mantled porphyroclast

Porphyroclast with an elongated mantle of the same mineral composition, stretched in the direction of the foliation. It is inferred to have formed at the expense of the porphyroclast by recrystallisation in its rim. Mantled porphyroclasts are common in mylo-nites and are used to determine sense of shear. See also 5-type object, a-type object and strain shadow

Related terms:

• porphyroclast aspect ratio method
• strain shadow
• porphyroclast
• stair-stepping
• mantled gneiss dome
• mica-fish or mica fish
• strain fringe
• tiling