Understanding Tectonic Plates and Ocean Formation

Posted on Nov 19, 2024 in Geology

Characteristics of Oceanic Ridges

The oceanic ridge is an undersea mountain range rising above the abyssal plain. Its route is interrupted by lateral fractures called transform faults.

Seabed Ages

1) Existing rock at the ridges: Basalts at the oceanic ridges are less than a million years old.

2) Older oceanic crust separating from the ridge: The age of basaltic rock increases as we move away from the ridge.

3) Sediment thickness related to seafloor age: The ridge is devoid of sediment.

Seafloor Spreading

The oceanic lithosphere is created at the ridges and spreads to both sides. Not all ridges are equally active.

Destruction of Oceanic Lithosphere

According to plate tectonics, the lithosphere is reintroduced into the deep Earth through subduction. Subduction zones are located near the deepest ocean trenches.

Initial Conclusions

1) Some areas are geologically active, while others are stable.

2) Large masses of materials move over others, causing earthquakes when rocks fracture.

Lithospheric Plate Boundaries

The boundary between plates is called a plate boundary.

Mid-Ocean Ridges

These are plate boundaries where new oceanic lithosphere is generated.

Subduction Zones

These are plate boundaries where lithosphere is destroyed. Ocean trenches mark subduction zones. Displacement is not uniform, and heat from friction facilitates rock fusion.

Transform Fault Boundaries

Plate boundaries where lithosphere is neither created nor destroyed, moving laterally.

Major Plates

There are 7 major plates: Eurasian, African, Indo-Australian, Pacific, North American, South American, Antarctic, Nazca, and Caribbean.

Plate Movement

Lithosphere creation at ridges and destruction at subduction zones cause movement. Continents are part of the plates and move with them.

Convection Currents

A heated fluid expands, becomes less dense, and rises. When it cools, it descends. These cyclic movements are mantle convection currents.

What Moves the Plates?

1) Thermal energy of the deep Earth: The mantle is stirred by convection currents, causing plate movement.

2) Gravity: Plays a key role in plate motion through two mechanisms: oceanic plates are raised at ridges and sunken in subduction zones; the subducted lithosphere is thick and cold, increasing its density, pulling the plate.

Continent Division

Deep plumes of hot material cause continent division, forming rifts.

Ocean Formation Process

1) Lithosphere rises and bows.

2) Rift formation.

3) Oceanic lithosphere formation.

4) Ocean formation.

Tectonic Plates

1) The lithosphere is divided into rigid plates.

2) Plate boundaries can be ridges, subduction zones, or transform faults.

3) Oceanic lithosphere is continually renewed, while continental lithosphere is permanent.

4) Lithospheric plates move over the plastic mantle.

5) Plate movement is caused by thermal energy and gravity.

6) The position, shape, and number of plates have changed throughout Earth’s history.

Wegener’s Arguments

  1. Geography: Continents fit like puzzle pieces.
  2. Geology: Continuity of geological formations across the Atlantic.
  3. Paleoclimate: Sedimentary rocks as climate indicators.
  4. Paleontology: Distribution of fossils in distant locations.

Theory of Continental Drift

  1. All lands were once united in Pangea.
  2. Pangea split, and fragments moved to form present continents.
  3. Ridges formed at the advancing front of continents.

Wegener’s Hypothesis Challenges

  1. Unknown cause of continental displacement.
  2. Centrifugal force and tidal braking were inadequate explanations.

Why Study the Deep Ocean?

  1. Oceans cover 71% of Earth’s surface.
  2. Layers of deposits reveal 4 billion years of history.

Ocean Secrets Revealed

  1. Existence of the oceanic ridge.
  2. Lack and distribution of sediment.
  3. Youth of the seafloor.

Facts About the Deep Earth

  1. The Earth’s interior is dense.
  2. The Earth’s interior is hot.
  3. The Earth has a magnetic field.
  4. The Earth is structured in layers, evidenced by seismic waves.

Earth’s Composition

Crust: Thin surface layer, granite and gneiss on continents, basalt in oceans.

Mantle: Thick layer separated from the crust by the Mohorovičić discontinuity, composed of peridotite.

Core: Central area, isolated from the mantle by the Gutenberg discontinuity, composed of iron and nickel.