Plate Tectonics

Cards · 52

Plate Tectonics

Scientific theory explaining how Earth's lithosphere is divided into large plates that move over the asthenosphere, driving geological activity.

Lithosphere

Rigid outer layer of Earth comprising the crust and uppermost mantle, broken into tectonic plates.

Asthenosphere

Ductile, semi-fluid upper mantle layer directly below the lithosphere where convection currents drive plate movement.

Continental Crust

Thick, low-density crust primarily composed of granitic rock that forms landmasses.

Oceanic Crust

Thin, dense crust composed primarily of basalt that forms ocean basins.

Mantle Convection

Primary driving force where heat transfer creates circulating currents in the mantle, moving tectonic plates above.

Slab Pull

Major gravitational force where cold, dense oceanic lithosphere sinks into the mantle at subduction zones, pulling the trailing plate.

Ridge Push

Gravitational sliding force exerted as elevated mid-ocean ridges push adjacent lithosphere outward and downward.

Basal Drag

Frictional force exerted on the base of a tectonic plate by the flowing asthenosphere beneath it.

Divergent Boundary

Boundary type where two tectonic plates move apart under tensional stress, leading to crust generation.

Convergent Boundary

Boundary type where two tectonic plates move toward each other under compressional stress, causing collision or subduction.

Transform Boundary

Boundary type where two plates slide horizontally past one another under shear stress without creating or destroying crust.

Mid-Ocean Ridge

Underwater mountain system formed at divergent boundaries by upwelling magma as oceanic plates separate.

Seafloor Spreading

Process at mid-ocean ridges where new oceanic lithosphere forms and gradually moves away from the ridge crest.

Continental Rift Valley

Steep-sided trough formed by tensional forces pulling continental crust apart, such as the East African Rift.

Subduction Zone

Convergent region where a denser oceanic plate sinks beneath an overriding continental or oceanic plate into the mantle.

Deep-Ocean Trench

Long, narrow depression formed on the ocean floor where a subducting plate bends downward into the mantle.

Volcanic Arc

Curved chain of volcanoes formed on continental crust above a subducting oceanic slab due to flux melting.

Island Arc

Curved chain of volcanic islands formed on oceanic crust above an ocean-ocean subduction zone, such as the Aleutian Islands.

Oceanic-Continental Convergence

Collision where dense oceanic crust subducts beneath continental crust, forming trenches and coastal volcanic mountain ranges.

Oceanic-Oceanic Convergence

Collision where older, denser oceanic crust subducts beneath younger oceanic crust, producing deep trenches and volcanic island arcs.

Continental-Continental Convergence

Collision of two buoyant continental masses under extreme compression, producing massive folded mountain ranges without subduction.

Orogeny

Process of mountain building, typically driven by compressional forces and crustal thickening at convergent boundaries.

Fold Mountains

Mountain ranges created by the crumpling and uplift of sedimentary strata under intense lateral compression, such as the Himalayas.

Transform Fault

Strike-slip fault cutting across lithospheric plates along transform boundaries, commonly linking segments of mid-ocean ridges.

San Andreas Fault

Prominent continental transform boundary where the Pacific Plate slides past the North American Plate, causing frequent shallow earthquakes.

Fracture Zone

Linear oceanic feature extending beyond active transform segments along mid-ocean ridges, representing fossil scar lines.

Hotspot

Volcanic region fed by an underlying mantle plume independent of plate boundaries, such as the Hawaiian Islands.

Mantle Plume

Column of abnormally hot rock rising from deep within the mantle toward the crust, generating localized volcanism.

Tensional Stress

Extensional tectonic force that pulls rocks apart, predominant at divergent boundaries.

Compressional Stress

Squeezing tectonic force that shortens and thickens crust, predominant at convergent boundaries.

Shear Stress

Parallel, opposing tectonic forces that cause rocks to slide past each other, predominant at transform boundaries.

Normal Fault

Fault created by tensional stress where the hanging wall drops downward relative to the footwall.

Reverse Fault

Fault caused by compressional stress where the hanging wall moves upward relative to the footwall.

Thrust Fault

Low-angle reverse fault characteristic of compressional regimes and major collision zones.

Strike-Slip Fault

Vertical fault formed by shear stress where rock blocks slip horizontally past one another.

Accretionary Wedge

Mass of deformed marine sediments scraped off a subducting oceanic plate and plastered onto the overriding plate margin.

Forearc Basin

Depression located between a subduction trench and the associated volcanic arc, trapping thick sedimentary deposits.

Backarc Basin

Basin formed by extensional forces behind a volcanic arc, occasionally developing into localized seafloor spreading centers.

Benioff Zone

Planar zone of dipping seismicity produced by the interaction of a down-going subducting plate with the mantle.

Flux Melting

Melting process in subduction zones where water released from hydrated minerals lowers the melting point of mantle rock.

Decompression Melting

Melting process at divergent boundaries and hotspots where upward-moving mantle rock melts as confining pressure decreases.

Paleomagnetism

Study of Earth's historic magnetic field recorded in cooled iron-bearing minerals, providing evidence for seafloor spreading.

Magnetic Striping

Symmetrical patterns of alternating normal and reversed magnetic polarity parallel to mid-ocean ridges.

Supercontinent Cycle

Quasi-periodic assembly and dispersal of Earth's continental crust over hundreds of millions of years (Wilson Cycle).

Pangaea

Late Paleozoic to early Mesozoic supercontinent that assembled about 335 million years ago and later broke apart.

Rift-to-Drift Transition

Geological stage where continental rifting evolves into oceanic crust formation and true seafloor spreading.

Triple Junction

Point on Earth's surface where boundaries of three tectonic plates intersect, exhibiting diverse geometric combinations.

Hydrothermal Vent

Seafloor fissure near divergent boundaries where mineral-rich water heated by underlying magma discharges into the ocean.

Passive Continental Margin

Transition between oceanic and continental crust lacking active plate boundaries, characterized by wide shelves and low seismicity.

Active Continental Margin

Continental border along a convergent or transform boundary marked by high seismic activity, volcanism, and narrow shelves.

Ring of Fire

Horseshoe-shaped belt surrounding the Pacific Ocean characterized by frequent earthquakes and extensive subduction volcanism.