3.4 Seafloor spreading and ocean basin evolution
4 min read•august 7, 2024
shapes our oceans. New crust forms at mid-ocean ridges, pushing older crust outward. This process creates patterns, providing evidence for plate movement. It's the engine behind ocean basin evolution.
Ocean floors aren't flat. They feature abyssal plains, , and deep trenches. These structures form through volcanic activity, , and plate interactions. Understanding them helps us grasp Earth's dynamic nature.
Seafloor Spreading and Oceanic Crust
Process of Seafloor Spreading
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- Seafloor spreading is the process by which new is formed through volcanic activity and gradually moves away from mid-ocean ridges
- Occurs at divergent plate boundaries where tectonic plates are moving apart ()
- Magma rises from the mantle and erupts along the , creating new oceanic crust
- As new crust is formed, older crust is pushed away from the ridge, causing the seafloor to spread outward
Magnetic Striping and Evidence for Seafloor Spreading
- Magnetic striping is a pattern of alternating magnetic polarities in the oceanic crust that provides evidence for seafloor spreading
- in the oceanic crust contain magnetic minerals that align with Earth's magnetic field at the time of their formation
- Earth's magnetic field periodically reverses polarity, causing the newly formed oceanic crust to record the alternating magnetic pattern
- Symmetrical magnetic stripes on either side of mid-ocean ridges indicate the seafloor has been spreading outward from the ridge over time ()
Characteristics and Formation of Oceanic Crust
- Oceanic crust is the thin, dense layer of the Earth's crust that underlies the ocean basins
- Composed primarily of basalt, a dark, fine-grained igneous rock formed from the rapid cooling of magma at or near the Earth's surface
- Oceanic crust is thinner (5-10 km) and denser than continental crust
- Forms at mid-ocean ridges through seafloor spreading and volcanic activity
- As oceanic crust moves away from the ridge, it cools, contracts, and becomes denser, causing it to sink lower into the mantle
Hydrothermal Vents and Unique Ecosystems
- are fissures in the seafloor that release geothermally heated water rich in dissolved minerals
- Form near mid-ocean ridges where seawater seeps into the oceanic crust, becomes superheated by magma, and rises back to the surface
- Hydrothermal fluids can reach temperatures up to 400°C and are highly acidic
- Vents support unique ecosystems that rely on as the primary producers (tubeworms, giant clams)
- These bacteria use the dissolved minerals and chemical energy from the hydrothermal fluids to produce organic compounds, forming the base of the food chain
Ocean Floor Features
Abyssal Plains and Seamounts
- Abyssal plains are vast, flat areas of the ocean floor that cover much of the deep ocean basins
- Formed by the accumulation of fine-grained sediments that settle out of the water column over millions of years
- Seamounts are extinct submarine volcanoes that rise abruptly from the seafloor but do not reach the ocean's surface
- Formed by volcanic activity associated with hot spots or mid-ocean ridges (Emperor Seamounts)
- Seamounts provide hard substrate for the growth of deep-sea corals and sponges, creating biodiversity hotspots
Guyots and Trenches
- are flat-topped seamounts that were once above sea level but have since subsided and become submerged
- Formed when a volcanic island is eroded by waves and currents at the surface, creating a flat top, and then gradually sinks due to the cooling and contraction of the oceanic crust
- Trenches are deep, narrow depressions in the seafloor that form at convergent plate boundaries where one tectonic plate subducts beneath another
- Deepest parts of the ocean (, reaching depths of over 11,000 meters)
- Trenches are often associated with high levels of seismic activity and volcanism as the subducting plate melts and generates magma
Plate Tectonics and Ocean Basins
Wilson Cycle and Ocean Basin Evolution
- The describes the formation, evolution, and destruction of ocean basins over geologic time
- Begins with the rifting of a continent and the formation of a new ocean basin through seafloor spreading (Atlantic Ocean)
- As the ocean basin widens, it reaches a mature stage characterized by a well-developed mid-ocean ridge and abyssal plains
- Eventually, initiates along one margin of the ocean basin, leading to the formation of a trench and the onset of basin closure
- The ocean basin narrows as subduction continues, ultimately leading to a continent-continent collision and the formation of a mountain range (Himalayas)
Interactions Between Oceanic Crust, Trenches, and Seafloor Spreading
- Oceanic crust is formed at mid-ocean ridges through seafloor spreading and is eventually destroyed at subduction zones
- As oceanic crust moves away from the ridge, it cools, contracts, and becomes denser, causing it to subside and form abyssal plains
- Older, denser oceanic crust will subduct beneath younger, less dense oceanic crust or continental crust at convergent plate boundaries, forming deep-sea trenches
- Subduction of oceanic crust at trenches drives plate motions and is a key component of the Wilson Cycle
- The subducting oceanic crust melts as it descends into the mantle, leading to the formation of magma that rises to feed volcanic arcs (, )
Key Terms to Review (23)
Abyssal plain: An abyssal plain is a flat or gently sloping area of the deep ocean floor, typically found at depths between 3,000 and 6,000 meters. These plains are among the Earth's most level surfaces, formed by sediment accumulation over millions of years and are characterized by their vast expanses, which often cover more than 50% of the Earth's ocean floor. Abyssal plains play a significant role in ocean basin evolution and are essential for understanding the processes of seafloor spreading and tectonic activity.
