P The Greenland Analogue Project. Geomodel version 1 of the Kangerlussuaq area on Western Greenland. Jon Engström, Geological Survey of Finland - PDF

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P The Greenland Analogue Project Geomodel version 1 of the Kangerlussuaq area on Western Greenland Jon Engström, Geological Survey of Finland Markku Paananen, Geological Survey of Finland Knud Erik

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P The Greenland Analogue Project Geomodel version 1 of the Kangerlussuaq area on Western Greenland Jon Engström, Geological Survey of Finland Markku Paananen, Geological Survey of Finland Knud Erik Klint, The National Geological Survey of Denmark and Greenland February 2012 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 250, SE Stockholm Phone ISSN Tänd ett lager: SKB P P, R eller TR. The Greenland Analogue Project Geomodel version 1 of the Kangerlussuaq area on Western Greenland Jon Engström, Geological Survey of Finland Markku Paananen, Geological Survey of Finland Knud Erik Klint, The National Geological Survey of Denmark and Greenland February 2012 Keywords: Greenland Analogue Project, Geomodel version 1, Kangerlussuaq area, West Greenland, Deformation zones/faults. This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the authors. SKB may draw modified conclusions, based on additional literature sources and/or expert opinions. Data in SKB s database can be changed for different reasons. Minor changes in SKB s database will not necessarily result in a revised report. Data revisions may also be presented as supplements, available at A pdf version of this document can be downloaded from Abstract During the 2nd annual Greenland Analogue Project modelling workshop in Toronto, November 2010, the hydrological modellers requested an updated geological map and structural model of the field area around Kangerlussuaq, Western Greenland. This report presents an updated GAP geomodel which utilizes all available information in order to improve the accuracy of the model, especially beneath the ice sheet. The modelling area was divided into two scales: The regional scale area and the site scale area. The site scale refers to the area were surface mapping has been performed, and where two boreholes (DH-GAP01 and DH-GAP03) were drilled during Geological and topographical maps from GEUS (sub-model 1) and data extracted from the geophysical map, GEUS, (sub-model 2) were used in the process to develop GAP geomodel version 1. These two interpretations were independent from each other and in the final stage these sub-models were integrated and developed into GAP geological model version 1. The integration resulted in a total of 158 lineaments. These lineaments are referred in the final model as deformation zones and faults, where deformation zones are larger features and faults are single fractures indicating some sense of movement. Four different sets of deformation zones and faults were identified in the regional area. The most prominent feature is the ductile/brittle roughly ENE-WSW trending zones crosscutting the whole area, referred as Type 1. Type 2 and Type 3 zones are in general smaller scale than Type 1 and mostly dominated by brittle deformation. The Type 2 system generally trends NW-SE, while the Type 3 system generally trends NE-SW. The Type 4 features are a brittle and roughly N-S orientated younger system, thus crosscutting all other types. Confirmation and validation of the regional model is based on detailed surface-based examination of fractures within the site area, although the scale is different the same orientations were also identified in the regional lineament interpretation. The site area lineament model is coupled with major tectonic events in Western Greenland to further improve the certainty of our interpretation. This report describes solely a structural 2-D model and the data produced in this report were developed into a 3-D model that together with hydrological properties serves as basis for the future hydrological modelling within the GAP project, however this work is described in a separate report (Follin et al. 2011). SKB P Sammanfattning I samband med den årliga GAP workshopen i Toronto i November 2010, begärde de hydrologiska modellörerna en uppdaterad geologisk och deformationszons modell i området runt omkring Kangerlussuaq, Västra Grönland. Denna rapport beskriver framtagandet av en uppdaterad GAP geomodell, vilken använder all tillgänglig information som finns, speciellt i syfte att förbättra modellen i de istäckta områdena. Modelleringsområdet delades in i två delområden det regionala området och vårt platsundersökningsområde. Geologisk och topografisk data från GEUS (sub-modell 1) samt data extraherat från GEUS geofysik karta (sub-modell 2) användes för att producera två olika sub-modeller. Dessa två modeller producerades skilt för sig och integrerades sedan till den slutgiltiga GAP geologiska modellen version 1. Denna modell innehöll 158 lineament och i den slutgiltiga versionen refereras lineamenten som