Continental Drift, Plate Tectonics, and Geological Processes
Continental Drift Theory
About 200 million years ago, the continents were united into a single landmass called Pangea, surrounded by a sea called Panthalassa. This supercontinent fragmented, and the pieces began to drift to their current positions. This theory was proposed by Alfred Wegener in 1912.
Convection Currents Theory
Convection currents are a powerful engine for moving continents. These currents are movements of materials caused by differences in density due to temperature variations. The continents move as if they were on a conveyor belt on underlying materials.
Continental Margin
Continental margins are of two types:
- Passive: These margins do not exhibit seismic or volcanic activity. They include the continental shelf, a gentle slope that extends to about 200m deep and is a prolongation of the continent.
- Slope: A very sharp slope that represents the edge of the continent, reaching depths of up to 4500m.
Seafloor
The seafloor is a plain with volcanic relief and signs of underwater volcanic activity.
Seafloor Spreading Theory
The ocean floor is continually being created from volcanic materials that emerge through the center of mid-ocean ridges. As these materials solidify, they push older materials to the sides. This process causes the continents on either side of the ridges, such as South America and Africa, to move further apart.
Plate Tectonics Theory
The lithosphere is divided into a series of interlocking plates. These pieces are called lithospheric plates. Most geological phenomena occur at the contact zones between these plates. There are seven major plates. Lithospheric plates are of varied and mixed nature. The oceanic crust is primarily found in the Nazca plate. Zones where two plates slide past each other are known as transform faults. The number and extent of plates have changed over time.
Lithosphere: The rigid outer layer of the Earth, including the crust and upper mantle. It is divided into lithospheric plates that are continually being created and destroyed.
Geothermal Gradient: The increase in temperature as one moves deeper into the Earth.
Heat Flow: The amount of heat that crosses a unit surface in a unit of time.
Fault: Occurs at the edges of tectonic plates, characterized by horizontal displacement where plates move past each other without creating or destroying lithosphere.
Tectogenesis: The geological processes that occur at the edges of tectonic plates, leading to the formation of orogens.
Diagenesis: The process of rock formation from loose sediments undergoing consolidation.
Orogenesis: The set of geological processes that occur at the edges of tectonic plates, leading to the formation of mountain ranges.
Metamorphism: The set of processes that rocks undergo when subjected to pressures and temperatures different from those of their formation.
Oceanic Ridges and Trenches
- Mid-Ocean Ridges: Pacific-Oriental Ridge, Chile Ridge.
- Oceanic Trenches Near the Americas: Peru-Chile Trench, Cayman Trench.
- Oceanic Trenches Near Continents: Mariana Trench, South Sandwich Trench.
- Island Arcs Near Continents: Greater Antilles.
- Island Arcs Off Continents: Mariana Islands, Tonga, Solomon Islands.
- Continental Platforms: Russian intraplate platform.
- Platform Phenomena: Hawaii.
- Atlantic Trenches: South Sandwich Trench, Peru-Chile Trench, Aleutian Trench.