Defining a Mantle Plume
A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle, originating from deep within the planet, possibly near the core-mantle boundary. Unlike conventional plate tectonics where magma forms at plate boundaries, mantle plumes are relatively stationary heat sources that rise buoyantly through the solid, yet ductile, mantle.
Formation and Characteristics
The intense heat from Earth's core warms sections of the lower mantle, causing the rock to become less dense and slowly rise. As this plume approaches the surface, the pressure decreases, leading to decompression melting, which generates magma. This magma then rises to erupt through the Earth's crust, forming volcanoes or volcanic fields. Mantle plumes are characterized by their narrow 'stalk' and broader 'head' at the top.
Example: The Hawaiian Islands
A classic example of volcanism caused by a mantle plume is the Hawaiian Islands. As the Pacific plate moves slowly over the relatively fixed Hawaiian hotspot (the surface expression of the mantle plume), new volcanoes are continuously formed, creating a chain of islands that get progressively older and more eroded farther from the current hot spot location.
Significance in Geology
Mantle plumes play a crucial role in shaping Earth's surface and understanding its deep interior dynamics. They are responsible for intraplate volcanism, often forming volcanic islands, large igneous provinces, and continental flood basalts. Studying plumes provides insights into the heat flow from the Earth's core and the convection processes within the mantle, which are fundamental to plate tectonics.