Plate Tectonics

Alfred Wagner

Proposed the concept of continental drift and Pangaea in 1915.

Plate Tectonics Theory

Developed in 1968, it states that Earth's outer shell is made up of about 20 plates that move over a weak layer of hot rock.

Divergent Boundaries

Boundaries where two lithospheric plates move apart, often found along mid-ocean ridges.

Mantle Convection

Hypothesis that the movement of Earth's plates is caused by the transfer of heat through the mantle, causing magma to rise and move the lithosphere.

Ridge Push

The force driving plates apart due to the cooling and sinking of old lithosphere away from mid-ocean ridges.

Slab Pull

A process at a subduction boundary where a denser plate sinks below a less dense plate, pulling the rest of the plate down.

Transform Boundaries

Boundaries where two plates slide past each other, characterized by fracture zones that can cause earthquakes.

Mid-Ocean Ridge

An underwater mountain range formed by the upwelling of magma at divergent boundaries.

Subduction Boundary

The area where one plate moves under another, leading to the formation of trenches and volcanic activity.

Convergent Boundaries

Boundaries where two plates collide, leading to collision or subduction.

Continental Drift

The hypothesis that continents have moved over geological time from a single supercontinent.

Pangaea

The supercontinent that existed during the late Paleozoic and early Mesozoic eras, around 335 million years ago.

Hotspots

Areas in the mantle from which heat rises as a thermal plume, leading to volcanic activity. (Hawaii)

Volcanic Arc

A chain of volcanoes formed above a subducting plate, typically parallel to a tectonic plate boundary.

Seafloor Spreading

The process by which new oceanic crust is formed at mid-ocean ridges as tectonic plates pull apart.

Oceanic Plate

A type of tectonic plate that is primarily composed of basalt and is denser than continental plates.

Continental Plate

A tectonic plate that is primarily composed of granitic rocks and is less dense than oceanic plates.

ocean-ocean subduction

forms deep-sea trenches, volcanic island arcs, earthquakes

oceanic-continental subduction

forms deep sea trench bordering continent, inland volcanoes, earthquakes

Types of plate boundaries

divergent, convergent, transform

What proof did Wegener provide for his continental drift theory?

apparent fit of continents, fossils, geological features (mountain ranges, type and age of rocks), climate discrepancies (glacial evidence in hot regions, coal in cold regions)

Formation of Pangea

about 250 million years ago Gondwana and the small landmasses converged to form Pangea

Destruction of Pangea

Gondwana and Laurasia split off, and eventually split into today's continents.

Craton

An expanse of ancient rock at the core of a continent

Sources of continent growth materials

Deep sea sediments, river sediments, Igneous rock, Terranes

How Igneous rock can contribute to continent growth

Plutons form from cooling magma, volcanoes at subduction boundaries eject material, volcanic island chains eject material and merge with continent

Terranes

A large chunk of lithospheric plate that travels very far to merge with a continental plate.

Collision Boundaries

Boundaries where two continental plates collide, often forming mountain ranges and causing earthquakes, as neither plate is subducted.

Shield Volcanoes

Volcanoes with broad bases and gently sloping sides formed by basaltic lava that flows long distances before hardening.

Cinder Cones

The simplest type of volcano, smaller than others, formed by fragments of molten lava that harden before hitting the ground.

Composite Volcanoes

Volcanoes that develop from layers of materials from explosive eruptions around a vent, including hardened lava flows and pyroclastic material.

Lahar

A fast-moving mudflow formed when hot ash from a volcanic eruption mixes with snow and ice.

Calderas

Large, crater-shaped basins formed when the top of a volcano collapses due to magma withdrawal; may be filled with water.

Lava Plateaus

Geological formations created when basaltic lava pours from a long crack or fissure, spreading across the land.