Beschreibung: The cruise leg MSM09/3 was conducted as a cooperative project between the Alfred Wegener Institute for Polar and Marine Research (AWI), the Federal Institute for Geosciences and Resources (BGR), the Geological Survey of Denmark and Greenland (GEUS) and Dalhousie University. A geophysical survey covered areas of Baffin Bay and Davis Strait between Greenland and the Canadian Baffin Island. A component of the IPY 2007/08 Lead Project Plate Tectonics and Polar Gateways in the Earth System (PLATES & GATES), this project DAVIS GATE is aimed to develop a tectonic and sedimentary reconstruction of the opening process of this oceanic gateway. Baffin Bay and Davis Strait play an important role in the shallow water exchange from the Arctic to the Atlantic Ocean. The plate-tectonic evolution as well as the magmatic history of this region has been sparsely known and required a careful geophysical investigation in order to construct a set of gridded detailed paleo-topographic maps for a complete geodynamic reconstruction of this gateway. With a set of three seismic refraction/wide-angle reflection profiles, using ocean-bottom seismometers on 62 stations, as well as multi-channel reflection seismic recordings with a 3000-m long streamer, data were acquired from the sedimentary cover to the deep crust and even from parts of the uppermost mantle. Additional seismic data supplement these profiles and provide insights into the structures of the basement and dominant fault zones such as the Ungava fault system. A parallel running magnetic survey aimed to resolve the temporal evolution of the oceanic crust of Baffin Bay. The extension and subsidence of the continental and transitional crust in the Davis Strait and the evolution of oceanic crust in the Labrador Sea and Baffin Bay could be investigated with dataset to which continuously recorded gravity anomaly data and sub-bottom profiler data also contribute. This dataset provides the basis of geometrical and physical properties of the crust required for a realistic geodynamic model which will describe the break-up and the ocean basin evolution between Greenland and Canada in terms of detailed paleo-topography.

Beschreibung: Baffin Bay is the northwest extension of the Labrador Sea spreading system. The transition zone between these two areas is characterized by the sinistral Ungava transform-fault system across Davis Strait. The crustal type within Baffin Bay is considered to be oceanic based on a few refraction seismic experiments of older vintage. However, the velocity-depth profiles obtained from these experiments also indicate deviations from normal oceanic crust. A refraction profile in northern Baffin Bay indicates that spreading there was amagmatic and that serpentinized mantle is encountered beneath the sedimentary sequence. In addition, no magnetic anomalies related to seafloor spreading could be detected in Baffin Bay so far. This leaves a relative uncertainty about the geodynamic evolution of the Davis Strait and Baffin Bay region. For this reason, a geophysical study was carried out onboard the research vessel Maria S. Merian in 2008, collecting wide-angle reflection/refraction seismic data, supplemented by coincident and additional deep reflection seismic profiles, potential field measurement, swath bathymetry and high-resolution sediment profiling (Parasound). The refraction seismic data set comprises three lines running across the centre part of Davis Strait and southern Baffin Bay extending from Greenland to Baffin Island. The seismic source was an airgun array with a total volume of 7006 cubic inches and the shots were recorded by up to 25 ocean bottom seismometers (OBS) deployed along each line. Initial velocity models will be presented for line AWI-20080600 extending from the Sisimiut Basin off Greenland across the Hellefisk well, farther towards the NW and parallel to the assumed extinct spreading axis (based on gravity data) up to the Baffin Island continental margin some 60 km to the south of ODP site 645. The record sections indicate considerable lateral variations of the crustal structure and character along the line.

