Earth Planet. Sci. Lett. (2013)

Crystals in the uppermost mantle are often aligned, but it is unclear whether these preferred crystal orientations reflect current or ancient deformation processes. A comparison between global patterns of mantle-crystal alignment and present-day plate movements shows that most of the alignment is caused by geologically recent plate movements, with the fastest-moving plates creating the strongest patterns at their base.

Eric Debayle and Yanick Ricard at the Laboratoire de Géologie de Lyon, France, used seismic data to map global patterns of crystal alignment in the upper mantle and analyse large-scale deformation along the base of the tectonic plates. They compared the patterns to models of present-day and ancient plate motions, and found that the patterns of preferred crystal orientation predominantly correlate with the directions of plate tectonic movements today. Crystal alignment is most pronounced beneath the fastest-moving plates: the Indian, Cocos, Nazca, Australian, Philippine Sea and Pacific plates. In contrast, crystal alignment is rarely observed beneath the slowest plates.

The data imply that only the fastest-moving plates produce sufficient shear at their base to deform and align the mantle minerals.