This contribution presents a new map of the Palaeoproterozoic Kangâmiut dyke swarm in Central West Greenland. The map is based on publicly available aerial imagery, the scale and quality of which allowed for quick and efficient interpretation across a large area. The Kangâmiut dyke swarm has played a pivotal role in the identification and characterisation of the southern margin of the Nagssugtoqidian orogen. Change in dyke orientation from NNE-trending in the south to ENE-trending farther north is accompanied by increasing deformation in both dykes and host rocks. The zone where dykes and host rocks are totally parallelised defines the southern structural and metamorphic front of the Nagssugtoqidian orogen. We document variable changes in orientation of the dykes and their density to estimate the crustal extension accompanying dyke emplacement. The average width of the 123 dykes is 25 m (80% are <50 m). These dykes occur with an average frequency of 3.4 dykes per km and make up 6–11% of the outcrops. These data reveal subordinate groups of dykes with ESE and NE orientations and track regional changes. At present, their ages relative to the dominant NNE-trending swarm are not known. The swarm generally extends from south of Maniitsoq northwards to the Ikertooq shear zone; however, we identified features north of the Ikertooq shear zone, which we speculatively interpret to represent the northernmost occurrence of the Kangâmiut dyke swarm. The tectonic consequences of this interpretation – if correct – allow us to estimate the amount of shortening across the Ikertooq shear zone during the Nagssugtoqidian orogeny to be more than 150 km. If the other major tectonic boundaries in the orogen, including the Nordre Strømfjord shear zone, were the loci of similar shortening, the current extent of the orogen may represent only a fraction of pre-Nagssugtoqidian crust in Central West Greenland.

The general extent and structural evolution of the southern Nagssugtoqidian orogen of West Greenland were first described by Hans Ramberg who based much of his paper on the deformation of the regional Kangâmiut dyke swarm. The southern boundary is marked by a transition from undeformed, discordant dykes in the south to highly deformed dykes and host rocks to the north. Our analysis of the southern Nagssugtoqidian orogen and its southern foreland uses a comprehensive compilation of available data and covers the area from Sisimiut in the north to Alanngua, south of Maniitsoq. This represents almost the entire c. 200 km latitudinal extent of the Kangâmiut dyke swarm and encompasses the complete range of Nagssugtoqidian overprint on these dykes and their country rocks. South of Itillip Ilua (Itilleq), the structural and metamorphic overprints on the dykes exhibit a considerable range in both intensity and P–T conditions between and even within outcrops. In contrast, north of Itillip Ilua, the rocks show more systematic gradual increases in the degree of structural overprints and metamorphic grade, culminating in the Ikertooq thrust zone where granulite facies rocks are brought southwards over amphibolite facies rocks. Currently, available age data from the Nagssugtoqidian orogen permits the identification of two metamorphic episodes at c. 1850–1800 Ma and c. 1780–1720 Ma. These groups of metamorphic ages are supported by recent 40Ar–39Ar ages from dykes in the same area, which cluster at c. 1860 Ma and c. 1740 Ma, respectively. Albeit geographically sporadic, both age intervals support a subdivision of the Nagssugtoqidian structural and metamorphic overprints across the southern Nagssugtoqidian orogen and its foreland into two distinguishable temporal phases. Further geochronological investigations may well, however, find these two phases to be part of a tectonic continuum. For now, it is thought that the older event records south-directed thrusting over the foreland and concomitant loading of this crust, at least as far south as Maniitsoq. This c. 1860–1800 Ma crustal shortening and thrusting likely also closed a depositional basin located at the current latitude of Ikertooq, which could have formed during an early-orogenic extensional event that enabled and accompanied the c. 2035 Ma emplacement of Kangâmiut dykes. Up to 50–100 Ma later, a younger (c. 1780–1720 Ma) phase of shearing and thrusting mainly affected the Itillip Ilua – Ikertooq area and likely overprinted elements of the former event. This local younger overprint generated a separate trend of distinctly northward-increasing deformation and metamorphism.

