VIEWS: 1 PAGES: 19 POSTED ON: 2/25/2012
Karen Black December 2, 2011 Geologic relationships of granitoid bodies in NW Turkey 1. Introduction Purpose This summer, I conducted fieldwork in NW Turkey and collected samples from granite plutons in order to better understand their tectonic evolution. I prepared for this work by collecting maps of my field area from Google Earth and Google Maps. These consisted mainly of road maps. I also used a paper geologic map. I would now like to create more useful and conclusive maps of my field area that can be used in my thesis. These maps will effectively display the geology of my field area as well as sample locations. I would also like to obtain DEMs of my field area to help interpret the relationship between faults and granite plutons in my field area. It will be very helpful to have all of this information stored in a usable GIS that I can manipulate as needed. I will also be able to create maps from the DEM that can be used to analyze that interaction between faults and the granite plutons in the region. Background Turkey is the amalgamation of numerous continental fragments that were sutured together by the opening and closing of Tethyan Oceans. Currently, Turkey is undergoing compressional tectonics in the east, strike-slip tectonics across the entire northern portion of the continent, and extensional tectonics in the west. As the African plate collides with the Eurasian plate, the Arabia platform collides with Anatolia in the west. A free lateral boundary in the west allows for strike-slip tectonics to occur and for Turkey to escape laterally southwestward via the North Anatolian Shear Zone. The retreat of the Hellenic Arc is believed to be caused by slab- roll back that results in extension in western Turkey. Northwest Turkey is a complex region that contains geologic evidence of the suturing of continental fragments followed by the current N-S extension and SW strike-slip movements. There are multiple granite bodies in this region that were exhumed during the current extensional regime. During my field season, I focused on collecting samples from three plutons including the Kozak, Eybek, and Kestanbolu. Objective The object of this project is to create a useable GIS that will be used to analyze the geologic relationships of granitoid bodies in northwest Turkey. Data will also be used to analyze the relationships of samples collected this past summer. The final products will be a geologic map of my field area, a road map with granite outcrops, contours and sample locations, and a hillshade and aspect map with granite outcrops and faults to help analyze the topography of the region. 2. Data Collection ASTER ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Global DEM v.2 data was obtained from NASA (http://reverb.echo.nasa.gov/reverb/#utf8=%E2%9C%93&spatial_map=satellite&spatial_type=re ctangle). This ASTER GDEM is a product of METI and NASA. ASTER data was sent to me via e-mail Mark Helper because a NASA account is needed to download data from this website. I needed two tiles to cover my field area and they are N39E026 and N39E027. This data is 30m resolution and is in a zipped folder that contains metadata and a GeoTiff. Geologic Map An online geologic map of Turkey with high resolution was hard to find. I scanned a paper version of a geologic map with my field area and saved it as a .jpeg that could be opened in ArcMap. Roads An online file containing an accurate and complete set of roads in Turkey was hard to find. During fieldwork, I found that Google Maps was very accurate with roads in my field area. Therefore, I used a screen shot of Google Maps for roads of my field area for this GIS. I was also able to find precise latitude and longitude coordinates for points on my screen shot that could be used to georeference my roads screen shot. Samples During field work, sample locations were recorded as waypoints on a handheld GPS unit. These latitudes and longitudes were exported as an excel file that could be imported into ArcMap. 3. ArcGIS Before any processing any data with ArcGIS, I first created a folder for my project on an external drive. This folder contained the two unzipped ASTER files, the scanned geologic map, screen shot of roads from Google Maps, and the excel table of my sample locations. I also, created a geodatabase for the geologic map I would be digitizing titled “NWTurkey”. Also, I created a folder titled ‘MyData’ to save anything I modified such as the ASTER files. I opened a black ArcMap document and connected it to this project folder I created. I initially set the data frame coordinate system to GCS_WGS1984 (Figure 3.1). Figure 3.1. The spatial reference of the data frame was set to GCS_WGS1984. 