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We analyse 498 faults identified in satellite imagery and interpret the height and width of associated footwall ranges with respect to co‐seismic elastic rebound from tectonic and erosional unloading. The dynamics of footwall uplift link uplands to catchment patterns and interrelated hanging wall sedimentary fans. Height–length relations of some catchments and associated alluvial fans scale linearly whereas others, such as fault‐slope catchments and related down‐fault fans (building out from faults) show a significant scatter without an obvious trend. Perched basins abandoned in the footwalls of younger faults offer catchment‐fan height–length relations like watergap and dipslope‐related fans and, besides, hint at reduction of dip angle due to rollback of larger faults before abandonment. Analysis of the width‐to‐height ratio (W/h) of footwall ranges offer a robust linear statistical trend, h = 0.06 W and is identical between datasets. This trend is valid for both arid and tropical rifts, the latter offering smaller rebounds. Contributions of elastic rebound on fault throw in our data are simplistically considered through comparison to global trends on fault length versus throw. This allows consideration around maximum throw (Tmax) linked to the maximum height of footwall ranges (h) and to their width (W) above the reference level. Basic calculations indicate that co‐seismic rebound contributes from <1% to 17% of extensional fault throw. Width‐to‐height ratios for large faults (L > c. 50 km) show less spread than smaller faults. Such large faults expectedly dissect the brittle crust, indicating that these large faults which root in the ductile–brittle transition approach a balanced, steady‐state kinematic pattern. We speculate that significant crustal thinning associated with these large faults triggers the onset of isostatic adjustments that drive fault rotation, instigating fault abandonment and disconnected perched basins. [ABSTRACT FROM AUTHOR]

Observations and modelling results from highly extended regions indicate that detachment fault systems recording displacements of 10 km or more become associated with footwall uplift and back‐rotation. This is commonly explained by the rolling hinge model, which predicts detachment fault back‐rotation and severe dip reduction (<20°) controlled by the amount of extension. Although detachment faults within necking domains at rifted margins often record displacements in orders consistent with those for the rolling hinge model, it is rarely invoked to explain the associated footwall configurations. Our study area encircles the necking domain of the mid‐Norwegian rifted margin, where the Middle Jurassic–Early Cretaceous Klakk Fault Complex (KFC) directly separates the Frøya High from the Rås Basin. The Frøya High represents the eroded footwall of the KFC detachment fault system which records displacements of 20–40 km. Seismic mapping and well correlation across the Frøya High reveal how three erosional unconformities correspond to three laterally extensive top basement segments which follow the strike of the sinuous KFC. The segments differ in terms of dip, basement geomorphology and the composition and age of the sediments that rest unconformably on the top of basement. We attribute the associated cross‐cutting basement unconformities across the Frøya High to footwall uplift and back‐rotation during fluctuating relative sea‐level and repeated subaerial exposure during Middle Jurassic–Early Cretaceous times. We herein introduce a revised tectono‐sedimentary model for the evolution of the Frøya High, with significant implications for sediment (re‐)routing across the high during rifting. The model indicates that spatio‐temporal sediment distribution was ultimately controlled by the process of necking and evolution of the KFC. Our findings indicate a rolling hinge‐type evolution for the KFC and further suggest that the associated mechanisms may be more common in the necking domains of rifted margins than previously assumed. [ABSTRACT FROM AUTHOR]

Late to post‐Caledonian, Devonian extension remains unresolved in the SW Barents Sea, despite considerable knowledge from onshore Norway, East Greenland and Svalbard. We analyse intrabasement seismic facies in high‐resolution 3D and reprocessed 2D data to investigate evidence for Caledonian deformation and post‐Caledonian detachment faulting in the central SW Barents Sea. These results are compared to published potential field models and analogue field studies from onshore Svalbard and Bjørnøya, substantiating that structures inherited from post‐orogenic extension influenced the Late Paleozoic and Mesozoic basin evolution. The Late Paleozoic Fingerdjupet Subbasin is underlain by a NNE‐striking, ESE‐dipping extensional detachment fault that records a minimum eastwards displacement of 22 km. The detachment fault and associated shear zone(s) separate post‐orogenic metamorphic core complexes from the syn‐tectonic deposits of a presumed Devonian supradetachment basin. Spatial variability in isostatically induced doming likely governed Devonian basin configurations. Pronounced footwall corrugations and faults splaying from the detachment indicate eastward extensional transport. This ultimately led to two interacting but subsequent, east‐stepping detachments. Local reactivation of the detachment systems controlled the extent of Carboniferous carbonate and evaporite basins in the Bjarmeland Platform area. Further, the Mesozoic Terningen Fault Complex and Randi Fault Set testify to how the inherited Devonian structural template continued to control spatial localisation and extent of rift structures during subsequent periods of extensional faulting in the Fingerdjupet Subbasin. [ABSTRACT FROM AUTHOR]

