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Abstract In this contribution we review our knowledge of the regional first order geometry of the Norwegian - Greenland Sea rift system, focusing on the evolution of the distal margins and on breakup. We include a description of selected published and unpublished geoseismic profiles considered as representative of the margins architecture, from the Møre - Jan Mayen conjugates to the Lofoten - North-East Greenland segment. The selected transects illustrate the geometry of the extensional system and outline the main structural units. Based on these transects, we discuss rifting evolution at the regional scale, focusing on along-strike architectural variability and on the relationship between the distal and outer margin domains and breakup. In that framework, we examine the definition of breakup, the lateral variations in terms of structures and magmatism, discuss the possible nature and role of transfer features, and the formation and isolation of microplates. We propose to consider the distal margin domains as segmented and multiphased basins, floored by exhumed altered crustal and/or mantle rocks, variously affected by magmatic additions in diverse forms, and capped by crustal allochthons of different dimensions. We favour the role of tectonic processes in the separation of the Jan Mayen microcontinent from the Møre and Vøring margins. And, along the same line of thought, we propose that it was the lateral change of structural roles of large-magnitude fault complexes that became responsible for the along-strike segmentation of the margin. Graphical abstract Image 1 Highlights • We summarize the architecture of the Norwegian-Greenland rift system at regional scale. • Based on geotransects, we discuss its final rifting evolution and lateral segmentation. • We consider the rift distal domain as a segmented and multiphased basin, floored by exhumed and altered crustal and mantle rocks. • The lateral change of structural role of fault systems is responsible for the along-strike margin segmentation. [ABSTRACT FROM AUTHOR]

Rifted margins mark a transition from continents to oceans and contain in their architecture a record of their rift history. Recent investigations of rift architecture have suggested that multiphase deformation of the crust and mantle lithosphere leads to the formation of distinct margin domains. The processes that control transitions between these domains, however, are not fully understood. Here we use high-resolution numerical simulations to show how structural inheritance and variations in extension velocity control the architecture of rifted margins and their temporal evolution. Distinct domains form as extension velocities increase over time and deformation focuses along lithosphere-scale detachment faults, which migrate oceanwards through re-activation and complex linkages of prior fault networks. Our models demonstrate, in unprecedented detail, how faults formed in the earliest phases of continental extension control the subsequent structural evolution and complex architecture of rifted margins through fault interaction processes, hereby creating the widely observed distinct margin domains. [ABSTRACT FROM AUTHOR]

Based on a 3D seismic cube and regional 2D long-offset seismic reflection profiles, we propose a reconsideration of the architecture of the Mid-Norwegian outer Vøring margin. A system comprising large-magnitude detachment faults and steeper fault arrays was mapped together with key sedimentary markers to provide constraints on the structural history of the outer Rån-Gjallar ridges system. Additionally, a detailed mapping of the so-called ‘T-reflection’ permitted a revision of the nature, origin and tectono-magmatic significance of this debated major reflector. Based on our results, we develop a more general discussion on the final evolutionary stages of rifted margins, including the construction of the outer domain, the birth of an oceanic spreading centre and the definition of breakup. [ABSTRACT FROM AUTHOR]

Terra Nova, 23, 349-361, 2011 Abstract The long-term evolution of kilometre(s) high, seaward-facing escarpments at passive margins is linked directly to the crustal thinning gradient. The development of 'post-rift' faults in the onshore parts of the margin and the associated distribution of drainage patterns, landscape types and sediment dispersal patterns reflect this linkage. For the seismically well-imaged Norwegian margin as well as for a number of passive margins worldwide, we identify a scaling relationship that correlates escarpment height with the distance to the highly extended distal margin or, more specifically, the taper break. The highest escarpments and the most asymmetric margin topography are found inboard of sharply tapering crystalline crust, independent of margin age. Conversely, escarpments are lower where the taper is gentle. Thus, the topography of passive margins does not primarily reflect age, magmatism, climate or mantle convection, but more probably the response to loading of the laterally variable, fault-controlled architecture of the crystalline crust. [ABSTRACT FROM AUTHOR]

Based on 2D and 3D seismic reflection data from the proximal margin offshore Norway, we document for the first time how Devonian transtensional collapse tectonics gave way to a Late Paleozoic into Early Triassic style of rifting which continued to facilitate removal of large parts of the Caledonian crust. The style of faults and basins partly resemble those associated with Devonian post-orogenic transtension but the crust is much thinner than under onshore post-orogenic basins and the associated basins are younger. It is, however, unclear how much of this system represents reactivation of structures formed originally in Devonian time. Structural evidence indicates, however, that Late Paleozoic-Early Mesozoic detachment faults cut a template consisting of folded Caledonian and Devonian rocks. A substantial part of the Late Paleozoic-Early Mesozoic extensional system was characterized by necking of brittle crust over deep-seated, domal core complexes and by sedimentation in broad, structurally complex supradetachment basins. Laterally, this deformation style gave way to steeper, landwards dipping faults and to areas of less extended crust, indicating regional-scale relay of extensional strains. In the next main deformation stage, necking of the entire crust took place across faults that cut deeper into the lithosphere and that combined into seawards-dipping necking breakaway complexes. The new data and interpretations open for a revised view on the Late Paleozoic-Early Mesozoic rift phase offshore Norway and its relations both to older Devonian 'orogenic collapse´ structures as well as to the younger generation of necking breakaway complexes. On the more conceptual level we demonstrate how the brittle crust was necked in at least two major stages and how the ductile crust became redistributed and molded into core complexes and extensional culminations. The geometry of these deep features and their flanking detachment faults successively affected the style of sedimentary basins that formed in the process. The data and interpretations from the proximal Norwegian margin fill a gap in our understanding of how proximal margins may form after orogenic collapse and how early rifting paved way for the large magnitudes of finite extension that characterizes the more distal parts of the Norwegian margin. [ABSTRACT FROM AUTHOR]

We propose a new method for stress inversion and separation of principal stress states from heterogeneous fault-slip data. The method is semi-automatic, and is based on the moment method of stress inversion ( Fry 1999 ) in combination with the objective function algorithm (OFA) for stress separation ( Shan et al 2003 ). In the presented routine we randomly partition the heterogeneous fault-slip dataset into subsets ranging between one and six. The number of subsets K represents the number of possible mixed stress states in the fault-slip dataset. For each partition number K , we run the OFA 1000 times. Following this we plot and contour the principal stress axes, corresponding to the minimum value of the objective function for each run, in a stereonet. By evaluating how solution clusters of principal stress axes change with increasing number of subsets K , we are able to determine the number of mixed stress states and their optimal solutions for heterogeneous fault-slip datasets. While the numbers of subsets are underestimated, solution-clusters of principal stress axes represent average stress states. However, once the correct number of subsets is reached, solution clusters align with the slip-generating principal stress axes. The solution clusters then become stable, and overestimating the number of subsets does not significantly alter their orientation. The partition number K when stability is obtained thus determines the number of mixed stress states in the heterogeneous dataset, while the corresponding highest density solution clusters give the best estimate of the slip-generating principal stress axes and corresponding stress shape ratios. The inversion routine is tested and confirmed using synthetic data and fault-slip data from the Gullkista fault in Northern Norway. Because the stress calculation is based on the moment method, the inversion routine is insensitive to the correct assessment of slip sense, and only requires the slip vector and orientation of the fault plane as input. It is therefore a robust method to evaluate the number of mixed stress states and their respective stress tensors for complex heterogeneous fault-slip data. [ABSTRACT FROM AUTHOR]