deformationszoner och förkastningar, där deformationszonerna är större spröda och plastiska zoner medan däremot förkastningarna är en spricka som uppvisar nån form av rörelse. Modellen uppvisar fyra olika typer av deformationszoner och förkastningar i det regionala området. De tydligaste zonerna är de spröda-plastiska Typ 1-zonerna som går igenom hela vårt regionala område i en ungefärlig öst-västlig riktning. Typ 2- och Typ 3-zonerna är för det mesta mindre zoner än Typ 1-zonerna och känne tecknas av att vara spröda. Typ 2-zonerna har sydostlig-nordvästlig riktning medan Typ 3-zonerna är av sydvästlig-nordostlig riktning. De yngsta zonerna är främst förkastningar och de har en nord-sydlig riktning och definieras i modellen som Typ 4. Den regionala modellen jämfördes sedan med sprickdata från vårt forskningsområde och liknande zoner samt förkastningar kunde även hittas där. Till sist gjordes en koppling mellan den tektoniska historien i vårt forskningsområde och den i Västra Grönland. Materialet från denna modell har sedan vidareutvecklats till en 3D-modell som tillsammans med den hydrologiska datan ligger som grund för den fortsatta hydrologiska modelleringen inom GAP-projektet, men detta arbete beskrivs i en separat rapport (Follin et al. 2011). 4 SKB P-11-38 Contents 1 Introduction 7 2 Objective and scope 9 3 Description of maps, data and software used during the development of the GAP geomodel Description of maps used during the development of sub-model 1; geological/topographical interpretation Description of data and software used during the development of the submodel 2; geophysical interpretation 11 4 Execution of the GAP geomodel General Sub-model 1; Lineament interpretation from geological and topographical data Sub-model 2; Geophysical lineament interpretation from GEUS data Combining the two separate sub-models into the final deformation zone model Processing the collected GAP mapping data Tentative tectonic history and related stress fields in the Kangerlussuaq area 21 5 Results and further work 25 References 27 Appendix 1 29 Appendix 2 33 SKB P 1 Introduction During the 2 nd annual GAP modelling workshop in Toronto, November 2010, the hydrological modellers requested an updated geological map and deformation zone model of the field area around Kangerlussuaq, Western Greenland. In the workshop it was concluded the previous model was insufficient to meet the demands of hydraulic modelling, this was mainly that due to the very simplistic and stochastic nature of the previous model, which was based on superficial interpretation of site scale lineaments and the mapping data collected from small key areas in 2008 (Aaltonen et al. 2010). The target area of the full-scale hydrogeological modelling is very large compared to the field area of the sub-project C (SPC) and a significant part of it is covered by ice. In order to response to the modellers request so that the updating could rest on sound argumentation, a sub-model area about 70 km by 110 km was defined so that it was mainly in the ice free region. In the east, the sub-model area is restricted by the availability of the airborne geophysical data to about 40 km east of the ice-margin (Figure 1-1). The model in this report is a lineament model constructed as an interpretation from GEUS ArcGIS data, with topographical, geological and geophysical data acquired from the updated GEUS map over Western Greenland (Garde and Marker 2010). The report includes a suggested connection to the regional tectonic history and also a possible simple stress history, however due to limited amount of collected site information these should be referred as a tentative analysis This report describes solely a structural 2-D model and the data produced in this report were developed into a 3-D model that together with hydrological properties serves as basis for the future hydrological modelling within the GAP project, however this work is described in a separate report (Follin et al. 2011). Figure 1 1. General overview over GAP modelling area. The GAP geomodel area is shown in lilac (larger box) and the site scale area in red (smaller box). The map is modified from GEUS (Geological Survey of Denmark and Greenland) Geological map 2010 (Garde and Marker 2010). SKB P 2 Objective and scope The updated GAP geomodel utilizes all available information in order to improve the accuracy of the model, especially beneath the ice sheet. The aim of the geomodelling work was to start with the large scale features and then work towards more detailed scales. Special attention is directed towards the identification of lineaments that constitutes potentially brittle structures, which may outline hydraulic conductive zones. The modelling area was divided into two scales the regional scale area and the site scale area (Figure 2-1). The site scale refers to the area were surface mapping has been performed in 2008 (Aaltonen et al. 2010), and where DH-GAP01 and DH-GAP03 were drilled during 2009 (SKB 2010). This separation into two different scales is done so that a more detailed