Expansion and formation of the earth's crust
Danilo Anton
According to Vicente Sánchez Cela's theory, the initial mineralogical composition of the planet consisted mainly of dense minerals. These minerals were originally in a relatively unstable phase. This instability was expressed more intensely in the outer layers of the planet subjected to lower pressures and temperatures than deep levels.
It was there, in these layers, close to the surface, that took place a variation in the crystalline structures of the silicate minerals from the dense phases (coesite, stishovite, K-holandite, Na-holandite, perovstarkite, psot- Perovskite, etc.) into less dense phases (quartz, potassium feldspar, sodium, calcium, olivine, pyroxenes). These changes implied an increase of volume due to the decrease of the density, causing an expansion in the surface rocky masses.
Due to the expansion of the upper mantle,a surface layer of lower density was generated. It corresponds to the structural element that we call "crust". In this sense, it is possible to define the earth's crust as the portion of the mantle where the density decreased due to the phase changes of the minerals.
These processes of mineral transformation with decrease of the density were increasing the volume of the planet giving rise to the preferred swelling of certain zones. These sites would probably be the regions where the ancient shields that would geologically constitute the bases of the continents would be established.
The increase in volume that led to the expansion of the planet resulted in new magmatic masses of the upper mantle being incorporated into the crust and causing upward pressures that were expressed through incipient fractures that later would give rise to the ocean ridges.
Origin of the ocean floor
According to the tectonic plate theory, oceanic bottoms would have been formed from materials ejected into "dorsal" fractures, which created a thin layer of rock (basaltic) concomitantly with the removal of the original crust blocks Continental).
In tectonic plate theory, the diameter of the planet did not change, and therefore with that formation of the new basaltic seabed with separation from the continents there would have been "subduction" of the denser oceanic plates below the less dense continental layers. According to this hypothesis the plates would be renewed in the divergent zones and would overlap each other in the zones of convergence.
However, this approach is not shared by some authors (among them S.W.Carey
And J. Maxlow) who argue that the volume of the Earth has increased during the course of geological times and that therefore it is not necessary to resort to subduction processes (from one plate below others) to explain the evolution of the Planetary crust.
According to these authors the terrestrial planetary expansion led to the gradual generation of oceanic crusts separating the continental plates until arriving at the present situation. These processes are illustrated by the shapes of continents that, by eliminating the oceans, coincide as a gigantic planetary puzzle.
As a dynamic testimony to the above, in the oceans, which began to be created at the same time, a system of fractures / ridges with volcanic extrusions that support the ocean basins can now be observed. One of these ridges extends from north to south in the central Atlantic Ocean at a similar distance from the African and South American coasts. Another dorsal with similar characteristics is found in the central Pacific Ocean, also extending in the direction of the meridians.
Due to these successive volcanic effusions, in the oceanic bottoms the ages of the rocks appear in symmetrical strips to both sides of the dorsal ones (the most modern formations in proximity of the dorsal ones and the oldest ones more in more distant positions).
This process, which generated the oceans and led to the separation of the continents, seems to have started (at least) about 200 million years ago (which is the age of the oldest oceanic basalts) and continues today.
According to Sánchez Cela, this fusion of the rocky masses of the upper mantle (new crust) that generated the basaltic eruptions in the ocean ridges occurred due to the heat generated by the exothermic conversion of higher density minerals to lower density minerals.
According to this author, the molten granite materials in "ascent" digest oceanic sediments composed of limestones and marls (rich in CaCO3 and MgCO3) and various percentages of clays) giving rise to basalts (which in a certain way are granites with additional calcium).
These rocks are called basalts and are mainly found in the oceanic basins.
