Microstructures of the Mantle:
an example from the Hilti mantle section, Oman Ophiolite

Michibayashi, K., Gerbert-Gaillard, L. and Nicolas, A., 2000. Marine Geophysical Researches, 21, 259–268.
Michibayashi, K. and Mainprice, D., 2004. Journal of Petrology, 45, 405–414.

Width of base: 15 mm.
Typical microstructure of the asthenospheric mantle hartzburgite (Deformed temperature: >1250 degree C). Strong lattice preferred orientation occurs. Crossed polars. (2KOK34)

Width of base: 15 mm.
Weakly deformed hartzburgite in the lithospheric mantle. Olivine grains are still coarse but are strongly elongated subparallel to the foliation (horizontal). Crossed polars. (2KOK45)

Width of base: 15 mm.
Inhomogeneously deformed hartzburgite in the lithospheric mantle. Some olivine grains are dynamically recrystallized into smaller grains. The foliation is horizontal. Crossed polars. (2KOK30)

Width of base: 15 mm.
Moderately deformed hartzburgite in the lithospheric mantle (Deformed temperature: ca. 1000 degree C). Olivine grains are dynamically recrystallized into smaller grains, whereas orthopyroxene grains occur as porphyroclast. The foliation is horizontal. Crossed polars. (2KOK23d)

Width of base: 15 mm.
Intensely deformed hartzburgite in the lithospheric mantle (Deformed temperature: ca. 1000 degree C or less). Dynamically recrystallized olivine grains are further dynamically recrystallized into finer grains, whereas orthopyroxene grains occur as porphyroclast with asymmetric geometry. The foliation is horizontal. Crossed polars. (2KOK31)

Width of base: 15 mm.
Intensely deformed hartzburgite in the lithospheric mantle, showing a typical mylonitic microstructure (Deformed temperature: ca. 1000 degree C or less). Olivine grains are intensely dynamically recrystallized into very fine grains, whereas some coarse olivine grains are preserved due to unlike LPO for dynamic recrystallization. Porphyroclastic orthopyroxene grains are also reduced their sizes. The foliation is horizontal. Crossed polars. (2KOK33)