examination and interpretation of the site scale area can be conducted in the future when more detailed data is gathered. The coordinates of the modelling area (regional area, lilac rectangle in Figure 2-1) are: NW corner: ; NE corner: ; SW corner: ; SE corner: ; These coordinates are in the Projected Coordinate System NAD 1983 Complex UTM Zone 23N, for which the GEUS geological map applies. However, the GAP project database is in the Projected Coordinate System WGS 1984 Complex UTM Zone 22N. The coordinates in this system of the regional modelling area are: NW corner: ; NE corner: ; SW corner: ; SE corner: ; The GAP site area (the smaller red rectangle in Figure 2-1) has the following coordinates: NW corner: ; NE corner: ; SW corner: ; SE corner: ; SKB P 10 SKB P Figure 2-1. Map showing the regional modelling area for the GAP geomodel in lilac and the site scale area in red. Geology is adapted from GEUS Geological map (Garde and Marker 2010). 3 Description of maps, data and software used during the development of the GAP geomodel Geological and topographical maps from GEUS (sub-model 1) and data extracted from the geophysical map, GEUS, (sub-model 2) were used in the process to develop the final GAP geomodel. These two interpretations were undertaken independently. The geophysical lineament interpretation (sub-model 2) was done on aeromagnetic data to confirm and validate sub-model 1, the two sub-models where then integrated and developed into GAP geological model version Description of maps used during the development of sub-model 1; geological/topographical interpretation GEUS recently published (Garde and Marker 2010) an updated geological map over West Greenland; which is an update of the work by Escher (1971). Together with the geological information from this map and the topography in the area, a lineament interpretation was performed for the regional area outlined in Figure Description of data and software used during the development of the sub-model 2; geophysical interpretation In order to study the occurrence of brittle deformation within the study area, interpretation of magnetic lineaments from the aeromagnetic data was carried out. This study was done totally independent from sub-model 1 and the outcome from it was defined as sub-model 2. The data were acquired from GEUS and it was extracted from aeromagnetic data that GEUS reported in 2004 (Jensen et al. 2004). Magnetic lineaments are linear, continuous features on a magnetic map possibly related to deformation zones or rock type contacts. In general, the magnetic properties of a deformation zone may vary depending on its geological history in the following ways (McIntyre 1980, Henkel and Guzmán 1977, Johnson and Merril 1972): Oxidizing fluid intrudes into the rock material during the metamorphism: deposition of magnetite; magnetic susceptibility increases. Reducing metamorphic fluid intrudes into the rock material: magnetite is transformed to nonmagnetic hematite; susceptibility decreases. Low temperature ( 250 C) weathering in a fracture zone: magnetite is decomposed; susceptibility decreases. According to these options, a deformation zone may induce a magnetic minimum or maximum. Brittle zones commonly carry water, allowing different chemical and physical weathering processes to take place within the zone, resulting in decomposition of magnetite to hematite. Since low-temperature weathering is supposedly the most recent chemical process in the brittle zones, it is therefore justified to assume that most linear magnetic minima represent their surface expressions. Also a sharp discontinuity or a displacement of magnetic anomalies may be an indication of a potential brittle deformation zone. For the lineament interpretation, the GEUS geophysical airborne data (Jensen et al. 2004) was further processed using Geosoft Oasis software, and the following series of maps was created: Magnetic total field, colour-shaded and grey-shaded map (shading from 0, 45, 90 and 135 ). Vertical derivative of magnetic total field, colour-shaded and grey-shaded map. Horizontal derivative of magnetic total field, colour-shaded and grey-shaded map. Analytic signal, colour-shaded map. Tilt derivative of magnetic total field and its horizontal derivative, colour-shaded map. Theta derivative (absolute value of tilt derivative), colour-shaded map. TDX derivative (complement angle of tilt derivative), colour-shaded map. SKB P 4 Execution of the GAP geomodel 4.1 General The work on updating the regional model started in January 2011, although some work on the site scale model and some general outlines for the regional model were already initiated in This work included processing of mapping data that the GAP project collected during and the analysis of fracture data from the pilot holes (DH-GAP01 and DH-GAP03) drilled in In addition, a regional lineament map was produced by integrating geological information and the topographical indications; sub-model 1, while a magnetic lineament map was produced from the aeromagnetic data as an independent study, thus