1.4 Plate tectonics and geodynamics
6 min read•august 14, 2024
is the grand unifying theory of Earth's dynamic surface. It explains how the planet's outer shell is divided into rigid plates that move, collide, and reshape our world. This process drives the formation of mountains, ocean basins, and continents.
Understanding plate tectonics is key to grasping Earth's structure and processes. It connects various geological phenomena, from earthquakes and volcanoes to the distribution of natural resources. This knowledge forms the foundation for studying Earth's past, present, and future.
Plate Tectonics Theory
Key Principles
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- Plate tectonics unifies and explains the formation, movement, and interaction of Earth's lithospheric plates
- The divides into several rigid plates that move relative to each other over the , a weaker, partially molten layer of the upper mantle
- Plates are created and destroyed at their boundaries
- New oceanic lithosphere forms at mid-ocean ridges
- Old lithosphere is consumed at zones
- The movement of plates is driven by convection currents in the mantle
- Hot material rises
- Cool material sinks
- Plate boundaries are characterized by distinct geological features and processes
- Earthquakes
- Volcanic activity
- Mountain building
Plate Creation and Destruction
- New oceanic crust is generated at mid-ocean ridges through seafloor spreading
- Magma from the upper mantle rises to the surface and solidifies, creating new oceanic lithosphere
- Examples: Mid-Atlantic Ridge,
- Old oceanic crust is recycled back into the mantle at subduction zones
- Dense oceanic lithosphere sinks beneath lighter continental or oceanic lithosphere
- The subducted plate is heated and undergoes metamorphism, eventually melting and becoming part of the mantle
- Examples: , Peru-Chile
Plate Boundaries and Features
Divergent Boundaries
- Two plates move away from each other, creating new oceanic crust at mid-ocean ridges
- Characterized by shallow earthquakes, basaltic , and hydrothermal activity
- Extensional forces cause rifting and thinning of the lithosphere
- Examples: Mid-Atlantic Ridge, East Pacific Rise, Red Sea Rift
Convergent Boundaries
- Two plates collide, resulting in subduction or continental collision
- Subduction zones: one plate dives beneath another
- Deep ocean trenches form where the subducting plate bends and descends
- Volcanic arcs develop on the overriding plate due to melting of the subducted plate
- Examples: Mariana Trench,
- Continental collisions: two continental plates collide
- Results in the formation of large mountain ranges
- Intense deformation, metamorphism, and uplift of the crust
- Examples: , Alps, Appalachians
Transform Boundaries
- Two plates slide past each other horizontally, creating strike-slip faults
- Characterized by shallow earthquakes and minimal volcanic activity
- Motion is accommodated along transform faults, which connect offset segments of mid-ocean ridges or subduction zones
- Examples: San Andreas Fault (California), Alpine Fault (New Zealand)
Plate Boundary Zones
- Broad regions where the edges of two or more plates interact
- Characterized by complex deformation and a combination of boundary types
- May involve microplates, diffuse plate boundaries, or triple junctions (where three plates meet)
- Examples: Caribbean Plate, Mediterranean Sea, Afar Triangle (East Africa)
Driving Forces of Plate Motion
Mantle Convection
- Primary driving force behind plate tectonics
- Hot, buoyant material rises from the deep mantle, while cooler, denser material sinks back down
- Convection cells in the mantle create a circulation pattern that drives plate motion
Ridge Push
- Force generated by the gravitational potential energy of the elevated mid-ocean ridges
- Newly formed oceanic lithosphere at the ridge crest is hotter and more buoyant than older lithosphere
- The elevated topography of the ridge creates a gravitational force that pushes the plate away from the ridge axis
Slab Pull
- Force generated by the weight of cold, dense lithosphere sinking into the mantle at subduction zones
- As the subducting slab descends, it pulls the attached plate along, driving plate motion
- is considered the strongest force acting on plates
Trench Suction
- Force that pulls the overriding plate towards the subducting plate at a subduction zone
- Caused by the sinking of the subducting slab, which creates a flow in the mantle that draws the overriding plate towards the trench
- Contributes to the overall compressional forces at convergent boundaries
Basal Drag
- Resistive force between the base of the lithosphere and the underlying asthenosphere
- Can either resist or enhance plate motion depending on the direction of mantle flow relative to the plate motion
- If mantle flow is in the same direction as plate motion, enhances the motion; if opposite, it resists the motion
Plate Tectonics and Earth's Surface
Continental and Oceanic Crust Formation
- Plate tectonics is responsible for the formation and distribution of continents and oceans
- Continental crust is formed through the accretion of island arcs, continental fragments, and sediments at convergent boundaries
