Lecture on Divergent Plate Boundaries and Ocean Basin Formation

Overview

• Earth is over four billion years old, but ocean basin rocks are less than 200 million years old.
• Ocean basins are recycled continuously, starting with new oceanic lithosphere at divergent plate boundaries.
• Lecture covers geological features, processes, and creation of ocean basins.

Divergent Plate Boundaries

• Definition: Areas where tectonic plates move away from each other.
• Geological Features:
  • Continuous oceanic ridge forming submarine mountain ranges.
  • Source of volcanic activity.
  • Location of the youngest oceanic lithosphere.

Observations

• Earthquakes are common along divergent boundaries.
• Bathymetry: study of ocean floor depth and topography.
• Ocean floor age increases with distance from divergent boundaries.
• Divergent boundaries are identifiable by ridges, young ocean floor, and earthquake activity.

Formation of Ocean Basins

• Begin with a continent splitting apart.
• Stages:
  1. Continental crust stretches and thins, forming a regional uplift.
  2. Rift valley forms, containing volcanoes or lava flows.
  3. Rift valley floor drops below sea level, forming a narrow ocean.

Case Study: Atlantic Ocean

• Formed after Pangaea breakup.
• African continent currently undergoing similar processes.
• Example: Red Sea, which started opening 30 million years ago.

Ocean Basin Expansion

• Ocean basins expand from a few hundred kilometers to several thousand.
• Expansion rate and size depend on plate motion speed and duration.
• Atlantic and Pacific Oceans began opening simultaneously with similar aged rocks.
• Pacific Ocean is wider due to faster plate separation.

Process Summary

• Plates separate along rift zones at oceanic ridges, driven by mantle convection.
• Shallow earthquakes occur due to faulting in rift zones.
• Magma fills gaps, forming new oceanic crust.
• Magma forms basaltic lava or plutonic rocks like gabbro.
• High heat flow creates lower density and higher elevations, forming ridges.
• Oldest crust near continents, youngest crust at ridge centers.

Practical Application

• Draw and label a sketch of divergent plate boundary features and processes.

Learning Objectives

• Understanding the formation and evolution of divergent plate boundaries.
• Knowledge of oceanic basin formation processes.