Clusters of aligned, highly elongate, prismatic quartz (Qtz) rods occur in a few fayalite (Fa) crystals in an eulysite from a recently identified similar to 1.8 Gy UHP site in central West Greenland (Glassley et al. 2014). Additional detailed analyses of the crystallography and phase compositions of these olivines were conducted to evaluate the postulate that the Qtz rods formed during inversion of super-silicic ahrensite to Fa+Qtz during decompression. These new observations show the Qtz rods consistently occur in crystallographically coherent clusters with the Qtz grains aligned parallel to [100] of Fa. The contrasting compositions of coexisting primary UHP Fa and Fa postulated to have formed by inversion of ahrensite are consistent with the inversion scenario. We thus conclude that all available data are consistent with the postulate that ahrensite was part of the equilibrium phase assemblage formed during UHP metamorphism and that it inverted to Fa+Qtz upon decompression. If true, this would represent the first occurrence of terrestrial ahrensite formed through natural tectonic processes.

The central and southern regions of the North Sea Basin are characterized by mobile Zechstein Salt and represent an excellent area to study listric normal fault development related to halokinesis. The North Sea Basin–in spite of being a mature explored hydrocarbon producing basin-contains a generally not fully understood hydrocarbon plumbing system. Faults and associated fluid migration routes represent critical elements of the plumbing system. Here we present a combined 3D seismic mapping of a listric fault and detailed seismic attribute analysis of shallow gas anomalies near the fault implying a close and complex relationship between a major detaching fault, hangingwall deformation and fluid migration and entrapment. The fault and associated antithetic and secondary synthetic faults is controlled by the growth of the underlying salt structure. Three separate segments of the fault are recognized showing distinct and varying characteristics of structural maturity and fluid migration. The studied fault and shallow gas anomalies thus represent an example of a complex faulted shallow fluid migration system developing in relation to an underlying salt structure which could be relevant for understanding similar salt, fault and fluid migration systems around the world.

The Nagssugtoqidian Orogen is a ca. 1.8 Ga belt of east-west trending, highly deformed rocks that bisects central Greenland. Although a variety of data have suggested this belt marks the location of a continent-continent collision zone, evidence of subduction has been lacking. We report here mineralogical evidence from four samples within a well-defined lithologic unit of metabasic and metasedimentary ocean floor rocks of a previously unrecognized UHP metamorphic episode. The UHP episode is recorded by remnants of orthopyroxene exsolved from majoritic garnet, graphitized diamond, exsolution of rutile from garnet and pyroxenes, exsolution of magnetite from olivine, and complex exsolution textures in ortho- and clinopyroxenes (including omphacite). Associated with these mineralogical features is an unusual occurrence of quartz needles in Mn-rich fayalite. From textural characteristics, we infer that the quartz needles exsolved from the fayalite. To our knowledge, olivine with exsolved silica has not been reported. We note, however, that experimental studies have shown that beta-spinel can incorporate excess silica. We therefore speculate these quartz needles may be silica that exsolved from Mn-rich ahrensite, the Fe analog of ringwoodite, upon decompression and inversion to fayalite. If correct, this occurrence would be the first reported sample of naturally occurring olivine (fayalite) that inverted from ahrensite. Corroborating an early UHP history are reaction relationships that delineate a path through high-pressure and high-temperature conditions during decompression. P-T conditions inferred for the UHP episode are similar to 7 GPa at similar to 975 degrees C. The unusually low T for this UHP system at similar to 1.8 Ga may reflect either very rapid subduction rates at that time, or unexpectedly cool mantle conditions. Preservation of the UHP assemblages probably is due, in large part, to the exceptionally low alpha(H2O) during decompression and cooling. These UHP rocks establish that the location of the subduction and suture zones that must have existed prior to and during the collision of continents was along what is now the northern edge of the Nordre Stromfjord shear zone.

