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A ghost, a ghost from the core-mantle boundary, is hovering on the surface of the earth's crust. Geologists all over the world banded together to round up the ghost. From the Hawaiian islands in the Pacific Ocean to Iceland in the Atlantic Ocean, from the igneous province of Siberia to the Deccan Plateau in India, from Mount Emei in China to Yellowstone National Park in the United States, is there any magmatic activity of unknown origin that has not been labelled as mantle plume genesis by geologists?

Figure 1 Iceland's erupting volcano

Figure 2 Seismic Wave Map of the Icelandic mantle plume geologists have found that most volcanic activity occurs at the boundary of plate activity, where the plate is weak, the most famous of which is the Pacific Rim volcanic belt that stretches for thousands of kilometers around the entire Pacific Ocean. At the expansive plate boundary at the ocean ridge, the thickness of the crust becomes smaller and the pressure decreases, resulting in partial melting of the rock; at the convergent plate boundary of the subduction zone, the addition of fluid reduces the melting point of the rock to produce magma 1. The theory of plate tectonics seems to perfectly explain the cause of all magmatic activity, and geologists seem to be proud to claim that the theory of plate tectonics has been perfected and that all it needs to do is to tinker with it.

Figure 3 Pacific Rim volcanic Belt however, volcanic activity in Hawaii does not seem to be explained by plate tectonics. Hawaii is located in the middle of the Pacific plate, thousands of kilometers away from any plate boundary. However, it is in this place far from the plate boundary that volcanic activity occurs. After careful observation, geologists found that Hawaii formed an island chain with the surrounding islands, and dating work found that the farther away from Hawaii, the older the islands were. In other words, the island of Hawaii is very young, and since it is young, there must be corresponding geological activities. Geologists speculate that beneath Hawaii, there is a heat source at rest relative to the lithosphere, heating the moving oceanic crust, which geologists call a hot spot.

Figure 4 how do Hawaiian volcanic island chain hotspots come into being? Geologists have different opinions. Geophysicists used seismic waves to measure the wave velocity of matter in lower Hawaii and put forward the mantle plume theory 4. They believe that a stream of high-temperature melt with low density and high temperature will flow from the deep mantle to the surface. The mantle stigma is large and small, just like a mushroom. When the stigma touches the earth's crust, it can produce several hot spots on the ground. Some people have even calculated carefully how many hot spots a mantle plume can produce on the surface.

Figure 5 mantle plume hot spot model, some people support, some people oppose to the mantle plume theory, geologists even set up a website "do mantle plumes really exist?" To collect opinions from all sides. Some people think that the mantle plume is formed at the deep core-mantle boundary of 2900km, some people think that the mantle plume is formed in the mantle transition zone of 660km, and some even think that the mantle plume does not exist, and the hot spot is caused by shallow melting at the depth of tens of kilometers.

Map of Figure 6 mantle plume except Hawaii, Yellowstone National Park 10 and Iceland 11 are considered to be the product of mantle plume activity. Some scientists believe that the Permian mass extinction was caused by large-scale volcanic eruptions caused by large-scale mantle plume activity. So when it comes to disasters, Yellowstone National Park in the United States is always photographed frequently and is believed to be the trigger for the next volcanic eruption. In addition, both Siberia and Deccan plateaus have thousands of square kilometers of large igneous provinces, which are considered by geologists to be the product of mantle plume activity.

Despite all the doubts, the mantle plume hypothesis is still the best explanation for the cause of isolated hot spots. However, the mantle plume is like a ghost, elusive, we do not know where it comes from, do not know its formation mechanism and material source 13. There are too many secrets worth digging and exploring. I hope readers can unravel the mystery of the mantle plume one day.

Picture

Fig. 1 Hamblin, W. K. & Christiansen, E. H. Earth's dynamic systems. (Prentice Hall, Pearson Education, 2004)

Figure 3 from https://zh.wikipedia.org/ zh-hans/% E7% 8e% AF% E5 A4% AA% E5 B9% B3% E6 B4% 8B% E7% 81% AB% E5% B1% B1% E5 B8% A6

reference

1.Stern, R. J. Subduction zones. Rev. Geophys. 40, 3-1 (2002).

2.Hauri, E. H. Major-element variability in the Hawaiian mantle plume. Nature 382415-419 (1996).

3.Eiler, J. M., Farley, K. A., Valley, J. W., Hofmann, A. W. & Stolper, E. M. Oxygen isotope constraints on the sources of Hawaiian volcanism. Earth Planet. Sci. Lett. 144,453,467 (1996).

4.DePaolo, D. J. & Manga, M. Deep origin of hotspots-the mantle plume model. Science 300,920,921 (2003).

5.Campbell, I. H. & Griffiths, R. W. Implications of mantle plume structure for the evolution of flood basalts. Earth Planet. Sci. Lett. 99, 79-93 (1990).

6.Clouard, V. & Bonneville, A. How many Pacific hotspots are fed by deep-mantle plumes? Geology 29,695-698 (2001).

7.Malamud, B. D. & Turcotte, D. L. How many plumes are there? Earth Planet. Sci. Lett. 174113124 (1999).

8.Condie, K. C. Mantle plumes and their record in Earth history. (Cambridge university press, 2001)

9.Zheng, Y.murf. Subduction zone geochemistry. Geosci. Front. 10, 1223-1254 (2019).

10.Pierce, K. L. & Morgan, L. A. Is the track of the Yellowstone hotspot driven by a deep mantle plume?-Review of volcanism, faulting, and uplift in light of new data. J. Volcanol. Geotherm. Res. 188,1-25 (2009).

11.Bijwaard, H. & Spakman, W. Tomographic evidence for a narrow whole mantle plume below Iceland. Earth Planet. Sci. Lett. 166121126126 (1999).

12.Ali, J. R., Fitton, J. G. & Herzberg, C. Emeishan large igneous province (SW China) and the mantle-plume up-doming hypothesis. J. Geol. Soc. 167,953-959 (2010).

13.Hamblin, W. K. & Christiansen, E. H. Earth's dynamic systems. (Prentice Hall, Pearson Education, 2004)

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), by Hu Lingzhi, edited by Liu Yuling

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