- Andesitic magmatism and partial melting of the lower crust contribute to continental growth
- Examples: North American Cordillera, Andes Mountains
- Oceanic crust is created at mid-ocean ridges and destroyed at subduction zones
- The oldest oceanic crust is about 200 million years old, while continental crust can be billions of years old
- Examples: Pacific Plate, Nazca Plate
Mountain Building (Orogeny)
- Occurs at convergent boundaries, where the collision of plates results in the uplift and deformation of the crust
- Subduction-related : volcanic arcs and accretionary wedges form as oceanic crust subducts beneath continental crust
- Examples: Andes Mountains, Cascade Range
- Collision-related orogeny: two continental plates collide, resulting in intense deformation, metamorphism, and uplift
- Examples: Himalayas, Alps, Appalachians
- Orogeny is accompanied by folding, thrusting, and the development of metamorphic core complexes
Volcanic and Seismic Activity Distribution
- Volcanic activity is concentrated at plate boundaries
- Divergent boundaries (mid-ocean ridges): basaltic volcanism due to decompression melting of the upper mantle
- Convergent boundaries (subduction zones): andesitic volcanism due to flux melting of the mantle wedge by fluids released from the subducting slab
- Examples: , Iceland, Hawaiian Islands
- Earthquakes occur primarily at plate boundaries due to the buildup and release of stress caused by plate motions
- Shallow earthquakes at divergent and transform boundaries
- Deep earthquakes (up to 700 km) at subduction zones due to the descent of the cold, brittle lithosphere into the mantle
- Examples: San Andreas Fault, Japan Trench, Chile Triple Junction
Influence on Resources and Natural Hazards
- Plate tectonics influences the global distribution of mineral and energy resources
- Hydrothermal mineral deposits (e.g., copper, gold, zinc) form at mid-ocean ridges and subduction zones
- Sedimentary basins, which can host oil and gas resources, develop at passive margins and foreland basins adjacent to mountain ranges
- Natural hazards such as earthquakes, tsunamis, and volcanic eruptions are closely related to plate boundary processes
- Subduction zones are prone to large, destructive earthquakes and tsunamis due to the accumulation of strain between the converging plates
- Volcanic hazards, including explosive eruptions, lava flows, and lahars, are associated with subduction-related volcanism
- Examples: 2011 Tohoku and tsunami, 1980 Mount St. Helens eruption
Climate and Plate Tectonics Interactions
- Long-term climate patterns and changes can be influenced by plate tectonics
- The opening and closing of ocean gateways affect ocean circulation patterns and heat transport
- Example: the formation of the Isthmus of Panama ~3 million years ago separated the Atlantic and Pacific oceans, intensifying the Gulf Stream and influencing Northern Hemisphere glaciation
- The uplift of mountain ranges affects atmospheric circulation, weathering rates, and carbon dioxide drawdown
- Example: the uplift of the Tibetan Plateau and the Himalayas strengthened the Asian monsoon and increased weathering rates, leading to increased carbon dioxide removal from the atmosphere
- Volcanic eruptions release gases (e.g., CO2, SO2) that can affect the Earth's climate on short (cooling) and long (warming) timescales
- Example: the Deccan Traps volcanism ~66 million years ago released large amounts of CO2, contributing to long-term global warming
Key Terms to Review (30)
Alfred Wegener: Alfred Wegener was a German meteorologist and geophysicist best known for proposing the theory of continental drift in the early 20th century. His ideas laid the groundwork for modern plate tectonics by suggesting that continents were once joined together and have since drifted apart due to tectonic forces. Wegener's work highlighted the interconnectedness of geological features, fossil distributions, and climate evidence across different continents.
Andes Mountains: The Andes Mountains are the longest continental mountain range in the world, stretching over 7,000 kilometers along the western edge of South America. They are formed primarily by the tectonic collision between the Nazca and South American plates, resulting in significant geological activity and diverse ecosystems along their length.
Asthenosphere: The asthenosphere is a semi-fluid layer of the Earth's mantle located beneath the lithosphere, characterized by its ability to flow slowly over geological timescales. This layer plays a crucial role in tectonic processes as it provides the necessary movement for the tectonic plates above, influencing various geological phenomena such as earthquakes and volcanic activity.
Basal drag: Basal drag refers to the frictional resistance that occurs at the base of tectonic plates as they move over the underlying mantle. This force plays a crucial role in the dynamics of plate tectonics, influencing the movement and interactions between plates. Understanding basal drag helps to explain phenomena such as continental drift and the behavior of tectonic boundaries, as it affects how easily plates can slide past one another.