The microstructures of cm-scale displacement faults offsetting unlithified sequences of finely interbedded sands, silts and clays from outcrops in Denmark have been examined. A variety of shear band types are recognised based on their grain-scale deformation mechanism and internal structure. Shear bands in a Jurassic sequence exposed along the coastline of Bornholm are characterised by intense cataclasis of both sand and clay layers. This deformation mechanism is accompanied by extensive grain scale mixing along discrete shear bands to give a fault rock composition that reflects the relative amount of sand and clay within the faulted sequence. In contrast, shear bands at Nr. Lyngby and Jensgaard, both on the Jutland coast, are characterised by granular flow within the sand units. Grain scale mixing is subdued at these locations so that layers maintain their integrity across the shear band to form a layered internal structure of sand, silt and clay smears. In some instances, particularly at Nr. Lyngby, clays have deformed in a brittle manner so that they do not contribute material to the shear band, which is then comprised exclusively of coarser-grained components. The different deformation mechanisms and internal structures of shear bands are thought to be controlled by burial depth at the time of faulting.

The stratigraphy of successions exposed in footwall crests of tilted fault blocks is commonly highly complex. Crestal stratigraphy and structure are particularly difficult to unravel in the subsurface due to poor seismic resolution across fault zones, footwall collapse, and coalescing syn- and post-rift unconformities. Crestal ridges are important elements in basin evolution, as they form drainage divides and sediment sources for aprons along footwall scarps and hangingwall deltas. A Middle Jurassic – lowermost Cretaceous footwall crest is exceptionally well exposed in the mountain Stratumbjerg in Wollaston Forland, East Greenland. Rifting and block tilting was initiated in the (?)Bajocian, intensified in the Oxfordian–Kimmeridgian, culminated in latest Jurassic, Volgian, time and faded out in the earliest Cretaceous. The main border faults of the westward tilted blocks trend roughly N–S. The first early syn-rift block was formed in the Middle–Late Jurassic and was 40 km wide. During rift climax in the latest Jurassic it was fragmented into three blocks, each 10–15 km wide. The early syn-rift succession rests on thin Upper Permian evaporites and carbonates or directly on peneplaned crystalline basement. It is composed of the stepwise backstepping marine Pelion, Jakobsstigen and Bernbjerg Formations deposited in progressively deeper water, reflecting the combined effects of increased rifting and long-term eustatic rise. The rift-climax and late syn-rift succession was deposited along the main western basin margin fault scarp. Up to several kilometres thick, it consists of coalesced, mainly conglomeratic, deep-marine–slope-apron fans. Over the block crest this succession unconformably overlies early syn-rift strata, whereas in the deeper parts of the halfgraben, the base of the succession is conformable. A post-rift unconformity was formed in the late Hauterivian, probably during early post-rift emergence and has an irregular, stratigraphically and structurally controlled erosional topography. The eroded early syn-rift, rift-climax and late syn-rift successions were subsequently draped by deep-marine Barremian, and younger post-rift strata. The outcrop example highlights the interplay between large-scale block faulting, minor synthetic intra-block faulting, crestal degradation, and development of rift-climax and post-rift unconformities with pronounced erosional topography. It provides an excellent structural–sedimentological field analogue to deeply buried marine halfgraben settings, which are key elements in many hydrocarbon reservoirs. Its tectonic and stratigraphic development is thus highly similar to a number of large oil fields in the North Sea and the Norwegian shelf.

A multidisciplinary research project 'Resources of the sedimentary basins of North and East Greenland' was initiated in 1995 with financial support from the Danish Research Councils. This is a joint project involving the Geological Survey of Denmark and Greenland (GEUS), the Geological Institute of the University of Copenhagen, the Department of Earth Sciences of the University of Aarhus and the Danish Environmental Research Institute (DMU). The participants include staffmembers ofthe insti tutes, four Ph.D. students and three post-doctorate stipen diates. The project is divided into three parts that all relate to exploration and exploitation of minerals and hydrocar bons in the sedimentary basins of North and East Green land (Fig. 1). The purpose of the hydrocarbon related studies de for in the three different of basins outcropping the East the selected basins are of tectonic and lithology. these results will used in of sedimen tary offshore East is petroleum

