APPLICATION OF THE NATIONAL SURVEYS AND ANALYSIS NATIONAL DIGITAL DATASETS: EXAMPLE MERGER OF THE AEROMAGNETIC AND GEOLOGIC DATASETS OF ALASKA

Aeromagnetic intensity levels for various lithologies were calculated by merging the statewide digital aeromagnetic dataset for Alaska, produced by Saltus and Simmons (1997), and the 1:250,000 scale integrated digital geologic map databases produced for Alaska (for example: Wilson and others, 2006, 2005, 1999, 1998). Geologic map unit polygons from the digital map databases were used to select regions of the aeromagnetic raster dataset to obtain aeromagnetic intensity cell value distributions for the regions outlined by each map unit. The lithologic attributes assigned to each geologic map unit allowed production of maps and charts showing the mean and ranges of aeromagnetic intensity levels by rock type. Although there are wide ranges between minimum and maximum aeromagnetic intensity levels for many of the rock types, the pattern of mean aeromagnetic intensity levels is similar to the magnetic susceptibility levels of common rock types as presented by Carmichael (1989). The highest aeromagnetic intensity levels (and susceptibility levels) are found in mafic igneous rocks and the lowest in metamorphic rocks. By applying this method to the entire state of Alaska, a table will be developed showing the expected aeromagnetic intensity levels and ranges for various rock types. This information could be useful for identifying map units with aeromagnetic intensity levels that don't match expected values for the mapped lithology, as well as for narrowing the range of possible rock types where limited geologic information is available or in areas of cover.