11.3 Driving forces of plate tectonics
3 min read•july 22, 2024
The Earth's mantle churns with , driving the motion of . These currents, caused by heat from the core, push and pull the plates, shaping our planet's surface. Understanding this process is key to grasping how our dynamic Earth works.
and are the main forces behind plate movement. Slab pull occurs when dense plates sink into the mantle, while ridge push happens as new crust forms at . These forces, along with , keep our planet's surface in constant motion.
Mantle Convection and Plate Motion
Mantle convection in plate motion
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- Mantle convection primary driving force behind plate tectonics
- Convection currents in mantle caused by heat transfer from Earth's core
- Hot, less dense material rises, while cooler, denser material sinks ()
- Convection currents exert dragging force on base of
- Force causes lithospheric plates to move in direction of convection currents
- Plates "ride" on top of convection cells in mantle
- Upwelling mantle material at mid-ocean ridges creates new oceanic crust ()
- Process contributes to movement of plates away from ridge
- form at mid-ocean ridges ()
- Downwelling mantle material at pulls plate downward
- Process known as slab pull, major driving force for plate motion
- form at subduction zones ()
Slab Pull and Ridge Push
Slab pull in plate tectonics
- Slab pull gravitational force acting on subducting plate
- As plate descends into mantle, becomes denser than surrounding mantle material
- Increased density causes plate to sink, pulling rest of plate along with it
- Subducting slab acts as "anchor" pulling plate towards mantle
- Slab pull considered strongest driving force in plate tectonics
- Accounts for significant portion of total force driving plate motion (60-90%)
- Subduction of oceanic lithosphere primary cause of slab pull ()
- Force of slab pull proportional to age and thickness of subducting plate
- Older, colder, and denser plates generate stronger slab pull force
- Younger, hotter plates have weaker slab pull ()
Ridge push for plate movement
- Ridge push force generated by elevated topography and at mid-ocean ridges
- Newly formed oceanic crust at ridge hotter and more buoyant than older crust
- Creates gravitational force that pushes plate away from ridge
- Plates "slide" down slopes of mid-ocean ridge
- Ridge push secondary driving force in plate tectonics
- Generally weaker than slab pull but still contributes to plate motion (10-40%)
- Most significant at fast-spreading ridges (East Pacific Rise)
- Force of ridge push decreases with distance from mid-ocean ridge
- As oceanic crust cools and becomes denser, gravitational potential energy decreases
- Older oceanic crust farther from ridge has lower ridge push force (Atlantic Ocean)
Driving forces of plate tectonics
- Slab pull considered primary driving force in plate tectonics
- Accounts for estimated 60-90% of total force driving plate motion
- Subduction of dense oceanic lithosphere generates strong pulling force
- Ridge push secondary driving force
- Contributes approximately 10-40% of total force driving plate motion
- Gravitational sliding of plates away from elevated mid-ocean ridges
- Mantle convection acts as conveyor belt, providing basal drag force on plates
- Force generally weaker than slab pull and ridge push but helps maintain plate motion
- Convection currents in mantle "carry" plates along surface
- Other factors, such as and , also influence plate motion
- Trench suction: Downward flow of mantle material at subduction zones pulls plates towards trench
- Transform fault resistance: Friction along transform faults opposes plate motion
- These forces relatively minor compared to slab pull and ridge push
Key Terms to Review (19)
Asthenosphere: The asthenosphere is a semi-fluid layer of the Earth's mantle located beneath the lithosphere, extending from about 100 km to 700 km below the surface. This layer plays a critical role in plate tectonics by allowing the rigid plates of the lithosphere to move on its softer, more pliable surface. The characteristics of the asthenosphere are vital for understanding how tectonic plates interact at boundaries, how plate tectonic theory has evolved over time, and what drives these movements.
Convection currents: Convection currents are the movement of fluid caused by the uneven heating of that fluid, resulting in a transfer of heat and material within the fluid. This process is fundamental in shaping geological structures and driving the dynamics of Earth's lithosphere, particularly in the context of plate tectonics, where these currents play a crucial role in the movement of tectonic plates over the semi-fluid asthenosphere.
Convergent Plate Boundaries: Convergent plate boundaries are regions where two tectonic plates move toward each other, often resulting in one plate being forced below the other in a process called subduction. These boundaries are critical in understanding geological features such as mountain ranges, earthquakes, and volcanic activity, as the intense pressure and friction generated during this interaction can lead to significant geological transformations.
Divergent plate boundaries: Divergent plate boundaries are geological features where two tectonic plates move away from each other, creating new crust as magma rises from the mantle to fill the gap. This process is a key aspect of plate tectonics and contributes to the formation of mid-ocean ridges and rift valleys. At these boundaries, the upwelling of magma not only leads to seafloor spreading but also influences volcanic activity and earthquake occurrences in these regions.
East Pacific Rise: The East Pacific Rise is a mid-ocean ridge located along the floor of the Pacific Ocean, characterized by tectonic plate activity and the formation of new oceanic crust. It serves as a significant example of seafloor spreading, where two tectonic plates are moving apart, allowing magma from the mantle to rise and solidify, thus creating new ocean floor. This process is a critical component in understanding the driving forces of plate tectonics.
