Life, LIPs, and Supercontinents: Jason and Tuzo


I don’t know the names of these two cats, but you will need a computer to see the amazing lower mantle structures that at least one researcher calls Jason and Tuzo. (Niu)



On this see-through globe, Jason is the red blob under the Pacific, Tuzo is the one under Africa and much of the eastern Atlantic Ocean, per McNamara, Figure 2. Multiple studies have confirmed that these structures really do rise up from the core-mantle boundary on opposite sides of the planet. (McNamara; Niu)


Here’s a closer look at them, imaged via CAT scan tomography and posted online five years ago:



The Hawaiian Islands are among volcanic hotspots associated with Jason; the Canary Islands Hotspot, site of 2021’s big eruption on La Palma, is one of those linked to Tuzo. Neither of these two LLSVPs gets anywhere close to the surface; the mantle plume feeding each hotspot apparently comes up from Jason or Tuzo’s top or outer edges.


For technical reasons, most scientists refer to these two things, whatever they may be, as “Large Low-Velocity Shear Provinces” (LLVSPs or LLVPs), but I much prefer “Jason” and “Tuzo,” at least until someone figures out what they actually are.

This one. (Image: NASA, Jeff Hester, and Paul Scowen/Arizona State University, public domain)

Yes, they look like that famous Hubble picture.

But we’re not talking about nebular dusty gas columns expanding outward into fairly empty space here.

Jason and Tuzo are rising up through the base of an almost 1800-mile-thick column of solid rock!

Solid things can flow — glaciers — for example.

So that movement in itself doesn’t faze the geoscientists, especially since both structures appear somehow to connect with the core-mantle boundary, where they get extremely hot and so more buoyant than typical mantle rock.

What boggles some of the best minds on the planet is the presence of something new inside Earth that’s obviously important (because of its size, location, and correlation with many of Earth’s hotspot volcanoes) and yet cannot be explained by any of the working models of the planet’s inner structure. (McNamara)

McNamara’s 2019 paper (PDF) is technical but goes into detail about possible explanations for Jason and Tuzo.

I’ll just close with one of the most recent close-up images of part of Tuzo. Scientists are so intrigued by these things that they scattered a seismic array on the nearby Indian Ocean floor and did their tomographic thing.

This is an interpretation of the data they collected:


For reference, the dark round thing is Earth’s core; on the surface, there is Antarctica up front, with the lower eastern edge of South America to the left (and part of a continent, probably Asia, behind the core); and a thin slice of Australia’s western coast showing in the lower right. The land mass at the top of this view is the bulging part of Africa to the north; southern Africa is over Tuzo, shown in shades of red. What do you think Tuzo is? (Image source)


The mantle clearly is a lot more complex than anyone expected. And yet it’s the source of all volcanism; its processes power plate tectonics and, as we’ll see next time, the supercontinent cycles that shaped how forms of life evolved in nearby oceans and seas.

Edited January 10th to correct Tuzo’s name spelling.


Featured image: Eugenia Terekhova/Shutterstock

Sources

Bryan, S. E., and Ernst, R. E. 2008. Revised definition of large igneous provinces (LIPs). Earth-Science Reviews, 86(1-4): 175-202.

Ernst, R. E.; Bond, D. P.; Zhang, S. H.; Buchan, K. L.; and others. 2021. Large Igneous Province Record Through Time and Implications for Secular Environmental Changes and Geological Time‐Scale Boundaries. Large Igneous Provinces: A Driver of Global Environmental and Biotic Changes, 1-26.

McNamara, A. K. 2019. A review of large low shear velocity provinces and ultra low velocity zones. Tectonophysics, 760: 199-220.

Mukherjee, I.; Large, R. R.; Corkrey, R.; and Danyushevsky, L. V. 2018. The Boring Billion, a slingshot for complex life on Earth. Scientific Reports, 8(1): 1-7.

Nance, R. D.; Murphy, J. B.; and Santosh, M. 2014. The supercontinent cycle: a retrospective essay. Gondwana Research, 25(1): 4-29.

Niu, Y. 2018. Origin of the LLSVPs at the base of the mantle is a consequence of plate tectonics–a petrological and geochemical perspective. Geoscience Frontiers, 9(5):1265-1278.

Palin, R. M., and Santosh, M. 2020. Plate tectonics: What, where, why, and when?. Gondwana Research. (PDF)

Pastor-Galán, D.; Nance, R. D.; Murphy, J. B.; and Spencer, C. J. 2019. Supercontinents: myths, mysteries, and milestones. Geological Society, London, Special Publications, 470(1): 39-64

Reddy, S. M., and Evans, D. A. D. 2009. Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere. Geological Society, London, Special Publications, 323(1), 1-26.

Tsekhmistrenko, M.; Sigloch, K.; Hosseini, K.; and Barruol, G. 2021. A tree of Indo-African mantle plumes imaged by seismic tomography. Nature Geoscience, 14(8): 612-619.



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