Plate Tectonics and Earth’s Dynamic Processes
1. The Birth of Geosciences
Neptune (Neptune = God of the Sea)
It is a mistaken theory about the origin of rocks, is heir to the design of the downpours. The followers of this theory believe that all rocks (including volcanic) have been formed by a process of sedimentation and crystallization in the primitive seas.
Catastrophism
Explains the formation of fossils and the current shape of our planet by the action of successive and major disasters, sudden and violent, such as the Flood. These originated the flooding of lands, seas disappearance, the appearance of mountains, etc.
Pluto (Pluto, God of the Deep)
Explains the consolidation of sediments and the origin of volcanic and plutonic rocks by cooling of magma from the Earth’s interior. Hutton proposed the theory of uniformitarianism.
Uniformitarianism or Actualism
Develops the theory proposed by Hutton. Advocates the idea that natural forces acting in the past consistently are the same as currently operating, although there may have been disasters (earthquakes, volcanoes, meteorites, etc.).
Neocatastrophism
Today is emerging as a combination of both. In addition to incremental changes proposed uniformitarianism, disasters have also been punctual, impacts from comets or meteorites. For instance, that caused the demise of the dinosaurs.
Fixist or Verticalist Theories
In force since the mid-nineteenth century to mid-twentieth century, only accepted on the vertical movements of the earth’s crust is sinking or rising ground.
Mobilist or Horizontalist Theories
They are based on horizontal movements of the crustal block. The accepted theory today is plate tectonics, which involves a change as revolutionary as it may be the Big Bang in Astronomy, or the evolution of species in Biology.
Plate Tectonics
It is a joint explanation of major geological events, which is completed with the effort and the scientific study of several geologists, geophysicists, seismologists. It is the product of international collaboration of all.
It added several aspects of this theory:
Continental Drift
The formula Wegener in 1912. He saw the horizontal movement of continents, like floating on a sea barge in this case would be the mantle. Although he knew that was the force causing this movement, I thought that perhaps this was related to the gravitational and f.centrífuga, which called f.polófuga.
Convection Currents in the Mantle
In 1945, Holmes proposed the existence of convection currents in the mantle as a theoretical model that would support the continental drift. This model in turn is supported by the explorations made in the 2nd World War seabed where a relief is formed by peculiaroceanic ridges and large pits.
Expansion of the Deep Ocean
In 1962, Hess hypothesized expansion of the oceans, which is created at the ridges, scrolls and destroyed at subduction zones. This hypothesis was supported by T. Wilson, who also justified the existence of some volcanic islands like Hawaii by the action of magmatic plumes from the deep mantle.
Banded Distribution of Magnetic Anomalies
On both sides of the ridges, in the early 60s by F. Vine, D. Matthews and L. Morley and A Larochelle. Also confirmed by studies of the seabed over the age of the basalts and sediments of the seafloor (oldest farther away from the ridge).
Plate Tectonics
Scientists like Jason Morgan in 1964 and later Mc Kenzie, R. Le Pichon X Parker and develop the ideas that show the land surface shaped by large lithospheric plates that move with respect to others.
2. Static Model of the Earth’s Interior
M. static or geochemistry of the Earth, which states that this is a giant rock structure distributed in concentric layers (crust, mantle and core) separated by discontinuities or zones of separation as different chemical composition (crust-mantle-core) different mineralogical composition (outer-inner mantle) and different physical state (outer-inner core).
2.1 Crust
It is the outermost layer and extends to the Moho, to an average depth of 35 km, contains mostly silicates of Al, Ca, Na and K. We can distinguish between two types of the continental crust and oceanic:
Oceanic Crust: less profound but if composed of denser rocks such as basalts and gabbros. Its depth is between 6 and 12 km. The oldest rocks do not exceed 180 million years.
2.2 Mantle
Olivine. The enormous pressure and temperature minerals make reorganize forming dense compact structures, thus causing two discontinuities or transition zones of Mohorovicic that marks the beginning of the mantle-Repetti, which separates the upper mantle below.
2.3 Core
It extends from the Gutenberg discontinuity to the center of the Earth.
Outer core: Composite principally by Fe, Ni and some S, Si and O.
Inner core: Probably comprising an alloy of Fe and Ni in solid state.
3. Plate Tectonics: The Changing Surface
The earth we tread is on the move. The rocky material of the crust and upper mantle form a rigid and brittle than unit called the lithosphere with a depth of about 100 Km. The lithosphere therefore understand the Earth’s crust and upper mantle part. The lithosphere in turn does not form a continuous layer but is fragmented into pieces that are: lithospheric plates.
Lithospheric plates fit together as if it were a giant puzzle. Each can be formed only by oceanic crust or be mixed, i.e. a part of another oceanic and continental. The lithospheric plates are limited by plate boundaries, which in turn can be of several types:
- Ocean ridges
- Subduction zones
- Transform faults
The plates float on the upper mantle, on which they move, they create and destroy, separate continents back together, crushed rocks and mountains stand where once were seas. The oceanic lithosphere is created at the ridges and destroyed at subduction.
