Plate Tectonics: Earth's Restless Planet

Flashcards covering key vocabulary related to Plate Tectonics, Earth's internal structure, and the behavior of rocks along plate boundaries based on the lecture notes.

Plate Tectonic Theory

Explains how the movement of plates is driven by convection currents and is about the movement of tectonic plates. It is supported by the Continental Drift Theory and evidenced by paleomagnetism and seafloor spreading.

Continental Drift Theory

A theory supported by Plate Tectonic Theory, observed by the fit of continents, and biological, geological, and climatological evidence. Alfred Wegener re-introduced this idea in 1912, suggesting a supercontinent called Pangaea once existed.

Alfred Wegener

A geophysicist and meteorologist who re-introduced the idea of continental drift in 1912 and is considered the father of the Plate Tectonics theory. He suggested a 'supercontinent' called Pangaea once existed.

Pangaea

A 'supercontinent' suggested by Alfred Wegener that once existed in the past, based on evidence like the fit of continents, climatological, geological, and biological data.

Fit of the Continents

Evidence for Continental Drift Theory, where continental shelves (up to $2000 \text{ m}$ deep) show an impressive match between landmasses like South America and Africa.

Climatological Evidence

Evidence for Continental Drift Theory, including the discovery of large coal deposits in glacier-laden Antarctica and matching glacial striation marks in Africa and South America.

Glacial striations

Depressions cut into bedrock by the process of glacial abrasion, used as climatological evidence for Continental Drift Theory when matching patterns are found on separate continents.

Geologic Evidence

Evidence for Continental Drift Theory, where rocks in regions like the Appalachian mountain belt match in age, type, and structure with those in the British Isles and Scandinavia.

Biological Evidence

Evidence for Continental Drift Theory based on several fossil organisms (like Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris) found on different, currently separated landmasses, suggesting they were once joined.

Mesosaurus

A type of reptile fossil found solely in South Africa and Eastern South America, providing biological evidence for Continental Drift Theory, as it was a freshwater coastal animal unlikely to cross a vast ocean.

Cynognathus

A mammal-like reptile fossil, as large as a modern wolf, found only in South Africa and South America, serving as biological evidence for Continental Drift Theory, as it was a land-dominant species.

Lystrosaurus

An herbivore reptile fossil found only in Antarctica, India, and South Africa, providing biological evidence for Continental Drift Theory, as it was a land-dwelling animal incapable of swimming across oceans.

Glossopteris

A woody, seed-bearing tree fossil found in Australia, Antarctica, India, South Africa, and South America, which is significant biological evidence for Continental Drift Theory because its large, bulky seeds could not have drifted or flown across oceans.

Paleomagnetism (Magnetic Stripping)

The record of Earth's magnetic field preserved in magnetic minerals through time. It revealed that the Earth's magnetic field varies substantially in orientation and intensity, demonstrating magnetic pole shifts, and supporting Plate Tectonic Theory.

Normal Polarity

A state of Earth's magnetic field where Magnetic North points roughly towards Geographic North, and Magnetic South points roughly towards Geographic South.

Reverse Polarity

A state of Earth's magnetic field in the distant past where Magnetic North pointed towards Geographic South, and Magnetic South pointed towards Geographic North.

Zebra-like Pattern

Alternate strips of normal and reverse polarity rocks found on both sides of the Mid-Atlantic Ridge, which is strong evidence for the Plate Tectonics Theory and seafloor spreading.

Sonar

A technology developed during WW2 for military purposes, which later allowed for the mapping of the ocean floor and contributed to the discovery of seafloor spreading.

Seafloor Spreading

The phenomenon where new oceanic crust is generated at mid-oceanic ridges (like the Mid-Atlantic Ridge) by upwelling magma, pushing older, cooled, and solidified lava further away from the center. This process is evident from magnetic striping and the increasing age of rocks with distance from the ridge.

Tectonic Plates

Rigid segments of the Earth's lithosphere, comprising a mix of continental and oceanic crust, that are constantly moving over the asthenosphere and are separated by different plate boundaries.

Earth's Internal Structure

Composed of the Core, Mantle, and Crust, with properties that drive the movement of tectonic plates.

Core (Inner)

The solid innermost layer of Earth, approximately $1400 \text{ km}$ thick, with temperatures from $3000 \text{ to } 5000\text{ }^\text{o}\text{C}$, composed mostly of iron and nickel.

Core (Outer)

The liquid layer of Earth surrounding the inner core, approximately $2100 \text{ km}$ thick, with temperatures from $3000 \text{ to } 5000\text{ }^\text{o}\text{C}$, composed mostly of iron and nickel.