4. ArcGIS Data Processing ASTER To process the ASTER data I dragged my two unzipped geotiff files from ArcCatalog into ArcMap. These files were automatically projected in my document. In order to see the elevation in documents I had to change the symbology of the layers (Figure 4.1). The symbology tab is located under properties when you right click on the ASTER layers in the Table of Contents (TOC). Symbology was changed to stretched with standard deviations of n=2. Figure 4.1 Screen shot of ArcMap and 2 ASTER data. Notice the line in the middle separating the two files. Because there are two ASTER datasets, the elevation scales are different for each file and there appears to be a line between the two sets (Figure 4.1). Therefore, I used to the Mosaic tool to create a new raster with the two datasets combined (Figure 4.2). The ‘mosaic to new raster’ tool is located in Arctoolbox under data management tools, then raster, and then raster dataset. Figure 4.2. Screen shot of ArcMap and one ASTER raster after using the mosaic tool Geologic Map I loaded the geologic map into my ArcMap document by dragging the scanned map I save as a .jpeg from ArcCatalog into my document. To georeference the map (Figure 4.3), I turned on the georeference toolbar and also opened the link table. I used the ‘add control points’ tool to add six points to intersecting latitude and longitude lines on the geologic map in my field area. I then changed the X Map and Y Map locations in the link table to the corresponding latitude and longitude points on the map. I rectified the image, saved it in the ‘My_Data’ folder, and opened the new georeferenced raster in ArcMap. In ArcCatalog, I defined the coordinate system of the image to GCS_WGS1984, the same as the data frame. Figure 4.3. Georeferencing the geologic map by adding six control point in ArcMap. Roads The screen shot of my field area that I took from Google Maps was loaded into ArcMap. By right clicking on a point in Google Maps and choosing ‘What’s Here?’, Google Maps will give the latitude and longitude of that location (Figure 4.4). In ArcMap, I georeferenced my roads screen shot by adding four points. In the link table, I changed the X Map and Y Map locations to precise latitude and longitude coordinates obtained from Google Maps (Figure 4.5). I then rectified the image, saved it in the ‘MyData’ folder, changed the coordinate system of the image to GCS_WGS1984 in ArcCatalog, and then loaded the newly georeferenced image into my Arcmap document. Figure 4.4. Using Google Maps ‘What’s Here?’ tool to determine precise latitude and longitude of map points. Figure 4.5. Georeferencing roads image in ArcMap with latitudes and longitudes obtained from Google Maps. Clipping The ASTER, geologic map, and roads datasets exceed the extent of my area of interest so, I needed to clip them. I added a polygon that encompassed my field area titled ‘Map_Area’ to my geodatabse (Figure 4.6). I then used the clipping tool located in ArcToolbox under ‘Spatial Analyst’, then ‘Extraction’, and then ‘Extraction by Mask’ to clip the ASTER, geologic map and roads rasters to my Map_Area polygon (Figure 4.7). These newly clipped rasters were automatically added to ArcMap and saved in the ‘MyData’ folder. I now have ASTER data, a geologic map, and a roads image that only cover my area of interest. Figure 4.6. Screen shot of Map_Area polygon overlaying the geologic map Figure 4.7. Clipped ASTER data to Map_Area polygon Digitizing To convert my geologic and roads maps from raster files to shapefiles, I had to digitize each raster. In my NWTurkey geodatabase I created a new feature line class named ‘roads’ and gave it the same coordinate system as the dataframe: GCS_WGS1984. I also created a new feature dataset titled ‘Geology’. Within this dataset I created a new feature line class titled ‘structures’, a new feature point class titled ‘cities’, and a new feature line class titled ‘contacts’. The ‘structures’ feature class has the domain of fault types which Figure 4.8. contains the codes of faults and sutures. The ‘contacts’ Construction of code values for the Units domain of the contacts feature class . feature class has the Domain Name of ‘Units’ that contains the coded values of the following unit names unit names: volcanics, ophiolitic mélange, undifferentiated metamorphic rocks, amphibolite, schist, granite, metagranite, marble, carbonates, sediments, and continental clastics (Figure 4.8). I can now edit these feature classes and digitize by geologic map (Figure 4.9). Figure 4.9. Newly created feature datasets and feature classes for digitizing the geologic map and roads image. To digitize the geologic map, I only displayed the geologic map layer and turned on the editor for the geologic map and contacts feature class. I then traced all contact lines in my research area while periodically saving my edits (Figure 4.10). I then repeated the same process to digitize faults and cities. I then built a topology for my contact lines (Figure 4.11) and Figure 4.10. Construction of code values for the Units fixed all errors until there were no more. I then domain of the contacts feature class. made the contact lines into polygons representing all the rock types in my geologic map. I could then assign the unit name attributes to each rock type and then change the symbology for each rock unit. I also assigned the fault type attributes to each of my faults or sutures and adjusted the symbology (Figure 4.12). I then labeled the cities, converted them to annotation and adjusted and edited their names. Figure 4.11. Screen shot of ArcMap with Topology rules (above) and generated topology (right). The pink lines and boxes were errors I had to correct. Figure 4.12. Screen shot of contact lines converted to polygons. Polygons were assigned unit names and appropriately symbolized. To digitize the roads layer, I only displayed the roads rater