Southeastern Section - 66th Annual Meeting - 2017

Paper No. 5-4
Presentation Time: 8:00 AM-12:00 PM


MCGROARTY, Fiona C., JOHNSON, Elizabeth A. and PHILLIPS, Ron, Dept of Geology and Environmental Science, James Madison University, Harrisonburg, VA 22807,

Scanning electron microscopes (SEMs) are commonly used to image objects at a magnification beyond the range of a standard microscope. In this study, we developed a protocol to take a series of BSE (back-scattered electron) images of a thin section that are stitched together using photo-stitching software. This technique was developed to determine mineral modal abundances in two thin sections of anorthosite xenoliths from a Jurassic basalt sample from Augusta County, VA. The mineral abundances and compositions will be used to understand magmatic underplating and the evolution of a magma chamber in the region at the time. We used a Phenom XL SEM and the Phenom Pro Suite Image Mapping software to take a series of small pictures of each thin section. Taking a picture of a standard thin section at 380x magnification will create over 2000 tiles to stitch, leading to problems using the photo-stitching software. When we used Microsoft Image Composite Editor (MICE), the software could only work with a maximum of 750 images, leaving holes throughout the thin section image. We found that the best method of collecting images was to divide the thin sections into quadrants and image map each quadrant individually. Each quadrant was mapped at 370-380x magnification, at 10kV. Although there were fewer images using this method, MICE was still only able to stitch about ¼ of the images at a time, leading to experiments with Autostitch and Photostitcher. The completed images were entered into Image Color Summarizer, a color percentage calculator, to determine the percentage of each mineral in the thin section quadrant. The results for the first thin section found 67.29% feldspar, 11.06% pyroxene, and 21.60% minerals produced by reaction between the xenolith and basalt. Future work will include completing the mineral compositions for all thin section quadrants and using the modal abundances and whole-rock chemical data to determine the relationship between the basalt and anorthosite xenoliths.
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