The Herald can use the Mark to close the Rift once all of the Demons it has spawned are dead in DA: Inquisition

Fade Rifts are Rifts that show up throughout the world in Dragon Age: Inquisition.

Fade Rifts are caused by weaknesses in the Veil.

Disrupting a Rift with your Mark will cause damage to nearby Demons

When all Demons are dead, close the Rift with your Mark.