Article

The oxidation state of Hadean magmas and implications for early Earth's atmosphere

Authors:
  • University of New England
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Magmatic outgassing of volatiles from Earth's interior probably played a critical part in determining the composition of the earliest atmosphere, more than 4,000 million years (Myr) ago. Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen and sulphur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure (fugacity) of oxygen. Reduced melts having oxygen fugacities close to that defined by the iron-wüstite buffer would yield volatile species such as CH(4), H(2), H(2)S, NH(3) and CO, whereas melts close to the fayalite-magnetite-quartz buffer would be similar to present-day conditions and would be dominated by H(2)O, CO(2), SO(2) and N(2) (refs 1-4). Direct constraints on the oxidation state of terrestrial magmas before 3,850 Myr before present (that is, the Hadean eon) are tenuous because the rock record is sparse or absent. Samples from this earliest period of Earth's history are limited to igneous detrital zircons that pre-date the known rock record, with ages approaching ∼4,400 Myr (refs 5-8). Here we report a redox-sensitive calibration to determine the oxidation state of Hadean magmatic melts that is based on the incorporation of cerium into zircon crystals. We find that the melts have average oxygen fugacities that are consistent with an oxidation state defined by the fayalite-magnetite-quartz buffer, similar to present-day conditions. Moreover, selected Hadean zircons (having chemical characteristics consistent with crystallization specifically from mantle-derived melts) suggest oxygen fugacities similar to those of Archaean and present-day mantle-derived lavas as early as ∼4,350 Myr before present. These results suggest that outgassing of Earth's interior later than ∼200 Myr into the history of Solar System formation would not have resulted in a reducing atmosphere.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Formaldehyde may have been produced more efficiently by photochemical reduction of bicarbonate and formate in Fe ++ -rich surface waters [8]. Magmatic outgassing of volatiles from Earth's interior probably played a critical role in determining the composition of the earliest atmosphere, more than 4000 Myr ago [9]. Magmatic outgassing of volatiles from Earth's interior probably played a critical role in determining the composition of the earliest atmosphere, more than 4000 Myr ago [9]. ...
... Magmatic outgassing of volatiles from Earth's interior probably played a critical role in determining the composition of the earliest atmosphere, more than 4000 Myr ago [9]. Magmatic outgassing of volatiles from Earth's interior probably played a critical role in determining the composition of the earliest atmosphere, more than 4000 Myr ago [9]. Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen, and sulfur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure of oxygen. ...
... Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen, and sulfur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure of oxygen. Samples from this earliest period of Earth's history are limited to igneous detrital zircons that pre-date the known rock record, with ages approaching~4400 Myr ago [9]. Wen et al. examined photochemical reactions in the early Earth's atmosphere in the prebiotic synthesis of simple organic molecules. ...
Article
Full-text available
The universe began 13.8 billion years ago, and Earth was born 4.6 billion years ago. Early traces of life were found as soon as 4.1 billion years ago; then, ~200,000 years ago, the human being was born. The evolution of life on earth was to become individual rather than cellular life. The birth of mitochondria made this possible to be the individual life. Since then, individuals have had a limited time of life. It was 1.4 billion years ago that a bacterial cell began living inside an archaeal host cell, a form of endosymbiosis that is the development of eukaryotic cells, which contain a nucleus and other membrane-bound compartments. The bacterium started to provide its host cell with additional energy, and the interaction eventually resulted in a eukaryotic cell, with both archaeal (the host cell) and bacterial (mitochondrial) origins still having genomes. The cells survived high concentrations of oxygen producing more energy inside the cell. Further, the roles of mitochondria in human being’s life and aging will be discussed.
... Magmatic arcs are geologically significant features that form above subduction zones, in both continental and oceanic settings. They are characterized by significant magma production, leading to the injection of magmatic rocks into the continental crust or the tectonic accretion of island arcs (e.g., Thorpe, 1982;Stern, 2010;Gill, 2012). These regions represent the thickest and most diverse associations of igneous rocks on Earth. ...
... Chondrite-normalized REE patterns of zircons from this magmatism reveal a pronounced enrichment in HREE, suggesting crystallization in a garnet-free melt. Additionally, these zircons exhibit combined positive Ce anomalies and negative Eu anomalies, potentially linked to the assimilation of Ce 4+ from a relatively oxidized and Eu-depleted magma composition due to plagioclase fractionation (Hinton and Upton, 1991;Pettke et al., 2005;Claiborne et al., 2010;Trail et al., 2011Trail et al., , 2012Yao et al., 2012;El-Bialy and Ali, 2013). ...
... Positive anomalies of Rb and Ba further support its classification as volcanic arc granites, as indicated by the geodynamic setting diagram Rb vs. Nb + Y of Pearce et al., (1984) (Fig. 11a). However, REE-normalized patterns of zircons show dispersion but maintain the previously described characteristics of HREE enrichment, positive Ce anomalies, and negative Eu anomalies, indicative of a highly oxidized, garnet and plagioclasefractionated magma (Hinton and Upton, 1991;Pettke et al., 2005;Claiborne et al., 2010;Trail et al., 2011Trail et al., , 2012Yao et al., 2012;El-Bialy and Ali, 2013). ...
... The consistent V/Sc ratios observed in the Archean and modern basalts suggest that the mantle fo 2 has been constant since the early Archean 15 . This perspective is reinforced by the cerium anomalies in Hadean zircons, which indicate that mantle fo 2 reached modern levels around 4.3 billion years ago 16 . However, this finding is subject to significant uncertainty, which may obscure potential oxidative trends. ...
... c The fo 2P of a mantle plume and ambient mantle remain constant since the Hadean. The timing of the Great Oxidation Event (GOE) and the fo 2 of Hadean mantle-derived zircons 16 are shown for comparison. The fo 2 of the mantle in equilibrating with the core was estimated to ΔFMQ −6 7 . ...
... Through the correction of the fo 2 of various mantle-derived melts to fo 2P , we observe that both the fo 2P of the ambient mantle and mantle plumes have the same fo 2 (−1 < ΔFMQ < +1), and this value has remained constant since the early Archean (Fig. 1c). These findings are identical to the fo 2 record in Hadean zircons 16 . In addition, experimental studies and first principles simulations shed light on the behavior of Fe 2+ in the Earth's deep magma ocean, demonstrating its disproportionation to Fe 3+ and Fe metal. ...
Article
Full-text available
Determining the evolutionary history of mantle oxygen fugacity (fo2) is crucial, as it controls the fo2 of mantle-derived melts and regulates atmospheric composition through volcanic outgassing. However, the evolution of mantle fo2 remains controversial. Here, we present a comprehensive dataset of plume-derived komatiites, picrites, and ambient mantle-derived (meta)basalts, spanning from ~3.8 Ga to the present, to investigate mantle thermal and redox states evolution. Our results indicate that fo2 of both mantle plume-derived and ambient mantle-derived melts was lower during the Archean compared to the post-Archean period. This increase in the fo2 of mantle-derived melts over time correlates with decreases in mantle potential temperature and melting depth. By normalizing fo2 to a constant reference pressure (potential oxygen fugacity), we show that the fo2 of both the mantle plume and ambient upper mantle has remained constant since the Hadean. These findings suggest that secular mantle cooling reduced melting depth, increasing the fo2 of mantle-derived melts and contributing to atmospheric oxygenation.
... We test the premise that the impactor's core is temporarily ejected and thereafter sheared and fragmented into small particles that descend as hail of molten iron in the post-impact phase. This scenario leaves open the possibility of supplying (and suspending) HSEs to Earth's mantle via oxidation reactions by a primordial surface hydrosphere (Abe, 1993) and/or a relatively high oxygen fugacity fayalite+magnetite+quartz (FMQ)-buffered early Hadean mantle (Trail et al., 2011). ...
... This would occur if the Hadean mantle was already relatively oxidized. A number of studies (Trail et al., 2011;Delano, 2001;Frost et al., 2008) support the notion that the oxidation state in the Hadean Earth's mantle was buffered at fayalite-magnetite-quartz (FMQ). When 1-mm iron fragments enter the Earth's mantle, those would be quickly oxidized. ...
Preprint
Overabundances in highly siderophile elements (HSEs) of Earth's mantle can be explained by conveyance from a singular, immense (3000 km in a diameter) "Late Veneer" impactor of chondritic composition, subsequent to lunar formation and terrestrial core-closure. Such rocky objects of approximately lunar mass (about 0.01 M_E) ought to be differentiated, such that nearly all of their HSE payload is sequestered into iron cores. Here, we analyze the mechanical and chemical fate of the core of such a Late Veneer impactor, and trace how its HSEs are suspended - and thus pollute - the mantle. For the statistically most-likely oblique collision (about 45degree), the impactor's core elongates and thereafter disintegrates into a metallic hail of small particles (about 10 m). Some strike the orbiting Moon as sesquinary impactors, but most re-accrete to Earth as secondaries with further fragmentation. We show that a single oblique impactor provides an adequate amount of HSEs to the primordial terrestrial silicate reservoirs via oxidation of (<m-sized) metal particles with a hydrous, pre-impact, early Hadean Earth.
... Arguments such as Miller and Urey (1959) invoke reducing atmospheric chemistry to synthesize organics, which can rain out of the atmosphere, accumulate on subaerial land surfaces, and polymerize through wet-dry or freeze-thaw cycles (Benner et al., 2020;Frenkel-Pinter et al., 2019;Frenkel-Pinter et al., 2022). However, studies based on analyses of the rare earth elements as a proxy for the mantle quartzfayalite-magnetite buffer indicate that Earth's earliest atmosphere was likely not reducing and had minor amounts of CH4 relative to CO2, N2, and H2O (Trail et al., 2011;Trail et al., 2012). These uncertainties warrant further investigations into the Hadean and the origins of life on Earth. ...
... Recent work has shown the production of prebiotic molecules in volcanic plumes and the role of volcanic lightning in prebiotic chemistry (Hess et al., 2021;Bada, 2023). However, the composition of these volcanic gasses is largely determined by the quartz-fayalite-magnetite mineral buffer in the mantle, which would likely have led to a weakly oxidizing atmosphere composed of CO2 and H2O (Trail et al., 2011;Zahnle et al., 2020). These weakly oxidizing atmospheres would present a challenge for many origin of life scenarios, although some studies suggest that in neutral conditions, inefficient production of prebiotic molecules remains possible, albeit slow to accumulate (Cleaves et al., 2008;Trainer, 2013). ...
Preprint
Full-text available
The Hadean, once thought to be uninhabitable and tumultuous, has more recently been recontextualized as a clement time in which oceans, land, and life likely appeared on Earth. This non-exhaustive chapter follows multiple threads from planet formation to the origin of life. We place significant emphasis on the solar system context for the Earth, the timing and nature of crustal formation and the evolution of the surface and atmosphere. Several scenarios for prebiotic chemistry are also discussed including atmospheric photochemistry, wet-dry and freeze-thaw cycles, and hydrothermal vent systems. We attempt to draw connections between the large-scale, planetary processes and various origin of life pathways to illustrate possible overlaps and correlations. In detail, we conclude with and discuss the "impact of impacts" to show how asteroid and comet impacts during the Hadean may have affected many of these processes and scenarios, from generating land to altering the chemical composition and oxidation state of the early Earth's atmosphere and surface.
... Indeed, classical models of magma ocean thermal-climate-redox evolution are typically limited to H 2 O and CO 2 (and occasionally O 2 ) bulk atmospheric compositions [24][25][26][27][28] . This assumption of a relatively oxidizing atmosphere is based on evidence for Earth's rapid differentiation and mantle oxidation after accretion 29,30 , along with the absence of any evidence for a long-lived H 2 -rich atmosphere 15 . Attempts to extrapolate these Earth-analog models to terrestrial exoplanets 26,28,31 typically ignore any H 2 -rich initial atmosphere under the assumption that such atmospheres are too short-lived to affect subsequent evolution. ...