Compression: Compression refers to the process where materials are subjected to squeezing or pushing forces that reduce their volume. In the context of plate tectonics and geodynamics, compression plays a crucial role in the formation of mountain ranges and the movement of tectonic plates, as it can lead to various geological features and phenomena like earthquakes and faulting.
Continental Drift: Continental drift is the theory that continents move over geological time across the Earth's surface, driven by forces such as plate tectonics. This movement explains the geographical distribution of continents and ocean basins, and helps in understanding past geological events and climate changes. The concept of continental drift laid the groundwork for modern theories of plate tectonics, connecting the movement of the Earth's plates to geological phenomena.
Convergent Boundary: A convergent boundary is a geological feature where two tectonic plates move toward each other, often resulting in one plate being forced beneath the other in a process known as subduction. This interaction leads to various geological phenomena such as mountain building, volcanic activity, and earthquake generation, showcasing the dynamic nature of Earth's crust.
Divergent boundary: A divergent boundary is a type of tectonic plate boundary where two plates move away from each other, leading to the creation of new crust as magma rises from the mantle. This movement typically occurs along mid-ocean ridges, where the upwelling of magma forms new oceanic crust, and can also lead to rift valleys on land. The activity at divergent boundaries is a crucial component in understanding plate tectonics and geodynamics, as it helps drive the continuous recycling of Earth's lithosphere.
Earthquake: An earthquake is a sudden and intense shaking of the ground caused by the movement of tectonic plates beneath the Earth's surface. This movement can release energy that has accumulated over time, creating seismic waves that travel through the Earth. The relationship between earthquakes and tectonic activity highlights how stress builds along fault lines, leading to various magnitudes and impacts depending on the location and geological conditions.
East Pacific Rise: The East Pacific Rise is a mid-ocean ridge located along the eastern boundary of the Pacific Ocean, characterized by tectonic plate divergence where the Pacific Plate moves away from the North American Plate and the Cocos Plate. This geological feature is significant for understanding seafloor spreading and the dynamics of plate tectonics, as it plays a crucial role in the formation of new oceanic crust and associated geological processes.
GPS Measurement: GPS measurement refers to the use of Global Positioning System technology to determine precise locations on Earth through satellite signals. This technology has become crucial in understanding plate tectonics and geodynamics by providing accurate data on the movement and deformation of the Earth's crust, which helps scientists track shifts in tectonic plates and assess geodynamic processes.
Harry Hess: Harry Hess was an American geologist and a major figure in the development of the theory of plate tectonics, particularly known for his work in the mid-20th century. His research on ocean floor mapping and seafloor spreading provided crucial evidence that helped to explain the movement of tectonic plates and the dynamic processes shaping Earth's surface.
Himalayas: The Himalayas is a vast mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. This range is home to some of the highest peaks in the world, including Mount Everest, and it plays a crucial role in the tectonic processes that shape the region due to the ongoing collision between the Indian and Eurasian tectonic plates.
Lithosphere: The lithosphere is the rigid outer layer of the Earth, composed of the crust and the uppermost part of the mantle. This solid layer plays a crucial role in various geological processes and is fundamental to understanding the Earth's structure, dynamics, and interactions.
Mantle convection: Mantle convection is the slow, churning motion of the Earth's mantle caused by heat transfer from the interior of the Earth to its surface. This process plays a crucial role in the dynamics of the Earth's internal structure, influencing plate movements and geological activity. As hotter, less dense material rises and cooler, denser material sinks, it drives the movement of tectonic plates and contributes to various geodynamic processes that shape our planet.
Mariana Trench: The Mariana Trench is the deepest oceanic trench in the world, located in the western Pacific Ocean, reaching a maximum depth of approximately 36,070 feet (10,994 meters) at a point known as Challenger Deep. This trench plays a critical role in understanding plate tectonics and geodynamics, as it is formed by the subduction of the Pacific Plate beneath the Mariana Plate, illustrating the complex interactions between tectonic plates and their impact on Earth's geological processes.
Mid-ocean ridge: A mid-ocean ridge is an underwater mountain range formed by plate tectonics, characterized by a divergent boundary where tectonic plates move apart, allowing magma to rise and create new oceanic crust. These ridges are significant features of the Earth's surface and play a crucial role in the process of seafloor spreading, leading to the formation of new ocean floor and the recycling of Earth's materials.
