[M-IS23] New frontiers in geology

[MIS23-01] Mantle rheology and oceanic plates

★Invited Papers

*Katsuyoshi Michibayashi^1,2 (1.Department of Earth and Planetary Sciences, GSES , Nagoya University, 2.Volcanoes and Earth's Interior Research Center, IMG, JAMSTEC)

Keywords:oceanic plate, mantle, rheology, crystal-fabric

The internal structure of the oceanic crust and uppermost mantle of the oceanic plate has been revealed by seismic wave velocity structures. In particular, the uppermost mantle just below the Mohorovicic discontinuity, the boundary between the crust and mantle, is known to have strong anisotropy in seismic wave velocity, with the fastest orientation parallel to the plate motion. However, a geological model based on structural analysis of mantle material such as olivine is necessary to explain these seismic wave velocity structures. In general, there are two types of physical properties (physical information) of deformed rocks: texture and crystal-fabric. However, in the case of olivine, textural analysis is often difficult due to serpentinization, so rheology and seismic anisotropy are commonly studied from the crystallographic analyses. Although peridotite is petrologically classified by mineral modes of olivine-orthopyroxene-clinopyroxene, rheological studies classify peridotite according to six types of crystallographic preferred orientations (called crystallographic fabrics or crystal-fabrics). The large picture of the upper mantle has been drawn on the basis of this classification scheme, whereas there are few examples that have verified it. In this talk, I will present research trends in mantle rheology and oceanic plates based on recent findings.