The African Plate is neither purely convergent nor purely divergent; its identity is defined by a complex perimeter where it interacts with surrounding plates in multiple ways across its vast extent. The African Plate is one of the largest on the planet, encompassing the majority of the African continent and a significant portion of the surrounding oceanic crust. Its immense size means that the type of boundary interaction changes dramatically from one edge to another. To understand the plate’s motion, it is necessary to examine the creation of crust occurring along its western and southern sides and the destruction and folding happening to the north and within the continent itself.
The Majority Boundary: Oceanic Divergence
The most extensive boundaries of the African Plate are characterized by divergence, where new crust is actively being formed through seafloor spreading along mid-ocean ridges. The plate is pulling away from the North American and South American plates to the west, manifested by the central and southern segments of the Mid-Atlantic Ridge.
Along the Mid-Atlantic Ridge, magma rises from the mantle to fill the gap created as the plates separate, solidifying to form new basaltic oceanic crust. This pulling apart is a relatively slow process, with the African and South American plates separating at approximately 2.5 to 3.0 centimeters per year. The African Plate is also diverging from the Antarctic Plate along the Southwest Indian Ridge, contributing to the expansion of the surrounding ocean basins. This dominant divergent force drives the African Plate’s general northeastward motion, causing it to push against the Eurasian Plate.
Complex Interactions: Convergence and Shearing
The African Plate’s northern edge is defined by a fundamentally different and more destructive interaction with the Eurasian Plate, characterized by both convergence and shearing. This boundary runs through the Mediterranean Sea, where the African Plate is moving northward toward Europe. The rate of convergence in this region is approximately one centimeter per year, forcing the plates into a complex collision zone.
In the central and eastern Mediterranean, the African Plate is subducting beneath the Eurasian Plate. This process results in high levels of seismic activity and volcanism, particularly around southern Italy and the Aegean Sea. Farther west, the collision has caused the folding and uplift of continental crust, creating mountain belts like the Atlas Mountains in northwestern Africa. The overall movement in the western Mediterranean is a blend of compression and lateral (shearing) forces, complicating the boundary into the diffuse Azores-Gibraltar Fault Zone.
Rifting Within the Continent: The East African Rift
A unique feature of the African Plate is the ongoing process of rifting occurring deep within the continent itself. This is the East African Rift System (EARS), a developing divergent boundary where the main African Plate (often called the Nubian Plate) is actively splitting away from a smaller segment known as the Somali Plate. The rift system extends for about 3,500 kilometers, from the Red Sea down toward Mozambique.
This continental rifting began about 22 to 25 million years ago, driven by extensional forces that are stretching and fracturing the continental lithosphere. The process is creating a series of deep, elongated valleys, or grabens, bounded by normal faults, which hold many of the African Great Lakes. The separation is occurring at a rate of approximately 6 to 7 millimeters per year, a pace that will eventually lead to the complete splitting of the continent. Associated with this stretching and thinning of the crust is intense volcanic activity, resulting in massive volcanic peaks such as Mount Kilimanjaro and Mount Kenya. This internal divergence provides a visible, active example of how a new ocean basin may begin to form over millions of years.