Aleutian Islands: The Aleutian Islands are a chain of islands located in the northern Pacific Ocean, forming part of the Alaska Peninsula and extending westward toward Russia. This archipelago is significant for its volcanic activity and its position along the convergent boundary between the North American Plate and the Pacific Plate, which has important implications for seafloor spreading and ocean basin evolution.
Andes: The Andes is the longest continental mountain range in the world, stretching over 7,000 kilometers along the western edge of South America. This magnificent range was formed primarily through tectonic plate interactions, particularly the subduction of the Nazca Plate beneath the South American Plate, leading to significant geological features such as volcanic activity and diverse ecosystems.
Atlantic Ocean: The Atlantic Ocean is the second-largest ocean on Earth, covering approximately 20% of the planet's surface and separating the continents of North and South America from Europe and Africa. Its formation and evolution are closely linked to processes such as seafloor spreading and the tectonic movements that shaped the ocean basin over millions of years.
Basaltic rocks: Basaltic rocks are dark-colored, fine-grained igneous rocks that are primarily composed of magnesium and iron-rich minerals such as pyroxene and olivine. These rocks typically form from the rapid cooling of lava at or near the Earth's surface and are most commonly found in oceanic crust, playing a crucial role in seafloor spreading and the evolution of ocean basins.
Chemosynthetic bacteria: Chemosynthetic bacteria are microorganisms that obtain energy through the oxidation of inorganic compounds, rather than from sunlight as in photosynthesis. These bacteria play a crucial role in the deep-sea ecosystems, particularly around hydrothermal vents, where they form the base of the food web by converting chemical energy into organic matter, supporting diverse marine life.
Divergent boundary: A divergent boundary is a type of plate boundary where two tectonic plates move away from each other, leading to the formation of new crust as magma rises to the surface. This movement can create features such as mid-ocean ridges and rift valleys, playing a crucial role in the dynamic processes of the Earth's lithosphere.
East Pacific Rise: The East Pacific Rise is a mid-ocean ridge located along the eastern part of the Pacific Ocean, marking a divergent boundary between tectonic plates. This underwater mountain range plays a crucial role in seafloor spreading, where new oceanic crust is formed as magma rises to the surface, leading to the expansion of ocean basins over geological time. The East Pacific Rise is characterized by its high volcanic activity and hydrothermal vent systems, which contribute to the unique ecosystems found in this region.
Guyots: Guyots are underwater volcanic mountains that have flat tops, formed by volcanic activity and subsequent erosion. They typically originate as seamounts, rising from the ocean floor but are flattened due to wave action and erosion over time, particularly when they are no longer active. Their formation provides insights into the geological processes of seafloor spreading and the evolution of ocean basins, linking them to the shifting dynamics of tectonic plates.
Harry Hess: Harry Hess was an American geologist and a key figure in the development of the theory of plate tectonics, particularly known for his concept of seafloor spreading. His work fundamentally changed the understanding of the Earth's internal structure and the processes that shape ocean basins, linking geological activity to the movement of tectonic plates.
Hydrothermal vents: Hydrothermal vents are underwater geothermal features where heated, mineral-rich water is expelled from the Earth's crust, typically found along mid-ocean ridges. These vents create unique ecosystems that support diverse marine life, thriving in extreme conditions without sunlight, and play a crucial role in the geological processes of seafloor spreading and ocean basin evolution.
