Hyunwoo Lee

Bio: Hyunwoo Lee is an academic researcher from Seoul National University. The author has contributed to research in topics: Mantle (geology) & Volcano. The author has an hindex of 7, co-authored 20 publications receiving 303 citations. Previous affiliations of Hyunwoo Lee include University of Tokyo & University of New Mexico.

Massive and prolonged deep carbon emissions associated with continental rifting

Abstract: Transfer of CO2 from Earth’s interior to the atmosphere happens largely by volcanic degassing. Measurements of CO2 emissions from faults in the East African Rift system imply that tectonic degassing is also important for deep carbon release. Carbon from Earth’s interior is thought to be released to the atmosphere mostly via degassing of CO2 from active volcanoes1,2,3,4. CO2 can also escape along faults away from active volcanic centres, but such tectonic degassing is poorly constrained1. Here we use measurements of diffuse soil CO2, combined with carbon isotopic analyses to quantify the flux of CO2 through fault systems away from active volcanoes in the East African Rift system. We find that about 4 Mt yr−1 of mantle-derived CO2 is released in the Magadi–Natron Basin, at the border between Kenya and Tanzania. Seismicity at depths of 15–30 km implies that extensional faults in this region may penetrate the lower crust. We therefore suggest that CO2 is transferred from upper-mantle or lower-crustal magma bodies along these deep faults. Extrapolation of our measurements to the entire Eastern rift of the rift system implies a CO2 flux on the order of tens of megatonnes per year, comparable to emissions from the entire mid-ocean ridge system2,3 of 53–97 Mt yr−1. We conclude that widespread continental rifting and super-continent breakup could produce massive, long-term CO2 emissions and contribute to prolonged greenhouse conditions like those of the Cretaceous.

Evolution of upper crustal faulting assisted by magmatic volatile release during early-stage continental rift development in the East African Rift

Abstract: During the development of continental rifts, strain accommodation shifts from border faults to intra-rift faults. This transition represents a critical process in the evolution of rift basins in the East African Rift, resulting in the focusing of strain and, ultimately, continental breakup. An analysis of fault and fluid systems in the younger than 7 Ma Natron and Magadi basins (Kenya-Tanzania border) reveals the transition as a complex interaction between plate flexure, magma emplacement, and magmatic volatile release. Rift basin development was investigated by analyzing fault systems, lava chronology, and geochemistry of spring systems. Results show that extensional strain in the 3 Ma Natron basin is primarily accommodated along the border fault, whereas results from the 7 Ma Magadi basin reveal a transition to intra-rift fault–dominated strain accommodation. The focusing of strain into a system of intra-rift faults in Magadi also occurred without oblique-style rifting, as is observed in Ethiopia, and border fault hanging-wall flexure can account for only a minor portion of faulting along the central rift axis (∼12% or less). Instead, areas of high upper crustal strain coincide with the presence of hydrothermal springs that exhibit carbon isotopes and N2-He-Ar abundances indicating mixing between mantle-derived (magmatic) fluids and air saturated water. By comparing the distribution of fault-related strain and zones of magmatic fluid release in the 3 Ma Natron and 7 Ma Magadi basins, we present a conceptual model for the evolution of early-stage rifting. In the first 3 m.y., border faults accommodate the majority of regional extension (1.24–1.78 mm yr–1 in Natron at a slip rate ranging 1.93–3.56 mm yr–1), with a significant portion of intra-rift faulting (38%–96%) driven by flexure of the border fault hanging wall. Fluids released from magma bodies ascend along the border fault and then outward into nearby faults forming in the flexing hanging wall. By 7 m.y., there is a reduction in the amount of extension accommodated along the border fault (0.40–0.66 mm yr–1 in Magadi at a slip rate ranging from 0.62 to 1.32 mm yr–1), and regional extension is primarily accommodated in the intra-rift fault population (1.34–1.60 mm yr–1), with an accompanying transition of magmatic volatile release into the rift center. The focusing of magma toward the rift center and concomitant release of magmatic fluids into the flexing hanging wall provides a previously unrecognized mechanism that may help to weaken crust and assist the transition to intra-rift dominated strain accommodation. We conclude that the flow of magmatic fluids within fault systems plays an important role in weakening lithosphere and focusing upper crustal strain in early-stage continental rift basins prior to the establishment of magmatic segments.

