Orogenic Theories and Plate Tectonics: A Comprehensive Study
Orogenic Theories
Fijist Theories
Fijist theories assumed that the geographical position of continents and oceans do not vary with time, and that the causes of internal processes are vertical movements of elevation and subsidence. The theory of greater importance was Dana’s. He considered that from an initial molten earth, the planet suffered a gradual cooling and consequent contraction. According to this theory, as the interior cooled and contracted, the external solid surface was deformed by crumpling to accommodate the decrease in volume.
Mobility Theories
Mobility theories consider that the continents move slowly and gradually, a process that generates enormous horizontal forces which are responsible for the formation of mountains. The theory of continental drift was proposed by Alfred Wegener. According to him, all continents were united in a single mass called Pangea; therefore, there was only one ocean. Pangea broke into various blocks that were moving along time.
Evidence of Continental Drift
- Coupling of the Continents: The edges of continents fit together if taken as the contact zone of the continental slope.
- Geological Evidence: In different continents, there are ancient mountain belts abruptly ending in continental margins but continuing to join.
- Paleoclimatic Evidence: Based on the existence of sedimentary formations that are indicative, such as moraines (glacial climate).
- Paleontological Evidence: Accurate in the presence of identical fossils in both plants and animals of the late Paleozoic and early Mesozoic areas, now separated by oceans.
Layers of the Earth
- Lithosphere: Solid, rigid layer covering the entire cortex.
- Asthenosphere: Plastic layer comprising part of the upper mantle.
- Mesosphere: Solid layer which encompasses the rest of the upper mantle and the entire lower mantle.
- Endosphere: Innermost layer covering the outer core and inner core.
Plate Tectonics
Destructive Limits
The creation of lithosphere at the ridge, which produces a compression plate, is solved by breaking the zone but weakly. The result is the formation of a border where two plates converge, where the denser bends and sinks beneath another (subduction).
Constructive Limits
Originate in areas where hot material rises from the asthenosphere, the lithosphere bulges and cracks (rift).
Limit Liabilities
Plates slide laterally one over the other. Its name is because there is no creation or destruction of lithosphere.
Distribution of Volcanoes and Earthquakes
- Circum-Pacific Circle: Subduction zone related to the ridges that line the coast of America.
- Asian Mediterranean Coast: It crosses the belt of fire.
- Ocean Ridges: Centroatlantica and Pacific highlight the areas of separation between plates.
Ocean Formation and Plate Convergence
Ocean Creation
Separation movement of the plates causes the breakup of the continents and fractured blocks away.
Ocean-Ocean Convergence
If two oceanic plates collide, one of them, the denser or the oldest, is subducted beneath the other through the trench.
Ocean-Continent Convergence
When an oceanic plate hits against the edge of another continental plate, the oceanic plate always subducts. The accumulated sediments on the continental margin are deformed and fractured, forming folds.
Continent-Continent Convergence
If, under the edge of a mixed plate, a subducting plate can consume the entire oceanic lithosphere that separates the two continental blocks, the subducting continental lithosphere cannot interpenetrate, and the two continents collide and form a single landmass, closing the ocean.
Folds and Faults
Folds
Folds are plastic deformations of layered rocks, ripples produced by compressive forces.
- Hinges: Lines of maximum curvature on each layer of the fold.
- Axial Plane: Imaginary plane connecting the hinges of all layers of the fold.
- Fold Axis: Line of intersection of the axial plane with the ground surface.
- Sides: Sides located on either side of the axis.
Inclination of Axial Plane
- Straight or Symmetric: Both sides are inclined.
- Inclined: Inclined axial plane, but the flanks are oriented on the same side.
- Lying: When the axial plane is horizontal.
Faults
Elements
- Fault Plane: Plane on which the movement has been made.
- Raised Lip: The raised side of the fault.
- Sunken Lip: The sunken side of the fault.
Types of Faults
- Normal Fault: The fault plane dips, and the side that is tilted toward the lip is sunk.
- Vertical Fault: The fault break is not zero, so there is an overpass and plunged lip.
- Reverse Fault: Caused by the rise of the high lip.
- Horizontal Fault: Horizontal displacement of the fault blocks are zero jump.