... In this case, the free oxygen in the fluid phase is similarly corrected using Eq. (29). ...
Article
Full-text available
Exoplanet exploration has revealed that many—perhaps most—terrestrial exoplanets formed with substantial H2-rich envelopes, seemingly in contrast to solar system terrestrials, for which there is scant evidence of long-lived primary atmospheres. It is not known how a long-lived primary atmosphere might affect the subsequent habitability prospects of terrestrial exoplanets. Here, we present a new, self-consistent evolutionary model of the transition from primary to secondary atmospheres. The model incorporates all Fe-C-O-H-bearing species and simulates magma ocean solidification, radiative-convective climate, thermal escape, and mantle redox evolution. For our illustrative example TRAPPIST-1, our model strongly favors atmosphere retention for the habitable zone planet TRAPPIST-1e. In contrast, the same model predicts a comparatively thin atmosphere for the Venus-analog TRAPPIST-1b, which would be vulnerable to complete erosion via non-thermal escape and is consistent with JWST observations. More broadly, we conclude that the erosion of primary atmospheres typically does not preclude surface habitability, and frequently results in large surface water inventories due to the reduction of FeO by H2.
... -6 , 指 示 着 壳 源 特 征 (Mao et al., 1999). (Trail et al., 2011). Trail et al. (2011) (Dilles et al., 2015). ...
... (Trail et al., 2011). Trail et al. (2011) (Dilles et al., 2015). (Smythe and Brenan, 2016). ...
Article
Full-text available
Dajiacuo silver polymetallic deposit is the firstly and newly discovered deposit dominated by silver in the western Gangdese metallogenic belt. In order to find out the time of diagenesis and mineralization, genesis of ore-bearing rocks and metallogenic significance of the deposit, zircon U ⁃Pb chronology, trace elements and Hf isotopes, whole rock geochemistry and molybdenite Re-Os chronology of the ore-bearing (sub-volcanic) volcanic rocks (rhyolitic crystal tuff and rhyolitic porphyry) exposed in the mine area are analyzed in this paper. The results show that the ore-bearing (sub-volcanic) volcanic rocks were formed at 66.6-67.4 Ma, and the late molybdenite isotopic Re ⁃ Os model age was 61.0±0.8 Ma. Combined with the mineralization characteristics of ore-bearing geological bodies and the interpenetration relationship between quartz-pyrite and molybdenite veins and ore-bearing rhyolite porphyry etc., it is confirmed that Dajiacuo has two stages of mineralization dominated by the high silicified (sub-volcanic) volcanic rock type and skarn type silver-polymetallic mineralization in the early stage and the quartz vein-type silver-polymetallic mineralization in the late stage. It has a metallogenic time limited of 66.6-61.0 Ma, forming the epithermal cryogenic metallogenic system related to the post-volcanic hydrothermal period. The geochemical data of the (subvolcanic) volcanic rocks indicate that they belong to the high-K series to shoshonite series with metaluminous to peraluminous, enriched in LREE and large ion lithophile elements (K, Rb, Pb), and depleted in HREE and high field strength elements (Nb, Ta, Ti). The average temperature of zircon is 712 ℃, the εHf(t) values are strongly negative (-16.5 to -3.6) and the TDM C is 1.2- 2.1 Ga. The geochemical characteristics indicate that the ore-bearing rocks were typical S-type granite, which were generated from the partial melting of the Paleo-Mesoproterozoic Lhasa crystallization basement. Their characteristics are consistent with those of the ore-forming magmatic rock associated with the Ag ⁃Pb ⁃Zn deposits in the central Lhasa subterrane, but are obvious different with erupted I-type granite related copper polymetallic mineralization in the south Lhasa subterrane. It is revealed that the south Lhasa subterrane has the same metallogenic potential as the central Lhasa subterrane related to S-type granites and has great theoretical and practical significance to enrich the mineralization types of the south Lhasa subterrane and promote the further exploration of this type deposits. Key words: prospecting significance; petrogenesis; magmatic oxygen fugacity and water content; silver polymetallic deposit; Dajiacuo; Gangdese; Tibet; petrology.
... Ga) and Archaean (4.0-2.5 Ga) eons cover the time in which the main terrestrial reservoirs (core, mantle, crust, hydrosphere, and atmosphere) formed, and in which life originated on our planet. Weathering-resistant zircon crystals provide the main, and often only, window through which to study these key stages in Earth's evolution (e.g., Wilde et al., 2001;Mojzsis et al., 2001;Harrison et al., 2005;Trail et al., 2011;Bauer et al., 2020;Ackerson et al., 2021;Roberts et al., 2024). Zircons from the Jack Hills, Western Australia, ranging in age from ca. 3 Ga to ca. 4.4 Ga (Harrison and Schmitt, 2007;Turner et al., 2020), include the oldest material on Earth's surface. ...
... Zircons from the Jack Hills, Western Australia, ranging in age from ca. 3 Ga to ca. 4.4 Ga (Harrison and Schmitt, 2007;Turner et al., 2020), include the oldest material on Earth's surface. The chemical and isotopic compositions of magmatic zircons are used to derive first-order information about the conditions under which they formed, including magma temperatures (e.g., Watson et al., 2006;Crisp et al., 2023) and magma major and trace element compositions (e.g., Rubatto and Hermann, 2007;Trail et al., 2011Trail et al., , 2017Taylor et al., 2015;Berry, 2012, 2017;Trail, 2019, 2022;Ackerson et al., 2021;Streicher et al., 2023). ...
Article
Full-text available
Zircons are the oldest remaining witnesses of Earth’s near-surface processes, and conditions in the Hadean and Archaean crust are derived predominantly from their trace element and isotopic compositions. However, quantitative assessment of element and isotope partitioning between zircon and melt remains incomplete. We experimentally determined the effect of phosphorus (P) abundance on zircon-melt partition coefficients of Al (DAl), Li (DLi), and P (DP). Results indicate that P content has opposite effects on DAl and DLi, whereas the partitioning of P itself and other trace elements is independent of P abundance. Parametrization of our results yields new assessments of the aluminum saturation index (ASI) and P and Li contents of Hadean magmas. Magma ASI values are ∼0.5 lower than previously thought and consistently remain below 1 during the first ∼1 Ga of Earth evolution, suggesting involvement of only igneous protoliths. First peraluminous (ASI > 1) melts do not appear until ca. 3.6 Ga, supporting the hypothesis that a transition from a tectonic style dominated by vertical motion to horizontal tectonics accompanied by partial melting of sediments did not occur before that time. New calculated magma Li concentrations for young zircons are in much better agreement with the continental crust Li abundance. Average calculated Archaean and Hadean magma Li concentrations are unrealistically large (>1000 ppm), suggesting that Li in zircons formed before 2 Ga is not primary. Calculated magma P abundances are uniform (∼1900 ± 400 ppm) throughout Earth history, suggesting sufficient crustal P was available throughout the Hadean to support the origin of life.
... horizontal tectonics has played a critical balancing act in influencing and modifying the geochemical cycles of critical life-sustaining elements like N, C, S and P on early Earth. This helped in the evolution of the redox state of Earth's mantle and atmosphere (Trail et al., 2011) and supplied life essential elements to continental crust. Weathering of this evolved crust supplied all these elements to the ocean and likely was critical for the evolution of the biosphere (Flament et al., 2013;Greber et al., 2017). ...
Article
Full-text available
The formation of cratons was a fundamental process on Earth during the Archean. Cratons are characterized by a stable lithosphere consisting of felsic continental crust overlying a lithospheric mantle. The spatial and temporal relationship of these two distinct reservoirs can be reconstructed from mafic dyke swarms that are sourced from the cratonic mantle and intruded the Archean cratons over time. Trace element abundances of four dyke swarms that intruded the Singhbhum Craton between 2.8 Ga and 1.8 Ga combined with stable Mo and radiogenic Hf and Nd isotopes indicate that the crustal enrichment signature in the parental magma of the dykes was due to earlier enrichment of their respective mantle sources. The covariation of δ 98/95 Mo with mobile/immobile element ratio indicate that hydrous melts originating from recycled surface-derived materials led to metasomatism in the mantle source region of the mafic dykes. A redox-dependent multicomponent element (Mo, Ce) and isotope (δ 98/ 95 Mo, εHf , εNd) mixing model affirms that the metasomatism of the Singhbhum cratonic mantle was facilitated by reduced low-degree melts derived from recycled sediments and hydrated mafic crust. The mixing model further suggests that the cratonic lithosphere of the Singhbhum Craton was metasomatized in the Paleoarchean around 3.44 Ga, which is synchronous with the formation of Singhbhum granitoids. This is one of the oldest geochemical indications of mantle metasomatism on Earth. The radiogenic isotopes and δ 98/95 Mo reveal that even in the Paleoarchean, recycling of surface-derived reduced material at least locally by horizontal tectonics was active on Earth and this process played a critical role in the formation of stable cratons.
... This would allow observations of HD 63433 d to be used to place constraints on the redox state of the magma ocean. There is evidence that Earth's upper mantle has remained oxidised since at least 3.48 Ga, and was oxidised within 200 Myr of formation (Trail et al. 2011;Nicklas et al. 2018). Detection of SO 2 or CO 2 within the atmosphere of HD 63433 d would then imply a similar redox history to Earth's. ...
Preprint
Full-text available
Atmospheric energy transport is central to the cooling of primordial magma oceans. Theoretical studies of atmospheres on lava planets have assumed that convection is the only process involved in setting the atmospheric temperature structure. This significantly influences the ability for a magma ocean to cool. It has been suggested that convective stability in these atmospheres could preclude permanent magma oceans. We develop a new 1D radiative-convective model in order to investigate when the atmospheres overlying magma oceans are convectively stable. Using a coupled interior-atmosphere framework, we simulate the early evolution of two terrestrial-mass exoplanets: TRAPPIST-1 c and HD 63433 d. Our simulations suggest that the atmosphere of HD 63433 d exhibits deep isothermal layers which are convectively stable. However, it is able to maintain a permanent magma ocean and an atmosphere depleted in H2O. It is possible to maintain permanent magma oceans underneath atmospheres without convection. Absorption features of CO2 and SO2 within synthetic emission spectra are associated with mantle redox state, meaning that future observations of HD 63433 d may provide constraints on the geochemical properties of a magma ocean analogous with the early Earth. Simulations of TRAPPIST-1 c indicate that it is expected to have solidified within 100 Myr, outgassing a thick atmosphere in the process. Cool isothermal stratospheres generated by low molecular-weight atmospheres can mimic the emission of an atmosphere-less body. Future work should consider how atmospheric escape and chemistry modulates the lifetime of magma oceans, and the role of tidal heating in sustaining atmospheric convection
... Середньозважена температура кристалізації циркону, розрахована за вмістом титану, за методом Watson et al. (2006), без урахування активностей TiO 2 та SiO 2 і тиску становить 765 °С. Слід також зауважити, що досліджені циркони характеризуються незначною або помірною церієвою аномалією, що свідчить про порівняно відновні умови кристалізації (Thomas et al., 2003;Ballard et al., 2002;Trail et al., 2011Trail et al., , 2012Shumlyanskyy et al., 2017), за високого парціального тиску СО 2 . Згідно з цими даними, протолітом гнейсу слугувала магматична гірська порода. ...
