10:45 AM - 12:15 PM
[SCG50-P03] Structural and petrological study
of layering of the Horoman Peridotite Complex, Hokkaido, Japan
Keywords:mantle, peridotite, crystallographic preferred orientation
The Horoman peridotite complex located in the southern end of the Hidaka Metamorphic Belt is an Alpine-type peridotite. The complex is divided into Upper and Lower Zone on the basis of geological and petrological features. The Upper Zone is characterized by layering structure that consists of layers of various types of peridotites and mafic rocks. We can see a layering structure on an outcrop scale of 3×70 meters at the Northern ridge of Mt. Apoi. The outcrop consists of three lithofacies: spinel-bearing harzburgite/lherzolite, plagioclase-rich lherzolite, and mafic rocks. We collected the rock samples from this outcrop to discuss the origin of the layering structure by analyzing structural and petrological features.
Microstructural analysis indicates that all analyzed rocks show deformation under dislocation creep. Electron Back Scattered Diffraction (EBSD) analysis shows that the crystallographic preferred orientations (CPO) of olivine have (010)[100] slip system with girdle distributions of [100] and [010] with strong alignment of (010) parallel to the foliation. These features of CPO fabric can be formed through deformation of partially melted peridotite. The CPOs patterns of olivine are consistent with each other regardless of lithofacies within the layering structure; therefore, these layered rocks including spinel and plagioclase peridotite can be deformed with the identical deformation event. The pressure-temperature stability boundary between spinel and plagioclase peridotite as well as common pargasite grains parallel to the lineation in both rocks and mafic rocks suggest that the layered rocks can be deformed at the same time at approximately 1000°C and 1 GPa.
Microstructural analysis indicates that all analyzed rocks show deformation under dislocation creep. Electron Back Scattered Diffraction (EBSD) analysis shows that the crystallographic preferred orientations (CPO) of olivine have (010)[100] slip system with girdle distributions of [100] and [010] with strong alignment of (010) parallel to the foliation. These features of CPO fabric can be formed through deformation of partially melted peridotite. The CPOs patterns of olivine are consistent with each other regardless of lithofacies within the layering structure; therefore, these layered rocks including spinel and plagioclase peridotite can be deformed with the identical deformation event. The pressure-temperature stability boundary between spinel and plagioclase peridotite as well as common pargasite grains parallel to the lineation in both rocks and mafic rocks suggest that the layered rocks can be deformed at the same time at approximately 1000°C and 1 GPa.