Day 63 – Q 1. What are mantle plumes? How do mantle plumes give rise to various geographical features? Illustrate.

1. What are mantle plumes? How do mantle plumes give rise to various geographical features? Illustrate. 

 मेंटल प्लम्स क्या हैं? मैंटल प्लम्स विभिन्न भौगोलिक विशेषताओं को कैसे जन्म देते हैं? उदाहरण देकर स्पष्ट करें।

Introduction:

A mantle plume is an upwelling of abnormally hot rock within the Earth’s mantle. It is a buoyant mass of material in the mantle that, because of its buoyancy, rises. The existence of mantle plumes in the Earth was first suggested by Wilson(1963) as an explanation of oceanic-island chains, such as the Hawaiian-Emperor chain, which change progressively in age along the chain. 

TLP Phase 1 – Day 63 Synopsis

Body

1. Hot mantle rock that rises toward the earth’s surface in a narrow column is called a mantle plume. Plumes can be located beneath continental or oceanic crust or along plate boundaries.
2. Wilson proposed that as a lithospheric plate moves across a fixed hotspot (the mantle plume), volcanism is recorded as a linear array of volcanic seamounts and islands parallel to the direction the plate is moving. 
3. However, it is known today that plumes can also move, so this simplified model does not hold for all hotspot tracks. There are even a few investigators who question whether mantle plumes exist.
4. The three-dimensional tomographic model of Earth’s interior, similar to a medical CT scan, revealed large swells of what is likely hot mantle material with diameters roughly 1,000 kilometers wide. The structures, dubbed plumes by the researchers, rise from areas at the core-mantle boundary with strongly reduced seismic velocities.
5. Further, Plumes are a secondary way that Earth loses heat, much less important in this regard than is heat loss at plate margins. Some scientists think that plate tectonics cools the mantle, and mantle plumes cool the core. Two of the most well-known locations that fit the mantle plume theory are Hawaii and Iceland as both have volcanic activity.

Mantle Plumes has considered as the reason for giving rise to following geographical features:

• Plumes are thought to spread out laterally at the base of a continent, creating increased pressure that stretches the crust and results in uplift, fracturing, rifting, or flood basalts.
• Mantle plumes emanating from the upper mantle may gush up through the lithosphere as hot spots.
• Mantle plumes are thought to be strong enough to induce rifting and the formation of plates. The pressure creates a domed region that eventually splits in a three‐pronged pattern (triple junction or triple point). The best example of a triple junction in the world is provided by the three faults marked by the Red Sea, the Gulf of Aden, and the inactive African Rift Valley.
• The high ratios in Hawaiian basalts were interpreted as evidence that plumes are fed by primordial material from deep in the mantle, while mid-ocean ridge systems tap recycled upper mantle material depleted in helium-3.
• As a mantle plume reaches the upper mantle, it melts into a diapir. This molten material heats the asthenosphere and lithosphere, triggering volcanic eruptions. These volcanic eruptions make a minor contribution to heat loss from Earth’s interior, although tectonic activity at plate boundaries is the leading cause of such heat loss.
• The potential of mantle plumes may go well beyond volcanism within plates. For example, the mantle plume that may lie under Réunion Island in the Indian Ocean has apparently burned a track of volcanic activity that reaches about 3,400 miles (5,500 km) northward to the Deccan Plateau region of what is now India. 

Conclusion

Although many details of plumes and their effects are still controversial and debated, the basic theory of mantle plumes is well established and there is considerable observational evidence to support the plume concept. Recently, as the resolution of seismic tomography improved sufficiently, it has led to at least some plumes in the upper mantle being detected seismically.