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.