Article
Full-text available
The geological structure of the Inhul Domain of the Ukrainian Shield is dominated by granites that develop after supracrustal rocks of the Inhul-Inhulets Group. The Group is subdivided, from the bottom to the top into the following Formations: Zelena Richka, Artemivka, Rodionivka, Kamyano-Kostuvate (and coeval Spasivka), and Roshchakhivka (and coeval Checheliivka). In this paper we report the results of the optical-microscopic study of the anatomy of crystals of accessory zircon from two-pyroxene plagioclase gneiss, and the results of U-Pb dating of zircon, hafnium isotope composition and trace element concentrations determination that were performed using the split-stream LA-ICP-MS technique. The results of multigrain monazite fraction U-Pb dating using the TIMS technique are also presented. It has been established that zircon has a complex internal texture with variable cores and thin overgrowths. The isotope age of the cores and overgrowths is the same — 2068 ± 22 Ma, while the age-corrected weighted average εHf value is –2.1±1.1. Based on the microelement composition, zircon from the studied gneisses can be defined as magmatic and epimagmatic, with a weighted average crystallization temperature of 765 ºС. The igneous rocks represented the protolith of the gneiss. The age of monazite crystallization (2017.2 ± 2.1 Ma) is a bit younger than the age of monazite from the main rock types of the Novoukrainka massif. The crystallization of monazite in the gneiss was related to the metasomatic processes caused by residual after Novoukrainka granite crystallization fluids.
... Reduced atmospheres are known to be an important source of organic matter as pointed out by the observation of Titan the largest satellite of Saturn (Tomasko and West, 2010;Waite et al., 2010) or by experiments realized by Miller about the reactivity of the early Earth atmosphere (Miller, 1953). However, if the question of the degree of oxidation of the early Earth atmosphere and so its composition is not completely solved, there is evidence that the upper mantle of the Earth was at the present redox state since 3.9 Ga (Delano, 2001) and probably 4.4 Ga (Trail, 2011) resulting in a relatively oxidant primitive atmosphere dominated by molecular nitrogen N 2 and carbon dioxide CO 2 (Kasting, 1993). The composition of the early Earth's atmosphere is an important parameter to consider for the production of organic matter. ...
Preprint
The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the early Earth.
... As oxygen fugacity decreases to the IW buffer and lower, chemical bonding of N to the silicate melt becomes important and solubility increases by orders of magnitude. Earth's mantle fO 2 has been close to the QFM buffer since around 3.8 Ga (Delano, 2001), and perhaps as far back as 4.35 Ga (Trail et al., 2011), but immediately after formation the mantle would have been highly reducing, at the IW buffer or lower (Wade and Wood, 2005). The idea that dissolution of N in an early reducing magma ocean led to significant incorpo-3 An approximate estimate of the equilibrium surface temperature for an H 2 -dominated atmosphere can be given by T s = T e (p s /p e ) R/cp where R is the specific gas constant, c p is the specific heat capacity at constant volume, T e is the emission temperature, p e is the emission pressure (around 0.2 bar for H 2 ) and p s is surface pressure. ...
Preprint
Nitrogen is the most common element in Earth's atmosphere and also appears to be present in significant amounts in the mantle. However, its long-term cycling between these two reservoirs remains poorly understood. Here a range of biotic and abiotic mechanisms are evaluated that could have caused nitrogen exchange between Earth's surface and interior over time. In the Archean, biological nitrogen fixation was likely strongly limited by nutrient and/or electron acceptor constraints. Abiotic fixation of dinitrogen becomes efficient in strongly reducing atmospheres, but only once temperatures exceed around 1000 K. Hence if atmospheric N2 levels really were as low as they are today 3.0 - 3.5 Ga, the bulk of Earth's mantle nitrogen must have been emplaced in the Hadean, most likely at a time when the surface was molten. The elevated atmospheric N content on Venus compared to Earth can be explained abiotically by a water loss redox pump mechanism, where oxygen liberated from H2O photolysis and subsequent H loss to space oxidises the mantle, causing enhanced outgassing of nitrogen. This mechanism has implications for understanding the partitioning of other Venusian volatiles and atmospheric evolution on exoplanets.
... Середньозважена температура кристалізації циркону, розрахована за вмістом титану, за методом Watson et al. (2006), без урахування активностей TiO 2 та SiO 2 і тиску становить 765 °С. Слід також зауважити, що досліджені циркони характеризуються незначною або помірною церієвою аномалією, що свідчить про порівняно відновні умови кристалізації (Thomas et al., 2003;Ballard et al., 2002;Trail et al., 2011Trail et al., , 2012Shumlyanskyy et al., 2017), за високого парціального тиску СО 2 . Згідно з цими даними, протолітом гнейсу слугувала магматична гірська порода. ...
Article
Full-text available
У геологічній будові Інгульського мегаблоку переважають гранітоїди, розвинуті по суперкрустальних утвореннях інгуло-інгулецької серії. У складі серії виділяють (знизу вгору): зеленоріченську, артемівську, родіонівську, кам’яно-костувацьку (віковий аналог спасівська) та рощахівську (віковий аналог чечеліївська) світи. У цій статті викладено результати оптико-мікроскопічного вивчення анатомії кристалів акцесорного циркону із двопіроксенового плагіогнейсу і результати датування циркону, визначення ізотопного складу гафнію та вмісту мікроелементів методом LA-ICP-MS, а також мультизернових наважок кристалів акцесорного монациту методом ТІМS. З’ясовано, що кристали циркону складні, представлені різнорідними ядрами, на які наростають тонкі оболонки. Ізотопний вік ядер та оболонок однаковий. Вік кристалів циркону становить 2068 ± 22 млн рр., а перераховане на цей вік середньозважене значення εHf становить –2,1 ± 1,1. За геохімічними ознаками циркони гнейсу належать до магматичних та епімагматичних, середньозважена температура їх кристалізації становить 765 °С. Згідно з отриманими даними, протолітом гнейсів слугувала магматична гірська порода. Час кристалізації монациту (2017,2 ± 2,1 млн рр. тому) є дещо молодшим за вік монацитів із основних типів гранітів Новоукраїнського масиву. Кристалізація монациту в плагіогнейсі обумовлена процесами метасоматозу, спричиненого флюїдами, що залишились після кристалізації гранітного розплаву.
... An oxidized upper mantle favors CO 2 over CH 4 and other reduced gases. Earth's mantle has been oxidized at present day levels since at least the early Archean (Delano, 2001), and possibly even since the Hadean (Trail et al., 2011). Oxidation of the mantle is thought to occur by disproportionation of FeO to Fe 2 O 3 -bearing perovskite and iron metal in the lower mantle during accretion and core formation. ...
Preprint
Earth's climate, mantle, and core interact over geologic timescales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.
... As to the sources of nucleobases, the early Earth's atmosphere was likely dominated by CO 2 , N 2 , SO 2 , and H 2 O [10]. In such a weakly reducing atmosphere, Miller-Urey type reactions are not very efficient at producing organics [11]. ...
Preprint
Prior to the origin of simple cellular life, the building blocks of RNA (nucleotides) had to form and polymerize in favourable environments on the early Earth. At this time, meteorites and interplanetary dust particles delivered organics such as nucleobases (the characteristic molecules of nucleotides) to warm little ponds whose wet-dry cycles promoted rapid polymerization. We build a comprehensive numerical model for the evolution of nucleobases in warm little ponds leading to the emergence of the first nucleotides and RNA. We couple Earth's early evolution with complex prebiotic chemistry in these environments. We find that RNA polymers must have emerged very quickly after the deposition of meteorites (< a few years). Their constituent nucleobases were primarily meteoritic in origin and not from interplanetary dust particles. Ponds appeared as continents rose out of the early global ocean but this increasing availability of "targets" for meteorites was offset by declining meteorite bombardment rates. Moreover, the rapid losses of nucleobases to pond seepage during wet periods, and to UV photodissociation during dry periods means that the synthesis of nucleotides and their polymerization into RNA occurred in just one to a few wet-dry cycles. Under these conditions, RNA polymers likely appeared prior to 4.17 billion years ago. Significance: There are two competing hypotheses for the site at which an RNA world emerged: hydrothermal vents in the deep ocean and warm little ponds. Because the former lacks wet and dry cycles, which are well known to promote polymerization (in this case, of nucleotides into RNA), we construct a comprehensive model for the origin of RNA in the latter sites. Our model advances the story and timeline of the RNA world by constraining the source of biomolecules, the environmental conditions, the timescales of reaction, and the emergence of first RNA polymers.
... Consequently, it is critical to understand the range of environmental conditions available on the early Earth for abiogenesis to proceed. Work over the past few decades has begun to constrain the environmental conditions that may have been available for abiogenesis, including but not limited to the past presence of liquid water, the availability of UV light at the surface, the mix of gases being outgassed to the atmosphere, the bulk pH of the ocean, and the conditions available at deep-sea hydrothermal vents (Bada et al. 1994;Farquhar et al. 2000;Mojzsis et al. 2001;Delano 2001;Holm and Charlou 2001;McCollom and Seewald 2007;Trail et al. 2011;Mulkidjanian et al. 2012;Beckstead et al. 2016;Sojo et al. 2016;Novoselov et al. 2017;Halevy and Bachan 2017). ...
Preprint
A key challenge in origin-of-life studies is understanding the environmental conditions on early Earth under which abiogenesis occurred. While some constraints do exist (e.g., zircon evidence for surface liquid water), relatively few constraints exist on the abundances of trace chemical species, which are relevant to assessing the plausibility and guiding the development of postulated prebiotic chemical pathways which depend on these species. In this work, we combine literature photochemistry models with simple equilibrium chemistry calculations to place constraints on the plausible range of concentrations of sulfidic anions (HS^-, HSO3_3^{-}, SO32_3^{2-}) available in surficial aquatic reservoirs on early Earth due to outgassing of SO2_2 and H2_2S and their dissolution into small shallow surface water reservoirs like lakes. We find that this mechanism could have supplied prebiotically relevant levels of SO2_2-derived anions, but not H2_2S-derived anions. Radiative transfer modelling suggests UV light would have remained abundant on the planet surface for all but the largest volcanic explosions. We apply our results to the case study of the proposed prebiotic reaction network of Patel et al. (2015), and discuss the implications for improving its prebiotic plausibility. In general, epochs of moderately high volcanism could have been especially conducive to cyanosulfidic prebiotic chemistry. Our work can be similarly applied to assess and improve the prebiotic plausibility of other postulated surficial prebiotic chemistries that are sensitive to sulfidic anions, and our methods adapted to study other atmospherically-derived trace species.
... The re-accretion of GIFs on the Earth after the solidification of magma ocean also has implications for the redox state of the Earth's earliest atmosphere. After core-mantle differentiation, oxygen fugacity of the Earth's uppermost mantle would have been defined by fayalite-magnetite-quartz (FMQ) buffer, in which H 2 O and CO 2 would dominate the magmatic volatile (Trail et al., 2011;Delano, 2001;Frost et al., 2008). ...
Preprint
The Earth was born in violence. Many giant collisions of protoplanets are thought to have occurred during the terrestrial planet formation. Here we investigated the giant impact stage by using a hybrid code that consistently deals with the orbital evolution of protoplanets around the Sun and the details of processes during giant impacts between two protoplanets. A significant amount of materials (up to several tens of percent of the total mass of the protoplanets) is ejected by giant impacts. We call these ejected fragments the giant-impact fragments (GIFs). In some of the erosive hit-and-run and high-velocity collisions, metallic iron is also ejected, which comes from the colliding protoplanets' cores. From ten numerical simulations for the giant impact stage, we found that the mass fraction of metallic iron in GIFs ranges from ~ 1wt% to ~ 25wt%. We also discussed the effects of the GIFs on the dynamical and geochemical characteristics of formed terrestrial planets. We found that the GIFs have the potential to solve the following dynamical and geochemical conflicts: (1) The Earth, currently in a near circular orbit, is likely to have had a highly eccentric orbit during the giant impact stage. The GIFs are large enough in total mass to lower the eccentricity of the Earth to its current value via their dynamical friction. (2) The concentrations of highly siderophile elements (HSEs) in the Earth's mantle are greater than what was predicted experimentally. Re-accretion of the iron-bearing GIFs onto the Earth can contribute to the excess of HSEs. In addition, the estimated amount of iron-bearing GIFs provides significant reducing agent that could transform primitive CO2-H2O atmosphere and ocean into more reducing H2-bearing atmosphere. Thus, GIFs are important for the origin of Earth's life and its early evolution.
