13:50 〜 14:15
[SCG51-01] Crystal-fabrics and deformation microstructure of the Horoman peridotite: An insight into the lithospheric mantle
★Invited Papers
キーワード：カンラン岩、結晶方位定向配列、幌満カンラン岩体
The past-kinematics of the uppermost mantle recorded in peridotite massifs worldwide have been extensively studied over the last five decades (e.g., Nicolas and Poirier, 1976; Basch et al., 2025). These investigations primarily focused on the crystallographic preferred orientation (CPO) of olivine, which develops through plastic deformation mechanisms such as dislocation creep (e.g., Mei and Kohlstedt, 2000) and diffusion creep (e.g., Miyazaki et al., 2013).
The Horoman peridotite complex, located at the southern edge of Hokkaido, is a large peridotite massif exhibiting diverse deformation microstructures (e.g., Sawaguchi, 2004; Odashima, 2008) and olivine crystal-fabrics (e.g., Matsuyama and Michibayashi, 2023; Tasaka et al., 2024). Here, we present new insights from olivine CPO using SEM-EBSD analysis and integrate them with previous geological (e.g., Niida, 1984), petrological (e.g., Takahashi, 1992), and microstructural (e.g., Tasaka et al., 2024) studies.
In this study, principal component analysis (PCA) was applied to explore the relationships among latitude, grain shape, and olivine crystal-fabrics. PCA revealed a systematic decrease in olivine grain size from the southern (structurally lower) to northern (upper) sections of the massif. This trend correlated with an increase in Fabric Index Angle (FIA; Michibayashi et al., 2016), indicating a gradual transition in olivine CPO from E to A to AG types (Matsuyama and Michibayashi, 2024).
E type CPO is possibly associated with dehydration from the Pacific slab (Ichihara et al., 2016), while AG type CPO is interpreted as a relic of thermal events and/or melt-rock interactions in the upper part of the complex (Matsuyama and Michibayashi, 2024). In this study, AG-type CPOs are characterized by an oblique girdle distribution of [100] and [001] axes relative to the foliation. This feature, previously demonstrated in experimental studies, has been attributed to melt segregation and strain partitioning (e.g., Holtzman et al., 2003; Qi et al., 2018). Based on these findings, we proposed that melt segregation or melt-rock interactions played a key role in developing olivine CPOs in the upper part of the Horoman peridotite complex.
The Horoman peridotite complex, located at the southern edge of Hokkaido, is a large peridotite massif exhibiting diverse deformation microstructures (e.g., Sawaguchi, 2004; Odashima, 2008) and olivine crystal-fabrics (e.g., Matsuyama and Michibayashi, 2023; Tasaka et al., 2024). Here, we present new insights from olivine CPO using SEM-EBSD analysis and integrate them with previous geological (e.g., Niida, 1984), petrological (e.g., Takahashi, 1992), and microstructural (e.g., Tasaka et al., 2024) studies.
In this study, principal component analysis (PCA) was applied to explore the relationships among latitude, grain shape, and olivine crystal-fabrics. PCA revealed a systematic decrease in olivine grain size from the southern (structurally lower) to northern (upper) sections of the massif. This trend correlated with an increase in Fabric Index Angle (FIA; Michibayashi et al., 2016), indicating a gradual transition in olivine CPO from E to A to AG types (Matsuyama and Michibayashi, 2024).
E type CPO is possibly associated with dehydration from the Pacific slab (Ichihara et al., 2016), while AG type CPO is interpreted as a relic of thermal events and/or melt-rock interactions in the upper part of the complex (Matsuyama and Michibayashi, 2024). In this study, AG-type CPOs are characterized by an oblique girdle distribution of [100] and [001] axes relative to the foliation. This feature, previously demonstrated in experimental studies, has been attributed to melt segregation and strain partitioning (e.g., Holtzman et al., 2003; Qi et al., 2018). Based on these findings, we proposed that melt segregation or melt-rock interactions played a key role in developing olivine CPOs in the upper part of the Horoman peridotite complex.