Transcript Plate Tectonics Before Pangaea

Plate Tectonics Before Pangaea
 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
 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
 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
 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.