Orogeny: Orogeny refers to the process of mountain formation, typically through tectonic plate movements that result in the folding, faulting, and uplifting of the Earth's crust. This geological phenomenon is closely tied to the dynamics of plate tectonics, which describes how the Earth's lithosphere is divided into several plates that move and interact, leading to various geological features and events.
Plate tectonics: Plate tectonics is a scientific theory that explains the movement of the Earth's lithosphere, which is divided into several large and small tectonic plates. These plates float on the semi-fluid asthenosphere beneath them and interact at their boundaries, leading to geological phenomena such as earthquakes, volcanic activity, and the formation of mountain ranges. Understanding plate tectonics is essential for studying various aspects of Earth science, including geophysics and geodynamics.
Ridge push: Ridge push is a geological process that occurs at mid-ocean ridges, where the elevation of the ridge causes a gravitational force that pushes tectonic plates away from the ridge. This phenomenon is significant in the movement of plates within the Earth's lithosphere, playing a key role in plate tectonics and geodynamics. As new oceanic crust is formed at these ridges and cools, it becomes denser, which enhances the driving force of ridge push in the movement of tectonic plates.
Ring of Fire: The Ring of Fire is a horseshoe-shaped zone of high seismic and volcanic activity that encircles the Pacific Ocean. It is characterized by numerous volcanoes and frequent earthquakes, primarily resulting from tectonic plate movements along subduction zones, where one plate is forced under another. This region not only hosts about 75% of the world's active and dormant volcanoes but also experiences around 90% of the world's earthquakes, showcasing the dynamic nature of Earth's geology.
Sea-floor spreading: Sea-floor spreading is the geological process by which new oceanic crust is formed at mid-ocean ridges and gradually moves away from the ridge, leading to the widening of ocean basins. This process is a fundamental aspect of plate tectonics, as it contributes to the movement of tectonic plates and helps explain the dynamic nature of Earth's lithosphere.
Seismic Tomography: Seismic tomography is a technique used to visualize the Earth's internal structure by analyzing seismic wave data from earthquakes and artificial sources. This method allows scientists to create detailed images of the Earth's layers, revealing features such as subducting plates, magma chambers, and other geological structures, which are crucial for understanding tectonic processes, the distribution of heat, and the overall dynamics of our planet.
Slab pull: Slab pull is a geophysical process that occurs when a tectonic plate sinks into the mantle due to its own weight, pulling the rest of the plate along with it. This force is primarily associated with subduction zones, where an oceanic plate converges with a continental plate or another oceanic plate, leading to significant geological activity. Slab pull is considered one of the main driving forces behind plate tectonics, influencing the movement and interactions of Earth's lithospheric plates.
Subduction: Subduction is the geological process where one tectonic plate moves under another and sinks into the mantle, forming a subduction zone. This process is essential for understanding plate tectonics as it drives geological activity, such as earthquakes, volcanic eruptions, and mountain building. Subduction zones are often characterized by deep ocean trenches and contribute to the recycling of the Earth's crust, impacting the planet's geodynamics over time.
Tension: Tension refers to the force that is applied when materials are pulled apart or stretched. In the context of plate tectonics and geodynamics, tension is crucial for understanding how tectonic plates interact, particularly at divergent boundaries where plates move away from each other, leading to the formation of new crust and geological features such as rift valleys.
Transform Boundary: A transform boundary is a type of plate boundary where two tectonic plates slide past each other horizontally. This movement does not create or destroy the crust but instead leads to significant geological activity, such as earthquakes, due to the friction and stress that builds up as the plates move. Understanding transform boundaries is crucial for grasping how tectonic forces shape the Earth's surface and contribute to seismic activity.
Trench: A trench is a deep, narrow depression in the ocean floor that forms at convergent plate boundaries where one tectonic plate is being forced beneath another, a process known as subduction. These features are often associated with intense geological activity, including earthquakes and volcanic eruptions, making them critical for understanding the dynamics of plate tectonics and the overall geodynamic processes of the Earth.
Trench suction: Trench suction refers to the geological process that occurs at subduction zones where a tectonic plate is being forced down into the mantle beneath another plate. This process creates a downward pull or suction effect on the overriding plate, which can lead to various geological phenomena such as earthquakes and volcanic activity. Understanding trench suction is crucial for grasping how plate tectonics and geodynamic processes interact in these regions.
Volcanism: Volcanism refers to the processes and phenomena associated with the movement of molten rock, or magma, from beneath the Earth's crust to the surface, resulting in volcanic eruptions and the formation of volcanic landforms. This process plays a crucial role in shaping the Earth's surface, influencing climate, and providing insights into the internal structure of the planet.