Plate Tectonics: Transform & Convergent Boundaries
Neutral Edges: Interactions
When two plates move horizontally in opposite directions, they are also known as transform faults, passive margins, or conservative margins. Oceanic lithosphere is neither created nor destroyed.
The Origin of Transform Faults
The origin of transform faults is not very clear. Some scientists believe that these fractures are inherited from when the old continent opened to form the ocean. Others say that their genesis is related to the plate movement described, which diverges on both sides of the oceanic ridge axis.
Convergent Edges
These are areas where there is a confrontation between two plates that are near or pushing against each other. The high pressures and temperatures reached in these edges are responsible for various geological phenomena like earthquakes and volcanoes. Oceanic lithosphere is destroyed in them. There can be three types:
- Ocean-Ocean Convergence: There is an active plate subduction process. The plate is introduced under the passive plate using a variable inclination plane, called the Benioff plane. An insular arc develops in the passive plate. The deepest ocean trenches are located on the convex part of the island arc.
- Ocean-Continent Convergence: By subduction, an oceanic plate sinks beneath a continental one, forming a smaller angle of convergence than the ocean-ocean plate. Strong pressure rises to a range of marginal points of inflection on the active subducting plate. Oceanic trenches extend, through which the convergent flow occurs along the entire edge.
- Continent-Continent Convergence: Occurs when a mixed plate faces the continental edge of another, also mixed. When the process of subduction collides, the two continental blocks then one of them rides on the other in a reverse mechanism called subduction obduction.
Wilson Cycle
- Fragmentation phase of a continental gulf.
- Oceanic basin closure phase with stable continental margins.
- Ocean basins reduce.
- Narrowing phase.
- Oceanic basin closure phase.
Paleontological Evidence
Many scientists, among them Wegener, have made several paleontological tests. Some are based on the presence of certain types of organisms on continents as far apart as South America and Africa.
Geodesic Evidence
These use highly advanced technologies based on the emission of laser beams or the reception, with powerful radio telescopes, of radio waves from distant objects in space.
Geographical Evidence
This is based on the coincidence of the coastlines of some continents, which supports the idea that the present continents were united in the past. The case of South America and Africa is very evident.
Tests Based on Seismic Sources
The distribution of seismic foci along the Benioff plane also makes an important test that confirms the existence of an active subducting plate. There are three types:
- Shallow Earthquakes: These are recorded on the trench line and produce fractures along the coasts due to the fracturing of the cold plate that sinks.
- Intermediate Earthquakes: These earthquakes are felt in areas far from the coast, so their foci or hypocenters are located at a greater depth.
- Deep Earthquakes: These register in inland areas far from the coasts. Seismic foci lines have been detected at more than 300km deep.
Oceanic Evidence
This is based on relative points of the oceanic floor. They confirm seafloor spreading, the origin of oceanic lithosphere from basaltic magma from the mantle, and explain the evolution of the oceans over time.
Paleoclimatic Evidence
This is based on past climates.