... Unlike other REE 3+ , Eu and Ce are common elements, especially in zircon, which can be used to measure the fo 2 (Wen et al., 2020;Ballard et al., 2002;Trail et al., 2011;Trail et al., 2012) due to their variable valency (Ce: +3, +4; Eu: +2, +3). Previous studies reported that the ionic radii of VII Ce 3+ (1.07 Å) and VII Ca 2+ (1.06 Å) are similar (Shannon, 1976). ...
Article
Full-text available
The Xiaoqinling gold province, located in the southern margin of the North China Craton (NCC), is the second largest gold-enriched region in China. In this region, the Mesozoic Huashan (HS) and Wenyu (WY) plutons are the major magmatic intrusions coeval with gold mineralization, although they show contrasting characteristics in the distribution of gold. In this study, we use geochemical features of titanite determined by LA-ICP-MS and EPMA analyses and elemental mapping to decipher the mechanisms that led to the difference in gold enrichment related to the two plutons. Titanite from the Wenyu granitic pluton exhibits significantly higher (La/Sm)N, (La/Yb)N, ΣLREE/ΣHREE ratios, and ΣREE concentration and slightly higher (Gd/Yb)N values than those of the Huashan Pluton, suggesting that the Wenyu pluton might have experienced more complex magmatic evolution, widespread hydrothermal alteration, and higher silica activity in the melt than the Huashan pluton. The titanite grains from the Huashan pluton show higher (Nb/Ta)N and (Lu/Hf)N values and significantly lower Zr concentration than those of the Wenyu pluton. The titanite grains from the Wenyu pluton show higher vanadium and gallium concentrations and Fe/Al ratio than those of the Huashan pluton, indicating comparatively higher f o 2 . Furthermore, the titanite grains from Wenyu pluton indicate higher water content in the magma. In addition, magma mingling and magmatic hydrothermal fluids derived from the crust/mantle are critical sources for ore-forming materials. These results suggest that the Wenyu pluton is more conducive to gold migration and enrichment than the Huashan pluton.
... Methane, once popular in early climate models and origin-of-life scenarios (Miller and Urey, 1959), has mostly been taken off the Hadean table because of compelling evidence for early core formation (Kleine et al., 2009;Carlson et al., 2014). The removal of reducing power during core formation would have left the mantle too oxidizing to support appreciable abiotic CH4 production (Trail et al., 2011). Biological production had to wait until the Archean at approx. ...
Preprint
Understanding planetary habitability is one of the major challenges of the current scientific era, particularly given the discovery of a large and diverse terrestrial exoplanet population. Discerning the primary factors that contribute to planetary habitability may be extracted through a detailed examination of the terrestrial planets within the Solar System, most particularly Venus, Earth, and Mars, and the evolution of their interiors and atmospheres through time. Here, we provide a detailed description of the fundamental properties of these three planets, the effects of solar evolution, and the potential contributions of these various aspects toward driving their evolutionary pathways. We argue that evolution of Venus, Earth, and Mars provide essential templates from which a more comprehensive approach toward the study of planetary habitability may be derived.
... The fortuitous separation of mass dependent fractionation in 138 Ce/ 140 Ce or 136 One potential area of interest for future cerium isotope studies is the mineral zircon, 637 which is a unique geochemical archive. This includes potential information about conditions 638 on the Hadean Earth (e.g., Trail et al., 2011). Zircon is observed to strongly concentrate cerium 639 relative to other rare earth elements, mainly because of a strong affinity for Ce(IV) (e.g., Smythe 640 and Brenan, 2016). ...
Article
Equilibrium cerium isotope fractionations in cerium-bearing minerals and aqueous species are estimated using electronic structure calculations that include both nuclear volume and mass dependent effects. As with europium and uranium, the nuclear volume effect in redox reactions goes in the opposite direction from equilibrium mass-dependent fractionation for ¹⁴²Ce/¹⁴⁰Ce because of the larger nuclear charge radius of the ¹⁴²Ce nucleus. Mass-dependent effects dominate ¹³⁶Ce/¹⁴⁰Ce and ¹³⁸Ce/¹⁴⁰Ce fractionations because ¹³⁶Ce, ¹³⁸Ce, and ¹⁴⁰Ce share very similar nuclear charge radii. ¹⁴²Ce/¹⁴⁰Ce is predicted to be lower in most Ce(IV)-bearing species than in coexisting Ce(III)-bearing species, particularly at high temperatures. However, species with Ce:Zr substitution, such as zirconium-rich compositions along the stetindite-zircon (CeSiO4-ZrSiO4) solid solution series and a model Ce-subsituted baddeleyite (CeZr3O8), may show higher ¹⁴²Ce/¹⁴⁰Ce at ambient to low-T metamorphic temperatures because of higher effective force constants acting on the smaller, more snug substitution sites. Ce(III)P(V) charge-coupled substitution into zircon is likewise associated with high ¹⁴²Ce/¹⁴⁰Ce relative to other Ce(III) species. ¹³⁶Ce/¹⁴⁰Ce and ¹³⁸Ce/¹⁴⁰Ce fractionations will tend to favor more massive isotopes in Ce(IV)-bearing species, by 0.1-1.0‰ at 25ºC and 0.01-0.1‰ at 727ºC depending on the species present. The models predict ~0.3‰ higher ¹⁴²Ce/¹⁴⁰Ce in Ce(III)-bearing solution than coexisting Ce(IV)-solids at ambient temperatures, roughly agreeing with measurements. Zircon in equilibrium with typical silicate melts is predicted to be slightly enriched in ¹⁴⁰Ce relative to ¹⁴²Ce, ¹³⁸Ce, and ¹³⁶Ce. Supplementary calculations based on ¹⁴¹Pr-Mössbauer spectroscopy literature suggest somewhat (~1/3) smaller nuclear volume fractionation effects than the electronic structure models.
... ± 4.97), KG ( 17.73 ± 2.76,18.83 ± 3.59), and LG ( 26.41 ± 2.90, 22.88 ± 3.61), detail data is given in Table S6 in Supporting Information S1, and the calculation methods follow Trail et al. (2011). Notably, these values are consistently lower than the average log f O 2 of the fayalite-magnetite-quartz (FMQ) and nickel-nickel oxide buffers, which are often considered representative of the redox conditions in average continental crust (Mattioli & Wood, 1986, 1988; Figure 12b and Table S6 in Supporting Information S1). ...
Article
Full-text available
The present continental crust is characterized by a felsic upper crust and a mafic lower crust, resulting from significant geochemical differentiation over geological time. While various processes have been proposed to explain this differentiation, subduction zones remain pivotal regions for understanding the compositional evolution of continental crust. This study focuses on the South Altyn (SA) continental subduction‐collision belt in western China, a unique setting that experienced ultra‐deep (>300 km) continental subduction followed by multi‐stage exhumation. We present a comprehensive study of four granitoid suites from Tatelekebulake (TTLK) area in SA: biotite granite (BG), monzogranite (MG), K‐feldspar granite (KG), and leucogranite (LG). Comprehensive studies on petrology, geochemistry and zircon U‐Pb dating show that these granitoids formed at 494, 451, 414, and 418 Ma, respectively, and originated from protoliths with affinity to the subducted continental crust in SA. Phase equilibrium modeling suggests that BG formed at ∼800°C and 0.6 GPa, while the MG, KG, and LG formed by differentiation crystallization of the BG magma under progressively decreasing temperature and pressure conditions (750°C, 0.5 GPa; 740–700°C, 0.2 GPa; and 700–640°C, 0.1 GPa, respectively). These results, combined with previous studies, allow us to reconstruct the tectonic processes of continental exhumation and subsequent orogenic collapse in SA during the Early Paleozoic. Importantly, our findings reveal that magmatism derived from partial melting of subducted continental crust can promote the geochemical evolution of continental crust toward more felsic compositions, even in the absence of significant crustal growth or mantle‐derived magmatism. This study provides a valuable case for understanding the compositional evolution of continental crust in deep subduction zones and challenges conventional models that rely heavily on arc magmatism for crustal differentiation. Moreover, our results contribute to a broader understanding of crustal evolution processes in collisional orogens worldwide and highlight the importance of recycling and differentiation of subducted continental material in shaping crustal compositions.
... Zircon is an excellent recorder of fluid information in the deep Earth due to its exceeding durability (Hermann et al., 2013). Therefore, the oxygen fugacity ( fO 2 ) of the interfacial fluid can be calculated by zircon oxybarometer using the Ce partition coefficient anomaly of zircon, employing the following equations (Trail et al., 2011(Trail et al., , 2012: ...
Article
Full-text available
Fluids in subduction zones significantly influence element mobility, isotope fractionation, and mass transfer. However, unraveling the source, composition, and redox state of fluids in continental subduction zones poses a significant challenge. This study focuses on a granitic melt‐eclogite contact interface, along with adjacent granite and eclogite from the Sulu ultrahigh‐pressure metamorphic belt in East China. The interface exhibits complex mineral assemblages, enriched rare earth elements (REEs), and high field strength elements (HFSEs). Zircon grains from the interface show an age of ∼217 ± 9 Ma, slightly later than peak metamorphism, along with the presence of coesite inclusions. These findings suggest that the interfacial fluid likely formed from the mixing of granitic anatectic melt and aqueous fluid from the eclogite during the initial exhumation of the Sulu terrane. The interaction resulted in the eclogite acquiring substantial REEs and HFSEs, suggesting the interfacial fluid's effective element‐transporting capability and potential supercritical fluid properties. Zircon Ce anomaly and Fe³⁺/Fe²⁺ oxybarometer data indicate a highly oxidizing interfacial fluid, analogous to arc magmas in oxygen fugacity. This led to the preferential loss of isotopically heavier Cr from the eclogite during fluid‐eclogite interaction, evidenced by heavier Cr isotopic compositions in the interface (δ⁵³Cr = −0.04 to −0.05‰) compared to adjacent eclogite (δ⁵³Cr as low as −0.11‰). In summary, our results highlight the presence of strong oxidizing and element‐mobilizing fluids in continental subduction zones, offering insights into supercritical fluid recognition and the genesis of oxidizing arc magmas in subduction zones.
... The oxidation state of Earth's present day upper mantle is close to the quartz-fayalite-magnetite (QFM) buffer (Canil & O'Neill, 1996;Frost & McCammon, 2008), which results in oxidized volcanic gases such as H 2 O and CO 2 . Measurements of redox proxies dating back to at least 3,900 Ma (Delano, 2001), and possibly as far back as 4.3 Ga (Trail et al., 2011), are consistent with present day values, indicating little secular change in the mantle oxidation state through time, although recent measurements suggest a slightly lower mantle oxidation state during the early Archean of ∼QFM-0.5/1 (Aulbach & Stagno, 2016;Nicklas et al., 2019). ...
Article
Full-text available
Magma ocean crystallization models that track fO2 evolution can reproduce the D/H ratios of both the Earth and Mars without the need for exogenous processes. Fractional crystallization leads to compositional evolution of the bulk oxide components. Recent work suggests that metal‐saturated magma oceans may contain near‐present‐day Fe³⁺ concentrations. We model the fractional crystallization of Earth and Mars, including Fe²⁺ and Fe³⁺ as separate components. We calculate Fe³⁺ partition coefficients for lower mantle minerals and compare the results of fractional crystallization for both Earth and Mars. We calculate oxygen fugacity (fO2) at the surface as the systems evolve and compare them to constraints on the fO2 of the last magma ocean atmosphere from D/H ratios, both with and without metal saturation. For Earth, we find that Fe³⁺ likely behaves incompatibly in the lower mantle in order to match the D/H constraint for whole mantle models, but shallow magma ocean models also provide reasonable matches. Disproportionation in whole mantle magma oceans likely overpredicts the amount of Fe³⁺ and metal that form or require subsequent reduction to return to present‐day values. For Mars, we cannot match the D/H constraints on last fO2 unless the magma ocean begins with <50% of the predicted Fe³⁺, but better match the present day mantle redox. We show that Fe³⁺ partitioning has a measurable effect on magma ocean redox, and that it evolves throughout the magma ocean's lifetime. We highlight the need for additional experimental constraints on ferric iron mineral/melt partitioning and more thermodynamic data for the Fe‐disproportionation reaction.
