Earth Science - Plate Tectonics

Study Notes

Earth Science - Plate TePlate tectonics is a scientific theory that explains

Plate tectonics theory states that the lithosphere behaves as a rigid layer divided into plates.
Continental drift theory proposes that continents were originally connected and have drifted apart.
Seafloor spreading is the process where new oceanic crust forms at mid-ocean ridges.
Plate Tectonics Theory - Evidence
Hotspots: Areas of volcanic activity that originate from deep within the mantle. The Hawaiian Islands are an example, with islands showing age progression.
Paleomagnetism: Study of magnetism in rocks. Changes in rock magnetism show evidence of plate movement and demonstrate an apparent polar wander path relative to the continent.
Apparent Polar Wandering: The apparent movement of Earth's magnetic poles over time relative to the continents.
Convection Currents and Forces
Layer Cake Model: The mantle is divided into two zones of convection, oceanic lithosphere at the trench, ridge push, volcanic trail, with a ridge.
Whole Mantle Model: Denser oceanic lithosphere sinks at subduction zones, causing descending oceanic plates, rising plumes, and hotspots.
Ridge Push: Warmer, less dense material rises at mid-ocean ridges and causes a force that pushes plates apart.
Slab Pull: Denser, colder oceanic lithosphere sinks at subduction zones, pulling the rest of the plate with it.
Continental Drift Theory - Evidence
Continental Fit: The shapes of continents, particularly South America and Africa, seem to fit together.
Fossil Evidence: Similar fossils of plants and animals are found on continents now separated by vast oceans, suggesting a connection in the past.
Rock and Mountain Similarities: Similar rock structures and mountain ranges are found on continents that are now separated.
Glacial Evidence: Glacial deposits and striations suggest that glaciers once covered land areas now in different locations.
Types of Stress
Tension: Plates move away from each other, causing stretches in rock. Examples include continental rifts and mid-ocean ridges.
Compression: Plates move towards each other, causing rocks to fold or break. Examples include ocean trenches and mountain ranges.
Shear: Plates slide past each other, causing rocks to break or change shape. Examples include faults and fault zones.
Types of Deformation
Elastic: Rock returns to its original shape after stress is removed.
Ductile: Rock reshapes without breaking.
Brittle: Rock fractures or breaks.
Faults
Faults are fractures in rocks where displacement occurs.
Normal Fault: Hanging wall moves down relative to the footwall.
Reverse Fault: Hanging wall moves up relative to the footwall.
Strike-Slip Fault: Rocks slide past each other horizontally.
Oblique Fault: Displacement involves both horizontal and vertical movement.