Plate Tectonics Lecture Notes Review

Flashcards covering key vocabulary from the Plate Tectonics lecture, including historical development, evidence, theory tenets, and boundary types.

Plate Tectonics

The unifying theory of geology that explains many natural sciences, representing a 'paradigm shift'.

Alfred Wegener

A German meteorologist who first proposed the concept of continental drift.

Continental Drift

Wegener's hypothesis that continents have separated over time from a single landmass (Pangea) to their current positions.

Pangea

The single ancient continent from which all current continents are hypothesized to have originated.

Evidence for Continental Drift (Fossils)

The distribution of ancient (Permian) fossils like Cynognathus, Mesosaurus, Glossopteris, and Lystrosaurus found on widely separated continents.

Evidence for Continental Drift (Continental Fit)

The jigsaw-puzzle like fit of the continents, especially across the Atlantic Ocean.

Evidence for Continental Drift (Rock Units)

The distribution of rock units, ages, types, and chemistry, with close matches in mountain ages found across oceans.

Evidence for Continental Drift (Climate Records)

The presence of impossible climate records, such as evidence of tropical glaciers, on continents now located in warm regions.

Rejection of Continental Drift

Wegener's hypothesis was initially hostilely rejected due to its highly implausible mechanism (continents plowing through oceanic crust) and seemingly high rate of movement.

Arthur Holmes

A supporter of continental drift who speculated that magma convection might drag crust, though he considered his own idea 'purely speculative' at the time.

Harry Hess

A geologist and admiral who extensively mapped the North Pacific sea floor using sonar during WWII, contributing to understanding ocean bathymetry.

Marie Tharp

A cartographer who, by drafting sea floor maps, noticed patterns and played a key role in identifying the Mid-Atlantic Ridge.

World-Wide Standardized Seismographic Network (WWSSN)

A network established during the Cold War to monitor seismic activity, which revealed highly ordered patterns of earthquake distributions and depths.

Earthquake Distribution (Plate Tectonics)

Highly ordered patterns of earthquakes, including depth, which outline distinct, rigid plates with activity concentrated at their edges.

GPS (Global Positioning System)

Used to precisely measure the speed and direction of current plate motion, typically a few centimeters per year.

Paleomagnetism

The study of Earth's ancient magnetic field, recorded in iron-rich minerals that 'lock in' the magnetic field that existed when they formed.

Polar Wander

The apparent movement of the magnetic poles over geologic time, reconstructed using paleomagnetism, which suggested continents had moved relative to each other.

Magnetic Reversals

Periodic flips in Earth's magnetic field where magnetic north becomes south and vice versa, recorded as symmetrical 'zebra stripe' patterns on the sea floor.

Age of the Sea Floor

Determined by combining paleomagnetic and radiometric dating, showing that oceanic crust is youngest at mid-ocean ridges and progressively older further away.

Sea Floor Spreading

The mechanism by which new oceanic crust is formed at mid-ocean ridges and then spreads outwards, explaining a mechanism for plate movement.

Mid-Ocean Ridges

Underwater mountain ranges where new oceanic crust is continuously formed through volcanism, marking divergent plate boundaries.

Subduction Zones

Regions where old oceanic crust is recycled back into the mantle as one plate slides beneath another, often forming oceanic trenches.

Lithosphere

The rigid outer layer of Earth, composed of the crust and uppermost mantle, divided into tectonic plates.

Asthenosphere

A plastic-solid layer of the upper mantle on which the rigid lithosphere 'floats'.

Isostasy

The concept that the rigid lithosphere 'floats' on the denser, plastic asthenosphere, with objects sinking until the weight of displaced fluid equals the object's weight.

Continental Crust

Old (3.9-2 Ga), thick (10-70km), low-density (e.g., granite) crust rich in silica, potassium, aluminum, and sodium, forming the core of continents.

Oceanic Crust

Young (up to 200 Ma), thin (5-10km), high-density (e.g., basalt) crust rich in iron and magnesium, forming the bottom of the oceans.

Continental Margin

The boundary between continental crust and oceanic crust.

Passive Margin

A continental margin where the continental crust transitions into oceanic crust on the same, stable plate, with no distinct plate boundary.

Active Margin

A continental margin where the continent and oceanic crust are on different plates, characterized by differential movement and seismic activity (a plate boundary).

Divergent Boundary

A plate boundary where plates are spreading apart from each other due to tensional stress, resulting in lithospheric thinning, decompression melting, and the creation of new crust (a constructive margin).

Continental Rifting

The initial stage of a divergent boundary within a continent, where tensional forces cause the continental lithosphere to thin and stretch, potentially leading to a new ocean basin.

Convergent Boundary

A plate boundary where plates are colliding towards each other, typically resulting in the destruction of crust (a destructive margin) through subduction or mountain building.

Trench

A deep valley formed at a convergent boundary where a subducting plate bends downwards into the mantle.

Accretionary Prism/Wedge

A chunk of sediments and other material scraped off the subducting plate and accumulated onto the overriding plate at a subduction zone.

Volcanic Arc

A chain of volcanoes formed on the overriding plate at a subduction zone, where subducted water causes melting in the overlying mantle.

Ocean-Continent Convergence

A type of convergent boundary where oceanic crust subducts beneath continental crust, forming an oceanic trench and a continental volcanic arc.

Ocean-Ocean Convergence

A type of convergent boundary where one oceanic plate (typically the older, denser one) subducts beneath another oceanic plate, forming an oceanic trench and an oceanic island arc.

Island Arc

A curved chain of volcanic islands formed above a subducting oceanic plate in an ocean-ocean convergent boundary.

Hotspot Arc

A chain of volcanoes that forms in the middle of a plate (not at a plate boundary) as the plate moves over a stationary mantle plume, indicating the direction of plate movement.

Continent-Continent Convergence

A type of convergent boundary where two continental plates collide, resulting in intense mountain building, crustal shortening, and thickening (no subduction of continents).

Wilson Cycle

The cyclical process by which ocean basins open and close, involving continental rifting, sea floor spreading, and continental collision.

Transform Boundary

A plate boundary where plates slip past each other horizontally without creating or destroying any crust, primarily characterized by fault lines.