Mantle has several different meanings:

1. A layer of something that covers or surrounds. Earth's mantle is the thick layer of hot rock between the planet's crust (where we live) and its core. You might also see a mantle of snow covering a mountain, or a mantle of fog settling over a valley. The word suggests something that drapes over and envelops what's beneath it.
2. A role or responsibility passed from one person to another. When a team captain graduates and a new student takes up the mantle of leadership, they accept the same responsibilities their predecessor had. Martin Luther King Jr. spoke of how leaders in the civil rights movement would need to take up the mantle and continue the work of those who came before them. The phrase comes from an ancient tradition in which a prophet would place his cloak on his successor.
3. The shelf above a fireplace, also called a mantelpiece. Families often display photographs, decorations, or holiday cards on the mantel. During winter holidays, people might hang stockings from their mantelpiece.