New Progresses of Micro-Area Elemental Analytical Techniques and Their Applications in the Field of Geoscience

The differentiated applications and innovative advances of the micro-area elemental analytical techniques are of great significance for the accurate characterization of material structures and microscale processes. In this paper, we summarized various kinds of analytical techniques including the Electron Probe Microanalysis (EPMA), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Laser-Induced Breakdown Spectroscopy (LIBS), and Synchrotron Radiation X-ray Fluorescence Spectroscopy (SR-XRF), and then comprehensively examined their application scenarios by combining the principal characteristics and respective strengths and weaknesses of those techniques. With the core advantage of the high-precision and non-destructive micro-area analytical technique, the EPMA, which is featured with a spatial resolution of 15 μm and accurate quantification capability for elements with atomic number Z≥4, can be used to meet the analysis demands of various materials in multiple fields. By adopting a variety of optimized quantitative algorithms and coupled imaging technologies, the EPMA has consistently been used to play an irreplaceable role in the fields of the micro-area phase analysis of materials, the study on occurrence states of elements in minerals, and the planetary science. The LA-ICP-MS is widely applied due to its excellent spatial resolution and high detection sensitivity. Through the development of calibration methods and software, the investigation of elemental fractionation mechanisms, the optimization of analytical conditions, and the innovation of analytical techniques, the data accuracy and analytical precision of the LA-ICP-MS have been continuously improved. These efforts further caused the enhancement of analytical capabilities of the LA-ICP-MS and the expansion of its application boundaries in the fields of environmental monitoring and geology. The LIBS, taking the rapid in-situ analysis as its prominent advantage, can be used to make the elemental distribution scanning of field outcrops by using its portable device. By improving the stability of laser focusing and adopting the machine learning-based spectral analytical methods, the LIBS has shown good potential for applications in the environmental research and the elemental analysis of extraterrestrial celestial minerals. The SR-XRF, by leveraging the high brightness and coherence of the synchrotron radiation light sources, can be used to achieve the analysis of micron-scale elemental distribution in centimeter-sized samples. This technique has led to notable progresses in the in-situ compositional analysis of paleontological fossils and in the mineral deposit researches. The combined application of these techniques is driving the earth sciences to continuously deepen from the macroscopic observation to the microscale mechanism interpretation, providing multi-dimensional chemical evidences for the mineral resource exploration, paleoenvironmental reconstruction, analysis of reservoir rocks and minerals, diagenesis of rocks, hydrocarbon accumulation tracing, and planetary evolution studies.