Earth's Interior: Composition, Structure, and Plate Tectonics
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Earth's Interior: Composition and Structure
Sudden and Gradual Changes in Earth's Layers
There are both sudden and gradual changes within Earth's interior. These variations occur because materials differ in their composition and/or hardness. Since S waves propagate through solids but not fluids, we can conclude that at approximately 2900km depth, there is a transition to a continuous layer of molten material.
Ocean Floor and Magnetic Stripes
It was discovered that the oceanic crust, specifically basalts, and the associated bands had a magnetization parallel to the axis of the ridge. To explain these magnetic stripes, F. Vine and D.H. Matthews developed the theory of seafloor spreading. This theory posits that ridges are places where new oceanic lithosphere is generated from magmatic material originating from the Earth's interior.
Metamorphism
Metamorphism refers to a set of changes in the composition, mineralogy, and texture of a rock that occur in a solid state. These changes result from increased pressure, temperature, or other factors. One common type of metamorphic rock is formed due to increased pressure.
Plate Tectonics and Continental Drift
Wegener's Arguments for Continental Drift
Alfred Wegener's theory of continental drift was supported by several arguments:
- Geographic: Based on the complementary shapes of continents.
- Paleontological: Study of the distribution of animal and plant fossils.
- Geological: Continuity of mountain ranges and geological formations.
- Paleoclimatic: The existence of glacial deposits of the same age in geographically distant locations.
Magnetic Stripes and the Earth's Magnetic Field
Through the study of magnetic stripes, we can determine the orientation of the Earth's magnetic field at the time the rock was formed.
Types of Plate Boundary Movements and Their Effects
| Movement Type | Effect | Topography |
|---|---|---|
| Divergent | Constructive | Mid-ocean ridge, rift valley |
| Convergent | Destructive | Trench, mountain range, folding |
| Transforming | Conservative | Unremarkable |
Rock Deformation
Deformation of rocks refers to changes in volume and size as a result of the stresses to which they are subjected.
Volcanism and the Canary Islands
Hypotheses on the Origin of the Canary Islands
Canary Islands as a Hot Spot
One hypothesis suggests that the Canary Islands are a hot spot due to the approximately linear disposition of the islands. However, arguments against this include volcanic activity at both extremes of the island chain and long periods of inactivity.
Canary Islands as a Fracture Zone
According to the propagating fracture hypothesis, the Canary Islands are located on a fracture zone connected to the Atlas Mountains, which is its geometrical prolongation. The compression exerted by the Atlantic Ridge on the continental edge causes the formation of faults that uplift the blocks, forming the islands.
Volcanic Features
- Cone: A volcanic structure formed by the accumulation of magmatic material around the crater.
- Stratovolcano: Formed by the accumulation of pyroclastic flows and lava flows, resulting in a large, steep-sided volcano.
- Caldera: A large, circular depression significantly larger than a crater.