Formation of Accretionary Prisms & Orogenic Belts
Training Ranges: Formation of Accretionary Prism
K carries sediment. Oceanic lithosphere subducting, not the majority. The front of the continental shelf traps sediments, which are folded and fractured, thus causing the accretionary prism.
Magmatism and Metamorphism
The presence of water in the subducting lithosphere and heat generated by the friction between plates favor the partial fusion of rocks. The magmas originated climb, and those that remain inside contribute to the thickening of the continental crust. High pressures and temperatures favor the formation of some metamorphic rocks.
Orogenic Elevation
The mountainous terrain is a consequence of:
- The thickening of the crust produced by the accumulation of materials.
- Isostatic elevation: Thickened crust produced by all materials, which are less dense than the mantle.
Process of Continental Acute MCL Violation
Oceanic Subduction
Subducting oceanic lithosphere transports sediments that accumulate, fold, and fracture.
Closure of the Ocean Basin
The entire stretch of oceanic lithosphere is consumed; the continent reaches the subduction zone. Continental materials are denser, making it more difficult for them to be subducted into the mantle. Otherwise, the continental lithosphere is thicker, which makes subduction far harder.
Continental Collision
The two continents end up colliding; the material between them is compressed, folded, fractured, and raised. If this continues, it will produce the inlay of a continent on the other, which can double the continental crust in the area. Therefore, the resulting isostatic elevation will be very important.
Equilibrium Between Internal and External Processes
The elevation of a ridge during development (orogenic elevation) can reach 800 cm in 1000 years. As ridges rise, erosion begins. The highest mountains experience erosion that reaches up to 100 cm in 1000 years. If the denudation rate averages 5 cm every 1000 years.
Mutual Influence
External processes affecting internal ones: The elevation of a ridge also activates erosion because erosion is more intense in the highlands than in the lowlands.
Internal processes and external influences: The withdrawal of materials from one area (and a corresponding increase in another) causes isostatic imbalances, which will be offset by daily movements of uplift and subsidence, respectively.
Principles of Stratigraphy
Principle of Original Horizontality
Strata deposited from sediments form horizontal layers. Therefore, if some strata are inclined, we conclude that they have been subjected to forces that changed their original disposition.
Principle of Superposition of Strata
Sediments are deposited over each other, i.e., in a series of strata that is in its original arrangement, the layer situated below will be the oldest, and the one above will be the most modern.
Principle of Cross-Cutting Relationships
According to this principle, every geological process is subsequent to the materials it affects.
Determining Which Stratum is Older
Using the following criteria:
- Fossils: The presence of fossils can guide us in ordering strata.
- Graded Bedding (Granoselection): Coarser sediments settle to the bottom, and finer sediments stay above, so we can determine the base and top of the stratum and its orientation.
- Desiccation Cracks: These form in drying clay sediments. They have a V-shape, whose apex points toward the base of the stratum.