... [76] On the other hand, graphite or graphene demonstrate conductive properties due to the overlap of HOMO and LUMO levels. [77] The physicochemical properties of carbon can be modified by doping it with elements present in the primordial Earth, including phosphorus (P), [78] boron (B), [79] sulfur (S), [80] nitrogen (N), [81] hydrogen (H), [82] and oxygen (O) [83] . These elements allow for π → π* transitions between carbon double bonds or n → π* transitions between carbon and other elements, resulting in adjustable HOMO and LUMO levels. ...
Article
Full-text available
Sunlight has long served as primary energy source on our planet, shaping the behavior of living organisms. Extensive research has been dedicated to unraveling the evolutionary pathways involved. When the formation of Earth atmosphere, it primarily consisted of small gas molecules, which are considered crucial for the emergence of life. Recent demonstrations have shown that these molecules can also be transformed into semiconductors, with the potential to harness solar energy and catalyze chemical reactions as photocatalysts. Building upon this research, this minireview focuses on the potential revolutionary impact of photocatalysis on Earth. Initially, it examines key reactions, such as the formation of prebiotic molecules and the oxygen evolution reaction via water oxidation. Additionally, various C−N complexes in photocatalysts are explored, showcasing their roles in catalyzing chemical reactions. The conclusion and outlook provide a potential pathway for the evolution of Earth, shedding light on the significance of metal‐free photocatalysts in development of Earth.
... The Levinthal 1.0 paradox asks how nature could have formed the needed sequencing of monomers in a linear chain of nucleosides or amino acids (primary structure) and have it wind up folding into the needed three-dimensional shape (secondary > tertiary structure) to become the needed specific enzyme [255,256]. ...
... Electrical discharge on CO, NH 3 , and water have also recently been shown to yield HCN [47]. Many of these experiments rely on gas mixtures that are more reducing than some recent estimates of the composition of the early atmosphere, which is currently thought to have been mildly reducing or neutral [48]. While HCN production under neutral conditions is certainly possible, as shown here and in previous studies [46], it might not have been enough to reach millimolar levels required in some prebiotic chemical schemes. ...
Article
Full-text available
Thioamide bonds are important intermediates in prebiotic chemistry. In cyanosulfidic prebiotic chemistry, they serve as crucial intermediates in the pathways that lead to the formation of many important biomolecules (e.g., amino acids). They can also serve as purine and pyrimidine precursors, the two classes of heterocycle employed in genetic molecules. Despite their importance, the formation of thioamide bonds from nitriles under prebiotic conditions has required large excesses of sulfide or compounds with unknown prebiotic sources. Here, we describe the thiol-catalyzed formation of thioamide bonds from nitriles. We show that the formation of the simplest of these compounds, thioformamide, forms readily in spark-discharge experiments from hydrogen cyanide, sulfide, and a methanethiol catalyst, suggesting potential accumulation on early Earth. Lastly, we demonstrate that thioformamide has a Gibbs energy of hydrolysis (ΔGr∘ΔGr\Delta G^{\circ }_r) comparable to other energy-currencies on early Earth such as pyrophosphate and thioester bonds. Overall, our findings imply that thioamides might have been abundant on early Earth and served a variety of functions during chemical evolution.
... On the other hand, diamond oxidized by the Fe 3+ released by the decomposition of bridgmanite forms a CO 2 -rich fluid, acting as a buffer for the oxygen fugacity of the upper mantle. This can explain why the oxygen fugacity of the upper mantle has remained stable for such a long time (Delano, 2001;Li and Lee, 2004;Trail et al., 2011;Rollinson et al., 2017). This model can also explain geophysical observations. ...
Article
The proto-atmosphere serves as a crucial starting point for the carbon cycle. Estimations based on atmospheric data from Mars and Venus suggest that Earth’s proto-atmosphere contained >110 bar of CO2 and >2.6 bar of nitrogen. The proto-atmosphere had over 1000 bar of water vapor during the magma ocean stage, assuming the proto-ocean had a volume of two oceans of water. During this stage both water and carbon dioxide were in a supercritical state at the magma-atmosphere interface. Intense serpentinization reactions occurred due to rock-water interaction, producing abundant hydrogen. Consequently, nitrogen is reduced to ammonia, and carbon dioxide to methane, forming carbonate simultaneously. The proto-atmosphere dominated by methane, ammonia, and hydrogen formed a significant amount of amino acids through lightning. This process is essential not only to the origin of life, but also to the early carbon-nitrogen cycle on Earth. By the Hadean eon, a large amount of CO2 was sequestered as carbonate and organic material. Subsequently, it mainly entered the deep mantle through mantle overturn or subduction. In the mantle transition zone, carbonate undergoes “Redox freezing”, where carbonate is reduced to diamond through oxidation of ferrous iron in the melt. In the lower mantle, Fe2+ undergoes disproportionation reactions, forming Fe3+ and metallic iron. Among these, Fe3+ mainly resides in bridgmanite, thereby increasing the oxygen fugacity of the lower mantle, while metallic iron falls to the Earth’s core. The distribution of carbon in the mantle is crucial for deep carbon cycling. The density curves of diamond and mantle peridotite melt intersect at the bottom of the mantle transition zone (about 660 km). This density crossover leads to the accumulation of diamond during the magma ocean stage. When materials such as subducting slabs enter the lower mantle, compensatory upwelling of lower mantle material occurs. Bridgmanite enters the upper mantle, decomposes, releasing Fe3+ ions and oxidizes diamond to carbonate, which under thermal disturbance from kimberlite and igneous carbonatites, moves upward. This carbonate layer may have caused significant topographic fluctuations at the 660 km boundary. Currently, diamond in this layer may still not have been completely oxidized to carbonate or carbon dioxide, serving as a redox buffering layer. This is a key factor in constraining deep carbon cycling. Subduction zones are important pathways for facilitating the cycling. Processes in the Earth’s deep carbon cycle significantly influence the carbon content of surface reservoirs. The fluctuations in atmospheric CO2 content since the Neogene are closely linked to the uplift of the Tibetan Plateau and the subduction of the western Pacific Plate. Around 60 million years ago, the closure of the Neo-Tethys Ocean led to subduction of the Indian passive margin. The massive sediments on the Indian margin carried down large amounts of carbonate and organic material into the mantle, and the resulting volcanism released large amounts of greenhouse gases such as CO2 and methane into the atmosphere. The subduction of the Neo-Tethys Ocean passive margin weakened at about 51 Ma, and subduction of the western Pacific began. The depth of the western Pacific Ocean generally exceeds the carbonate compensation depth, and the amount of carbonate carried by subducting oceanic crust is minimal. Consequently, the input of subducted carbonate decreased significantly, leading to a substantial reduction in CO2 emissions from volcanoes. Based on volcanic data from the past 12,000 years, the average rate of volcanic eruptions in subduction zones is estimated to be about 3 cubic kilometers per year. The weathering rate of volcanic ash is much higher than that of continental crust materials such as granite. The calcium, magnesium, and other ions provided by weathering of global volcanic ash are equivalent to the flux of global rivers into the oceans. The increase in volcanic ash and the decrease in CO2 emissions from subduction zones have led to a decrease in atmospheric CO2 levels, which is a key factor in the sustained global cooling since 51 million years ago.
... Further, zircon's ability to survive the processes of physical and chemical weathering, 55 transportation, and diagenesis makes it possible for Hadean zircons to survive in the present 56 (Froude et al., 1983;Harrison et al., 2007;Trail et al., 2011;Burnham and Berry, 2012). 57 ...
... Oxygen fugacity (fO 2 ) is a fundamental thermodynamic property governing the 36 speciation and behavior of multivalent elements (e.g., S, Ce, Eu, Fe, and V) during 37 magma evolution, which in turn controls their solubility, mobility, and compatibility 38 in silicate magmas (Brounce et however, have pointed out that these oxybarometers are only applicable in a limited 47 range of conditions. For example, the bulk Fe 2+ /Fe 3+ ratio of a glass is easily reset by 48 the subsequent metamorphism or alteration (Trail et al. 2011b), the Fe-Ti oxide 49 oxybarometer is only applicable rapidly quenched volcanic rocks (Loucks et al. 2018), 50 and the hornblende oxybarometer is only suitable for rocks emplaced deep in the crust 51 because hornblende is unstable in the shallow crust (Rutherford and Hill 1993). 52 Therefore, a more broadly applicable and robust oxybarometer is needed to unravel 53 the complex interplay between fO 2 , magmatic evolution, and metallogenesis through 54 geological time. ...
Article
Magmatic oxygen fugacity (fO2) is a fundamental property to understanding the long-term evolution of the Earth’s atmosphere and the formation of magmatic-hydrothermal mineral deposits. Classically, the magmatic fO2 is estimated using mineral chemistry, such as Fe-Ti oxides, zircon, and hornblende. These methods, however, are only valid within certain limits and/or require a significant amount of a priori knowledge. In this contribution, a new oxybarometer, constructed by data-driven machine learning algorithms using trace elements in zircon and their corresponding independent fO2 constraints, is provided. Seven different algorithms are initially trained and then validated on a data set that was never utilized in the training processes. Results suggest that the oxybarometer constructed by the extremely randomized trees model has the best performance, with the largest R2 value (0.91 ± 0.01), smallest RMSE (0.45 ± 0.03), and low propagated analytical error (~0.10 log units). Feature importance analysis demonstrates that U, Ti, Th, Ce, and Eu in zircon are the key trace elements that preserve fO2 information. This newly developed oxybarometer has been applied in diverse systems, including arc magmas and mid-ocean ridge basalts, fertile and barren porphyry systems, and global S-type detrital zircon, which provide fO2 constraints that are consistent with other independent methods, suggesting that it has wide applicability. To improve accessibility, the oxybarometer was developed into a software application aimed at enabling more consistent and reliable fO2 determinations in magmatic systems, promoting further research.
... In the present experimental study, however, we chose to use higher temperatures (1,250-1,300°C) since these provide a closer analogue of the thermal conditions of the Hadean and early Martian upper mantle (Herzberg et al., 2010;Sautter et al., 2016). Redox conditions expressed relative to the conventional quartzfayalite-magnetite f O2 buffer [ΔQFM log 10 f O2 (experiment)-log 10 f O2 (QFM) +1.8 to +4.6] established in our experiments are comparable to those characteristic of the Jack Hills zircon crystals in equilibrium with the mantle (Trail et al., 2011). In addition, higher temperatures should substantially increase the rates of serpentinite-basaltic melt reactions. ...
Article
Full-text available
Current theories suggest that the first continental crust on Earth, and possibly on other terrestrial planets, may have been produced early in their history by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients for this crustal formation remain elusive. To fill this gap, we conducted time-series experiments to investigate the reaction of serpentinite with variable proportions (from 0 to 87 wt%) of basaltic melt at temperatures of 1,250–1,300°C and pressures of 0.2–1.0 GPa (corresponding to lithostatic depths of ∼5–30 km). The experiments at 0.2 GPa reveal the formation of forsterite-rich olivine (Fo90–94) and chromite coexisting with silica-rich liquids (57–71 wt% SiO2). These melts share geochemical similarities with tonalite-trondhjemite-granodiorite rocks (TTG) identified in modern terrestrial oceanic mantle settings. By contrast, liquids formed at pressures of 1.0 GPa are poorer in silica (∼50 wt% SiO2). Our results suggest a new mechanism for the formation of the embryonic continental crust via aqueous fluid-assisted partial melting of peridotite at relatively low pressures (∼0.2 GPa). We hypothesize that such a mechanism of felsic crust formation may have been widespread on the early Earth and, possibly on Mars as well, before the onset of modern plate tectonics and just after solidification of the first ultramafic-mafic magma ocean and alteration of this primitive protocrust by seawater at depths of less than 10 km.
