times, Greenland was bordered by two mid ocean spreading systems, active at the same time between 56 and 35 Ma before present - an unusual plate tectonic configuration (Fig.).
From process studies in the Labrador Sea, it is known that the Greenland Plate has undergone a two-phase movement history: first towards the Northeast, caused by active spreading on the ridge system between Canada and Greenland only, then towards the North, caused by contemporaneous spreading on both mid ocean ridges between Canada and Greenland on the one hand, and Greenland and Norway on the other. Applying this concept to the Nares Strait area, one would expect evidence for strike slip followed by compression and fold belt formation.
This model had yet to be tested in the field. CASE 4 focussed on the compressional Eurekan fold belt and its south- and eastward directed thrusts onto the foreland. During CASE 5 and 6, several parallel strike slip faults were found near the Nares Strait and analysed in detail. The sense of movement of the strike slip faults is uniformly sinistral. Maximum offset of the strike slip faults parallel to the Nares Strait is in the order of 20 km, although the whole system may have a cumulative sinistral offset of about 100 km. It is possible, however, that a larger main fault remains hidden under the Nares Strait. Field analysis was able to corroborate the concept of strike slip faulting followed by compression as predicted from the Labrador Sea studies. The driving force for both phenomena, strike slip and Eurekan fold belt, is the movement of the Greenland plate with its two phases. This, in turn, is caused by the spreading activities on both mid ocean ridges encompassing Greenland. The strike slip fault between Greenland and Spitsbergen, on the other hand, has been triggered at a later stage, when spreading had moved to the Mid Atlantic ridge, representing a connecting transform fault to the Arctic Ocean. Therefore in this part of the fold belt, the compressional event took place before strike slip activation.
The CASE project was the first to cover all parts of the Tertiary fold belt in Spitsbergen, Greenland, and Canada, and to examine it as a whole. It has revealed the driving force for this intraplate compressional belt and has therefore made its impact on the understanding of the geodynamic evolution of this part of the Arctic.
Project CASE 3
Since the beginning of BGR's Arctic activities, it has been envisioned to cooperate with Russia as well. The first research target were the Novosibirskiye Islands in the Laptev Sea, where the mid ocean ridge of the Eurasian Basin reaches the Asiatic continent. Similar to Spitsbergen, Greenland, and Canada, onshore geological studies were planned to expand on marine cruises in the Laptev Sea, carried out by BGR in cooperation with SEVMORNEFTEGEOFISIKA, Murmansk, since 1993. Increasing difficulties with the logistics, however, inhibited the field campaign despite good contacts to the Academy of Sciences in Yakutsk, who wanted to examine the islands as well. Finally, the field campaign of CASE 3 was carried out in the alternative target area of the Moma Rift east of the river Lena and the Verkhoyansk fold belt. In the arctic summer of 1998, 15 German and Russian scientists took part in this project. Difficult weather and logistics disturbed the progress, but nonetheless it was possible to achieve results correlating the Moma Rift to the rift system of the Laptev Sea (Paech et al. 1998).
Literature:
CASE 1: F. Tessensohn (ed.) (2001): Intra-Continental Fold Belts, CASE 1: West Spitsbergen. - Geologisches Jahrbuch, B91: 773 pp.
CASE 2: Contributions in the journal "Polarforschung“ 68 (1998) and 69 (1999)
CASE 3: Paech, H.-J., Prokopiev, A.V., Gosen, W.v., Grinenko, O.V., Smetannikova, L.I. & Belolyubskij, I.N. (1998): New results of the Moma Rift System and coeval structures in Yakutia, Russian Federation. – Polarforschung, 68: 59-63.