Plate Tectonics and the Ocean Floor

This set of vocabulary flashcards covers key terms and concepts related to Plate Tectonics and the Ocean Floor, including early ideas, evidence, plate boundaries, and related geological features, based on the provided lecture notes.

Plate Tectonics

A theory stating that Earth's thin, rigid blocks (plates) move horizontally, and their interactions build major features of Earth's crust such as volcanoes, earthquakes, and mountain belts.

Continental Drift

Wegener's hypothesis from 1912 proposing that the continents once formed a single large landmass (Pangaea) surrounded by a single large ocean (Panthalassa) before breaking apart approximately 250 million years ago.

Pangaea

The supercontinent proposed by Alfred Wegener, meaning 'all land'.

Panthalassa

The single, large ocean that surrounded the supercontinent Pangaea, meaning 'all sea'.

Paleomagnetism

The study of the record of the Earth's magnetic field in rocks, providing evidence for plate tectonics through magnetic alignment and inclination.

Magnetic Polarity Reversals

Changes in the Earth's magnetic field where the magnetic north and south poles swap positions, recorded in basalts on the seafloor.

Seafloor Spreading

Harry Hess's theory (1962) that new ocean crust is created at mid-ocean ridges and destroyed at oceanic trenches through subduction.

Mid-Ocean Ridge

An underwater mountain range where new ocean crust is formed through seafloor spreading at a divergent plate boundary.

Oceanic Trench

A long, narrow, deep depression in the ocean floor, typically marking the site where oceanic crust is subducted and destroyed.

Subduction

The process by which one tectonic plate moves beneath another, sinking into the mantle.

Lithospheric Plates

Large, rigid blocks of the Earth's lithosphere that move and interact, causing geological phenomena.

Asthenosphere

A weak, ductile layer of the Earth's upper mantle that lies beneath the lithosphere, allowing the tectonic plates to move or 'float'.

Slab Pull

A major tectonic force where the weight of a dense, subducting oceanic plate pulls the rest of the plate into the mantle.

Slab Suction

A major tectonic force caused by the downdrag of a subducting plate on the mantle, which can pull an overriding plate towards the trench.

Divergent Boundary

A plate boundary where two plates move apart, resulting in the creation of new crust (e.g., mid-ocean ridges, rift valleys) and shallow earthquakes.

Oceanic Rise

A type of divergent spreading center characterized by a fast spreading rate (up to 16 cm/year) and a smoother topography.

Oceanic Ridge

A type of divergent spreading center characterized by a slower spreading rate (around 2.5 cm/year) and a more rugged topography.

Convergent Boundary

A plate boundary where two plates move toward each other, leading to the destruction of oceanic crust (e.g., ocean trenches, volcanic arcs) and deep earthquakes.

Oceanic-Continental Convergence

A type of convergent boundary where an oceanic plate is subducted beneath a continental plate, forming a continental volcanic arc and an oceanic trench.

Continental Arc

A chain of volcanoes formed on the overriding continental plate above an oceanic-continental convergent boundary.

Oceanic-Oceanic Convergence

A type of convergent boundary where one oceanic plate is subducted beneath another oceanic plate, forming an island arc and the deepest oceanic trenches.

Island Arc

A curved chain of volcanic islands formed on the overriding oceanic plate above an oceanic-oceanic convergent boundary.

Continental-Continental Convergence

A type of convergent boundary where two continental plates collide, leading to the formation of uplifted mountain ranges and deep earthquakes.

Transform Boundary

A plate boundary where two plates slide horizontally past each other, causing shallow but strong earthquakes and offsetting features like mid-ocean ridges.

Transform Fault

A type of transform boundary that can be wholly within the ocean floor or extend from a mid-ocean ridge across a continent.

Mantle Plumes

Columns of superheated rock rising from deep within the Earth's mantle, thought to be responsible for hotspots.

Hotspots

Volcanic regions located away from plate boundaries, created by mantle plumes, often resulting in chains of volcanic islands with systematic age variations.

Seamounts

Underwater mountains that do not reach the ocean surface.

Tablemounts (Guyots)

Flat-topped seamounts that were once volcanic islands eroded by wave action and subsequently subsided below sea level.

Paleogeography

The study of geographical features of the Earth's past, including the ancient distribution of continents and oceans.

Continental Accretion

The process by which continental material is added to the edges of continents through plate motion.

Continental Separation (Rifting)

The process where continents move apart from each other, often initiated by processes like seafloor spreading.