... On the other hand, diamond oxidized by the Fe 3+ released by the decomposition of bridgmanite forms a CO 2 -rich fluid, acting as a buffer for the oxygen fugacity of the upper mantle. This can explain why the oxygen fugacity of the upper mantle has remained stable for such a long time (Delano, 2001;Li and Lee, 2004;Trail et al., 2011;Rollinson et al., 2017). This model can also explain geophysical observations. ...
Article
原始大气是碳循环的重要起点。利用火星和金星的大气数据估算,地球原始大气含有>110个大气压的CO2和>2.6个大气压的氮气。在岩浆海阶段,地球获得水之后,原始大气有超过1000个大气压的水蒸气。此时气-岩界面,水和二氧化碳均处于超临界状态,与岩浆海表面发生强烈的蛇纹石化反应,形成大量的氢,将氮气还原为氨气;将二氧化碳还原为甲烷,同时形成碳酸盐。甲烷、氨气和氢主导的原始大气在闪电的作用下形成大量氨基酸,为生命起源奠定了基础,也控制了地球早期的碳-氮循环。到冥古宙,大量CO2以碳酸盐和有机物的形式被固定下来,之后主要通过地幔倒转或者板块俯冲进入深部地幔。碳酸盐在地幔转换带发生“还原固定”(Redox freezing),在熔体中被二价铁还原转化为金刚石。在下地幔,Fe2+发生歧化反应,形成Fe3+和铁单质。其中,Fe3+主要赋存在布里奇曼石中,因此并未提高下地幔的氧逸度;而金属铁由于密度大,倾向进入地核。 地幔中碳的分布对深部碳循环极其重要。金刚石与地幔橄榄岩熔体的密度曲线在地幔转换带底部(约660km)相交。这种密度反转导致岩浆海阶段金刚石聚集于此。当深俯冲板片等进入下地幔时,下地幔物质补偿性上涌。进入上地幔的布里奇曼石分解,释放Fe3+,将金刚石氧化为碳酸盐和二氧化碳,在热扰动下形成金伯利岩、火成碳酸岩等,造成了660km边界处“地形”强烈起伏。目前这一层中金刚石仍未完全被氧化为碳酸盐或二氧化碳,起到氧化还原缓冲层的作用。这是制约深部碳循环的关键因素。 俯冲带是深部碳循环的重要途径。地球深部碳循环过程会显著影响地表储库的碳含量。新生代以来大气CO2含量的波动与青藏高原的隆升和西太平洋板片的起始俯冲紧密联系。约60Ma前,新特提斯洋闭合,印度大陆被动陆缘开始俯冲。具有巨厚沉积的被动陆缘俯冲将大量碳酸盐和有机物带入地幔,形成的火山将大量的CO2和甲烷等温室气体释放到大气中。约51Ma前,新特提斯洋被动陆缘俯冲减弱,西太平洋俯冲开始。西太平洋水深普遍超过碳酸盐补偿深度,俯冲洋壳所携带的碳酸盐很少。因此,俯冲带碳酸盐输入大幅度减少,火山释放的CO2大幅度降低。根据过去12000年火山数据估算,俯冲带火山喷发的平均速率为约3立方千米/年。火山灰风化速率远高于花岗岩等大陆地壳物质。全球火山灰风化所提供的钙、镁等离子与全球河流入海通量相当。火山灰的增加和俯冲带二氧化碳排放的减少导致大气CO2含量降低,是51Ma年以来全球持续降温的关键。
Article
Atmospheric energy transport is central to the cooling of primordial magma oceans. Theoretical studies of atmospheres on lava planets have assumed that convection is the only process involved in setting the atmospheric temperature structure. This significantly influences the ability for a magma ocean to cool. It has been suggested that convective stability in these atmospheres could preclude permanent magma oceans. We develop a new 1D radiative-convective model in order to investigate when the atmospheres overlying magma oceans are convectively stable. Using a coupled interior-atmosphere framework, we simulate the early evolution of two terrestrial-mass exoplanets: TRAPPIST-1 c and HD 63433 d. Our simulations suggest that the atmosphere of HD 63433 d exhibits deep isothermal layers which are convectively stable. However, it is able to maintain a permanent magma ocean and an atmosphere depleted in H2O. It is possible to maintain permanent magma oceans underneath atmospheres without convection. Absorption features of CO2 and SO2 within synthetic emission spectra are associated with mantle redox state, meaning that future observations of HD 63433 d may provide constraints on the geochemical properties of a magma ocean analogous with the early Earth. Simulations of TRAPPIST-1 c indicate that it is expected to have solidified within 100 Myr outgassing a thick atmosphere in the process. Cool isothermal stratospheres generated by low molecular-weight atmospheres can mimic the emission of an atmosphere-less body. Future work should consider how atmospheric escape and chemistry modulates the lifetime of magma oceans, and the role of tidal heating in sustaining atmospheric convection.
Preprint
The early Earth's environment is controversial. Climatic estimates range from hot to glacial, and inferred marine pH spans strongly alkaline to acidic. Better understanding of early climate and ocean chemistry would improve our knowledge of the origin of life and its coevolution with the environment. Here, we use a geological carbon cycle model with ocean chemistry to calculate self-consistent histories of climate and ocean pH. Our carbon cycle model includes an empirically justified temperature and pH dependence of seafloor weathering, allowing the relative importance of continental and seafloor weathering to be evaluated. We find that the Archean climate was likely temperate (0-50 {\deg}C) due to the combined negative feedbacks of continental and seafloor weathering. Ocean pH evolves monotonically from 6.6 (+0.6,-0.4) (2{\sigma}) at 4.0 Ga to 7.0 (+0.7,-0.5) (2{\sigma}) at the Archean-Proterozoic boundary, and to 7.9 (+0.1,-0.2) (2{\sigma}) at the Proterozoic-Phanerozoic boundary. This evolution is driven by the secular decline of pCO2, which in turn is a consequence of increasing solar luminosity, but is moderated by carbonate alkalinity delivered from continental and seafloor weathering. Archean seafloor weathering may have been a comparable carbon sink to continental weathering, but is less dominant than previously assumed, and would not have induced global glaciation. We show how these conclusions are robust to a wide range of scenarios for continental growth, internal heat flow evolution and outgassing history, greenhouse gas abundances, and changes in the biotic enhancement of weathering.
Chapter
Abstract In parts 1 and 2, concepts related to reduction-oxidation chemistry in the silicate Earth are reviewed. Part 3 examines the available samples and analytical, theoretical, and computational methods available to place constraints on the redox state of Earth’s mantle. Part 4 discusses various igneous and metamorphic processes that drive changes in the redox state of silicate materials. Parts 5–7 examine variations in the redox state of today’s mantle with depth (5) and laterally (6), as well variations in these spatial components with time (7). Finally, we discuss the key challenges for the consideration of future studies. Key points • The redox state of Earth’s mantle is linked to the oxidation states of polyvalent elements and thus mineral phase stability, partial melting, and first-order chemical behaviors of life-supporting and economically important elements. • The redox state of Earth’s mantle is predominantly studied through direct ultramafic samples, partial melts of the mantle in the form of basaltic, picritic, and/or komatiitic lavas, and experimentally produced assemblages that mimic the mantle and partial melts. • There are a variety of measurements of these samples that can be made that can be combined with thermodynamic and/or computational models to place constraints on fO2. • There are a variety of redox processes that occur during petrogenesis related to plate tectonic processes and mantle convection on Earth. The least well understood of these processes are highlighted for the consideration of future research. • The redox state of the mantle is thought to vary with depth, laterally across the upper mantle today, and through time. Keywords Continental lithospheric mantle; Diamond; Flank method; Mantle xenoliths; Mantle-derived melts; Mössbauer; Multivalent element; Ophiolite; Oxybarometry; Oxygen fugacity; Peridotite; Redox budget; Synchrotron; Volatiles; XANES
Article
Active continental margins are the major sites of continental magmatism and associated hydrothermal ore deposits with a broad metal spectrum. Mineralization across active continental margins typically displays spatial zonation, with porphyry copper-(molybdenum-gold) deposits in volcanic arcs and tin- and tungsten-dominated mineralization occurring further inland in a back-arc setting. Particularly, tin and tungsten commonly form separate deposits in back-arc regions, even though both metals exhibit similar lithophile behavior. The key factors governing this metallogenic zonation remain unclear. The world-class South China metallogenic province hosts over 50% of the global tungsten resources, along with a significant amount of tin and copper resources distributed in different mineralization belts, making it an ideal location in which to study regional metal zonation. Here, we comprehensively integrate a very large dataset of the halogen volatile composition (F, Cl) and oxygen fugacity of granites related to tin, tungsten, and copper mineralization in the South China continental margin. Our compilation, derived from a substantial collection of zircon, apatite, mica, and whole-rock geochemistry data, suggests that lateral variations in granite magmatism (away from the trench), transitioning from chlorine-rich and oxic to fluorine-rich and reduced conditions, exert the primary control on copper versus tin-tungsten mineralization in the arc and back-arc regions, respectively. Differences in oxygen fugacity have a minor impact on the decoupling of tin and tungsten mineralization despite tin granites being universally reduced (ΔFMQ = -1.8 to -0.1, where FMQ is the fayalite-magnetite-quartz redox buffer) and tungsten granites having a broader redox range (ΔFMQ = -1.5 to +1.2). Instead, the disparity in fluorine content plays a more crucial role in controlling the spatial separation of tin and tungsten mineralization observed in the back-arc setting. Nd-Hf and He-Ar isotopic modeling calculations suggest that magmas linked to tin mineralization have a more pronounced involvement of F-rich mantle components compared to those associated with tungsten. Elevated fluorine (ca. 650-8000 ppm) in tin-associated magmas allowed an extreme degree of magmatic differentiation and delayed fluid exsolution due to high H2O solubility in F-rich silicate melts, ensuring Sn enrichment in highly evolved melts. In contrast, early fluid exsolution under less F-rich conditions (ca. 100-700 ppm) led to early tin loss from the melts, ultimately resulting in tungsten-dominant mineralization. This work emphasizes the combined influence of halogen composition and redox state on the regional mineralization zonation in world-class metallogenic provinces, providing vectors for global metal exploration in both past and currently active continental margins.
Article
Sunlight has long served as primary energy source on our planet, shaping the behavior of living organisms. Extensive research has been dedicated to unraveling the evolutionary pathways involved. When the formation of Earth atmosphere, it primarily consisted of small gas molecules, which are considered crucial for the emergence of life. Recent demonstrations have shown that these molecules can also be transformed into semiconductors, with the potential to harness solar energy and catalyze chemical reactions as photocatalysts. Building upon this research, this minireview focuses on the potential revolutionary impact of photocatalysis on Earth. Initially, it examines key reactions, such as the formation of prebiotic molecules and the oxygen evolution reaction via water oxidation. Additionally, various C‐N complexes in photocatalysts are explored, showcasing their roles in catalyzing chemical reactions. The conclusion and outlook provide a potential pathway for the evolution of Earth, shedding light on the significance of metal‐free photocatalysts in development of Earth.
