Plate Tectonics: Evidence, Types, and Interactions

Plate Tectonics: Key Concepts

• Biological Puzzles

  The existence of land bridges or island chains that connected the ancient continents.

• Geographic Enigmas

  The outer edge of the continent is under the sea where the continental shelf terminates.

• Geological Riddles

  There is a correspondence between geological structures present on both sides of the Atlantic Ocean.

Scenarios of Continental Drift

According to Wegener, all continents were part of a large landmass (supercontinent called Pangea).

• Paleomagnetic Tests

  During the cooling of lava, ferrous minerals align. Studying these minerals indicates the position of the north pole.

• Oceanographic Evidence

  The discovery of the oceanic ridge system that splits the great oceans.

• Seafloor Spreading Hypothesis

  Harry Hess proposed that mantle upwelling collides with the crust, creating ocean ridges. Paleomagnetism: Earth's magnetic field reverses from north pole to south pole, and vice versa.

• Plate Tectonics

  This theory, arising from contributions of different scientists, explains geographical and geological aspects of the planet. The crust is divided into plates that move on the lithospheric mantle. Ridges create new oceanic crust.

Causes of Plate Motion

1. Convection currents: Hot material rises, dragging the crust plates.
2. Trawl boards: Oceanic crust has a lower temperature and higher density, moving away from the dorsal.
3. Thrust of plates: Plates shift to deeper areas of the seabed.

Types of Plates

Plates consist of the crust and mantle (lithosphere). Lithospheric plates are on the asthenosphere. They can be divided according to their size, with 7 major plates: African, Eurasian, Indo-Australian, North American, South American, Pacific, and Antarctic.

Contact Between Plates

1. Divergent Edges

   Both plates are separated from one another, with high volcanic activity.

2. Convergent Edges

   Two plates collide, destroying the crust. This type of contact has three variations:

   • Convergence between oceanic and continental plates: The oceanic plate subducts under the continental plate until melted.
   • Convergence between two oceanic plates: The denser plate subducts under the other.
   • Convergence between two continental plates: The collision of two landmasses is called obduction.

3. Transformable Edge

   There is a slippage between the plates that follow the same or opposite direction. The line of contact is a transform fault.

Isotropic Materials

An object or substance having the same uniform physical properties in any direction.

Anisotropic Materials

An object or substance with different physical properties in different directions.

Crust

The crust extends from the surface to the Mohorovičić discontinuity. It is composed of rocks, and its pressure, temperature, and density are low but increase with depth. The temperature increase with depth is called the geothermal gradient. There are two kinds of crust: continental (thick and less dense) and oceanic (thin, denser, and basaltic).