Coevolution of Deformation Microstructures and Crystal‐Fabrics in the Uppermost Mantle: Unraveling the Imprint of Multiple Processes in the Horoman Peridotite Complex, Japan

Abstract Mantle peridotites exhibit complex microstructures due to the interaction of various deformation processes in the upper mantle. Thus, analysis of deformation microstructures can provide essential insights into the sequence of deformation events within the upper mantle. In this study, we conducted microstructural and intracrystalline analyses based on previous studies on crystal‐fabrics in the Horoman peridotite complex in Japan. This complex is distinguished by variations in olivine crystal‐fabrics, especially the crystallographic preferred orientation (CPO), which is linked to different structural positions. We quantitatively compared the microstructural features of olivine and orthopyroxene grains with those of olivine crystal‐fabrics. Our analysis showed that the E type CPOs (i.e., [100](001) patterns) of olivine were associated with mylonitic/porphyroclastic textures and high intracrystalline strains, whereas the AG type CPOs (i.e., axial‐[010] or fiber‐[010] patterns) corresponded to equigranular textures. Additionally, our rheological modeling, combined with previous petrological studies, suggests that the plausible deformation mechanisms in the lower and upper sections of the complex are dislocation creep and diffusion creep, respectively.