Displaced cratonic mantle concentrates deep carbon during continental rifting

Abstract: Continental rifts are important sources of mantle carbon dioxide (CO2) emission into Earth's atmosphere1-3. Because deep carbon is stored for long periods in the lithospheric mantle4-6, rift CO2 flux depends on lithospheric processes that control melt and volatile transport1,3,7. The influence of compositional and thickness differences between Archaean and Proterozoic lithosphere on deep-carbon fluxes remains untested. Here we propose that displacement of carbon-enriched Tanzanian cratonic mantle concentrates deep carbon below parts of the East African Rift System. Sources and fluxes of CO2 and helium are examined over a 350-kilometre-long transect crossing the boundary between orogenic (Natron and Magadi basins) and cratonic (Balangida and Manyara basins) lithosphere from north to south. Areas of diffuse CO2 degassing exhibit increasing mantle CO2 flux and 3He/4He ratios as the rift transitions from Archaean (cratonic) to Proterozoic (orogenic) lithosphere. Active carbonatite magmatism also occurs near the craton edge. These data indicate that advection of the root of thick Archaean lithosphere laterally to the base of the much thinner adjacent Proterozoic lithosphere creates a zone of highly concentrated deep carbon. This mode of deep-carbon extraction may increase CO2 fluxes in some continental rifts, helping to control the production and location of carbonate-rich magmas.

Release of radiogenic noble gases as a new signal of rock deformation

Abstract: In this study we investigate the release of radiogenic noble gas isotopes during mechanical deformation. We developed an analytical system for dynamic mass spectrometry of noble gas composition and helium release rate of gas produced during mechanical deformation of rocks. Our results indicate that rocks release accumulated radiogenic helium and argon from mineral grains as they undergo deformation. We found that the release of accumulated 4He and 40Ar from rocks follows a reproducible pattern and can provide insight into the deformation process. Increased gas release can be observed before dilation and macroscopic failure is observed during high pressure triaxial rock deformation experiments. Accumulated radiogenic noble gases can be released due to fracturing of mineral grains during small scale strain in earth materials. Helium and argon are highly mobile, conservative species and could be used to provide information on changes in the state of stress and strain in earth materials, and as an early warning signal of macroscopic failure. These results pave the way for the use of noble gases to trace and monitor rock deformation for earthquake prediction and a variety of other subsurface engineering projects.

Atmospheric Evolution on Inhabited and Lifeless Worlds

Abstract: As the search for Earth-like exoplanets gathers pace, in order to understand them, we need comprehensive theories for how planetary atmospheres form and evolve. Written by two well-known planetary scientists, this text explains the physical and chemical principles of atmospheric evolution and planetary atmospheres, in the context of how atmospheric composition and climate determine a planet's habitability. The authors survey our current understanding of the atmospheric evolution and climate on Earth, on other rocky planets within our Solar System, and on planets far beyond. Incorporating a rigorous mathematical treatment, they cover the concepts and equations governing a range of topics, including atmospheric chemistry, thermodynamics, radiative transfer, and atmospheric dynamics, and provide an integrated view of planetary atmospheres and their evolution. This interdisciplinary text is an invaluable one-stop resource for graduate-level students and researchers working across the fields of atmospheric science, geochemistry, planetary science, astrobiology, and astronomy.

