Distribution of volatiles in mantle xenoliths at nano-lengthscales visualized with Photo-induced Force Microscopy

Rocks are commonly treated as simple aggregates of minerals with well-defined compositions and crystal structures. However, they also contain nano- to micro-scale interstitial phases and grain boundaries with distinct geochemical properties that may represent an underappreciated reservoir for volatiles [1]. Resolving the distribution and speciation of these components requires analytical techniques with nanometer-scale spatial resolution. Photo-Induced Force Microscopy (PiFM) integrates atomic force microscopy (AFM) with infrared (IR) spectroscopy to enable phase identification at spatial resolutions of ~5 nm, well below the optical diffraction limit of conventional IR methods [2, 3]. In PiFM, a tunable IR laser is directed at a metal-coated AFM tip, inducing a photo-induced force (PiF) that corresponds to the sample’s IR absorption properties. Scanning the laser over a range of wavenumbers generates a PiF-IR spectrum, which aligns closely with conventional FTIR spectra, allowing for reliable phase identification through FTIR reference libraries [3]. Here, we resolve volatile speciation and spatial distributions in mantle xenoliths and phases from high-pressure experiments. Spatially resolved volatile maps provide direct insight into their relationships with mineral phases and grain boundaries. References[1] Alard et al., (2022) Nature Geoscience, 15, 856–857 [2] Nowak et al., (2016). Science Advances, 2(3), e1501571. [3] Otter, Förster et al., (2021). Geostandards and Geoanalytical Research. 45(1), 5-27.