Extended Data Figure 3: Angles between crystallographic axes of forsterite and apparent long axes of forsterite grains in the Fo+Di samples.

Crystallographic a, b and c axes were measured by SEM/EBSD, whereas the long axes were determined from the grain shapes. Highly anisotropic grains were selectively measured. N, number of measured grains. a, Angle frequency in the sample statically annealed at 1,330 °C for 20 h (NV-323). b, CPO of the grains analysed in a. c, Angle frequency in the sample compressed at 1,330 °C (KF-125). The angles were measured in sections cut perpendicularly to the compression axis in the deformed sample. d, CPO of the grains analysed in c. Note that b and c axes are perpendicular to the long axes in the deformed samples, whereas only b axes are clearly perpendicular to the long axes in the non-deformed samples. The CPO in b indicates that the highly anisotropic grains were well identified when the b axes of forsterite grains were parallel to the sample section when the grains were randomly oriented, whereas the CPO in d indicates that the highly anisotropic grains were well identified when the b axes of the grains were perpendicular when the grains were preferentially oriented in the sample. Thus, we can conclude that the longest axis of each grain was parallel to the a axis and that the second longest axis was parallel to the c axis. The shortest grain axis should be parallel to the b axis.