Lineament mapping and geological history of the Kangerlussuaq region, southern West Greenland Knud Erik S. Klint, Jon Engström, Andrew Parmenter, Timo Ruskeeniemi, Lillemor Claesson Liljedahl and Anne Lehtinen How could future ice ages affect deep nuclear waste reposito- analogue for future nuclear fuel waste repositories affected ries in crystalline basement rocks? Deep repositories may be by glaciation in Fennoscandia and Canada. Accordingly, a affected by a number of glacially induced processes includ- wide range of field surveys were conducted for the analogue ing, but not limited to, (1) fault activation or re-activation project (Fig. 1). This paper describes a detailed structural and associated seismicity, (2) changing hydraulic and chemi- investigation of lineament zones and the establishment of cal groundwater dynamics and (3) enhanced erosion. Such an event succession for fault and fracture zone evolution in processes are likely to affect not only man-made barriers in central parts of the study area (Figs 1B, 2), as well as an inter- spent fuel repositories such as copper canisters and bentonite pretation of the distribution of fracture and fault zones with clay buffers, but also the rock masses that contain and iso- potentially increased permeability. Three deep holes were late the repositories. In order to increase our understand- drilled in the study area, and instruments were installed in ing of this problem, an international study (the Greenland two of them for subsequent down-hole sampling and moni- Analogue Project) was set up in 2008. The aim of the study toring of groundwater to a depth of c. 600 m. The cores were was to use crystalline bedrock at the margin of the Inland used to compare the subsurface fracture patterns with those Ice near Kangerlussuaq airport in West Greenland as an established on the basis of surface mapping. Nagssugtoqidian 52°W Disko Bugt Greenland ice sheet Nordreshear Strømfjord zone A Northern‘flat belt’ CNO NNO Nordresteep Isortoq belt Ikertôq thrust zone CNO 67°N 67° Kangerlussuaq Sisimiut C Proterozoic reworked gneiss, mainly SNO Palaeoproterozoic granodioritic or quartz dioritic with basic schlieren and lenses of metadolorite dykes Syntectonic granite suite Arfersiorfik igneous suite Granite Pegmatite 66°N Amphibolite Sisimiut charnockite 51°W Fault Kangâmiut mafic dykes Quaternary Southern Archaean Lineament systems Archaean Orthogneiss foreland Late Archaean granite Area A 1 4 Early Archaean gneiss 2 5 50 km Undifferentiated 10 km Area B (Fig. 2) B Supracrustal rocks 3 6 C Fig. 1. A: Map of Greenland showing the extent of the Nagssugtoqidian orogen and the location of Fig. 1B (rectangle). B: Regional geology of southern West Greenland, modified from Garde & Hollis (2010) and Garde & Marker (2010). CNO, NNO and SNO are central, northern and southern Nagssug- toqidian orogen, respectively. C: Lineament map of the area around Kangerlussuaq airport. Areas A and B were mapped in detail. © 2013 GEUS. Geological Survey of Denmark and Greenland Bulletin 28, 57–60. Open access: www.geus.dk/publications/bull 57 Geological setting casional, deformed mafic dykes also occur, mainly members The Kangerlussuaq area is located close to the southern mar- of the rift-related Nagssugtoqidian Kangâmiut dyke swarm gin of the c. 1.85 Ga old collisional Nagssugtoqidian orogen that preceded the Nagssugtoqidian orogeny (Mayborn & (van Gool et al. 2002). The study area covers a 100 × 50 km Lesher 2006). Brittle structures such as faults and fractures large area in front of and below the western margin of the In- are abundant and were probably formed in a younger, shal- land Ice (Fig. 1). Detailed geological mapping was carried out lower, colder and hence more rigid environment. along a transect from Kangerlussuaq airport to the margin of the Inland Ice, and of a smaller area around the three drilling sites in the valley in front of the Inland Ice (Fig. 2). Regional lineament mapping and geology The bedrock is mainly reworked Archaean orthogneiss of the study area with minor Palaeoproterozoic metavolcanic amphibolite Most lineaments in crystalline rocks represent structural and metasedimentary rocks that were deformed under high- features such as faults and shear zones, rock fabrics and grade metamorphic conditions during the Nagssugtoqidian lineaments that were created at discontinuities due to dif- orogeny (van Gool et al. 2002). The Nagssugtoqidian struc- ferences in rheology or competence. Our lineament mapping tures are generally ductile and include a penetrative gneissic comprised four steps. First, lineaments were identified using fabric, macroscale folds and pronounced shear zones. Oc- remotely sensed GIS-data compiled from aerial photographs, F1 14 ( (( (! (( ( (! (!! ((!