[1] The Nordfjord-Sogn Detachment (NSD) zone of western Norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits, suggesting that the zone experienced substantial displacement during Devonian extensional denudation of the Caledonides. Renewed activation occurred in Permian and Jurassic-Cretaceous times. The detachment zone consists of a succession of fault-related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing. In more detail, the lower 1-2 km thick section of the NSD zone consists of mylonites with various protoliths, showing a general upward decrease in metamorphic grade. The mylonitic section is truncated by the NSD fault, defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins. In an attempt to provide precise descriptions of the observed fault rocks, we classify these rocks into (1) noncohesive breccias, (2) cemented and indurated breccias of secondary cohesion, and (3) cataclasites, phyllonites, and mylonites formed with primary cohesion. Along and across-strike sections of the fault reveal the spatial and temporal relationships of the NSD fault. The fault zone consists of a lower section of phyllonites and cataclasites, reaching a total thickness of 50-70 m. Significant volumes of pseudotachylyte were injected into these fault rocks, and were later reworked. Reactivation of the fault is suggested by overprinting carbonate-cemented breccias that are cut by a discrete fault itself associated with breccias and gouge. By comparing the various fault rocks and their formation mechanisms, some constraints can be applied to the unroofing history. The NSD fault developed in the ductile-brittle transition zone of the crust, where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening, before hardening caused a return to frictional flow. At the same time, repeated pulses of pseudotachylyte were generated, possibly lubricating the fault zone and contributing to strain localization. These pseudotachylyte pulses also show that the fault was affected by seismic slip events, before returning to a creep regime within a wider section than that ruptured by earthquakes. Younger cemented breccias and noncohesive breccias and gouge reflect earthquake-rupturing and frictional flow within the seismogenic Crust. INDEX TERMS: 5112 Physical Properties of Rocks: Microstructure; 5114 Physical Properties of Rocks: Permeability and porosity; 5120 Physical Properties of Rocks: Plasticity, diffusion, and creep; 8010 Structural Geology: Fractures and faults; 8159 Tectonophysics: Rheology--crust and lithosphere: KEYWORDS: fault rocks, detachment, Norway, extension, brittle-ductile transition. Citation: Braathen. A., P. T. Osmundsen, and R. H. Gabrielsen (2004), Dynamic development of fault rocks in a crustal-scale detachment: An example from western Norway, Tectonics, 23, TC4010, doi: 10.1029/2003TC001558.

The geology of western Norway was bidiretional, orogen-parallel, and opposed during the Devonian extension. The More-Trondelag Fault acted as a transfer zone for the Hoybakken detachment, triggering significant magmatic activity.

A transition from supradetachment to rift basin signature is recorded in the ~1,500 m thick succession of continental to shallow marine conglomerates, mixed carbonate‐siliciclastic shallow marine sediments and carbonate ramp deposits preserved in the Bandar Jissah Basin, located southeast of Muscat in the Sultanate of Oman. During deposition, isostatically‐driven uplift rotated the underlying Banurama Detachment and basin fill ~45° before both were cut by the steep Wadi Kabir Fault as the basin progressed to a rift‐style bathymetry that controlled sedimentary facies belts and growth packages. The upper Paleocene to lower Eocene Jafnayn Formation was deposited in a supradetachment basin controlled by the Banurama Detachment. Alluvial fan conglomerates sourced from the Semail Ophiolite and the Saih Hatat window overlie the ophiolitic substrate and display sedimentary transport directions parallel to tectonic transport in the Banurama Detachment. The continental strata grade into braidplain, mouth bar, shoreface and carbonate ramp deposits. Subsequent detachment‐related folding of the basin during deposition of the Eocene Rusayl and lower Seeb formations marks the early transition towards a rift‐style basin setting. The folding, which caused drainage diversion and is affiliated with sedimentary growth packages, coincided with uplift‐isostasy as the Banurama Detachment was abandoned and the steeper Marina, Yiti Beach and Wadi Kabir faults were activated. The upper Seeb Formation records the late transition to rift‐style basin phase, with fault‐controlled sedimentary growth packages and facies distributions. A predominance of carbonates over siliciclastic sediments resulted from increasing near‐fault accommodation, complemented by reduced sedimentary input from upland catchments. Hence, facies distributions in the Bandar Jissah Basin reflect the progression from detachment to rift‐style tectonics, adding to the understanding of post‐orogenic extensional basin systems. [ABSTRACT FROM AUTHOR]

