Structural Geology and Plate Tectonics Review

Comprehensive vocabulary flashcards covering basic plate tectonics, driving forces, convergent/divergent boundaries, and the geological history of the Appalachian Mountains.

Plates

The Earth's crust and upper mantle, approximately $100\,\text{km}$ thick.

Plate Tectonics theory

A theory stating that the outer shell of Earth is divided into approximately 12 lithospheric plates in relative and absolute motion.

Lithosphere

The 'zone of strength' composed of the crust and brittle upper mantle, extending $0\text{-}100\,\text{km}$ beneath oceans and $100\text{-}250\,\text{km}$ below continents.

Asthenosphere

The 'zone of weakness' approximately $200\,\text{km}$ thick beneath the lithosphere that flows when stress is applied.

Crust

The brittle, cold outermost layer of Earth consisting of oceanic and continental material, making up less than $1\%$ of the Earth.

Mantle

The layer beneath the crust that extends up to $3000\,\text{km}$.

Absolute motion

The motion of lithospheric plates with respect to the underlying lower mantle.

Euler’s theorem

A mathematical principle applied to plate tectonics stating all plate motions on a sphere are defined by a rotation around an axis with an angular velocity.

Thermal Convection

The physical transfer of warmer material to cooler areas and cooler material to warmer areas.

Thermal Conduction

Heat loss at the molecular level where energy is transferred during collisions; it occurs in the direction of decreasing temperature.

Hydrothermal circulation

The process responsible for approximately $30\%$ of Earth's heat loss near mid-ocean ridges through convective heat loss.

Ridge push force ($F_{RP}$)

A driving force for plate motion resulting from gravity acting down-slope away from a mid-ocean ridge.

Ridge resistance force ($RR$)

A resistive force near mid-ocean ridges resulting from the extension of newly formed oceanic crust and associated shallow earthquakes.

Transform fault resistance force ($R_{TF}$)

A resistive force occurring at oceanic transform faults where plates sliding past each other encounter friction.

Ocean driving force ($F_{DO}$)

A driving force acting along the bottom surface of an oceanic plate, assuming the lithosphere is carried by a faster-moving asthenosphere.

Ocean drag force ($R_{DO}$)

A resistive force acting along the bottom of the oceanic lithosphere when the asthenosphere moves slower than the plate.

Continental drag force ($R_{DC}$)

A resistive force caused by the thick 'keel' of continental lithosphere projecting downward into the mantle.

Slab pull force ($F_{SP}$)

A driving force pulling a plate down due to the negative buoyancy ($F_{NB}$) of the subducting oceanic lithosphere; it is the most important force for plate velocity.

Slab resistance ($R_S$)

A resistive force encountered by a sinking slab from frictional drag and the viscosity of the displaced mantle material.

Bending resistance ($R_B$)

A resistive force caused by the subducting plate flexing at the trench before sliding beneath the opposing plate.

Overriding plate resistance ($R_O$)

A resistive force due to the subducting slab pushing against the overriding plate, producing shallow and deep earthquakes.

Trench suction force ($F_{SU}$)

A driving force that pulls the overriding plate toward the trench, induced by convection in the asthenospheric wedge above a subducted plate.

Collisional resistance force ($R_{CR}$)

A resistive force generated by the collision of plates and associated deformation processes.

Lherzolite

Asthenospheric peridotite containing $40\text{-}90\%$ olivine, significant orthopyroxene, and some clinopyroxene that can split into basalt and harzburgite.

Harzburgite

A solid peridotitic residual composed mainly of olivine and enstatite that remains after lherzolite has undergone partial melting.

Pressure-Release melting

The process where hot solid mantle rock melts as it rises and pressure decreases without the addition of extra heat.

Marine magnetic anomalies

Differences between observed and predicted geomagnetic field strengths ($200\text{-}500\,\text{nT}$) used to determine the age of the oceanic crust.

Active rifting

Rifting driven by mantle plumes causing uplift and magma production prior to surface extension, characterized by a lack of large central grabens.

Passive rifting

Rifting driven by far-field tectonic forces that stretch the crust first, typically amagmatic or with minor later volcanism.

Mariana-type subduction zone

Subduction of old, dense lithosphere characterized by steep dipping slabs, trench roll-back, back-arc basins, and deep trenches.

Chilean-type subduction zone

Subduction of young, less dense lithosphere characterized by coupling between plates, high mountain ranges, and shallow, sediment-filled trenches.

Trench roll-back

The process where a subducting plate sinks into the mantle while the trench move backward, often triggering extension and sea-floor spreading in the overriding plate.

Accretionary wedge

A mass of sediments that builds up at the edge of the overriding plate at a subduction zone.

Flux melting

Magma formation at subduction zones triggered by water and volatiles released from the sinking plate lowering the melting temperature of the mantle wedge.

Serpentinization

A low-temperature metamorphic process where mafic and ultramafic rocks are oxidized and hydrolyzed into serpentine, causing density to decrease and volume to increase.

Calc-alkaline rocks

Volcanic rocks (andesite, basalt, dacite, rhyolite) characteristic of subduction zones with high calcium and alkaline element concentrations.

Fracture zone

A scar left over from a transform boundary located outside the active transform segment, where material on both sides moves in the same direction.

Transtension

The combination of extension and strike-slip motion within a transform fault boundary.

Transpression

The combination of compression and strike-slip motion within a transform fault boundary.

Wilson Cycle

The cyclic process of opening and closing ocean basins, encompassing the breakup and formation of supercontinents.

Grenville orogeny

A Middle to late Proterozoic event ($1.3\text{-}1.1\,\text{bya}$) involving the formation of the supercontinent Rodinia.

Taconic orogeny

An orogenic event beginning in the Cambrian ($550\,\text{mya}$) marked by the collision of an island arc with proto-North America.

Acadian orogeny

A Devonian-era event ($\sim 400\,\text{mya}$) where Laurentia, Baltica, and Avalonia collided to form the supercontinent Laurasia.

Alleghanian orogeny

The final Appalachian orogenic event ($325\text{-}260\,\text{mya}$) involving the collision of Laurasia and Gondwana to form Pangea.