Ridge push | Wikipedia audio article

Summary

Ridge push, a driving force in plate tectonics, is caused by the gravitational sliding of the lithosphere down the asthenosphere at mid-ocean ridges. This force, active mainly in younger lithospheres (<90 Ma), is crucial for plate motion. Initially, ridge push was thought to be due to magma upwelling, but it's now understood as a body force throughout the ocean plate. Despite slab pull being stronger, recent research suggests ridge push remains a significant factor in plate movement, especially in plates with small or young subducting slabs where it can be the predominant force.

Takeaways

• 🌐 Ridge push is a driving force in plate tectonics, resulting from the gravitational sliding of the lithosphere down the asthenosphere at mid-ocean ridges.
• 🔍 Although named 'ridge push,' it is a body force acting throughout an ocean plate due to gravity, not just at the ridge.
• 🏞️ Mid-ocean ridges are underwater mountain chains at divergent plate boundaries where new oceanic crust forms due to tectonic plate spreading.
• 🌡️ The upwelling mantle and fresh crust at mid-ocean ridges are hotter and less dense, leading to an isostatic response that causes the young regions to rise.
• ⏳ Ridge push is most active in lithosphere younger than 90 million years, after which it cools and reaches thermal equilibrium, reducing its effectiveness.
• 📚 Early models of plate tectonics did not include ridge push, with the concept emerging after the discovery of mid-ocean ridges and seafloor spreading.
• 🌟 Egon Orowan proposed the first gravitational mechanism for spreading at mid-ocean ridges, suggesting it could be derived from principles of isostasy.
• 🔄 Ridge push is one of the dominant factors in plate motion, alongside slab pull, which was once thought to be the primary driver.
• 🚫 Ridge push is opposed by plate drag, the force of the lithosphere moving over the asthenosphere, and is just sufficient to maintain plate motion in most areas.
• 🌍 In plates with small or young subducting slabs, ridge push may be the predominant driving force, such as with the South American and Nazca plates.

Q & A

What is ridge push in plate tectonics?

Ridge push, also known as gravitational sliding or sliding plate force, is a driving force for plate motion in tectonics, occurring at mid-ocean ridges due to the rigid lithosphere sliding down the hot, raised asthenosphere beneath.

Why is the term 'ridge push' considered misleading?

The term 'ridge push' is misleading because it suggests a push only at the ridge, while it is actually a body force that acts throughout the ocean plate as a result of gravitational pull.

How does ridge push operate in terms of gravitational forces?

Ridge push occurs due to gravitational forces acting on young, raised oceanic lithosphere at mid-ocean ridges, causing it to slide down the sloped asthenosphere and push the lithospheric material away from the ridge.

What is the role of mid-ocean ridges in ridge push?

Mid-ocean ridges, which are underwater mountain chains formed at divergent plate boundaries, play a crucial role by raising the oceanic lithosphere due to upwelling mantle material. This elevation creates the slope necessary for ridge push to occur.

Why is ridge push mostly active in lithosphere younger than 90 million years?

Ridge push is primarily active in younger lithosphere because the newly formed crust is hotter and less dense, creating a slope in the lithosphere-asthenosphere boundary. After 90 million years, the lithosphere reaches thermal equilibrium, and the slope becomes effectively zero.

How did early theories on plate tectonics view ridge push?

Early models of plate tectonics, like Harry Hess's seafloor spreading model, viewed plate motion as being driven by mantle convection currents. Ridge push was later suggested as a supplementary force that helped keep the plates moving.

What is slab pull, and how does it compare to ridge push?

Slab pull is the force exerted by a subducting plate as it sinks into the mantle, pulling the attached plate along. It is generally considered stronger than ridge push but is opposed by mantle resistance, limiting its strength to only 2-3 times that of ridge push.

What are the opposing forces to ridge push?

Ridge push is primarily opposed by plate drag, which is the frictional resistance caused by the lithosphere moving over the weaker asthenosphere. Slab pull is also opposed by resistance to subduction at convergent boundaries.

What factors can affect the strength of ridge push in different tectonic plates?

The strength of ridge push can vary based on the age of the lithosphere and the presence of subducting slabs. In areas with younger or smaller slabs, ridge push may be the dominant force, as seen in the South American and Nazca plates.

What is flat slab subduction, and how is it related to ridge push?

Flat slab subduction occurs when a subducting plate is less dense and resists sinking steeply into the mantle. This phenomenon is seen in the Nazca plate, where ridge push is comparable to slab pull due to the young, less dense lithosphere.