3.1 Geological Phenomena Relating to Plate Boundaries
The belts of earthquakes and volcanoes are associated with the edges of plates: mid-ocean ridges (creation of plaques), subduction zones (destruction of plates) and transform faults (one plate moves over another through a fractured land). Upon returning to the depths materials describe an incline: Benioff plane, which is where we generate most of the seismic foci.
The engine that moves horizontally plates is (1) Earth’s internal heat coming from the core and mantle, together with (2) gravitational pull exerted when the oceanic lithosphere sinks into the mantle.
The Earth’s internal heat: It is a remnant of the primordial heat during the formation of the planet, along with the decay of radioactive elements present in the mantle. There are two types of convective flows:
1. Because of the subduction of the oceanic lithosphere cools the upper mantle and descends to the D layer, causing the rise of hot material from the bottom by convection currents. This is possible by the plastic behavior of materials from the mantle. That is evacuated by these currents heat from hot spots and deep (D) to the cold (most external).
2. The second flow is due to the large amount of heat accumulated over millions of years in the layer D, which escapes erratically and episodic spurts. Each bubble produces a jet or plume of magma rising through the mantle, pierces the lithosphere and causes a hot spot of intense volcanic activity. Hot spots can participate in the fragmentation of continents by oceanic ridges.
3.1.1 Oceanic Ridges
Are undersea magma emitted continuously (volcanism) are edge construction as the magma from the partial melting of the mantle surface areas.
3.1.2 Subduction Zones
Borders destructive, are sinks located in the depths of the oceans. Oceanic lithosphere is destroyed continuously forming ocean trenches. Upon returning to the depths materials describe an incline: Benioff plane, which is where we generate most of the seismic foci.
In the process of subduction can be given the following three situations:
Oceanic lithosphere beneath oceanic lithosphere: The subducting plate partially melts and produces magma, some of this rises through fissures leading to the formation of arc-shaped islands with high volcanic and seismic activity.
Oceanic lithosphere beneath continental lithosphere: It forms an active continental margin orogenic or mountain pericontinental (e.g., the Andes) with high volcanic and seismic activity. These are mountain ranges that can span hundreds or thousands of km along convergent plate margins, folding large amounts of sediment derived from erosion of nearby continents.
Intercontinental collision: The advancing subduction process in a mixed plate, where the oceanic lithosphere is depleted, they face the two continental masses collide, marine sediments are fractured and folded. Leads to an intercontinental or collision orogenic.
3.1.3 Transform Faults
Borders neutral which is neither created nor destroyed land. These are tears appearing in areas of tension. They are cutting through the ridges and edges of plates.
3.2 Plate Tectonics: A Global Theory
So give a joint explanation to all the great geological phenomena, all of them motivated by a common cause.
Earthquakes: In subduction zones, where oceanic ridges and transform faults. Large rock masses collide and cause earthquakes. In the continents are called earthquakes, tidal waves on the ocean floor that may cause giant waves or tsunamis.
Volcanoes: In the mid-ocean ridges, in subduction zones and hot spots. The magma escapes through the cracks.
Expansion of the oceans: Oceanic lithosphere is created on both sides of the ridges. And the oceans are becoming larger.
Mineral and oil deposits: We can predict the location of oil fields, natural gas and a variety of minerals.
4. Volcanoes: Mountains of Fire
They form when magma comes from the mantle rises to the surface through fissures in the oceanic and continental crust, causing the eruption of the volcano. The eruption of a volcano suddenly released large amounts of energy that come from within Earth, molten rock materials are released (above 1000 ° C) the amount, that together with the decrease in pressure causes the formation of magma.
4.1 Volcanism in Hot Spots
A deep magma plume and hot from layer D, amounts to reach the lithosphere acts as a torch, deforming, fracturing and drilling the lithosphere. There may be three different situations:
1 – Drilling the oceanic lithosphere and the appearance of a chain of volcanoes: The hot spot remains fixed and the oceanic lithosphere is being drilled as this moves (moves the plaque). It causes a chain of submarine volcanoes. Young and active closer to point c. and old and eroded the farther away, forming guyots (Seamount) and atolls. One example is the Hawaiian Islands that form a chain of volcanic islands.
2 – Origin of large igneous provinces or basalt: These are large areas of the planet buried by basaltic lavas, which were issued in a relatively short period of 1 to 5 million years. What causes the potent activity of a hotspot, resulting in the formation of huge basalt layers of overlapping of several kilometers thick, which can cover thousands of square kilometers as the Trapp Deccan in India.
3 – Thinning of the continental lithosphere and formation of a rift. The lithosphere thins and bulges to cause three radial fractures that converge at a point (triple point). These fractures can become depression or valleys of collapse. This is the case of the African Rift Valley, which could in future become a column.