Magnetic striping: Magnetic striping refers to the pattern of magnetic anomalies found on either side of mid-ocean ridges, where the oceanic crust is formed and expanded. This phenomenon occurs due to the periodic reversals of Earth's magnetic field, which are recorded in the igneous rock as it cools and solidifies at these ridges. The resulting symmetrical pattern provides crucial evidence for seafloor spreading and plays a significant role in understanding ocean basin evolution.
Mariana Trench: The Mariana Trench is the deepest oceanic trench in the world, located in the western Pacific Ocean, reaching depths of approximately 36,000 feet (about 10,972 meters). This trench is a significant geological feature resulting from the process of subduction, where the Pacific Plate is being pushed beneath the smaller Mariana Plate, contributing to our understanding of seafloor spreading and the evolution of ocean basins.
Mid-ocean ridge: A mid-ocean ridge is an underwater mountain range formed by the process of seafloor spreading, where tectonic plates diverge and new oceanic crust is created. This feature plays a crucial role in the theory of plate tectonics, as it highlights the dynamic nature of Earth's lithosphere and the movement of plates. Mid-ocean ridges are also associated with volcanic activity and hydrothermal vents, showcasing the interplay between geology and oceanography.
Oceanic crust: Oceanic crust is the outermost layer of Earth's lithosphere that lies beneath the ocean basins. It is primarily composed of basaltic rock and is generally thinner and denser than continental crust, playing a vital role in processes such as seafloor spreading and the evolution of ocean basins.
Oceanic trench: An oceanic trench is a deep, narrow depression in the ocean floor that forms where one tectonic plate is being subducted beneath another. These trenches are typically associated with convergent plate boundaries and play a critical role in the recycling of the Earth's crust, influencing seafloor spreading and the evolution of ocean basins. They are often the deepest parts of the ocean and are characterized by their steep sides and unique geological features.
Plate Tectonics: Plate tectonics is the scientific theory that describes the large-scale movement of the Earth's lithosphere, which is divided into tectonic plates that float on the semi-fluid asthenosphere beneath. This movement explains many geological processes, including the occurrence of earthquakes, volcanic activity, and the formation of mountain ranges, as well as how ocean basins evolve over time.
Seafloor Spreading: Seafloor spreading is the process by which new oceanic crust is created at mid-ocean ridges as tectonic plates pull apart, causing magma to rise from the mantle and solidify. This mechanism plays a critical role in understanding plate tectonics and how continents drift, as it provides evidence for the movement of Earth's lithospheric plates and the formation of ocean basins over geological time.
Seamounts: Seamounts are underwater mountains that rise from the ocean floor but do not reach the water's surface. They are typically formed by volcanic activity and can be found throughout the world's oceans, often serving as important habitats for marine life. Their formation and distribution are closely linked to processes like seafloor spreading, contributing to the evolution of ocean basins.
Sediment accumulation: Sediment accumulation refers to the process of sediment deposition over time in a specific area, resulting in the build-up of materials such as sand, silt, and clay. This phenomenon plays a crucial role in the formation and evolution of ocean basins, where sediments from continental margins and the ocean floor contribute to geological features and influence plate tectonics.
Subduction: Subduction is the geological process where one tectonic plate moves under another and sinks into the mantle as the plates converge. This process is crucial for understanding plate tectonics, as it leads to the recycling of the Earth’s crust and significantly influences geological activity such as earthquakes, volcanic eruptions, and mountain building.
Vine and Matthews: Vine and Matthews refers to a significant model developed in the early 1960s by geologists Robert Vine and Dr. William Matthews, which helped to explain the mechanisms of seafloor spreading and plate tectonics. This model demonstrated how magnetic stripes on the ocean floor provided evidence for the movement of tectonic plates away from mid-ocean ridges, supporting the idea that new oceanic crust is formed at these ridges and older crust is pushed away. Their research significantly contributed to our understanding of ocean basin evolution and the dynamic processes of Earth’s lithosphere.
Wilson Cycle: The Wilson Cycle refers to the cyclical process of ocean basin formation and closure due to tectonic plate movements, leading to the formation of supercontinents. This cycle illustrates how continents break apart, drift apart, and eventually collide again, influencing geological features and patterns over millions of years. Understanding this cycle helps explain the dynamics of plate boundaries, the process of seafloor spreading, and the evolution of ocean basins.