Seafloor spreading rates have slowed down- Study

Seafloor spreading rates have slowed down- Study

Subject: Geography

Section: Geomorphology

Context: According to a study Seafloor spreading rates have slowed down by roughly 35 per cent globally, growing mountains might be one of the factors driving the slowdown, the analysis found.

Concept:

• Seafloor spreading is a geological process that creates crusts, the outermost shell of Earth.
• Tectonic plates separate, allowing magma from the earth’s interior to fill the gap in this phenomenon.
• The magma cools to form a new oceanic crust. These activities occur along mid-ocean ridges — large mountain ranges rising from the ocean floor.

Process:

• Seafloor spreading and other tectonic activity processes are the result of mantle convection.
• Mantle convection is the slow, churning motion of Earth’s mantle.
• Convection currents carry heat from the lower mantle and core to the lithosphere.
• Convection currents also “recycle” lithospheric materials back to the mantle.
• Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor.
• Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill these fractures and spills onto the crust.
• This bubbled-up magma is cooled by frigid seawater to form igneous rock.
• This rock (basalt) becomes a new part of Earth’s crust.

Mid-Ocean Ridges

• Seafloor spreading occurs along mid-ocean ridges— large mountain ranges rising from the ocean floor.
• The Mid- Atlantic Ridge, for instance, separates the North American plate from the Eurasian plate, and the South American plate from the African plate.
• The East Pacific Rise is a mid-ocean ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the North American plate, the Cocos plate, the Nazca plate, and the Antarctic plate.
• The Southeast Indian Ridge marks where the southern Indo- Australian plate forms a divergent boundary with the Antarctic plate.
• Seafloor spreading is not consistent at all mid-ocean ridges.
• Slowly spreading ridges are the sites of tall, narrow underwater cliffs and mountains. Rapidly spreading ridges have a much more gentle slopes.
• The Mid-Atlantic Ridge, for instance, is a slow spreading center. It spreads 2-5 centimeters (.8-2 inches) every year and forms an ocean trench about the size of the Grand Canyon.
• The East Pacific Rise, on the other hand, is a fast spreading center. It spreads about 6-16 centimeters (3-6 inches) every year. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for one to develop!
• The newest, thinnest crust on Earth is located near the center of mid-ocean ridge—the actual site of seafloor spreading. The age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge.

Geographic Features:

• Oceanic crust slowly moves away from mid-ocean ridges and sites of seafloor spreading. As it moves, it becomes cooler, more dense, and more thick. Eventually, older oceanic crust encounters a tectonic boundary with continental crust.
• Active Plate Margins: In some cases, oceanic crust encounters an active plate margin.
  • An active plate margin is an actual plate boundary, where oceanic crust and continental crust crash into each other.
  • Active plate margins are often the site of earthquakes and volcanoes. Oceanic crust created by seafloor spreading in the East Pacific Rise, for instance, may become part of the Ring of Fire, the horseshoe-shaped pattern of volcanoes and earthquake zones around the Pacific ocean basin.
• Passive Plate margins: In other cases, oceanic crust encounters a passive plate margin.
  • Passive margins are not plate boundaries, but areas where a single tectonic plate transitions from oceanic lithosphere to continental lithosphere.
  • Passive margins are not sites of faults or subduction zones. Thick layers of sediment overlay the transitional crust of a passive margin.
  • The oceanic crust of the Mid-Atlantic Ridge, for instance, will either become part of the passive margin on the North American plate (on the east coast of North America) or the Eurasian plate (on the west coast of Europe).
• New geographic features can be created through seafloor spreading. The Red Sea, for example, was created as the African plate and the Arabian plate tore away from each other.