Plate Tectonics Before Pangaea

1. Plate movements since the breakup of Pangaea is well understood, but tectonic movements prior to Pangaea is not as clear because much of the tectonic evidence (ocean floors) is destroyed by geologic and tectonic forces that existed over 200 million years ago. Clues to past plate tectonics can only be observed on the present-day continents, in rocks, fossils, and structures older than 200 million years old. No clues can be found in the oceanic crust because the oldest oceanic crust is approximately 180 million years old, which indicates that the ocean crust is recycled every 150 - 200 million years. Plate Tectonics Before Pangaea

2. Continents are built of blocks of crust varying in age, size, rock composition, structure, and fossil assemblages (both plants and animals). In general, most continents have stable, older interiors called cratons. Bordering these cratons are younger, structurally more complicated rocks composed of remnants of oceanic lithosphere, volcanic arcs, and mountain ranges older than 200 million years old. These areas are interpreted as geologic events that pre-dated Pangaea plate tectonics. Plate Tectonics Before Pangaea

3. Scientist now have an understanding of the complex continental margins and recognize that they are often mixtures of fragments of different tectonic plates that joined sometime in the past. Newfoundland is an example of this, demonstrating plate collision in the past when the African plate and North American plate collided to form the Appalachian Mountains. The process by which lithospheric fragments become attached to continents (craton) is called accretion. Plate Tectonics Before Pangaea

4. Such studies of plate tectonics suggest that plate movement have been ongoing since Earth’s early history. It appears that their have been several cycles of super continent formation, each followed by breakup and drifting of the fragmented plates. Pangaea may have been formed by the collision of separate continents that drifted back together after the breakup of an older super continent that existed approximately one billion years ago. Scientist refer to this super continent as Rodinia. Plate Tectonics Before Pangaea