~Archaean Crustal Evolution and the Formation of Continents~
The earth began in a state similar to the moon with a crustal (lithospheric) surface composed dominantly of mafic/ultramafic igneous rocks and Anorthosites. With the formation of the oceans the early earth would have been a relatively simple world - oceans from pole to pole, with occasional scattered hot spot volcanoes. Convection cells were established and divergent and convergent plate boundaries arose where fractionation processes began to build the continents.
The sequence of cross sections below illustrate the kinds of processes by which initial volcanic arcs could increase in size to form Protocontinents, then through cordilleran orogenies and collisions form protocontinets, which would grow to form microcontinents, which would eventually grow to form supercontinents. All of these processes constitute variations on the Wilson Cycle. The combinations and permutations of relationships is virtually endless.
Contributed by Lynn Fichter
Tuesday, October 07, 2014