Nav: Home

Scientists reveal the links between deep carbon cycle and geodynamics of big mantle wedge

July 19, 2018

High-resolution P wave tomography shows that the crust-mantle structure beneath eastern Asia is composed by the stagnant subducted Pacific slab in the mantle transition zone (410-660km in depth), continental lithosphere and a wedge upper mantle in between. This crust-mantle structure is so called "big mantle wedge". Timing of the big mantle wedge formation beneath eastern Asia is critical to understanding of the interaction between the west Pacific subducting plate and continental margin in eastern Asia. In addition, the continental lithosphere in the North China, which is a part of lithosphere of the big mantle wedge, had been an ancient and thick (~200km) lithosphere that is so called "North China craton". However, the eastern part of the North China craton has been thinned since 130 Ma, with the thinnest portion about 70km in depth. Formation time of the big mantle wedge and mechanism of the lithospheric thinning of the North China craton are two important issues puzzling the world Earth scientists. Previous studies have ignored the influences of recycled carbonates into the big mantle wedge through Pacific plate subduction on lithospheric thinning of the North China craton, which has been investigated by a recent study.

Recent systematic studies on the Mg isotope geochemistry of Cretaceous and Cenozoic continental basalts from eastern China and circum-Pacific island arc basalts revealed that the upper mantle beneath eastern China is a vast store of subducted carbon. The subducted oceanic crust carrying sedimentary carbonates was partially melted in the mantle transition zone. Carbonated silicate melts derived from partial melting of stagnant subducted slab in the mantle transition zone rose, penetrated into and reacted with the overlying mantle to form carbonated peridotite (Figure 1). Based on the oldest age of alkaline basalts derived from the carbonated peridotite in the big mantle wedge, this study demonstrates that the big mantle wedge in eastern Asia was formed 125 Ma. The carbonated silicate melts produced by partial melting of the carbonated peridotite in the big mantle wedge migrated upward and interacted with the overlying lithospheric mantle, resulting in carbonated peridotite and partial melting in the bottom of continental lithosphere beneath eastern China, thus its physical characters are similar to the asthenosphere and it could be easily replaced by convective mantle. As a result, the cratonic lithosphere in North China would be thinning and the carbonated silicate melts will be transformed from low-SiO2 strongly alkali melts to high-SiO2 alkali melts. This study opens a new research field concerning geodynamic effects of deep carbon cycles, provides a new constraint on timing of the big mantle wedge beneath eastern Asia, a new mechanism for lithospheric thinning of the North China craton, and a new model for chemical transformation from low-SiO2 nephelinite or basanite to high-SiO2 alkali basalts.
This research was funded by the National Natural Science Foundation of China (Grant No. 41730214) and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB18000000).

See the article: Li S. G. and Wang Y. 2018. Formation time of the big mantle wedge beneath eastern China and a new lithospheric thinning mechanism of the North China craton--Geodynamic effects of deep recycled carbon. Science China Earth Sciences, 61(7): 853-868,

Science China Press

Related Lithosphere Articles:

Seismic CT scan points to rapid uplift of Southern Tibet
Rice University geophysicists have conducted a three-year seismic CT scan of the upper mantle beneath the Tibetan Plateau and concluded that the southern half of the 'Roof of the World' formed within 10 million years, or less than one-quarter of the time since the beginning of the India-Eurasia continental collision.
Project Hotspot
In their study published in Lithosphere this week, James Kessler and colleagues examine the geology of a scientific borehole drilled into the Snake River Plain, Idaho, USA, to investigate the potential for geothermal energy at depth.
Geologists publish new details about evolution of East African Rift Valley
Researchers in the College of Arts and Sciences at Syracuse University have published new details about the evolution of the East African Rift (EAR) Valley, one of the world's largest continental rift zones.
What's up with Madagascar?
The island of Madagascar off the coast of Africa was largely unexplored seismically until recently.
Giant 'great valley' found on Mercury
A giant valley on the planet Mercury makes the Grand Canyon look tiny by comparison.
Geologic imaging technique measures strength of Earth's outer shell
An advanced imaging technique used to map Earth's outer shell also can provide a measure of strength, finding weak spots and magma upwellings that could point to volcanic or earthquake activity, according to a new study by geologists at the University of Illinois at Urbana-Champaign and the University of Adelaide in Australia.
The August 2016 issue of Lithosphere is now online
The August issue of Lithosphere presents papers that provide insights into Tyrrhenian margin neotectonics in Italy; the Wrangellia composite terrane in Canada; fault-related fissures on Gower Peninsula, Wales; blueschist facies rocks and serpentinites from Kochi in Shikoku Island, Japan; the Shuswap metamorphic complex in southern British Columbia; and paleo-Pacific plate subduction along northeastern China.
Oceans may be large, overlooked source of hydrogen gas
Serpentinized rocks formed near fast-spreading tectonic plates under Earth's seafloor could be a large and previously overlooked source of free hydrogen gas, a Duke University study finds.
New study upends a theory of how Earth's mantle flows
A new study carried out on the floor of Pacific Ocean provides the most detailed view yet of how the earth's mantle flows beneath the ocean's tectonic plates.
Plate tectonics without jerking
The earthquake distribution on ultra-slow mid-ocean ridges differs fundamentally from other spreading zones.

Related Lithosphere Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#529 Do You Really Want to Find Out Who's Your Daddy?
At least some of you by now have probably spit into a tube and mailed it off to find out who your closest relatives are, where you might be from, and what terrible diseases might await you. But what exactly did you find out? And what did you give away? In this live panel at Awesome Con we bring in science writer Tina Saey to talk about all her DNA testing, and bioethicist Debra Mathews, to determine whether Tina should have done it at all. Related links: What FamilyTreeDNA sharing genetic data with police means for you Crime solvers embraced...