Mantle

The layer of Earth between the crust and the core, approximately $2900 \text{ km}$ thick, consisting of solid to mostly molten rocks with a range of mineral compositions, with temperatures from $800 \text{ to } 3000\text{ }^\text{o}\text{C}$.

Crust

The thin outermost solid layer of the Earth, divided into Continental and Oceanic types, with temperatures ranging from $-40 \text{ to } 800\text{ }^\text{o}\text{C}$.

Continental Crust

A type of crust that is older, thicker ($35 \text{ to } 70 \text{ km}$), less dense ($2.6 \text{ g/cm}^3$), rich in silicon and aluminum (sial), and usually consists of lighter rocks like granite.

Oceanic Crust

A type of crust that is denser ($3.0 \text{ g/cm}^3$), newer, thinner ($5 \text{ to } 8 \text{ km}$), rich in iron and magnesium (sima), and usually consists of basaltic rocks less than $200 \text{ million}$ years old.

Lithosphere

The rigid solid layer of Earth, approximately $100 \text{ km}$ thick, composed of the crust and the uppermost mantle. It is broken into about a dozen rigid plates.

Asthenosphere

The upper part of the mantle, approximately $600 \text{ km}$ thick, where solid rock is in a semi-molten state and is capable of flow.

Mohorovičič or Moho Discontinuity

The junction between the Earth's crust and the mantle where seismic waves are modified.

P-waves (Primary Waves)

Seismic compressional waves that travel through both solid and liquid mediums, providing insight into Earth's interior composition.

S-waves (Secondary Waves)

Seismic shear waves that can only travel through solid mediums, which helps identify liquid layers within the Earth such as the outer core.

Outer Core (State)

Determined to be liquid based on seismic wave data, as S-waves cannot pass through it, and P-waves are bent or refracted when they move through this zone.

Convection Currents

Movements of heat within the mantle that drive plate movements. Mantle materials are heated by the core, causing them to expand, rise, and spread out beneath the plates, dragging them along.

Ridge Push

A force driving plate tectonics, exerted by rising magma through cracks in oceanic plates along mid-oceanic ridges, creating new ridges and pushing older ones away.

Slab Pull

A force driving plate tectonics, exerted when a denser oceanic crust meets another crust and is forced to sink into the asthenosphere (subduction), pulling the rest of the oceanic crust along due to gravity.

Plate Boundaries

Areas where tectonic plates are separated by different types of movements: divergent (moving apart), convergent (moving towards each other), or transform (sliding past each other).

Divergent Plate Movement (Constructive Boundaries)

Occurs when plates pull apart from each other, primarily along submarine ridges (oceanic-oceanic divergence) or within continental plates (continental-continental divergence). This process constructs new crustal material.

Mid-Oceanic Ridge (MOR)

Prominent submarine mountain ranges where oceanic plates pull apart, leading to seafloor spreading and the formation of new oceanic crust. The Mid-Atlantic Ridge is a prime example.

Mid-Atlantic Ridge (MAR)

The most prominent example of a mid-oceanic ridge, which divides the Atlantic Ocean into two halves and is almost exactly parallel to the coastlines of Africa/South America and Europe/North America. Iceland straddles this ridge.

Rift Valley

A lowland with a flat floor and steep sides, formed when two continental plates are pulled apart (continental-continental divergence) by tensional forces, causing the land to stretch, weaken, and break into fractures, with the area between them sinking.

Block Mountains

Rocks which sometimes surround a rift valley, formed in areas of continental-continental divergence.

Red Sea

An example of a sea formed due to continental-continental divergence, located between the diverging Arabian and African plates, resulting from ancient rifting.

East African Rift Valley System (EARS)

An approximately $6400 \text{ km}$ long system stretching from Syria to Mozambique, where Earth's tectonic forces are creating new plates by splitting the African plate into the Nubian and Somali plates.

Afar Triple Junction

A critical point within the East African Rift System where the Arabian, Nubian, and Somali plates are all tearing away from each other, located where the Horn of Africa straddles the Red Sea and the Gulf of Aden.

Convergent Plate Movement (Converge)

Occurs when plates move towards each other, resulting in either subduction (destruction of crustal material) or collision (uplifting of crustal material without destruction).

Subduction Zones

Destructive convergent boundaries where one plate (typically oceanic) sinks below another plate into the asthenosphere, leading to the destruction of crustal materials and often associated with oceanic trenches, volcanoes, and earthquakes.