Gravitational potential energy: Gravitational potential energy is the energy an object possesses due to its position in a gravitational field, primarily determined by its height above a reference point and the mass of the object. This energy plays a vital role in various geological processes, influencing how tectonic plates interact with one another and how energy is transferred within Earth's systems.
Juan de Fuca Plate: The Juan de Fuca Plate is a small tectonic plate located off the northwest coast of North America, primarily situated beneath the Pacific Ocean. It plays a crucial role in the dynamics of plate tectonics, particularly in relation to the North American Plate and the Pacific Plate, as it is subducting beneath the former, creating significant geological features and activity in the region.
Lithosphere: The lithosphere is the rigid outer layer of the Earth, composed of the crust and the uppermost portion of the mantle. It plays a crucial role in the movement of tectonic plates, which interact at various plate boundaries, influencing geological phenomena such as earthquakes and volcanic activity. Understanding the lithosphere is essential for grasping the historical development of plate tectonic theory and recognizing the driving forces behind plate movements.
Mantle convection: Mantle convection is the slow, churning motion of the Earth's mantle caused by heat from the Earth's interior. This process plays a crucial role in driving plate tectonics, redistributing heat, and influencing the rock cycle by bringing material from the deep mantle to the surface and vice versa. The movement of molten rock in the mantle not only affects the geological features we see but also contributes to the dynamic nature of Earth's systems.
Mariana Trench: The Mariana Trench is the deepest part of the world's oceans, located in the western Pacific Ocean, with a maximum known depth of about 36,000 feet (11,000 meters) at a point known as Challenger Deep. Its formation is closely tied to the process of plate tectonics, specifically subduction zones where one tectonic plate is forced beneath another, leading to significant geological activity and the creation of deep oceanic features.
Mid-ocean ridges: Mid-ocean ridges are underwater mountain ranges formed by the process of seafloor spreading, where tectonic plates pull apart and magma rises to create new oceanic crust. These features are significant because they represent the boundary between diverging tectonic plates, playing a crucial role in plate tectonics, geological processes, and the formation of metamorphic rocks under specific pressure and temperature conditions.
Nazca Plate: The Nazca Plate is a tectonic plate located in the southeastern Pacific Ocean, primarily situated off the west coast of South America. It is an oceanic plate that is moving eastward and is known for its role in the formation of significant geological features, including the Andes Mountains and the Peru-Chile Trench. The interactions of the Nazca Plate with adjacent plates contribute to volcanic activity and earthquakes in the region.
Ridge push: Ridge push is a geological process that occurs at mid-ocean ridges, where new oceanic crust is formed and pushes older crust away from the ridge. This force is driven by the elevation of the ridge due to hot, upwelling magma, which creates a slope that causes the tectonic plates to slide away from the ridge. Ridge push contributes to the movement of tectonic plates, impacting various geological processes like seafloor spreading and the dynamics of plate tectonics.
Seafloor Spreading: Seafloor spreading is the process by which new oceanic crust forms at mid-ocean ridges and gradually moves away from the ridge, allowing tectonic plates to shift and create geological features. This phenomenon is key in understanding how ocean basins expand, as well as the interactions between tectonic plates that shape Earth's surface.
Slab pull: Slab pull is a geophysical process that refers to the force exerted by a subducting tectonic plate as it sinks into the mantle. This force is primarily due to the weight of the cold, dense oceanic lithosphere, which creates a downward pull on the rest of the plate, driving tectonic plate movement. Slab pull is considered one of the main forces driving plate tectonics, influencing the dynamics of Earth's lithosphere.
Subduction Zones: Subduction zones are regions of the Earth's crust where one tectonic plate moves under another and sinks into the mantle. These zones are critical areas of geological activity, leading to the formation of deep ocean trenches, volcanic arcs, and earthquakes, as well as influencing metamorphic processes and rock classification.
Tectonic plates: Tectonic plates are large sections of the Earth's lithosphere that move and interact with each other, shaping the planet's surface through processes such as earthquakes, volcanic activity, and mountain building. These plates float on the semi-fluid asthenosphere beneath them and are driven by various geological forces, which contribute to their movement and the dynamic nature of the Earth.
Transform fault resistance: Transform fault resistance refers to the frictional force that opposes the movement of tectonic plates along transform faults, which are boundaries where two plates slide past each other horizontally. This resistance plays a critical role in determining how stress builds up along these faults, eventually leading to earthquakes when the accumulated energy is released as the plates finally move. Understanding this resistance is essential in comprehending the dynamics of plate tectonics and the processes that drive geological activity.
Trench suction: Trench suction refers to the process in which the weight of the descending tectonic plate in a subduction zone generates a pulling force that helps draw the plate into the mantle. This phenomenon is crucial for understanding how plates interact at convergent boundaries and plays a significant role in the dynamics of plate tectonics. The trench suction mechanism influences geological activity, including earthquakes and volcanic eruptions, as the subduction process reshapes the Earth’s crust.