Notes: We looked at extinction angles as a proxy measure of plagioclase An content. In these histograms one can see a unimodal population that must include a significant amount of oligoclase, and minor andesine, and some mixture of andesine and albite. The simplest interpretation that would maintain a unimodal population of An contents would be that the uncertain material is mainly andesine. A histogram chart of An contents from a HALIP diabase sill on Midterhuken shows a large spread, and lava flows in Kong Karls Land to the east have reported An contents that vary from andesine to labradorite. A wide variance in An contents within a single sandstone sample suggests that depositional variation is being preserved and post-depositional modification has been moderate to absent. The more sodic composition of the plagioclase in the sandstones likely reflects a weathering bias where more calcic plagioclases are preferentially destroyed.


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