Multi-scale and multi-modal imaging study of mantle xenoliths and petrological implications

Abstract

22 The accurate textural characterization of mantle xenoliths is one of the fundamental steps to 23 understanding the main processes occurring in the upper mantle, such as sub-solidus 24 recrystallization, magmatic crystallization and metasomatism. Texture, composition, and 25 mineralogy reflect the temperature, pressure, stress conditions, melting and/or contamination events 26 undergone before and during the entrapment in the host magma. For these reasons, characterizing 27 the three-dimensional (3D) texture of silicate, oxide, sulfide and glass phases has great importance 28 in the study of mantle xenoliths. We performed a multi-scale and multi-modal 3D textural analysis 29 based on X-ray computed microtomography (μ-CT) data of three mantle xenoliths from different 30 geodynamic settings (i.e. mobile belt zone, pericraton, oceanic hotspot). The samples were selected 31 to represent different, variably complex, internal structures, composed of grains of different phases, 32 fractures, voids and fluid inclusions of different sizes. We used an approach structured in increasing 33 steps of spatial and contrast resolution, starting with in-house X-ray μ-CT imaging (working at 34 spatial resolution from 30 μm down to 6.25 μm) and moving to high-resolution synchrotron X-ray 35 μ-CT at the micron scale. 36 We performed a 3D characterization of mantle xenoliths comparing the results with the analysis of 37 conventional 2D images (thin sections) obtained by optical microscopy and simulating the random 38