Beschreibung: Während des Merian-Fahrtabschnitts MSM09/3 wurden Ende 2008 in einer Kooperation zwischen dem Alfred-Wegener-Institut für Polar- und Meeresforschung (AWI), der Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), dem Geologischen Dienst von Dänemark und Grönland (GEUS) und der Dalhousie University geophysikalische Untersuchungen in der Baffinbucht und Davisstraße zwischen Grönland und dem kanadischen Baffininsel durchgeführt. Als Teilvorhaben des IPY-2007/08-Kernprojekts Plate Tectonics and Polar Gateways in the Earth System (PLATES & GATES) hat das Projekt DAVIS GATE das Ziel, eine tektonische und sedimentäre Rekonstruktion des Öffnungsprozesses dieser Meeresstraße zu entwickeln. Die Baffinbucht und Davisstraße spielen eine wichtige Rolle für den Flachwasseraustausch zwischen dem arktischen und dem atlantischen Ozean. Die plattentektonische Entwicklung sowie die magmatischen Ereignisse im Laufe dieser Entwicklung sind bisher kaum bekannt und erforderten eine eindringliche geophysikalische Untersuchung, um akkurate paläobathymetrische und paläogeographische Datensätze für eine vollständige geodynamische Rekonstruktion dieses Gateway zu erstellen. Entlang von drei refraktions/weitwinkelseismischen Profilen unter Nutzung von Ozeanbodenseismometern auf insgesamt 62 Stationen sowie dem Einsatz der Mehrkanal-Reflexionsseismik mit einem 3000 m langen Streamer sind Daten von der sedimentären Bedeckung bis in die tiefe Kruste und teilweise vom obersten Mantel gewonnen worden. Weitere seismische Profildaten ergänzen diese Messungen und lassen Einblicke in die Strukturen des Grundgebirges sowie der dominanten Verwerfungszonen, z.B. der Ungava-Störung, zu. Eine parallel angelegte Magnetfeldvermessung ist auf die Auflösung der zeitlichen Entwicklung der ozeanischen Kruste der Baffinbucht ausgerichtet worden. Ausdünnung und Absenkung der kontinentalen Kruste und Übergangskruste in der Davisstraße und die Entwicklung der ozeanischen Kruste der Baffinbucht konnten mit diesen geophysikalischen Daten, zu der auch kontinuierlich aufgezeichnete Schwerefeld- und Sedimentechographiedaten gehören, untersucht werden. Diese Daten liefern die Informationen über die geometrischen und physikalischen Eigenschaften der Kruste und ihrer Sedimentbedeckung, die für ein realistisches tektonisches, geodynamisches und sedimentäres Modell notwendig sind, das den kontinentalen Abbruchs und der Entwicklung des Ozeanbeckens zwischen Grönland und Kanada paläo-topographisch im Detail beschreibt.

Beschreibung: The geology of the wide shelves surrounding the South Atlantic is closely linked to the kinematics and history of the opening of the ocean. However, several wide sedimentary basins, which developed along the margins show peculiarities that are not yet understood in the context of the evolution of the South Atlantic. The Colorado Basin, a wide sedimentary basin on the broad shelf of Argentina, extends in EW direction. The basin's evolution oblique or orthogonal to the continent–ocean boundary indicates that it is not a product of simple progressive extension and crustal thinning. In addition a basement high, paralleling the continental margin and separating the Colorado Basin from the deep-sea basin is a common interpretation. These findings are hardly in accordance with the idea that the Colorado Basin is an extensional basin that developed in conjunction with the early E–W opening phase of the South Atlantic in the Late Jurassic/Early Cretaceous. The composition, type, and structure of the basement, key points for the evaluation of the basins evolution, are widely speculative. In this context multichannel seismic reflection data from the Argentine Shelf and a 665-km-long onshore–offshore refraction profile, running across the Colorado Basin onto the coast are discussed in combination with gravity data. The stratigraphy for the sedimentary successions was adopted from the literature and the reflection seismic marker horizons formed besides the interval velocities the input for the starting model for refraction seismic traveltime modelling. The modelling strategy was an iterative procedure between refraction seismic traveltime and gravity modelling. The preparation of the density models was coarsely orientated on published velocity–density relations. The modelling results are in favour of a continuation of the main onshore geological features beneath the sedimentary infill of the Colorado Basin. We interpret the basement along the line from west to east as offshore continuation of the Ventana Hills, the Claromecó depocentre, and of Palaeozoic to Middle Mesozoic rocks of the Patagonia terrane. In the deepest part of the pre-/ synrift graben within the Colorado Basin a volcanic/igneous intrusion was interpreted forming an injection into an extensional fault. According to our interpretation most of the Colorado Basin developed in conjunction with an early opening phase of the South Atlantic (150–130 Ma) and thus represents a typical rift basin instead of an intracontinental sag basin. The origin of the oblique rift most probably resulted from extensional stress, acting either through or interfering with the prevailing Palaeozoic basement fabric, oriented NW–SE. Although there was certainly a strike-slip component in the basins evolution and it may be interpreted as pull-apart basin we suggest that the Colorado Basin represents a failed rift structure: The basin's floor is more or less flat across the shelf, shows a slow rise at the shelf break and deepens towards the deep-sea basin where it finally merges with the seaward-dipping reflector sequences, and the basin probably was affected by magmatic/volcanic intrusives/extrusives associated with the opening of the South Atlantic.