Geological Survey of Denmark and Greenland Bulletin 26 ... - Geus

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A Basement A Skaergaard intrusion 68°11´N B 31°43´W B C Fig. 2. Simplified workflow diagram describing the process of generating 3D data from photographs to 3D modelling. A: polylines representing geological boundaries or structures are extracted from a 3D stereo plotter. B: The nodes of the polylines are converted into structural readings (here shown as small blue discs) using the GEUS Planes tool. Measurements with a poorly defined plane (high standard deviation on either the dip, dip-azimuth or plane) are discarded. C: The structural readings are imported into a 3D modelling software (Leapfrog 3D) where surfaces and volumes can be generated and compiled to a 3D model of the geological object. 1 km Fig. 3. Example of a polyline (blue) representing the boundary between the Skaergaard intrusion (dark grey in Fig. 3A, light yellow to red in Fig. 3B, representing different lithological units) and the basement (light grey in Fig. 3A, light skin tone in Fig. 3B). The same polyline is drawn on the 1:27 000 aerial photographs (A) and shown on the geological map of McBirney (1989) (B) for comparison. The difference between the locations of the two lines is up to 100 m. 58
points and polylines (Fig. 2C). In standard surface modelling, only a couple of structural readings are used for generating surfaces. The great number of structural readings produced by GEUS Planes present a problem to the modelling software making it necessary to manually select which strike-dip measurements to use for the construction of surfaces. This complication will be solved in a forthcoming upgrade of the GEUS Planes tool by changing the output and by using modelling software that can import the standard deviation as a parameter and use it to estimate the quality of the structural readings in the creation of surfaces. In areas with no pre-Quaternary exposures, such as glaciated areas or water-covered areas, support points were introduced to guide the surfaces. Drill-hole data were also imported along with a geophysical gravity model of the floor of the intrusion (T.M. Rasmussen, personal communication 2011) to further improve the model. Due to erosion and lack of exposures the locations of the roof and northern boundary A Elevation East B Elevation 5 km ? Upper Border Series Basistoppen Sill Upper Zone Triple Group Middle Zone Lower Zone Layered Series Hidden Zone Marginal Border Series East Fig. 4. 3D model of the Skaergaard intrusion in E–W (A) and N–S (B) sections. The view is towards 320° at a plunge of 15°. No vertical exaggeration. Notice the wedge-like shape of the Hidden Zone (black arrow in A). 59
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Geological Survey of Denmark and Greenland Bulletin 26 ... - Geus

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