Mantle Plumes
Mantle convection is the slow creeping motion of Earth's rocky mantle in response to perpetual gravitationally unstable variations in its density. Material near the surface of Earth, particularly oceanic lithosphere, cools down by conduction of heat into the oceans and atmosphere, then thermally contracts to become dense, and then sinks under its own weight at convergent plate boundaries. This subducted material sinks to some depth in the Earth's interior where it is prohibited, by inherent density stratification, from sinking further. This stoppage creates a thermal boundary layer where sunken material soaks up heat via thermal conduction from below, and may become buoyant again to form upwelling mantle plumes.
Styles of convection
There is a current debate within the geophysics community as to whether convection is likely to be 'layered' or 'whole'. Geochemical studies of mid ocean ridge basalts (MORB) and tectonically emplaced upper mantle material have found it to be depleted in 'incompatible' elements such as U and Th; whereas material thought to be derived from the lower mantle i.e. ocean island basalts (OIB) is found to be enriched in incompatible elements. This suggests that the upper and lower mantle are not well mixed so that convection cells are layered with the boundary being between the upper and lower mantle at about 670 km depth. However, geophysicists have employed seismic tomography and have detected features reminiscent of slabs at subduction zones penetrating through the 670 km and down to at least 1800 km depth, this supports the whole mantle convection hypothesis.
Watch the animation to see mantle convection. The left side is cold material being subducted and the right side is hot material rising. Other static view file: Quanta Magazine 2020
Questions:
Go to the following website: http://www.mantleplumes.org/Convection.html
1. What effects drive convective motions?
2. While the mantel is generally thought to convect as a single layer or at most two, what is a more likely scenario and why?
3. Why is the mantle likely to convect in multiple layers?
4. What controls the rate of heat loss from the Earth’s core?
5. What are the three basic gravitational forces generated by cooling plates?
Go to the following website:http//www.quantamagazine.org/continents-of-the-underworld-come-into-focus-20200107/
1. How do these patterns in the mantle leave traces on our surface world?
2. What are thermochemical piles?
3. How was the islands of Hawaii formed? Animation
4. Is Yellowstone similar to Hawaii?
Go to the following website and view the animation full screen:https://youtu.be/HTGaRfMHvtQ
1. How much time passes?
2. What do the black dots on earths surface represent?
Most of the known volcanic hot spots are linked to plumes of hot rock (red) rising from two spots on the boundary between the metal core and rocky mantle 1,800 miles below Earth’s surface.