Abstract Geological strain analysis of sedimentary rocks is commonly carried out using clast-based techniques. In the absence of valid strain markers, it can be difficult to identify the presence of an early tectonic fabric development and resulting layer parallel shortening (LPS). In order to identify early LPS, we carried out anisotropy of magnetic susceptibility (AMS) analyses on Mississippian limestones from the Sawtooth Range of Montana. The Sawtooth Range is an arcuate zone of north-trending, closely spaced, west-dipping, imbricate thrust sheets that place Mississippian Madison Group carbonates above Cretaceous shales and sandstones. This structural regime is part of the cordilleran mountain belt of North America, which resulted from accretion of allochthonous terrains to the western edge of the North American continent. Although the region has a general east–west increase in thrust displacement and related brittle deformation, a similar trend in penetrative deformation or the distribution of tectonic fabrics is not observed in the field or in the AMS results. The range of magnetic fabrics identified in each thrust sheet ranges from bedding controlled depositional fabrics to tectonic fabrics at a high angle to bedding.

Abstract Analyses of consolidation state, fabrics and physical properties were conducted on rock samples from the Plio-Pleistocene Boso forearc basin, central Japan. Consolidation tests identified that the trend in consolidation yield stress was systematically 8 MPa smaller than expected for the overburden from the sediment thickness of the Kazusa Group. An excess fluid pressure interval was also identified in the lower part of the basin fill, where several large-scale (several kilometres in length and several tens of metres thick) mass-transport deposits (MTDs) are intercalated. This interval is characterized by high porosity and small consolidation yield stresses, indicating that consolidation had been retarded by the excess fluid pressure. The estimated excess fluid pressure was c. 5–7 MPa. In addition, outcrop-scale fluidization and minor liquefaction features were identified within and below the high fluid pressure interval. The excess fluid pressure reduced the effective stress in the Boso forearc basin and, subsequently, the stability of the slope, allowing small tectonic events to generate submarine landslides. Therefore, the formation of these large-scale MTDs was probably related to the excess fluid-pressure generation.

Abstract The 400 km long transect through Ellesmere Island is located perpendicular to the North American continental margin between the Arctic Ocean in the NNW and the Greenland–Canadian Shield in the SSE. It provides an insight into the structural architecture and tectonic history of the upper parts of the continental crust. The northernmost segment of the transect is dominated by the composite Pearya Terrane, which amalgamated with the Laurentian margin during the Late Devonian–Early Carboniferous Ellesmerian Orogeny. The Neoproterozoic to Devonian Franklinian Basin is exposed south of the terrane boundary and most probably overlies the crystalline basement of the Greenland–Canadian Shield. The structures along the transect in this area are dominated by kilometre-scale Ellesmerian folding of the Franklinian Basin deposits above a deep-seated detachment, which is suggested to be located at the boundary between the basement of the Canadian Shield and the overlying >8 km thick Franklinian Basin. Following the development of the Late Mississippian–Palaeogene Sverdrup Basin, the complex Eurekan deformation reactivated Ellesmerian thrust faults and probably parts of the associated deep-seated detachment. In addition, large Eurekan strike-slip faults affected and displaced pre-Eocene deposits and tectonic structures, particularly in the northern part of the transect. Supplementary material: The complete transect (Segment 1 to 5) through Ellesmere Island between the Arctic Ocean in the NNW and Kane Basin in the SSE is available at https://doi.org/10.6084/m9.figshare.c.3783608

Abstract The New Siberian Islands are affected by a number of Mesozoic tectonic events. The oldest event (D1a) is characterized by NW-directed thrusting within the South Anyui Suture Zone combined with north–south-trending sinistral strike-slip in the foreland during the Early Cretaceous. This compressional deformation was followed by dextral transpression along north–south-trending faults, which resulted in NE–SW shortening in the Kotelny Fold Zone (D1b). The dextral deformation can be related to a north–south-trending boundary fault zone west of the New Siberian Islands, which probably represented the Laptev Sea segment of the Amerasia Basin Transform Fault in pre-Aptian–Albian times. The presence of a transform fault west of the islands may be an explanation for the long and narrow sliver of continental lithosphere of the Lomonosov Ridge and the sudden termination of the South Anyui Suture Zone against the present Laptev Sea Rift System. The intrusion of magmatic rocks 114 myr ago was followed by NW–SE-trending sinistral strike-slip faults of unknown origin (D2). In the Late Cretaceous–Paleocene, east–west extension (D3) west of the New Siberian Islands initiated the development of the Laptev Sea Rift System, which continues until today and is largely related to the development of the Eurasian Basin.