Chapter
The composition of the Earth's ocean-atmosphere system is maintained over a geologic timescale via the outgassing of volatile elements from the Earth's mantle. Two major settings where volcanic outgassing occurs from the oceanic mantle are the mid-ocean ridges (MORs) and intraplate ocean islands (OIs). The outgassing flux of various volatiles such as water (H2O), carbon dioxide (CO2), sulfur (S), nitrogen (N), and halogens (e.g., chlorine, Cl) depend on their abundances, storage mechanisms, and fates during mantle partial melting and magma emplacement in the crust. This chapter synthesizes existing constraints on the major volatiles in the mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) and their mantle sources. We present and discuss various techniques and approaches used to gather concentration, speciation, and elemental and isotopic compositions of carbon (C), hydrogen (H), sulfur (S), nitrogen (N), and halogens in submarine glasses, melt inclusions, and mantle-derived gases. We summarize literature estimates of elemental concentrations and isotopic compositions of the volatiles for MORB and OIB source mantles, as well as the flux estimates of these volatiles from these mantle domains. To gain a process-level understanding of the extraction of the major volatiles from MORB and OIB source mantles, we also evaluate the storage mechanisms in the mantle and the fates and influence of different volatiles during mantle melting. We discuss the relative efficiencies of release via mantle melting and exsolution for each of the major volatiles and how the redox states of the mantle impact such processes. Finally, we provide a perspective for open questions and challenges in the knowledge of volatiles and volatile-involved melting for the MORB and OIB source mantles from the Hadean to the present.
Article
Full-text available
Heat delivered from accretionary impacts is thought to have led to extensive melting of early Earth’s silicate mantle, resulting in a deep magma ocean covering the surface. The mantle’s oxygen fugacity is thought to have increased over accretion and core formation due to increasingly oxidated impactors and lower mantle self-oxidation, but the influence of this on the solidus of deep primitive mantle materials has not been well constrained. Here we assess the effect of oxygen fugacity on conditions at the bottom of a magma ocean by experimentally determining the solidus of mantle pyrolite at pressures of 16–26 GPa at high oxygen fugacities. We find that over this pressure range, the solidus in experiments conducted under oxidizing conditions is at least 230–450 °C lower than in experiments conducted under more reducing conditions. Assuming constant magma ocean temperature, this would imply a magma ocean floor that deepens by about 60 km for each log unit increase in mantle oxygen fugacity. The strong influence of oxygen fugacity on mantle melting suggests that models of early Earth thermal evolution and geochemical models of core formation should be reassessed.
Article
Full-text available
In the southeastern Tibetan Plateau, region‐scale dextral strike‐slip shear zones, crucial for India‐Asia convergence, were investigated along the Dulongjiang shear zone near the Eastern Himalayan Syntaxis (EHS). Structural, kinematic, and geochronological data from Dulongjiang and Nabang regions in western Yunnan, China, reveal dextral strike‐slip shearing between 30 and 15 Ma. Various rocks were affected by moderate‐temperature shear deformation (∼450–550°C), inferred from microstructures and quartz CPO patterns, during dextral strike‐slip and exhumation of the shear zone. Combined with structures of pre‐, syn‐, and post‐shearing leucogranites, zircon U‐Pb dating indicates that the dextral shear along the shear zone began in the Early Oligocene (30–29 Ma) subsequent to the India‐Asia collision. Micas in mylonitic granites yield ⁴⁰Ar/³⁹Ar ages, suggesting that the principal dextral shear deformation occurred approximately between 18 and 15 Ma. The Dulongjiang shear zone is linked to the Parlung, Nabang shear zone, and Sagaing Fault, forming a regional Cenozoic dextral shear system around the EHS. The study, combined with tomographic anomalies beneath the India‐Asia collision zone, highlights distinct lithospheric‐scale evolution in southeastern and eastern Tibet. Continuous intracontinental strike‐slip shearing indicates a tectonic shift from Tibetan extension to block rotation around the EHS. From 30 to 15 Ma, slab tear, accompanied by clockwise rotation and dextral strike‐slip shearing, suggests a warmer geodynamic setting influenced by hot mantle flow associated with ongoing subduction of the Indian lithosphere. Oligocene‐Miocene dextral strike‐slip shearing around the EHS, linking southwards with the Sagaing Fault, may correspond to the rotation necessary for slab to bend, stretch, and eventually tear beneath the region.
Article
Full-text available
Vanadium exists in multiple valence states in silicate and oxide systems, namely V2+, V3+, V4+ and V5+. This special characteristic has been exploited in several ways to estimate the redox conditions of high-temperature planetary processes, such as partial melting and core formation. However, the use of V as a universal redox indicator (i.e. suitable for the entire range of oxygen fugacities found in the inner Solar System) requires precise knowledge of the partitioning of all of its several valence states. Here we report the results of a series of 1 atm (1300°C) and high-pressure (1-3 GPa, 1315-1450°C) experiments carried out over a range of redox conditions sufficiently large (from QFM-13.3 to QFM+11.4, where QFM is the quartz-fayalite-magnetite oxygen buffer) to constrain the full panoply of V chemical behaviour. Partition coefficients between the major upper-mantle minerals (olivine, clinopyroxene, orthopyroxene, spinel and garnet) and silicate melt were precisely measured with laser ablation inductively coupled plasma mass spectrometry for V and other selected heterovalent and homovalent elements (Al, P, Ca, Sc, Ti, Cr, Fe, Ga, Y, Zr and Nb). The particularly large range of redox conditions investigated here enabled concentrations of V2+ and V5+ to be constrained along with V3+ and V3+, allowing modelling of the change in bulk V partition coefficient with oxygen fugacity to be performed in a robust thermodynamic fashion. As in previous studies, we found a trend of increasing incompatibility from V3+ to V4+ to V5+ for all phases. Partition coefficients for V2+ can be either higher or lower than for V3+, depending on the phase. Additionally, we found evidence for changes in the oxidation state of Cr (Cr2+ ↔ Cr3+), Fe (Fe2+ ↔ Fe3+) and Ti (Ti3+ ↔ Ti4+). There is also indication that P may behave as a heterovalent element, occurring as a trivalent cation at very reducing conditions (P3+ ↔ P5+). For all other trace elements, the oxidation state remained constant. The data presented here can be used to implement methods of estimating the redox state of mantle and mantle-derived planetary samples from bulk-rock concentration and crystal/melt partitioning with only minor extrapolation and bias, allowing better precision and accuracy than previously possible. The method of estimating the redox conditions of basalt suites from bulk-rock V concentrations relative to homovalent elements with similar compatibility (e.g. V/Sc and V/Ga) was tested using databases for mid-ocean ridge, ocean island and island arc basalts. Within the many assumptions involved in forward trace-element modelling (e.g. degree and style of melting, source composition, constant partition coefficients), we show that the redox states of the source regions of these different types of terrestrial basalts are indistinguishable from each other, having relative oxygen fugacities at ∼QFM ± 1. The fact that arc magmas have higher Fe3+Fe2+ ratios than other types of basalts, making them appear to be more oxidized, may be due to late-stage processes rather than derivation from a more oxidized part of the asthenosphere. © The Author 2009. Published by Oxford University Press. All rights reserved.
Article
Full-text available
Compositional data for >400 pumice clasts, organized according to eruptive sequence, crystal content, and texture, provide new perspectives on eruption and pre-eruptive evolution of the >600 km3 of zoned rhyolitic magma ejected as the Bishop Tuff during formation of Long Valley caldera. Proportions and compositions of different pumice types are given for each ignimbrite package and for the intercalated plinian pumice-fall layers that erupted synchronously. Although withdrawal of the zoned magma was less systematic than previously realized, the overall sequence displays trends toward greater proportions of less evolved pumice, more crystals (0·5–24 wt %), and higher FeTi-oxide temperatures (714–818°C). No significant hiatus took place during the 6 day eruption of the Bishop Tuff, nearly all of which issued from an integrated, zoned, unitary reservoir. Shortly before eruption, however, the zoned melt-dominant portion of the chamber was invaded by batches of disparate lower-silica rhyolite magma, poorer in crystals than most of the resident magma but slightly hotter and richer in Ba, Sr, and Ti. Interaction with resident magma at the deepest levels tapped promoted growth of Ti-rich rims on quartz, Ba-rich rims on sanidine, and entrapment of near-rim melt inclusions relatively enriched in Ba and CO2. Varied amounts of mingling, even in higher parts of the chamber, led to the dark gray and swirly crystal-poor pumices sparsely present in all ash-flow packages. As shown by FeTi-oxide geothermometry, the zoned rhyolitic chamber was hottest where crystal-richest, rendering any model of solidification fronts at the walls or roof unlikely. The main compositional gradient (75–195 ppm Rb; 0·8–2·2 ppm Ta; 71–154 ppm Zr; 0·40–1·73% FeO*) existed in the melt, prior to crystallization of the phenocryst suite observed, which included zircon as much as 100 kyr older than the eruption. The compositions of crystals, though themselves largely unzoned, generally reflect magma temperature and the bulk compositional gradient, implying both that few crystals settled or were transported far and that the observed crystals contributed little to establishing that gradient. Upward increases in aqueous gas and dissolved water, combined with the adiabatic gradient (for the ∼ 5 km depth range tapped) and the roofward decline in liquidus temperature of the zoned melt, prevented significant crystallization against the roof, consistent with dominance of crystal-poor magma early in the eruption and lack of any roof-rind fragments among the Bishop ejecta, before or after onset of caldera collapse. A model of secular incremental zoning is advanced wherein numerous batches of crystal-poor melt were released from a mush zone (many kilometers thick) that floored the accumulating rhyolitic melt-rich body. Each batch rose to its own appropriate level in the melt-buoyancy gradient, which was self-sustaining against wholesale convective re-homogenization, while the thick mush zone below buffered it against disruption by the deeper (non-rhyolitic) recharge that augmented the mush zone and thermally sustained the whole magma chamber. Crystal–melt fractionation was the dominant zoning process, but it took place not principally in the shallow melt-rich body but mostly in the pluton-scale mush zone before and during batchwise melt extraction.
Article
Full-text available
The MgO content of komatiite lavas is an important measure of their formation temperature deep in the Archaean mantle, and forms the basis for models of the early Earth's thermal and chemical evolution. Estimates of the primary MgO content of komatiites are sensitive to the oxidation state-characterized by the oxygen fugacity (fO2)-assumed for the magmas during their crystallization. Despite two decades of study, however, fO2 is still poorly constrained for these lavas. Here I present an estimate of the fO2 for komatiite flows, based on the systematics of vanadium partitioning between komatiitic liquid and olivine in six well-characterized komatiite flows of varying ages. This approach shows that the oxidation state of several of these Archaean lava flows was the same as, or possibly more oxidizing than, that of present-day oceanic basalts. These results may require a downward revision of the mantle melting temperature estimated for many komatiites by about 50°C, and suggest that the mantle was unlikely to be much less oxidized during the Archaean era than at present.
Article
Full-text available
A new capsule technique has been developed to maintain a constant sample geometry at the high pressures and temperatures obtainable with a piston-cylinder apparatus. The capsule consists of a thick-walled transition metal cylinder, open on one end, and an inner noble metal sleeve. A noble metal lid welds to the capsule during cold pressurization, eliminating the need for arc welding to seal the loaded capsule. The high strength of the thick-walled capsules protects delicate samples such as single crystals during pressurization. At high temperature and pressure capsules shorten in the direction of compression but deform homogeneously. Pressure calibrations show that the pressure correction for the assembly is negligible. Ni powder can be used to buffer the f[sub O[sub 2]] in an aqueous charge at NNO for > 24 h at 1,000C. Applications of the capsule technique to hydrothermal experiments on single crystals are discussed. These experiments allow measurement of mineral solubilities, partition coefficients, and diffusion coefficients in minerals. Thick-walled capsules are also useful for experiments that require constant sample geometry, such as diffusion couples and textural studies.