Collision Zones

Convergent boundaries where two continental plates collide. Neither plate subducts due to similar densities, resulting in the buckling and uplifting of crustal material to form fold mountain ranges (orogenesis) with little volcanic activity.

Oceanic Trench

A deep, narrow depression in the ocean floor formed at the boundary where a denser oceanic plate subducts under another plate (continental or oceanic). Examples include the Chile-Peru Trench and Sunda Trench.

Fold Mountains

Mountain ranges formed by the bending of rock layers (folding) due to compressional forces at convergent plate boundaries. This can occur from continent-continent collision or continent-oceanic plate collision, like the Himalayas and Andes.

Andes Mountain Range

An example of fold mountains in South America, formed at a continental-oceanic convergent boundary by the subduction of the Nazca plate under the South American plate.

Rocky Mountain Range

An example of fold mountains in North America, formed at a continental-oceanic convergent boundary by the subduction of the Juan De Fuca plate under the North American plate.

Himalayan Mountain Range

An example of fold mountains, formed at a continental-continental collision zone when the Indian plate collided with the Eurasian plate, resulting in significant uplift and marine fossils found at high altitudes.

Alps

A fold mountain range formed at a continental-continental collision zone when the African plate drifted towards the Eurasian plate.

Orogenesis

The geological process of fold mountain range formation, typically occurring at continental-continental collision zones where plates buckle and uplift.

Continental Volcanic Arc

A chain of volcanoes formed along the edge of a continental plate above a subduction zone, where magma from the melting oceanic crust rises through fractures. The Andean Arc is an example.

Volcanic Islands (Island Arc)

Chains of volcanoes that rise above sea level, formed at oceanic-oceanic convergent boundaries where the denser plate subducts and magma rises through the overriding plate. The North Marianna Islands are an example.

North Marianna Islands

An example of volcanic islands (island arc) formed in the Pacific Ocean on the Philippine plate at an oceanic-oceanic convergent boundary.

Transform Plate Movement (Conservative Boundaries)

Occurs when two plates slide horizontally past each other, neither generating nor destroying crustal material, but often accompanied by frequent earthquakes due to accumulated stress.

Strike-Slip Faults

Nearly vertical fractures where blocks have mostly moved horizontally relative to each other, resulting from shearing/sliding forces at transform plate boundaries.

San Andreas Fault

A prime example of a transform fault in California, USA, where the Pacific and North American plates slide past one another, causing devastating earthquakes.

North Anatolian Fault

An example of a transform fault in Turkey, where the Anatolian and Eurasian plates slide past one another.

Faults

Fractures or lines of weakness in rock masses formed when enormous stresses exceed the strength of brittle rocks, leading to horizontal or vertical displacement of rock blocks. Can cause earthquakes.

Normal Fault

A type of fault with vertical displacement, where the hanging wall moves down relative to the footwall, caused by tensional forces that lengthen the crust.

Reverse Fault

A type of fault with vertical displacement, where the hanging wall moves up relative to the footwall, caused by compressional forces that shorten the crust.

Tensional Forces

Stress that causes lengthening and stretching of rocks, leading to the formation of normal faults and rift valleys.

Compressional Forces

Stress that causes shortening and squeezing of rocks, leading to folding (like anticlines and synclines) and the formation of reverse faults and fold mountains.

Shearing Forces

Stress that causes tearing and smearing of rocks, leading to horizontal displacement along strike-slip faults.

Fault Scarp

A small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other.

Fault Plane

The surface along which movement occurs in a fault.

Hanging Wall Block

The block of rock located above the fault plane in an inclined fault.

Footwall Block

The block of rock located below the fault plane in an inclined fault.

Folding

A geological process where compressional forces bend rock layers, resulting in structures like anticlines (upfolds) and synclines (downfolds).

Anticline

An upward-arching fold in rock layers, created by compressional forces.

Syncline

A downward-arching fold in rock layers, created by compressional forces, often found adjacent to anticlines.

Ductile Manner (Rock Behavior)

How rocks behave under stress at depths greater than $15 \text{ km}$ within the Earth's surface, allowing them to contort and change shape, which results in folding.

Brittle Manner (Rock Behavior)

How rocks behave under stress nearer to the Earth's surface, fracturing and resulting in faulting when the exerted stress exceeds their strength.

Earthquakes

Result from the sudden, quick movement along faults at plate boundaries, particularly common at transform and convergent boundaries, caused by the release of built-up stress.

Hot Spots

Areas away from plate boundaries where local plumes of rising magma punch through the plates, creating a line of volcanoes as the plate moves over the hot spot. Hawaii is a well-known example.