Final answer:
The zone surrounding the igneous intrusion is characterized by contact metamorphism, which is the local alteration of rocks by heat from an igneous body.
Step-by-step explanation:
The gray zone surrounding the igneous intrusion would best be characterized as a zone of contact metamorphism. Contact metamorphism occurs when molten rock from an igneous body heats the surrounding rocks, leading to a metamorphic change primarily due to the high temperature. This type of metamorphism is typically restricted to the areas immediately surrounding the intrusion and does not include large-scale deformation since it is mostly thermal and not due to significant pressure changes.