3D Raman mapping combined with FIB-SEM on multiphase fluid inclusions: A tool to unravel complex phase assemblages

In this study, we performed high resolution 3D Raman mapping on primary multiphase fluid inclusions from a granulite and an eclogite of the Cabo Ortegal Complex (NW Spain), the latter representing a former subduction zone environment. Several microns-sized inclusions are great targets to test the advantages and limitations of 3D Raman mapping. We show how optical and Raman scattering properties of the phases inside the inclusions can affect the veracity of both 2D and 3D Raman maps. As an independent control, 3D Raman models were compared with focused ion beam-scanning electron microscopy submicron-scale slicing of three previously 3D Raman mapped inclusions, allowing us to optimize Raman spectroscopy data evaluation and provide volume proportion calculations. We found that a non-optimized evaluation procedure might result in even an order of magnitude over- or underestimation of phase volume properties. We propose that correcting the Raman maps even with empirically determined Raman cross sections of the phases inside the inclusions can vastly improve the quality of the maps. The results provide valuable input data for thermodynamic modeling and draw implications for fluid/rock interactions.

Automated summary

In this study, high resolution 3D Raman mapping was performed on primary multiphase fluid inclusions from the Cabo Ortegal Complex in NW Spain. The study demonstrates that the optical and Raman scattering properties of phases inside the inclusions can affect the accuracy of both 2D and 3D Raman maps. By comparing 3D Raman models with submicron-scale slicing, the evaluation of Raman spectroscopy data was optimized and volume proportion calculations were provided. The results have implications for thermodynamic modeling and fluid/rock interactions.