The Nordre Strømfjord Shear Zone (NSSZ) in West Greenland is the northernmost zone of intense deformation within the 1.7–2.0Gya Nagssugtoqidian Orogen (NO). The NO preserves a record of continent–continent collision and crustal-scale shearing associated with the assembly of the Columbia super-continent. Also preserved in the NO is a complex of calc-alkaline rocks that formed in the root zone of an arc system during the pre-collision period when ocean floor subduction was occurring. Chemical analysis of the calc-alkaline rocks provide strong evidence that large volumes of hypersaline fluids metasomatically altered the pre-existing rocks as fluid flowed along preferential pathways within the NSSZ. The minimum integrated fluid volume flux required to accomplish the observed chemical modification is 4.66×104m3/m2. The composition of the fluid was such that it resulted in highly enriching the rock in K, Rb, Th, P, Zr, Pb, LREE, Nb and Ba. The likely fluid source was devolatilization reactions in hydrated, subducted ocean crust and mantle, the underthrust continental mass, and the release of trapped pore fluids. The extent and magnitude of the mass transfer from deep crustal levels to intermediate and shallow levels represents a significant mechanism for modification of the compositional features of deep and intermediate continental crust. Hence, the processes recorded in the NSSZ may provide an important mechanism that would influence compositional stratification of the continental crust.

The pre-Cretaceous basin evolution of the Feda Graben area in the vicinity of the Norwegian-Danish basin has been reconstructed utilizing geological and structural interpretation. The analysis reveals that the basin was faulted at its borders prior to the salt deposition in the Late Permian. Salt movement was initiated in Late Triassic and thick Triassic and Lower Jurassic pods were deposited in the graben area due to this movement. Salt pillows were developing along the Feda Graben bordering faults until Middle Jurassic when the pillows were collapsed. Salt diapirs within the study area preferentially occupy the crest of the Feda Graben and their occurrence is controlled by the underlying faulted topography. The diapirs were fed by salt from the central and southern parts of the basin and were developed by different processes i.e. upbuilding, downbuilding. Various raft structures were developed in the graben area hanging wall while some uplift occurred in the footwall during Mesozoic rifting. The Feda Graben area experienced rifting from Late Jurassic to Early Cretaceous. The most pronounced subsidence episode related with this rifting in the Feda Graben area took place along the eastern bounding Gert Fault. The Mesozoic rifting event is marked by a major unconformity on the seismic sections throughout the study area. Furthermore, the region experienced basin inversion in Late Cretaceous. The effects of inversion are more pronounced in the western part and along the Gert Fault. The inversion phenomenon can be properly understood only when considered together with the geometry of the Late Jurassic half-graben. Due to some inconsistencies in the previously proposed models for the development of the Feda Graben, a new conceptual model has been constructed.

Serial cross-sections of faults within soft sediments of Miocene age, on the East coast of Denmark, were collated to provide 3D data sets with which to study the geometry of minor faults (displacements < 10 cm). From the wide variety of geometrical complexities displayed by these faults, many due to mutually cross-cutting relationships between opposed dipping faults, we present relatively simple structures considered to demonstrate stages in the evolution of relay zones between overlapping fault segments. The structures described are: (1) initial embayments in fault tip-lines, (2) established relay zones displaying transfer of displacement between overlapping fault segments, (3) breached relay zones, and (4) fault bound lenses. An individual relay zone may display more than one of these structures along its length and relay zones that are intact on one cross-section may be breached along strike on another. Examples of relay zones that are isolated from the fault tip-line and are effectively holes within a continuous fault are also observed. The observed relay zones breach by propagation of the initial parent fault through the relay zone rather than by the formation of a new breaching fault.

A clay- or shale-rich fault gouge can significantly reduce fault permeability. Therefore, predictions of the volume of clay or shale that may be smeared along a fault trace are important for estimating the fluid connectivity of groundwater and hydrocarbon reservoir systems. Here, we show how fault smears develop spontaneously in layered soil systems with varying friction coefficients, and we present a quantitative dynamic model for such behavior. The model is based on Mohr-Coulomb failure theory, and using discrete element computations, we demonstrate how the model framework can predict the fault smear potential from soil friction angles and layer thicknesses.