1. Multi-scale and multi-modal imaging study of mantle xenoliths and petrological implicationsMarco Venier, Luca Ziberna, Lucia Mancini, Alexander P. Kao, Federico Bernardini, Giacomo Roncoroni, Sula Milani, Nasrrddine Youbi, Yondon Majigsuren, Angelo De Min, Davide Lenaz, 2024, original scientific article Abstract: The accurate textural characterization of mantle xenoliths is one of the fundamental steps to understanding the main processes occurring in the upper mantle, such as sub-solidus recrystallization, magmatic crystallization, and metasomatism. Texture, composition, and mineralogy reflect the temperature, pressure, stress conditions, melting, and/or contamination events undergone before and during the entrapment in the host magma. For these reasons, characterizing the three-dimensional (3D) texture of silicate, oxide, sulfide, and glass phases has great importance in the study of mantle xenoliths. We performed a multi-scale and multi-modal 3D textural analysis based on X-ray computed microtomography (µ-CT) data of three mantle xenoliths from different geodynamic settings (i.e., mobile belt zone, pericraton, oceanic hotspot). The samples were selected to represent different, variably complex internal structures composed of grains of different phases, fractures, voids, and fluid inclusions of different sizes. We used an approach structured in increasing steps of spatial and contrast resolution, starting with in-house X-ray µ-CT imaging (spatial resolution from 30 µm down to 6.25 µm) and moving to high-resolution synchrotron X-ray µ-CT at the micrometer scale. We performed a 3D characterization of mantle xenoliths, comparing the results with the analysis of conventional 2D images (thin sections) obtained by optical microscopy and simulating the random sectioning of several thin sections to estimate the probability of correct modal classification. The 3D models allow the extraction of textural information that cannot be quantified solely from thin sections: spinel layering, distribution of silicic glass, and related vesicles. Moreover, high-density volumes identified as sulfides were detected in two xenoliths, showing no relation with the spinel layering in one case and a preferential concentration along fractures in the other. Given the variety of textures and mineral assemblages of mantle xenoliths worldwide, the results are used to suggest experimental and analytical protocols for the characterization of these materials.
Keywords: petrology, mantle xenoliths, X-ray microtomography, multi-scale image analysis
Published in DiRROS: 23.05.2024; Views: 79; Downloads: 18
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2. Outgassing behaviour during highly explosive basaltic eruptionsEmily C. Bamber, Giuseppe La Spina, Fabio Arzilli, Margherita Polacci, Lucia Mancini, Mattia de’ Michieli Vitturi, Daniele Andronico, Rosa Anna Corsaro, Mike R. Burton, 2024, original scientific article Abstract: Explosivity of basaltic eruptions is related to the efficiency in which exsolved gas can separate from the melt during ascent, which is controlled by magma permeability. However, basaltic pyroclasts from eruptions of varying explosivity can show similar permeability, indicating a possible complex relationship between permeability, outgassing and eruptive style. Here, we provide 3D measurements of basaltic pyroclasts using X-ray microtomography. We investigate the role of permeability and outgassing on magma ascent dynamics by using a numerical conduit model. Among the permeable parameters, bubble number density and friction coefficient largely affect explosivity. However, for fast ascending basaltic magmas, gas-melt coupling is maintained independent of magma permeability. In this case, magma storage conditions may determine eruptive style, driving rapid magma ascent, crystallisation and bubble nucleation, producing a highly explosive eruption. Monitoring parameters which reveal pre-eruptive conditions may assist hazard mitigation, particularly for basaltic systems which exhibit a wide range in eruptive style.
Keywords: natural hazards, petrology, volcanology
Published in DiRROS: 12.01.2024; Views: 246; Downloads: 145
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