Seafloor spreading that creates crust slowed 35%, growing mountains may be driving it: Study
1.Seafloor spreading at around 140 millimetres per year at present.
2.Seafloor spreading rates have slowed down by roughly 35 per cent globally, according to a study that analysed data from the last 19 million years. Growing mountains might be one of the factors driving the slowdown, the analysis found.
3.Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other.
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.
5.Determining the rate is crucial because seafloor spreading influences sea level and carbon cycle, the study published in the journal Geophysical Research Letters noted.
6.So, researchers selected 18 of the world’s largest spreading ridges for this study. By studying magnetic records in the rocks on the oceanic crust, they calculated how much oceanic crust had formed over the last 19 million years.
7.Basalt rocks on the oceanic crust contain magnetic properties. Their magnetism is influenced by the Earth’s magnetic field when the magma reached the surface and began cooling to form the crust, researchers found.
8.But the records are incomplete. This is because the crusts, according to the analysis, get destroyed at subduction zones, a point where two tectonic plates collide, causing one of them to sink into the Earth’s mantle beneath the other plate.
9.Their analysis of the preserved magnetic records showed that the seafloor is spreading at rates of around 140 millimetres per year, down from around 200 millimetres per year just 15 million years ago in some places
10.For example, as the Andes — where the Nazca oceanic plate is sinking beneath the South American continental plate — grows, it causes the Earth's crust to shorten and thicken. The rapidly growing range could be slowing the seafloor spreading along the ridges, the researchers explained.
11.About 200 million years ago, he explained, when the supercontinent Pangea started breaking, there weren’t any major plate collisions or related mountain chains. The continents were fairly flat back then, he added.
12.As Pangea progressively broke apart, new ocean basins formed, Muller highlighted. Eventually, the widely fragmented continents started running into each other.
source: down to earth and national geography
0 Comments