defined as sub-model 2. Combination of these sub-models 1 and 2 comprise the GAP geological model version 1. The result was validated against mapping and drillhole data in the site area and a connection to the tectonic history was tentatively suggested by reviewing literature and examination of the limited amount of mapping data. 4.2 Sub-model 1; Lineament interpretation from geological and topographical data The geologic and the topographic maps of the regional area were examined and formed the basis for the lineament interpretation in sub-model 1. From these maps 104 lineaments were interpreted (Figure 4-1). The most prominent features are the roughly ENE-WSW trending Type 1 (lilac) lineaments that crosscut the entire area. The Type 2 (green) and the Type 3 (blue) lineaments are in general a smaller scale system than the Type 1. The Type 2 system generally trend NW-SE, while the Type 3 system generally trends NE-SW. The Type 4 (black) is an N-S system that crosscuts all other types, therefore it is younger. 4.3 Sub-model 2; Geophysical lineament interpretation from GEUS data The standard maps utilized in the interpretation comprise magnetic total field, horizontal, vertical and total gradient (analytic signal) and different normalized magnetic derivatives (tilt, theta and TDX derivative). The suitability of normalized gradients in structural mapping is well known, and their interpretational meaning is discussed in e.g. Fairhead and Williams (2006), Fairhead et al. (2007), and Salem et al. (2008). Their main advantage is that they help normalize the signatures in images of magnetic data so that weak, small amplitude anomalies can be amplified relative to stronger ones. Figures 4-2 to 4-5 show some examples of the compiled maps used in the interpretation. In addition to the standard maps, a grid curvature analysis (Phillips 2007) was done, revealing the locations of local and continuous magnetic minima (Figure 4-6). Data processing and map compilations were done by using Geosoft Oasis software. The interpretation was carried out by visually inspecting the different geophysical maps in ArcGIS and by digitizing the geometry of each interpreted lineament. The lineaments were collated into a single ArcGIS theme, accompanied by an attribute table (Appendix 1) that includes the identifier and a reference to the data for each interpreted feature. The number of interpreted lineaments shown in Figure 4-7 is 133. Their main trend is ENE-WSW (Type 1) with a clear cross-cutting trend NNE-SSW (Type 4). Other less distinct trends are NW-SE (Type 2) and NE-SW (Type 3). A number of lineaments could also be followed to the eastern part of the studied area covered by the ice sheet. In Figure 4-8, a statistical trend distribution of the lineaments is presented, showing the significance of the main trend ENE-WSW. SKB P 14 SKB P Figure 4-1. Map showing the lineaments/deformation zones in the regional area, interpreted from geological and topographical data. The different line colours refer to different Types of lineaments/deformation zones. Geology is adapted from GEUS geological map (Garde and Marker 2010). Figure 4-2. Geophysical map showing the magnetic total field. The black line indicates the ice-margin. Figure 4-3. Geophysical map showing the analytic signal (total gradient) of magnetic field. The black line indicates the ice-margin. SKB P Figure 4-4. Geophysical map showing the vertical derivative of magnetic field. The black line indicates the ice-margin. Figure 4-5. Geophysical map showing the tilt derivative of magnetic field. The black line indicates the ice-margin. 16 SKB P-11-38 Figure 4-6. Geophysical map showing the locations of local magnetic minima (troughs) from grid curvature analysis. The thick black line indicates the ice-margin. Figure 4-7. Geophysical map showing all interpreted lineaments in (white colour) on magnetic total field map. The black line indicates the ice-margin. SKB P Figure 4-8. Rose diagram showing the strikes of the interpreted geophysical lineaments (n = 133). 4.4 Combining the two separate sub-models into the final deformation zone model As could be expected, the two separate lineament interpretations produced different results so a joint interpretation of the two sub-models was carried out. This is illustrated in Figure 4-9, where it is evident that some modifications to the initial interpretations had to be performed. This was done by modifying the sub-model 1 lineaments to follow the lineaments from the geophysical interpretation. Also a number of new lineaments were added to the final model based on the geophysical lineament interpretation. The joint interpretation of Sub-model 1 and Sub-model 2 were merged into a final interpretation and the final model; GAP geological model version 1. The integration of the two sub-models into one resulted in a total of 158 lineaments. These lineaments are referred in the GAP geological model version 1 as deformation zones and faults (Figure 4-10). Even though this model is mere
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