PROCESSING MICROPIXE LINESCAN DATA - STUDIES OF ARSENIC ZONING IN SKARN GARNETS

In many applications, particularly in Earth Sciences, the main interest for microPIXE analysis is in determining one-dimensional trace element profiles. In these cases it is advantageous to carry out scanning along a line rather than over an area or as a series of points, since both the counting statistics and the spatial resolution are optimised. This paper describes the system used in Oxford to collect linescan data and the off-line processing techniques used to calibrate the linescan profiles. As an example of the use of linescan data results of a study of As zoning in skarn garnets are presented. Skarn garnets are formed during contact metamorphism and hydrothermal alteration of carbonate rocks and often show strong zoning with respect to major and minor elements. Samples from the Central Oslo Rift have been studied using microPIXE and in particular show a strong zoning in As and W, probably reflecting a sudden change in the growth conditions. In addition to the striking zonation patterns, the As and W levels are to our knowledge the highest ever recorded in these types of garnet. Elemental maps and linescan data are presented