33
The lower and upper part of the mantle is separated by a transitional zone between the depths
of 410 and 660 km (layer C in Fig. 2.15). The
lower mantle found between the depths of 660 km
and 2900 km has a higher viscosity that of the
upper mantle. This zone gives 50% of the mass of
Earth (67% together with the upper mantle) while
its chemical composition is relatively homogeneous with magnesium and iron dominating in it.
The bottom-most 200–300 km thick layer of
the lower mantle at an average depth of 2900 km
(layer D in Fig. 2.15) has a major role in mechanical and heat energy transfer between the core
and the mantle.
The outer core is composed of iron in 90%
(with some silica and sulphur) and its state is liquid. Currents in the outer core cause the presence
of a magnetic field around Earth.
The state of the inner core is solid due to the
enormous pressure prevailing in it. Its material is
made of iron in even greater ratio (95%) than in
the case of the outer core.
PREM model simplifies the internal structure
of Earth focusing on the changes of the physical
properties of Earth in radial direction. With modern research methods geophysicists developed
the method of seismic tomography with which
the changes in the velocity of seismic waves can
be plot into three dimensions producing velocity
anomaly images with good spatial resolution of
the entire mantle. Based on the results, a new globalgeodynamic model (Romanowicz 2002;
Courtillot et al. 2003; Jellinek and Manga 2004;
Horváth and Dombrádi 2008) was created. This
contains several new features compared to the
PREM model and adds some new elements to the
traditional theory of plate tectonics as well.
One of the most important arguments of plate
tectonics in the 1960s and 1970s was that oceanic
lithosphere produced at mid-oceanic ridges converge to continental plates subducting under
them. After some ten million years of the formation of the oceanic lithospheric plates their cooled
material has higher density than that of the asthenosphere. Thus it is pulled by a force called slab
pull when it enters the asthenosphere. According
to recent investigations, this pull gives around
90% of the force moving the lithospheric plates.
Fig. 2.15 Schematic model of the geosphere showing the geometry of the subducted oceanic lithospheric slab (after
Horváth and Dombrádi 2008)
2.6 Earth Models, “World Models”
The lower and upper part of the mantle is separated by a transitional zone between the depths
of 410 and 660 km (layer C in Fig. 2.15). The
lower mantle found between the depths of 660 km
and 2900 km has a higher viscosity that of the
upper mantle. This zone gives 50% of the mass of
Earth (67% together with the upper mantle) while
its chemical composition is relatively homogeneous with magnesium and iron dominating in it.
The bottom-most 200–300 km thick layer of
the lower mantle at an average depth of 2900 km
(layer D in Fig. 2.15) has a major role in mechanical and heat energy transfer between the core
and the mantle.
The outer core is composed of iron in 90%
(with some silica and sulphur) and its state is liquid. Currents in the outer core cause the presence
of a magnetic field around Earth.
The state of the inner core is solid due to the
enormous pressure prevailing in it. Its material is
made of iron in even greater ratio (95%) than in
the case of the outer core.
PREM model simplifies the internal structure
of Earth focusing on the changes of the physical
properties of Earth in radial direction. With modern research methods geophysicists developed
the method of seismic tomography with which
the changes in the velocity of seismic waves can
be plot into three dimensions producing velocity
anomaly images with good spatial resolution of
the entire mantle. Based on the results, a new globalgeodynamic model (Romanowicz 2002;
Courtillot et al. 2003; Jellinek and Manga 2004;
Horváth and Dombrádi 2008) was created. This
contains several new features compared to the
PREM model and adds some new elements to the
traditional theory of plate tectonics as well.
One of the most important arguments of plate
tectonics in the 1960s and 1970s was that oceanic
lithosphere produced at mid-oceanic ridges converge to continental plates subducting under
them. After some ten million years of the formation of the oceanic lithospheric plates their cooled
material has higher density than that of the asthenosphere. Thus it is pulled by a force called slab
pull when it enters the asthenosphere. According
to recent investigations, this pull gives around
90% of the force moving the lithospheric plates.
Fig. 2.15 Schematic model of the geosphere showing the geometry of the subducted oceanic lithospheric slab (after
Horváth and Dombrádi 2008)
2.6 Earth Models, “World Models”