A groundbreaking investigation carried out by scientists at the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences (GIG-CAS), in collaboration with global partners, has brought new insights into how subducted carbonates influence the redox state of Earth’s deep mantle. Published in the prestigious journal Science Advances, this study sheds light on the pivotal role that deeply recycled carbon plays in controlling mantle chemistry, diamond genesis, and the stability of ancient continental blocks known as cratons. By replicating pressure and temperature conditions at depths ranging from 250 to 660 kilometers, the research team provides a sophisticated window into the fundamental processes governing Earth’s interior and its geological evolution over billions of years.
The mantle’s redox state—essentially its oxidation-reduction condition—directly governs the behavior and cycling of volatile elements, particularly carbon, between the Earth’s surface and its deeper regions. This research highlights that carbonatite melts derived from subducted oceanic slabs can substantially modify the redox environment of the mantle. These melts, upon interaction with the metallic iron contained within the surrounding mantle peridotite, induce chemical transformations that vary considerably depending on localized mantle temperatures and thermal regimes. Understanding these mechanisms bridges critical gaps in our knowledge of how volatile compounds are sequestered and mobilized in Earth’s inner depths.
Experimental simulations conducted by the team employed state-of-the-art high-pressure and high-temperature apparatus to mimic mantle conditions beneath continental lithosphere. The experiments revealed a fundamental dichotomy controlled by mantle thermal gradients. Under cooler, nonplume settings characteristic of stable mantle regions, carbonatite melts progressively reduce themselves and the surrounding mantle, facilitating the formation of immobile sublithospheric diamonds. These ultra-deep diamonds become integral to the structural resilience of cratons, acting as time capsules that preserve records of early Earth processes and mantle compositions. The reduction process stabilizes the lithosphere and contributes to the enduring nature of these ancient continental cores.
Conversely, in hotter mantle environments influenced by thermal plumes, carbonatite melts behave distinctly. They act as oxidizing agents, increasing the oxidation state of the hosting mantle rocks. This oxidation weakens the mineralogical framework of the lithosphere, making it prone to delamination—where the dense lower part of the lithosphere peels off and sinks into the mantle. Such delamination events are closely associated with uplift of the continental surface and episodes of widespread volcanic activity. This dynamic interplay offers a compelling explanation for variations in mantle strength and surface geological phenomena often observed in plume-modified tectonic regions.
The research conducted by Prof. YU Wang and colleagues emphasizes that these redox transformations are not merely isolated chemical curiosities but have profound implications for the long-term evolution of cratons, which constitute the stable nuclei of continents. Their findings suggest that mantle temperature and redox state variations governed by subducted carbonatite melts drive divergent evolutionary pathways—one leading to craton stabilization via diamond formation and the other to craton weakening through oxidation and lithospheric recycling. Such insights redefine our understanding of continental lithosphere survival and destruction across geological timescales.
To corroborate their experimental results, the researchers compared mineral assemblages formed under laboratory conditions with natural inclusions found inside diamonds extracted from cratonic regions in Africa and South America. They uncovered distinct redox fingerprints that align closely with the nature of the mantle environment the diamonds originated from. This direct link between experimental mineralogy and natural samples provides robust validation for the hypothesis that mantle redox state exerts a controlling influence over diamond genesis and craton viability.
The study also advances the broader scientific discourse surrounding the deep carbon cycle, an essential Earth system process. Carbon, one of Earth’s most crucial volatiles, undergoes complex transformations during subduction and mantle processing. The manner in which subducted carbonates evolve chemically controls both their capacity for deep storage and their eventual release, which can influence volcanic outgassing and atmospheric composition over geological time. The delineation of redox-dependent behavior in the mantle adds a vital dimension to models of how Earth’s interior interacts with the surface environment.
Furthermore, the implications of this research extend to the interpretation of diamond ages and their formation environments. Since diamonds effectively record the redox conditions prevailing at the time of their crystallization, enhanced understanding of how mantle thermal regimes influence redox state enables more accurate reconstructions of tectonic and thermal histories of cratons. This knowledge may prove pivotal in refining geochronological frameworks and enhancing predictive models concerning diamond deposits and their geological settings.
The interplay between subducted slabs, mantle redox chemistry, and continental lithosphere evolution also offers fresh perspectives on volcanic and tectonic activity’s timing and distribution. In plume settings, oxidative processes destabilizing the lithosphere can trigger surface uplift and enhanced volcanism, phenomena routinely observed in Earth’s geological record. These findings provide a mechanistic basis for linking deep Earth processes to surface dynamics, a longstanding challenge in Earth science.
From a methodological standpoint, this study exemplifies the power of integrating advanced experimental petrology with natural sample analyses to tackle complex geological questions. The precision achieved in replicating sublithospheric conditions within laboratory settings underscores the robustness and reliability of the conclusions drawn. Such experimental approaches will continue to be indispensable in unraveling Earth’s deep interior mysteries and their surface manifestations.
Moreover, the international collaboration underpinning this research highlights the global effort required to unlock Earth’s secrets. The cross-institutional synergies and sharing of expertise enabled detailed investigations spanning geochemistry, mineral physics, and tectonics, fostering a comprehensive understanding that solitary studies might not achieve. This collaborative spirit is essential for advancing fundamental geoscience disciplines.
This pivotal research was made possible through funding and support from several major Chinese scientific programs, including the National Natural Science Foundation of China, the National Key R&D Program of China, and the Chinese Academy of Sciences’ Strategic Priority Research Program. Their backing was crucial in enabling the high-pressure experimentation and extensive analytical work required for these findings.
In sum, this study revolutionizes our comprehension of how the redox processes activated by subducted carbonatite melts govern mantle chemistry, diamond creation, and continental lithosphere longevity. By delineating contrasting mantle behaviors under plume and nonplume scenarios, it opens new avenues in understanding craton dynamics and deep Earth volatile cycles. The implications for geology, tectonics, mineral exploration, and deep carbon cycle science are profound and far-reaching, promising to influence research directions and our interpretation of Earth’s complex inner workings for years to come.
Subject of Research: Deep mantle redox processes influenced by subducted carbonatite melts, diamond formation, and craton evolution
Article Title: [Not explicitly provided in source content]
News Publication Date: [Not explicitly provided in source content]
Web References: http://dx.doi.org/10.1126/sciadv.adu4985
References: Original article published in Science Advances by researchers at Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, and collaborators
Image Credits: Image by Prof. XU Yigang’s group
Keywords: Earth sciences, Earth structure, Physical geology
