Plate Tectonics: Divergent Boundaries (Video Notes)

Vocabulary flashcards covering key terms and concepts from the video notes on plate tectonics, focusing on divergent boundaries, plate types, and how continents can form new ocean basins.

Plate tectonics

The theory that Earth's surface is divided into moving lithospheric plates that float on the viscous asthenosphere, driving earthquakes, volcanism, and crust formation/destruction.

Lithospheric plate

Rigid pieces of the Earth's outer shell that move on the asthenosphere and interact at plate boundaries.

Major lithospheric plates

The seven large plates: Pacific, Australian, Eurasian, North American, South American, African, and Antarctic.

Minor / microplates

Smaller plates (e.g., Nazca, Cocos, Caribbean, Philippines) and numerous microplates that influence global tectonics.

Divergent margin

Boundary where plates move apart, allowing mantle upwelling and creation of new oceanic crust (seafloor spreading).

Seafloor spreading

Process by which new oceanic crust forms as magma rises at divergent margins and solidifies at mid-ocean ridges.

Mid-ocean ridge

Undersea mountain ranges formed by seafloor spreading at divergent margins (examples: East Pacific Rise, Mid-Atlantic Ridge).

Ocean trench

Deep topographic depressions marking subduction boundaries where one plate sinks beneath another.

Convergent margin

Boundary where plates collide; one plate often subducts beneath the other, producing crust destruction and volcanic activity.

Subduction zone

Region where an oceanic plate sinks into the mantle beneath another plate, generating deep earthquakes and volcanic arcs.

Transform margin (conservative boundary)

Boundary where plates slide past one another; friction causes earthquakes but no net crust creation or destruction.

Rift valley

Long, narrow valley formed when continental crust stretches and thins at divergent margins; can host lakes and eventual ocean formation.

Continental divergence and Red Sea

Continental plates pulling apart, forming rift valleys that can fill with water and become new ocean basins, as seen in the Red Sea and East Africa Rift.

Pangaea breakup

Hypothesized breakup of the supercontinent Pangaea into continents via rifting and seafloor spreading, forming new oceans.

Earthquake distribution as evidence for plate tectonics

Global earthquake patterns (1900–2020) align with plate boundaries; deep earthquakes at subduction zones and shallow earthquakes at mid-ocean ridges support plate tectonics.

J. Tuzo Wilson (1965)

Geophysicist who helped formalize plate tectonics, introducing the concept of moving lithospheric plates in 1965.

Plate tectonics

The theory that Earth's lithosphere is divided into moving plates that float on the underlying asthenosphere, regulating heat flow and elemental cycles.

Lithospheric plate

A rigid slab comprising the crust and upper mantle that moves as part of the tectonic plate system.

Major plates

The seven large lithospheric plates: Pacific, Australian, Eurasian, North American, South American, African, and Antarctic.

Minor plates

Smaller plates and many microplates (e.g., Philippines, Cocos, Caribbean, Nazca) that also participate in plate tectonics.

Divergent margin

A plate boundary where two plates move apart, forming new crust via seafloor spreading; can occur at oceanic or continental margins.

Convergent margin

A boundary where plates collide, often with one plate subducting beneath the other, causing crust destruction and volcanic activity.

Transform margin

A boundary where plates slide horizontally past one another, producing earthquakes without creating or destroying crust.

Seafloor spreading

The formation of new oceanic crust at divergent boundaries as magma rises, cools, and solidifies, pushing plates apart.

Mid-ocean ridge

An underwater divergent boundary system where seafloor spreading occurs; examples include the East Pacific Rise and the Mid-Atlantic Ridge.

Ocean trench

A deep underwater trench marking a convergent boundary where subduction consumes oceanic crust.

Subduction zone

Region where one plate sinks beneath another, driving crust destruction and often volcanic activity.

Oceanic crust

Crust that is primarily basaltic, denser, and forms at oceanic divergent boundaries and trenches.

Continental crust

Thicker, less dense crust that forms the continents and differs in composition from oceanic crust.

Asthenosphere

Weak, partially molten layer beneath the lithosphere on which tectonic plates float and move.

Decompression melting

Melting of mantle rock caused by a drop in pressure as magma rises at spreading centers.

Magma

Molten rock that feeds igneous activity and rises at divergent margins to form new crust.

Hydrothermal vents

Hot, mineral-rich water vents powered by magma at mid-ocean ridges, supporting unique ecosystems.

Rift valley

A depression formed when continental crust is stretched and cracks, often a precursor to new ocean basin formation.

Red Sea (as an example of continental divergence)

A current region of continental divergence between Africa and the Arabian Plate, where a spreading center is actively forming new ocean crust.

East Africa Rift

A major continental rift in Africa illustrating active crustal thinning and segmentation toward a future ocean basin.

Pangaea breakup

The hypothesized breakup of the ancient supercontinent Pangaea into separate landmasses due to continental divergence.

Crust creation vs destruction balance

Global balance in which new crust is created at divergent margins while old crust is destroyed at subduction zones; overall plate size stays roughly constant.