The most new continental crust is created at divergent boundaries, specifically those associated with continental rifting.
Here's a breakdown:
Continental Rifting and Divergent Boundaries
-
Divergent Boundaries Explained: Divergent boundaries are zones where tectonic plates move apart. This separation allows magma from the Earth's mantle to rise to the surface.
-
Continental Rifting: When this happens under a continent, it's called continental rifting. Think of it as the continent being pulled apart. A classic example is the East African Rift Valley.
-
Crust Formation Process: As the plates separate, magma rises and cools, solidifying to form new crust. Initially, this new crust is oceanic (basaltic), but as the rifting continues and the continent splits, the edges of the separated landmasses can experience further volcanic activity and differentiation of magma, leading to the formation of new continental crust. The differentiation process typically involves partial melting and fractional crystallization, which leads to magmas enriched in silica and other elements characteristic of continental crust.
-
The Role of Magma Differentiation: Although oceanic crust is formed directly from mantle-derived magmas, continental crust is often created through complex processes involving the differentiation of these magmas. This process can occur at divergent boundaries within continents where the initial mantle melts interact with and melt the existing continental crust, leading to the formation of new, more felsic (continental-like) material.
Why Divergent Boundaries, Especially Continental Rifts, are Key
-
Volume of Crust: While some continental crust can be formed at convergent boundaries (through arc volcanism), the sheer scale and sustained nature of crustal generation during continental rifting events contribute significantly to the formation of large volumes of new continental material over geological timescales.
-
Long-Term Process: Continental rifting is a long-term geological process. Over millions of years, the continuous creation of new crust results in a substantial addition to the continental landmass.
-
Example: The eventual formation of the Atlantic Ocean by the rifting of Pangea is a prime example of the significant role of divergent boundaries in shaping continental landmasses.
Therefore, although other plate boundaries contribute to crustal formation and modification, divergent boundaries, especially those within continents, are the sites where substantial amounts of new continental crust are generated.
