High-Resolution, Quantitative Element Imaging of an Upper Crust, Low-Angle Cataclasite (Zuccale Fault, Northern Apennines) by Laser Ablation ICP Time-of-Flight Mass Spectrometry

Abstract Laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-ToF-MS) was used to generate quantitative elemental images of a mineralogically and texturally complex fault rock of the Northern Apennines of Italy (Zuccale Fault, eastern Island of Elba). Using LA-ICP-ToF-MS combined with a low-dispersion LA cell, we were able to generate large format (4 mm × 2 mm), high-resolution (5 μm), high dynamic range (1–106 μg g−1), and quantitative multi-elemental two-dimensional compositional maps within a data acquisition time of a few hours. To quantify element mass fractions across the heterogeneous sample of the Zuccale Fault, we used a 100% species-mass normalisation approach that took into account different mineral phases across the specimen. To assign mineral phase directly from LA-ICP-ToF-MS data, we exploited the segregation of sulfur and calcium between distinct phases to threshold element images and develop mineral-phase-specific masks. Moreover, we demonstrate agreement between elemental mass fractions determined by LA-ICP-ToF-MS imaging with 100% normalisation quantification and conventional LA-ICP-MS analysis with internal standard element-based quantification. Finally, we discuss how this elemental imaging provides unique insights into the genesis of the Zuccale Fault.