Tierra

2.2. Internal processes
The internal processes are those directly or indirectly caused by the Earths
internal heat:
„h Metamorphism
„h Magmatism
„h Isostasy (epirogenic movements)
„h Orogenesis (orogenic movements)
2.2.1. Magmatism and plate tectonics
Rock melting can be produced by the following processes
o A raise in the rock temperature
o A drop in the confining pressure
o The presence of fluids (water)
According to plate tectonics, three igneous environments exist:
o Continental rifts, mid-ocean ridges: Mantle rocks melt by a drop in
pressure
o Ocean trenches: Crustal rocks melt by a raise in temperature
(friction) and a presence of fluids produced by dehydration of the
subducing plate
o Hot spots: (intraplate volcanism) Deep mantle rocks melt by an
increase in temperature (mantle plumes)
Continental rifting, ocean ridges and hot spots show rich-iron, richmagnesium,
and poor-fluid magmatism, since it comes from mantle melting.
However, magmatism related to ocean trenches present rich-silica, richaluminium,
and rich-fluid magmas, produced my melting of crustal rocks.
2.2.2. Metamorphism and plate tectonics
Magmatism is a geological process in which pre-existent rocks reorganise their
minerals and texture, according to an increase in temperature and/or pressure
inside the Earth. Rocks, however, remain basically with the same global chemical
composition, and thats why metamorphism is an isochemical process. When it is
clear that an exchange of elements between the previous rock and internal fluids
has taken place, that process is called metasomatism, or metasomatic
metamorphism.
The metamorphic areas develop in plate boundaries:

3. Isostasy
Since the rigid lithosphere lays over either the asthenosphere or mesosphere,
which are plastic layers, if a lithospheric slab gains or loses weight, vertical
movements appear in order to reach a new floating equilibrium, in the same way a
boat goes up or down when it is loaded or unloaded.