4.2 Volcanism in the Ocean Ridges
Fissure volcanoes form, giving calm and effusive eruptions, lava flows from fissures in the form of huge casting forming horizontal layers. On cooling basaltic rocks are formed which constitute the oceanic lithosphere.
4.3 Volcanism in Subduction Zones
There can be two different situations:
1 – Oceanic lithosphere beneath oceanic lithosphere, resulting in an archipelago of islands in an arc of high volcanic activity. For example Japan and the Philippines.
2 – Oceanic lithosphere beneath continental lithosphere that causes a continental volcanic arc associated with a range (e.g. Andes, the Alps).
4.4 Volcanic Eruptions
Surface pools in a sac called the magma chamber (between 3 and 30 km from the surface).
1 – Magnus fluids: The ridges and hot spots. They have low gas content and form lava flows. With effusive eruptions and quiet.
2 – Viscous magma. In subduction zones, and high gas content and therefore cause violent explosions, escaping gas, brutally, throwing high and long distance lava and volcanic fragments of the chimney, together with pyroclastics that according to their size: When a volcano goes off, fireplaces are filled with solidified lava, which because of erosion can be exposed, forming vertical columns. In the Canary Islands are called rooks. If a volcano is inactive for a long time is said to be asleep. It’s normal for volcanoes to alternate periods of activity with others that seem off. If you are off for a long time are said to be extinct or extinct.
5. Earthquakes: When the Earth Trembles
Most earthquakes are caused by the dynamics of plate separation, collision or sliding of these in the opposite direction causes it to generate tensions that accumulate slowly, causing elastic deformation in the rocks until they are fractured and release the energy stored in a violent way, in the form of vibrations. The brutal earthquakes are ground shaking caused by the fracturing of rocks deep in where suddenly released large amounts of energy. If it takes place on land are called earthquakes, and if they occur at sea, tsunamis.
The vibrations propagate as seismic waves, which form spherical wavefront and walk inside the globe from side to side and in all directions. These waves are generated in the focus or hypocenter which is located several km deep that after a while can be picked up by seismographs in the seismograms. The epicenter is the area of the earth’s surface located directly above the focus.
5.1 Types of Seismic Waves
Are matter waves, such as sound, require a physical medium to propagate. They are of three types:
P or primary waves. Compression waves are created at rock succession of compressions and expansions, backward and forward, following the same direction that the wave moves. They are the fastest and transmitted in all media.
Secondary or S waves. Are transverse waves, causing the rocks move up and down, perpendicular to the direction in which the wave propagates. Are the second to appear, only propagate in solids.
L or surface waves: These are the last to arrive, spread over the surface. Rayleigh waves produce an elliptical motion that shakes the rocks up and down and forward. Love And waves that cause horizontal movement from one place to another.
5.2 Magnitude and Intensity of an Earthquake
The scales measure the energy released by an earthquake and assesses the damage caused.
Richter Scale: Measures the magnitude of an earthquake is a measure of energy released. It is calculated from a seismogram by measuring the maximum amplitude of the waves P and S. It has no limits in theory can reach all the values (1,2,3,4,5,6,7,8 ….. ..) depending on the energy released. The largest earthquake was magnitude known from Valdivia, Chile in 1960, 9.6.
MSK Scale: Measures the intensity of an earthquake is a subjective estimate of the effects produced by the earthquake on people, objects, buildings and land. This depends not only on the energy released in the earthquake but also the terrain and type of buildings that are in the area, for example if the area is poor, overcrowded and poor quality housing, the damage is greater. An earthquake will unique and different intensity scale in each place it varies with distance from the area epicentro.Los points that represent the same intensity are joined by curves called ISOs.
6. Continental Drift: The Wilson Cycle
It is an evolutionary cycle that explains the opening and closing of ocean basins and changes in the distribution of continents and oceans along the same tectonic processes that cause the breakup of a supercontinent are the cause of his after reunification, in cycles lasting about 500 ma.
7. Plate Tectonics, Science and Society
Fossil fuels: Coal, oil and natural gas formed by geological processes of burial and decomposition of organic matter. Wood of ancient forests, and old oil from plankton in shallow seas (rifting processes).
Geothermal: Widely used in countries of volcanic activity, using the heat of the earth for heating and for electricity (e.g. Iceland).
Fertile soil: Volcanic regions where they were formed fertile soils for agriculture.
7.2 Risks
Many civilizations past and present volcanic zones are located in or near active faults.
Volcanic risk: With devastating eruptions at grave risk to people and property.
Seismic risk: Especially the devastating waves L, that wiped out the buildings and roads and what is even worse loss of life.
Environmental Impacts: By throwing large amounts of toxic gases and CO2 to the atmosphere increases the greenhouse effect, which allowed the emergence of life, but at other times throw together with large amounts of ash originated in the past climate changes, causing and mass extinctions of living beings.