Extended Data Fig. 8: Evidence (CTEM images) of grain-boundary sliding in specimen NF1050-1.

a, Arrows indicate where grain-boundary opening occurs in response to tensile stress components. These displacements must be accompanied by some shear along the neighbouring boundaries. Without markers, these shear displacements cannot be quantified. b, Assemblage of two micrographs. This region, which was probably under horizontal tensile loading, shows large displacements along vertical boundaries. Owing to differential ion-thinning rates between crystalline and amorphous materials, the region with the black star shows no remaining amorphous material (as in a). In the boundary on the left, located in a thicker region, some amorphous olivine (‘am’) is preserved. The extensional displacement at this boundary (about 190 nm) is used to evaluate the local strain (Methods). The boundaries indicated by the white asterisks show strong morphological evidence of ductile flow. The one on the right is still filled with amorphous olivine. c, The grain at the centre was probably subjected to complex triaxial loading, which has been accommodated by amorphization (some is remaining, ‘am’) and flow involving rotational, tensile and shear components (arrows). On the bottom right is a grain boundary still filled with amorphous material under tensile loading. The neighbouring grain boundary (white diamond) must also have experienced some shear. This is also probably the case for the boundary (white triangle) that is close to an opening boundary.