Elemental Mapping by LA-ICP-MS
Elemental mapping is a cutting-edge tool for quantifying the 2D distribution of major and trace elements in geological materials. The high sensitivity, low backgrounds and ability to measure most elements in the periodic table makes LA-ICP-MS applicable to a broad range of investigations in metamorphic and igneous petrology, economic geology, geochronology, and thermochronology.
Elemental Mapping Approaches
Our lab uses two main approaches to elemental mapping. The first, point mapping, involves the acquisition of discrete edge-matched measurements of the material, usually using a square mask. Depending on the concentration of the element being measured and the required precision of the measurements, pixel dimensions as small as 5 µm are possible. Point mapping allows for the most precise spatial positioning of measured elemental data. This method is comparatively slow and best suited for investigations of small regions (i.e., a single accessory mineral grain) at high resolution. A good example of its application is in our recent Chemical Geology paper.
The second technique, line mapping, involves the measurement of elemental concentrations while the ablation location is scrolled across the surface of the material. By this method adjacent 1D profiles are combined to form a 2D map of elemental concentration. Interplay between the signal response function of the instrument (wash-in/wash-out), ablation rate (Hz), beam diameter, and the scroll rate make precise spatial positioning of measured concentrations more difficult and can introduce dynamic effects (smearing) where high concentration gradients are present in the sample. However, the technique is much faster and well suited to investigations of larger regions (i.e., a garnet porphyroblast) at somewhat lower resolution. An example of line mapping is shown in the image above from a ~2 mm garnet porphyroblast.