World‐class examples of fault‐controlled growth basins with associated syn‐kinematic sedimentary fill are developed in Upper Triassic prodelta to delta‐front deposits exposed at Kvalpynten, SW Edgeøya in East Svalbard. They are interpreted to have interacted with north‐westerly progradation of a regional delta system. The syn‐kinematic successions consist of 4 to 5 coarsening‐upward units spanning from offshore mudstones to subtidal heterolithic bars and compound tidal dunes, which were blanketed by regional, post‐kinematic sandstone sheets deposited as laterally continuous, subaqueous tidal dune fields. The rate of growth faulting is reflected in the distribution of accommodation, which governs sedimentary architecture and stacking patterns within the coarsening‐upward units. Fully compartmentalized basins (12, 200–800 m wide and c. 150 m high grabens and half grabens) are characterized by syn‐kinematic sedimentary infill. These grabens and half‐grabens are separated by 60–150 m high horsts composed of pro‐delta to distal delta‐front mudstones. Grabens host tabular tidal dunes (sandwaves), whereas half‐grabens bound by listric faults (mainly south‐dipping) consist of wedge‐shaped, rotated strata with erosive boundaries proximal to the uplifted fault block crests. Heterolithic tidal bars (sand ridges) occur in narrow half‐grabens, showing migration oblique to the faults, up the dipslope. Structureless sandstone wedges and localized subaqueous slumps that formed in response to collapse of the block crests were only documented in half‐grabens. Late‐kinematic deposition during the final stages of faulting occurred in partly compartmentalized basins, filled with variably thick sets of continuous sandstone belts (compound tidal dunes). [ABSTRACT FROM AUTHOR]

Significant post-orogenic extension of the renowned Semail Ophiolite and substrata in Oman resulted in the formation of metamorphic core complexes juxtaposed with an array of Maastrichtian-Paleogene extensional basins. During this evolution, basins became progressively localized. The geometry of the large-scale and long-lived extensional system changes laterally across the core complexes and reveals several generations of domes and detachments, some of which were progressively exhumed. Progressive excision and dismemberment of the ophiolite link to major fabrics in the core complexes and gradual focusing of extensional basins. [ABSTRACT FROM AUTHOR]

Palaeomagnetic data from fault rocks along major faults in the Laerdal-Gjende Fault System Cutting the Caledonian structure in the Jotunheimen area of central south Norway reveals a multi-component remanence pattern. Sample and site-mean directions from the fault rocks obtained by thermal cleaning demonstrate a simple pattern of normal polarity low blocking components and reverse polarity high-blocking directions. The magnetic signature of the Laerdal-Gjende Fault System fault rocks is identical to that observed on breccias on late faults along the west coast of Norway. Based on available palaeomagnetic reference data, we assign ages of mid-late Permian and late Jurassic-early Cretaceous for important phases of faulting and breccia formation along the Laerdal-Gjende Fault System in central south Norway. Structural windows, partly exposing basement along the axis of the Caledonides in southern Norway were exhumed by footwall uplift on major faults in the Laerdal-Gjende Fault System. The consanguinity of fault rock data from the Laerdal-Gjende Fault System and fault rocks in western Norway, and comparison with displacement on the offshore continuation of the Laerdal-Gjende Fault System along the Hardangerfjorden Shear Zone, indicate that the main tectonic events responsible for the development of the North Sea basin also significantly affected the geology of central south Norway. Keywords: Norway, Permian, Mesozoic, fault rocks, palaeomagnetism.

Abstract: At the junction of the Atlantic and Arctic margins, the crustal‐scale Keisarhjelmen detachment of north‐west Svalbard records previously unrecognised magnitudes of extension. The detachment separates a corrugated metamorphic core complex in the footwall from a mantling Devonian supradetachment basin in the hangingwall. The detachment has a top‐N displacement of more than 50 km, which is aligned with the map‐scale corrugations, and an upwards ductile to brittle transition with shear related footwall retrogression. This configuration has striking similarities to extensional collapse detachments in the paired Scandinavian–Greenland Caledonides, but orientation and position link the detachment with the Ellesmerian orogen. [ABSTRACT FROM AUTHOR]