( (!! ((! ( DH-GAP04 DH-GAP03 84 F2 86 65° 84 85 79 70 62 60° 67°08´N F2 88 F F1 82° D 1 F2 76 74° 2 1 F2 3 DH-GAP01 2 4 peg intr + 3 5 4 6 78° E 5 6 Décollement F2 folding? D 1 C Kang. dyke intr 2 80 3 80 Mafic dyke intr 1 F2 4 peg intr + F2 2 5 85 1 79 2 3 dyke intr 6 3 4 4 5 peg intr 5 6 6 Structures 79 B Lineament system Fold peg intr 1 Strike slip fault 1 2 Dip slip fault 2 3 Thrust fault A 3 4 Fault Kang. dyke intr 4 5 Foliation 1 5 6 2 6 Fold axis 3 1 km Rock fabric peg intr Russell Glacier 4 Syncline hinge line 5 74 6 Anticline hinge line Lithology: Banded felsic gneiss Kangerlussuaq–Russell fault line 50°09´W Mafic gneiss Fig. 2. Aerial image of area B (Fig. 1C) with mapped and inferred rock fabric (foliation), rock types and structural elements. Local event stratigraphic models were developed for locations A–F. The macro-scale structures outline large-scale ductile folds overprinted by various shear and fault zones. Three deep holes were drilled (DH-GAP01, DH-GAP03 and DH-GAP04). 58 Table 1. Event succession of the Kangerlussuaq area compared with the general history of central West Greenland* Age General tectonic events in central West Greenland Correlation to the Kangerlussuaq area >2.5 Ga (Archaean) Formation of ‘banded gneiss’ protoliths F1 folding + multiple healed structures c. 2.04 Ga Continental rifting coupled with mafic dyke intrusions Intrusion of Kangâmiut mafic dykes 1.92–1.75 Ga Nagssugtoqidian orogen. Continental collision. Reworking, System 1 dextral, strike-slip shear and F2 folding folding and thrusting of gneiss/mafic rocks followed by System 2 WSW–ENE-trending faulting (K–R fl†) peak metamorphism and large-scale folding during N–S Reactivation of Kangerlussuaq–Russell fault sinistral contraction. Finally formation of steep belts with sinistral strike slip movements System 3 sinistral strike-slip shear zones c. 1.78 to present day Various stress conditions. Formation and reactivation System 4 normal faults with shallow dip towards of open mode fractures at more shallow depths during SE and NW accompanied by pegmatite intrusions 20–25 km uplift 1.2 Ga Diamond-bearing, ultramafic lamprophyre intrusions S and W of Kangerlussuaq 600 Ma Kimberlite intrusions S and W of Kangerlussuaq 100–50 Ma Faulting related to sea-floor spreading during the System 5 sinistral strike-slip faults trending NE–SW opening of Labrador Sea and Baffin Bay. NNE–SSW System 6 dextral strike-slip faults trending N–S sinistral strike-slip faulting and conjugate dextral strike- slip faulting At least the last 2 Ma Repeated glaciations resulting in erosion, glacier-induced Reactivation of existing fault zones reactivation of fractures during glacial subsidence and rebound of the basement * based on van Gool et al. (2002) and Garde & Hollis (2010) † Kangerlussuaq–Russell fault line topographical and geological maps and geophysical data. The E–W-trending, 10–100 m wide, foliation-parallel, steeply in- second step was a descriptive and kinematic field analysis of clined and steeply N-dipping dextral shear zones (Figs 1C, 2). the remotely detected lineaments. In the third step, a local These shear zones may have acted as décollement planes for event succession model was developed by determination of the F2 folding (see below). overprinting relationships. Finally, the local geological histo- System 2 lineaments constitute the most pronounced lin- ry of the Kangerlussuaq area was interpreted and correlated ear feature and represent regional, SW-trending shear zones, with the regional geological evolution (van Gool et al. 2002; including the zone outlining Søndre Strømfjord itself and es- Garde & Hollis 2010). pecially the northern margin of Sandflugtdalen that extends In order to provide an overview of the geological frame- from Kangerlussuaq to Russell Glacier, hereafter named the work of the study area, the measured and interpreted struc- Kangerlussuaq–Russell fault line. Other lineaments farther tures (foliation, fold hingeline, fault and shear zone traces) north with similar orientations (Fig. 1B) comprise the Iker- are shown on a high-resolution aerial image (Fig. 2). Close tôq zone (van der Molen 1984), the Nordre Isortoq steep belt to the margin of the Inland Ice in the north-eastern part of and the Nordre Strømfjord shear zone (van Gool et al. 2002). the area, the bedrock is characterised by folded mafic gneiss Along the Kangerlussuaq–Russell fault line this lineament that defines an open, NNW-trending and shallowly plung- is dominated by sinistral strike-slip movement overprinting ing (c. 14°) F1 fold structure. This structure gradually turns elements of thrust faulting dipping towards the north. Large into a tight to isoclinal fold that can be traced southward and boudins of deformed Kangâmiut mafic dykes (Mayborn & westward around an open, steeply-plunging, kilometre-scale Lesher 2006) are included in this zone, which is therefore F2 fold structure with a NW- to N-trending axial surface younger than the intrusion of the Kangâmiut dykes. (Figs 1C, 2). System 3 lineaments are a major NW-trending system Five general lineament systems were outlined from the along pronounced valleys and extend all the way up to Aas- GIS analysis, and a sixth, subhorizontal system was identified siaat and Disko Bugt (Fig.