and turned on the editor for the roads feature class (Figure 4.13). I then traced all roads in my area of interest while periodically saving my edits. Figure 4.13. Digitizing roads in editing mode. I also wanted to be able to display just the granite bodies in some of my maps. To separate these from the other rock units I used the ‘select by attribute’ option from the ‘selection’ menue. I adjusted the layer to ‘RockUnits’ and the method to ‘create new selections’ I then set up my query to select the units that were equal to granites (Figure 4.14). This way only the granite would be highlighted. In the TOC, I right clicked on the ‘rockunits’ layer and chose the ‘exportdata’ option. I set it to export only the selected features and saved this within my geodatabase as ‘granitebodies’ (Figure 4.14). Now I can display only the granite rock units from my geologic map to be displayed on other maps I make. Figure 4.14. The ‘Select by Attributes’ tool (left) used to select only granite rock units that could then be exported (right). Sample Locations To add my sample locations I used the ‘Add XY data’ option to upload the Excel table (Figure 4.15) with my latitude and longitude coordinates. I then adjusted the symbology for the samples and labeled the features by ‘identity’, the sample names. I then converted the labels to annotation by right clicking on the data set in the TOC. When the labels were converted, I was then able to move them independently to more appropriate locations in the document. Figure 4.15. Excel spreadsheet (left) of GPS sample locations imported into ArcMap by the ‘Add XY Data’ tool (right). ASTER Processing continued To further process my ASTER data I first changed the coordinate system of my data frame to WGS_1984_UTM_Zone35N. I then created I00m contours of the ASTER data by using the ‘contour’ tool in ArcToolbox (Figure 4.16). It is located under ‘Spatial Analyst’ tools and then ‘surface analysis’. I then labeled the contour lines. Figure 4.16. Contour lines produced from the ASTER data by using the ‘contour’ tool. I also produced a hillshade and aspect map (Figure 4.17). To create a hillshade and aspect map I used the ‘hillshade’ and ‘aspect’ tools located in ArcToolbox. These are located under the ‘Spatial Analyst’ tools and then ‘surface analysis’. My input rasters were the ASTER data and the output rasters were saved in the ‘My_Data’ folder. Figure 4.17. Hillshade map generated by using the ‘hillshade’ tool located in ArcToolbox as seen on the left side of the image. 5. Data Calculations I wanted to be able to compare the surface area of my three plutons. To do this I went to the properties tab of my ‘sampleplutons’ layer in the TOC. I then added a new field titled ‘Area’. This new field is then available in the attribute table of this data layer. By right-clicking on the ‘Area” column a ‘calculate geometry’ tool is available. This tool can be used to calculate the area of the plutons in units of square kilometers (Figure 4.18). Figure 4.18. The ‘Select by Attributes’ tool (left) used to select only granite rock units that could then be exported (right). Surface Area of Plutons Pluton Surface Area (km2) Kozak 494 Eybek 96 Kestanbolu 129 6. Data Presentation Geologic Map The geologic map (Figure 6.1) displays active faults, suture zones, geological units, and sample locations of my field area. I can use this map to examine location of samples within the pluton area as well as the proximity of faults to the granite plutons. Kestanbolu Eybek Pluton Pluton Kozak Pluton Figure 6.1. Finalized geologic map of field area in northwest Turkey. Aspect Map The aspect map (Figure 6.2) simultaneously shows the direction and degree of slope for the terrain of my field area. The faults and sample locations in this area are also included. Figure 6.2. Aspect map of field area and associated faults. The large island in the bottom left corner is the Greek island of Lesbos, not associated with the field area. . Hillshade Map The hillshade map (Figure 6.3) provides a 3D effect of visual relief for my field area. This is useful to better analyze the location of my granite plutons with respect to active fault in the area. It is also, useful in analyzing the terrain around faults. Kestanbolu Eybek Pluton Pluton Kozak Pluton Figure 6.3. Hillshade map of field area with granite bodies and associated faults. Various lineament patterns can be seen throughout the area. This may be a result of N-S extension and SW strike-slip motion. The large island in the bottom left corner is the Greek island of Lesbos, not associated with the field area. Contours Map The contour map (Figure 6.4) displays the topography of the region through contour lines. This map also, contains the granite plutons and sample locations. Kestanbolu Eybek Pluton Pluton Kozak Pluton Figure 6.4 . Contour lines of the field area with granite plutons. Field Map with Granites and Roads This field map (Figure 6.5) is useful in displaying the roads around the granite plutons in my sampling area. This map also displays the location of my collected samples with respect to the roads. Contour lines are also, displayed. Figure 6.5. Field map of area of interest that includes contour lines, roads, granite bodies, and locations of samples collected.
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