Flow of mantle fluids through the ductile lower crust: Helium isotope trends

Abstract: Flow of Mantle Fluids Through the Duct,le Lower Crust: Helium Isotope Trends I B. Mack Kennedyl andlMatthijs C. van Soest ICenter for Isoto~e Geochemistry Earth Scienoes Division Lawrence Berkeley National Laboratory Berkeley, (:A 94720 2Noble Gas Geochemistry and Geochronology Laboratory School of Earth and Space Exploration Arizona State University Tempe, AZ 85287-1404 Abstract Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3 He /4 He ratios in surface fluids from the northern Basin and Range province, western North America increase systematically from low, crustal values in the east to high, mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of helium isotope ratios and active trans-tensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere in regions even where there is no significant magmatism. Superimposed on the regional trend are local, high- He/ He anomalies signifying hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.

An essential role for continental rifts and lithosphere in the deep carbon cycle

Abstract: The continental lithosphere is a vast store for carbon. The carbon has been added and reactivated by episodic freezing and re-melting throughout geological history. Carbon remobilization can lead to significant variations in CO2 outgassing and release in the form of magmas from the continental lithosphere over geological timescales. Here we use calculations of continental lithospheric carbon storage, enrichment and remobilization to demonstrate that the role for continental lithosphere and rifts in Earth’s deep carbon budget has been severely underestimated. We estimate that cratonic lithosphere, which formed 2 to 3 billion years ago, originally contained about 0.25 Mt C km–3. A further 14 to 28 Mt C km–3 is added over time from the convecting mantle and about 43 Mt C km–3 is added by plume activity. Re-melting focuses carbon beneath rifts, creating zones with about 150 to 240 Mt C km–3, explaining the well-known association of carbonate-rich magmatic rocks with rifts. Reactivation of these zones can release 28 to 34 Mt of carbon per year for the 40 million year lifetime of a continental rift. During past episodes of supercontinent breakup, the greater abundance of continental rifts could have led to short-term carbon release of at least 142 to 170 Mt of carbon per year, and may have contributed to the high atmospheric CO2 at several times in Earth's history. Continental rifts are stores and sources of abundant carbon, according to calculations of carbon storage, enrichments and mobilization in rift systems. Continental rift systems are likely to play an important role in Earth’s deep carbon cycle.

Remobilization of crustal carbon may dominate volcanic arc emissions.

Abstract: The flux of carbon into and out of Earth's surface environment has implications for Earth's climate and habitability. We compiled a global data set for carbon and helium isotopes from volcanic arcs and demonstrated that the carbon isotope composition of mean global volcanic gas is considerably heavier, at -3.8 to -4.6 per mil (‰), than the canonical mid-ocean ridge basalt value of -6.0‰. The largest volcanic emitters outgas carbon with higher δ13C and are located in mature continental arcs that have accreted carbonate platforms, indicating that reworking of crustal limestone is an important source of volcanic carbon. The fractional burial of organic carbon is lower than traditionally determined from a global carbon isotope mass balance and may have varied over geological time, modulated by supercontinent formation and breakup.

Potential links between continental rifting, CO 2 degassing and climate change through time

Abstract: The concentration of CO2 in the atmosphere is a key influence on Earth’s climate. Today, significant quantities of CO2 are emitted at continental rifts, suggesting that the spatial and temporal extent of rift systems may have influenced deep carbon fluxes and thus climate change throughout geological time. Here we test this hypothesis by conducting a worldwide census of continental rift lengths over the last 200 million years. We estimate tectonic CO2 release rates through time and show that along the extensive Mesozoic and Cenozoic rift systems, rift-related CO2 degassing rates reached more than 300% of present-day values. Using a numerical carbon cycle model, we find that two prominent periods of enhanced rifting 160 to 100 million years ago and after 55 million years ago coincided with greenhouse climate episodes, during which atmospheric CO2 concentrations were more than three times higher than today. We therefore propose that continental fragmentation and long-term climate change could plausibly be linked via massive CO2 degassing in rift systems. Degassing of large amounts of CO2 from continental rifts may have contributed to greenhouse climate episodes over the past 200 million years, according to numerical models.