New Insights into Earth’s Continental History and Stability Challenge Conventional Beliefs

by Henrik Andersen
5 comments
craton deformation

A recent scientific study from the University of Illinois Urbana-Champaign challenges the long-standing notion of stable cratons on Earth, revealing that these regions have undergone repetitive deformation beneath their crust throughout their existence. This groundbreaking research contradicts previous theories and uncovers a new understanding of continental evolution and plate tectonics by demonstrating that the supposedly buoyant and stable mantle keels are, in fact, dense and subject to significant changes over time.

According to the study led by geology professor Lijun Liu, the stable cratons on Earth’s continental plates, which were previously considered structurally stable, have experienced repetitive deformation beneath their surface since their formation in the ancient past. This finding raises questions about why most cratons have remained stable while undergoing substantial changes underneath.

To investigate this phenomenon, the researchers examined the relationship between craton surface topography and the thickness of the underlying lithosphere layer. They utilized density data collected from the Earth’s uppermost rigid layers of crust and mantle, known as the lithosphere. The results of their study have been published in the journal Nature Geosciences.

The study reports that the cratons, which have remained relatively unchanged since their formation, are the oldest tectonic units on Earth, surviving supercontinent cycles such as the formation and breakup of Pangea and the ancient supercontinent Rodina.

Liu challenges the widely accepted belief that cratons are protected by their thick and buoyant mantle roots or keels, which were thought to be stable over time. Recent papers from Liu’s research group reveal that these mantle keels are actually dense, contrary to conventional wisdom.

In a study conducted in 2022, the team demonstrated that the traditional view of buoyant craton keels would position most cratons about 3 kilometers above sea level. However, the actual elevation is only a few hundred meters, implying that the lithospheric mantle beneath the crust is of high enough density to cause the surface to sink by approximately 2 kilometers.

Through gravity field measurements, the team further investigated the density structure of the craton keels. Their findings suggest that the lower portion of the mantle keel, where high-density material is located, tends to peel away repeatedly from the lithosphere above during supercontinent breakup initiated by mantle upwellings called plumes. These delaminated keels could eventually return to the base of the lithosphere after being heated within the hot mantle.

Liu describes this process as similar to what occurs in a lava lamp, where cool material near the surface sinks while warm material near the bottom rises.

The study reveals that this deformation history accounts for some puzzling geophysical properties observed in the lithosphere. For example, the repetitive vertical deformation of the lower half of the mantle keel causes seismic waves that vibrate the rock vertically to travel faster compared to the upper half of the keel, which experiences less vertical deformation.

Additionally, the team found that mantle delamination leads to the rising of the craton surface, resulting in erosion. This is reflected in the strong correlation between crustal thickness and lithospheric thickness, a previously unnoticed observation. Notably, two major uplift and erosion events occurred during the separation of supercontinents Rodinia and Pangea. The former event caused the Great Unconformity, a feature in the Earth’s rock record indicating no evidence of new deposition, only extensive craton erosion. As a result, ancient lower crust pieces are exposed on the craton’s surface today.

Numerical simulations conducted by the team suggest that this episodic deformation of the lower craton keels is the mechanism by which craton crusts have survived throughout Earth’s long geological history.

Liu emphasizes that this newly proposed understanding of cratons will significantly alter perspectives on continental evolution and the mechanisms of plate tectonics on Earth.

The study received support from the National Science Foundation and the National Natural Science Foundation of China, with contributions from Illinois geology professor Craig Lundstrom, graduate students Yaoyi Wang, Zebin Cao, Lihang Peng, and Diandian Peng, as well as Chinese Academy of Sciences professor Ling Chen.

Frequently Asked Questions (FAQs) about craton deformation

What does the new study reveal about Earth’s cratons?

The new study reveals that Earth’s seemingly stable cratons have undergone repetitive deformation beneath their surface since their formation. This challenges previous beliefs about their stability and provides insights into continental evolution and plate tectonics.

How have the findings contradicted conventional theories?

The findings contradict conventional theories by showing that the mantle keels, previously thought to be buoyant and stable, are actually dense and subject to significant changes over time. This challenges the notion of their long-term stability and necessitates a reevaluation of our understanding of cratons.

How have cratons survived throughout Earth’s history?

According to the research, cratons have survived through episodic deformation of their lower keels. These keels peel away from the lithosphere during supercontinent breakup initiated by mantle upwellings. After being heated in the hot mantle, the delaminated keels can return to the base of the lithosphere, enabling the crust to endure the geological ages.

What are the geophysical properties affected by craton deformation?

The study reports that the repetitive vertical deformation of the lower half of the mantle keel affects the speed of seismic waves that vibrate the rock vertically. Additionally, mantle delamination causes the craton surface to rise, leading to erosion. These properties shed light on the observed correlations between crustal thickness and lithospheric thickness.

How will this research impact our understanding of continental evolution?

This research will significantly impact our understanding of continental evolution by providing new insights into the behavior of cratons and the operation of plate tectonics. It challenges traditional views, suggesting that cratons are not as stable as previously believed and highlighting the importance of repetitive deformation in shaping the continents.

More about craton deformation

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5 comments

EarthLover91 June 14, 2023 - 1:24 pm

Wow, nature is so dynamic! I can’t believe those seemingly stable cratons have been through so much deformation. It makes me appreciate the Earth’s geological history even more. Mother Nature is full of surprises!

Reply
GeologyRockstar June 14, 2023 - 3:01 pm

Finally, some fresh insights into continental evolution! The seismic wave speed differences and the correlation between crustal and lithospheric thickness are mind-boggling. This research will revolutionize the field!

Reply
JohnDoe1987 June 14, 2023 - 5:27 pm

this study is amazing, it challenges everything we thought we knew about cratons. its fascinating how the mantle keels are actually dense, not buoyant. changes our whole perspective!

Reply
ScienceNerd24 June 14, 2023 - 6:04 pm

omg this research is mind-blowing! the repetitive deformation of cratons beneath the surface, who would’ve thought? it’s like a lava lamp, with cool material sinking and warm material rising. so cool!

Reply
CuriousMind123 June 15, 2023 - 12:19 am

This study challenges traditional theories and shakes up our understanding of plate tectonics. The fact that cratons have survived supercontinent cycles and undergone significant changes beneath the surface is mind-boggling. Can’t wait to learn more about this!

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