Horizontal cleavage in southeastern Sinai: the case for a coaxial strain history

A horizontal cleavage and associated lineation are developed in a low-pressure igneous-related metamorphic terrain in southestern Sinai. The cleavage is axial planar to recumbent folds, which are never large, and varies from a smooth slaty cleavage to a discrete crenulation cleavage. Structural evidence on the macro, meso and microscales suggests that cleavage and lineation were formed during irrotational extension and not by simple shear. Estimates of strain using the March method indicate 50–70% vertical shortening. This structural evidence when combined with metamorphic and age data strongly suggests that the cleavage was formed by the forceful emplacement of a pluton at depth.