Abstract The NW–SE-trending Pai-Khoi fold–thrust belt links the Permian Uralian Orogen in the Polar Urals with the early Mesozoic fold belt on Novaya Zemlya. An interpretation of structural lineaments present in southern Novaya Zemlya suggests that the NW–SE-trending fold belt in southernmost Novaya Zemlya may have formed contemporaneously with parallel sinistral strike-slip faults. Analysis of regional-scale geological maps of the adjacent Pai-Khoi fold–thrust belt reveals large-scale structural relationships indicative of sinistral shear along the fold–thrust belt, including the presence of left-stepping en echelon folds within the Kara Shale Allochthon. This interpretation is corroborated by a field study of the allochthon-bounding Main Pai-Khoi Thrust, which reveals a consistently oblique tectonic stretching lineation, pitching 56° towards the east, suggesting tectonic displacement towards the west. It is therefore proposed that the Pai-Khoi fold–thrust belt is best described as a zone of sinistral inclined transpression. The interpretation of the Pai-Khoi fold–thrust belt as a zone of sinistral transpression has important implications for the interpretation of this tectonic boundary. This is reflected in a new structural cross-section through southernmost Novaya Zemlya, which is characterized by thick-skinned tectonics and steep strike-slip faults. These faults may link at depth with the Baidaratsky Fault.

Abstract Epithermal veins and breccias at the Kainantu gold–copper deposit in Papua New Guinea, host gold mineralization in NW–SE steeply dipping lodes. The lodes are parallel to a pre-mineralization dextral strike-slip shear-zone network, which is itself parallel in places to an early greenschist-facies cleavage in basement schists. The cleavage, shear zone and veins are all cut by dextral strike-slip faults. High Au grades correlate with areas of obliquity between the shear-zone fabrics and the cleavage, and plunge at approximately 40° SE in the plane of the lodes – coincident with minor fold axes related to a crenulation cleavage in the basement rocks. This clear structural history shows that gold mineralization was confined to a particular late structural event, but lode geometry was influenced by all previous structures, as well as being displaced by post-mineralization faulting. The north–south shortening recorded through most of the tectonic history can be related to Tertiary convergence along the major plate boundary located approximately 15 km north of the mine. However, mineralization occurred under a different tectonic regime from the current north–south convergence, when there was a change of tectonics between 9 and 6 Ma, possibly related to delamination.

Abstract Field, drillcore and geochemical data are used to create a three-dimensional implicit model to assess the controls on gold mineralization at the Nalunaq orogenic gold deposit in South Greenland. Gold occurs in narrow quartz veins with variable dips averaging 34° SE that cut meta-basic rocks. The bulk of the mineralization is contained within a single gold–quartz vein, named the Main Vein. Within this vein, gold is concentrated into three ore shoots plunging 20–25° NE, corresponding to the South, Target and Mountain blocks of the Nalunaq gold mine. Gold anomalies in drillcores are identified updip and downdip from the current mine workings. Modelling reveals that structural controls have the greatest influence on the location of gold. Flexures in the Main Vein correspond to changes in the host rock lithology and the gold grade is highest where the quartz vein is steepest. Where late-stage faults intercept the Main Vein, gold grades are lower. The comprehensive gold assay data from the mine, which are integrated with structural observations in the implicit model, refine the structural interpretation of the Nalunaq gold deposit, highlighting the ore shoot geometry and delineating the minimum extents of mineralization beyond the currently mined areas.