Earth's Structure: Geochemical, Dynamic Models & Plate Tectonics

Earth's Structure and Dynamics

Geochemical Modeling

• Crust: A rigid layer, either continental or oceanic.
• Mantle: Includes the upper mantle, transition zone, the Repetti discontinuity, and the Gutenberg discontinuity.
• Core: The outer core is distinguished by its properties.

Dynamic Model

• Lithosphere: Formed by the crust and the lithospheric mantle.
• Asthenosphere: Located between 100-250 km depth.
• Mesosphere: Located between 250-2900 km. Hot spots, thermal plumes, and feathers originate in this layer.
• Endosphere: Located between 2900-6371 km.

Plate Tectonics

Plate tectonics can be summarized as follows:

• The lithosphere is not a continuous layer but is divided into lithospheric or tectonic plates.
• Lithospheric plates rest on the asthenosphere, whose plasticity allows the plates to move.
• As a result of this movement, friction and impacts occur at plate edges.

Evidence of Plate Tectonics

• Geographical distribution of earthquakes: Volcanoes and areas of active volcanism coincide with recent seismicity. The three major unstable regions of the planet—the circum-Pacific belt and the Mediterranean-Asiatic belt—correspond to subduction zones where plate collisions occur.
• Ocean floor expansion: The age of the ocean floor depends on its distance from the ridge; the more distant areas are older.
• Plate movement: The speed and direction of plate motion are calculated by determining the distance from a location with known-age oceanic crust to the center of the ridge.

Plate Boundaries

A. Constructive or Divergent Boundaries: Found at oceanic ridges, where plates move apart and new oceanic lithosphere is generated from the asthenosphere.

B. Continental Drift and Ocean Formation: The separation of plates causes the breakup of continents, the formation of ridges, and the removal of fractured blocks, leading to the creation of oceans.

C. Destructive or Convergent Boundaries: Oceanic lithosphere created at ridges is destroyed in ocean trenches where plates converge, and materials are incorporated back into the interior. Plate collisions also result in the formation of orogenic or mountain ranges.

D. Transform or Conservative Boundaries: These boundaries connect areas of converging or diverging plates. Most are divided by ridges and are known as transform faults.