Plate Tectonics: Boundaries, Magmatism, and Earthquakes

Vocabulary flashcards covering key terms from the lecture notes on plate tectonics, including boundaries, crust types, and associated phenomena.

Plate tectonics

Theory that Earth's lithosphere is divided into moving plates, whose interactions shape earthquakes, volcanoes, and mountain building.

Divergent boundary

Plate boundary where two plates move apart; crust is created and oceans or rift valleys form.

Convergent boundary

Plate boundary where two plates collide; may involve subduction or continental collision, with earthquakes and volcanism.

Transform boundary

Plate boundary where plates slide horizontally past each other; linked to earthquakes and little to no volcanism.

Oceanic crust

Dense crust forming the ocean floor; forms at mid-ocean ridges and subducts beneath less dense crust.

Continental crust

Thicker, less dense crust that underlies continents; tends to override at subduction zones and collides in continent-continent events.

Mid-Ocean Ridge

Undersea mountain range formed by divergent boundary; site of new ocean crust formation.

Rift Valley

Down-dropped block in continental crust due to divergence and stretching; associated with continental breakup.

Subduction

Process by which one plate sinks beneath another into the mantle, forming trenches and volcanic arcs.

Island arc

Arc-shaped chain of volcanic islands formed by subduction of one oceanic plate beneath another.

Deep-sea trench

Very deep ocean trench marking the downgoing plate at subduction zones.

Volcanism at subduction zones

Magma generation when subducting slab releases water at depth, lowering melting point and forming volcanoes on the overriding plate.

Ocean-ocean collision

Subduction of older oceanic crust beneath younger oceanic crust, creating trenches and island arcs.

Ocean-continent collision

Subduction of oceanic crust beneath continental crust, creating a continental volcanic arc and trench.

Continental-continental collision

Collision of two continents; no subduction or volcanism; significant mountain building.

Seismic waves

Elastic waves produced by earthquakes that propagate through Earth.

P-waves

Primary, compression waves; fastest seismic waves; travel through solids and liquids.

S-waves

Secondary, shear waves; slower than P-waves; travel only through solids.

Thrust fault

Low-angle reverse fault common at compressional boundaries associated with mountain building.

Andes Mountains

Mountain range formed by the subduction of oceanic crust beneath the South American plate.

Cascade Range

Volcanic mountain range in the Pacific Northwest formed by subduction of the Juan de Fuca plate beneath North America.

San Andreas Fault

Transform boundary between the Pacific and North American plates; lateral (sliding) motion.

Pacific Ring of Fire

Global ring around the Pacific Ocean with many subduction zones and volcanic arcs.

Passive margin

Coastline far from plate boundaries; tectonically quiet with no active earthquakes/volcanoes.

Active margin

Coastline near a plate boundary with active tectonics, earthquakes, and/or volcanism.

Subduction angle

Steep or shallow angle at which a downgoing slab descends; affects distance of the volcanoes from the trench.

Overriding plate

The plate that remains on top in a subduction zone.

Downgoing plate

The subducting plate that sinks into the mantle.

Suture zone

Boundary where two colliding continents weld after consuming the intervening ocean; often no volcanism.

Transform fault

Fault along transform boundaries that accommodates lateral plate motion and offsets other boundaries.

Lithosphere

Rigid outer layer of Earth comprising crust and upper mantle where tectonic plates reside.

Asthenosphere

Weaker, ductile layer beneath the lithosphere allowing plate motion.

Volatile (water) in mantle

Water released from subducting rock lowers melting point, enabling magma generation.

Volcanic arc

Chain of volcanoes forming parallel to a subduction trench; can be island arc or continental arc.

East Africa Rift

Modern example of a continental divergent boundary producing a rift valley.

Himalayas

Mountain range formed by continent-continent collision (India-Asia); no volcanism.