Article
Full-text available
Analysis of δ18O in igneous zircons of known age traces the evolution of intracrustal recycling and crust-mantle interaction through time. This record is especially sensitive because oxygen isotope ratios of igneous rocks are strongly affected by incorporation of supracrustal materials into melts, which commonly have δ18O values higher than in primitive mantle magmas. This study summarizes data for δ18O in zircons that have been analyzed from 1,200 dated rocks ranging over 96% of the age of Earth. Uniformly primitive to mildly evolved magmatic δ18O values are found from the first half of Earth history, but much more varied values are seen for younger magmas. The similarity of values throughout the Archean, and comparison to the composition of the “modern” mantle indicate that δ18O of primitive mantle melts have remained constant (±0.2‰) for the past 4.4billion years. The range and variability of δ18O in all Archean zircon samples is subdued (δ18O(Zrc)=5–7.5‰) ranging from values in high temperature equilibrium with the mantle (5.3± 0.3‰) to slightly higher, more evolved compositions (6.5–7.5‰) including samples from: the Jack Hills (4.4–3.3Ga), the Beartooth Mountains (4.0–2.9Ga), Barberton (3.5–2.7Ga), the Superior and Slave Provinces (3.0 to 2.7Ga), and the Lewisian (2.7Ga). No zircons from the Archean have been analyzed with magmatic δ18O above 7.5‰. The mildly evolved, higher Archean values (6.5–7.5‰) are interpreted to result from exchange of protoliths with surface waters at low temperature followed by melting or contamination to create mildly elevated magmas that host the zircons. During the Proterozoic, the range of δ18O(Zrc) and the highest values gradually increased in a secular change that documents maturation of the crust. After ∼1.5Ga, high δ18O zircons (8 to >10‰) became common in many Proterozoic and Phanerozoic terranes reflecting δ18O(whole rock) values from 9 to over 12‰. The appearance of high δ18O magmas on Earth reflects nonuniformitarian changes in the composition of sediments, and rate and style of recycling of surface-derived material into magmas within the crust.
Article
Full-text available
Garnet is the most commonly used mineral in thermobarometry, whereas zircon is the most robust chronometer to date high-grade metamorphic rocks. To provide a basis for correlation of zircon and garnet growth, we determined experimentally the trace element partitioning between zircon, a hydrous granitic melt and garnet at 20 kbar and 800–1000 °C for P, Y, rare earth elements (REE), Zr, Hf, Th and U. In respect to melt, zircon preferentially incorporates all investigated elements apart from REE with atomic number lower than Sm. At this pressure and in the chosen composition, the distribution coefficient between zircon and melt (DZrn/Melt) for REE increases with increasing atomic number of the REE and with decreasing temperature. DYbZrn/Melt is ∼ 20 at 1000 °C, but more than an order of magnitude higher at 800 °C. The solubility of Zr in hydrous granitic melts buffered by zircon is about a factor of two lower at 20 kbar than what has been previously established for mid-crustal pressures. Large garnet produced in the experiments allowed determination of garnet/melt trace element partitioning (DGrt/Melt) at temperatures of 800–1000 °C, conditions relevant for partial melting of crustal rocks. There is a systematic increase in DREEGrt/Melt with decreasing temperature. Zircon contains significantly more heavy-REE than garnet at temperatures of 800–850 °C. Zircon/garnet partition coefficients of heavy-REE decrease with increasing temperature from DLuZrn/Melt of 12 at 800 °C to 1.4 at 1000 °C. Middle-REE partitioning is close to unity for the whole investigated temperature range. Different empirically determined zircon/garnet partition coefficients from granulites and ultra-high temperature granulites can potentially be explained by the experimentally determined change of partitioning as a function of temperature. These data can assist in establishing equilibrium between garnet and zircon zones in natural rocks, and in the construction of detailed pressure–temperature–time paths in high-grade metamorphic rocks.
Article
Full-text available
Partition coefficients (zircon/meltDM) for rare earth elements (REE) (La, Ce, Nd, Sm, Dy, Er and Yb) and other trace elements (Ba, Rb, B, Sr, Ti, Y and Nb) between zircon and melt have been calculated from secondary ion mass spectrometric (SIMS) analyses of zircon/melt inclusion pairs. The melt inclusion-mineral (MIM) technique shows that DREE increase in compatibility with increasing atomic number, similar to results of previous studies. However, DREE determined using the MIM technique are, in general, lower than previously reported values. Calculated DREE indicate that light REE with atomic numbers less than Sm are incompatible in zircon and become more incompatible with decreasing atomic number. This behavior is in contrast to most previously published results which indicate D > 1 and define a flat partitioning pattern for elements from La through Sm. The partition coefficients for the heavy REE determined using the MIM technique are lower than previously published results by factors of ≈15 to 20 but follow a similar trend. These differences are thought to reflect the effects of mineral and/or glass contaminants in samples from earlier studies which employed bulk analysis techniques.
Article
Full-text available
The concentrations of all rare earth elements (REE: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in silicate glass, apatite and zircon were measured by an ion microprobe method with a high mass resolving power of 9300 at 1% peak height. Observed contents of REE in apatite extracted from a dacite agree well with those measured by the isotope dilution-thermal ionization mass spectrometry (ID-TIMS) method within 30% error at 2σ. The contents of heavy REE in several zircons are consistent with those measured by ID-TIMS and instrumental neutron activation analysis (INAA), while the light REE abundances are significantly lower by ion microprobe than by the other methods. The discrepancy is partly due to the presence of 1–5-μm inclusions of apatites within zircon crystals. Secondary ion yields of REE observed in a silicate glass show a very similar trend to those in apatite and zircon. Since the chemical composition of the silicate glass is appreciably different from the apatite and zircon, relative secondary ion yields of REE are probably independent from matrix effect, which is the most important finding of this work. Calculated partition coefficients of REE between melt and apatite agree well with reported values while the coefficients between melt and zircon are discrepant from those in literature. The REE coefficients in zircon increase with increase of the ionic radius logarithmically, suggesting power law dependence of the coefficients.
Article
Full-text available
The titanium concentrations of 484 zircons with U-Pb ages of ˜1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zircons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413-433) without making corrections for reduced oxide activities (e.g., TiO2 or SiO2), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500° to 850°C, and are lower than either zircon saturation temperatures (for granitic rocks) or predicted crystallization temperatures of evolved melts (˜15% melt residue for mafic rocks). Temperatures average: 653 ± 124°C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 ± 111°C (261 zircons) for mafic rocks, and 758 ± 98°C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced a_{TiO2} or a_{SiO2}, variable pressure, deviations from Henry's Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystallization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with significantly lower crystallization temperature for the last 10-15% melt residue than that of the main rock. While some magmatic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti content from core to rim, or correlation with zoning, age, U content, Th/U ratio, or concordance in U-Pb age. Thus, it is likely that other variables, in addition to temperature and a_{TiO2}, are important in controlling the Ti content of zircon. The Ti contents of igneous zircons from different rock types worldwide overlap significantly. However, on a more restricted regional scale, apparent Ti-in-zircon temperatures correlate with whole-rock SiO2 and HfO2 for plutonic rocks of the Sierra Nevada batholith, averaging 750°C at 50 wt.% SiO2 and 600°C at 75 wt.%. Among felsic plutons in the Sierra, peraluminous granites average 610 ± 88°C, while metaluminous rocks average 694 ± 94°C. Detrital zircons from the Jack Hills, Western Australia with ages from 4.4 to 4.0 Ga have apparent temperatures of 717 ± 108°C, which are intermediate between values for felsic rocks and those for mafic rocks. Although some mafic zircons have higher Ti content, values for Early Archean detrital zircons from a proposed granitic provenance are similar to zircons from many mafic rocks, including anorthosites from the Adirondack Mts (709 ± 76°C). Furthermore, the Jack Hills zircon apparent Ti-temperatures are significantly higher than measured values for peraluminous granites (610 ± 88°C). Thus the Ti concentration in detrital zircons and apparent Ti-in-zircon temperatures are not sufficient to independently identify parent melt composition.
Article
Full-text available
The first approximately 600 million years of Earth history (the 'Hadean' eon) remain poorly understood, largely because there is no rock record dating from that era. Detrital Hadean igneous zircons from the Jack Hills, Western Australia, however, can potentially provide insights into the conditions extant on our planet at that time. Results of geochemical investigations using these ancient grains have been interpreted to suggest the presence of a hydrosphere and continental crust before 4 Gyr. An underexploited characteristic of the >4 Gyr zircons is their diverse assemblage of mineral inclusions. Here we present an examination of over 400 Hadean zircons from Jack Hills, which shows that some inclusion assemblages are conducive to thermobarometry. Our thermobarometric analyses of 4.02-4.19-Gyr-old inclusion-bearing zircons constrain their magmatic formation conditions to about 700 degrees C and 7 kbar. This result implies a near-surface heat flow of approximately 75 mW m(-2), about three to five times lower than estimates of Hadean global heat flow. As the only site of magmatism on modern Earth that is characterized by heat flow of about one-quarter of the global average is above subduction zones, we suggest that the magmas from which the Jack Hills Hadean zircons crystallized were formed largely in an underthrust environment, perhaps similar to modern convergent margins.
Article
Full-text available
The timescales and mechanisms for the formation and chemical differentiation of the planets can be quantified using the radioactive decay of short-lived isotopes. Of these, the (182)Hf-to-(182)W decay is ideally suited for dating core formation in planetary bodies. In an earlier study, the W isotope composition of the Earth's mantle was used to infer that core formation was late (> or = 60 million years after the beginning of the Solar System) and that accretion was a protracted process. The correct interpretation of Hf-W data depends, however, on accurate knowledge of the initial abundance of (182)Hf in the Solar System and the W isotope composition of chondritic meteorites. Here we report Hf-W data for carbonaceous and H chondrite meteorites that lead to timescales of accretion and core formation significantly different from those calculated previously. The revised ages for Vesta, Mars and Earth indicate rapid accretion, and show that the timescale for core formation decreases with decreasing size of the planet. We conclude that core formation in the terrestrial planets and the formation of the Moon must have occurred during the first approximately 30 million years of the life of the Solar System.
Article
Full-text available
We show that the escape of hydrogen from early Earth's atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have been more efficient than either exogenous delivery or synthesis in hydrothermal systems. The organic soup in the oceans and ponds on early Earth would have been a more favorable place for the origin of life than previously thought.
Article
Full-text available
Volatiles carried by magmas, either dissolved or exsolved, have a fundamental effect on a variety of geological phenomena, such as magma dynamics and the composition of the Earth's atmosphere. In particular, the redox state of volcanic gases emanating at the Earth's surface is widely believed to mirror that of the magma source, and is thought to have exerted a first-order control on the secular evolution of atmospheric oxygen. Oxygen fugacity (f(O2) estimated from lava or related gas chemistry, however, may vary by as much as one log unit, and the reason for such differences remains obscure. Here we use a coupled chemical-physical model of conduit flow to show that the redox state evolution of an ascending magma, and thus of its coexisting gas phase, is strongly dependent on both the composition and the amount of gas in the reservoir. Magmas with no sulphur show a systematic f(O2) increase during ascent, by as much as 2 log units. Magmas with sulphur show also a change of redox state during ascent, but the direction of change depends on the initial f(O2) in the reservoir. Our calculations closely reproduce the H2S/SO2 ratios of volcanic gases observed at convergent settings, yet the difference between f(O2) in the reservoir and that at the exit of the volcanic conduit may be as much as 1.5 log units. Thus, the redox state of erupted magmas is not necessarily a good proxy of the redox state of the gases they emit. Our findings may require re-evaluation of models aimed at quantifying the role of magmatic volatiles in geological processes.
Article
Ideas about atmospheric composition and climate on the early Earth have evolved considerably over the last 30 years, but many uncertainties still remain. It is generally agreed that the atmosphere contained little or no free oxygen initially and that oxygen concentrations increased markedly near 2.0 billion years ago, but the precise timing of and reasons for its rise remain unexplained. Likewise, it is usually conceded that the atmospheric greenhouse effect must have been higher in the past to offset reduced solar luminosity, but the levels of atmospheric carbon dioxide and other greenhouse gases required remain speculative. A better understanding of past atmospheric evolution is important to understanding the evolution of life and to predicting whether Earth-like planets might exist elsewhere in the galaxy.
Article
We investigated the incorporation of hydrogen into zircon at 1650 and 1550 degrees C, and pressures of 2.5 and 1.5 GPa under water-saturated conditions in a piston-cylinder apparatus. Concentrations were determined by polarized Fourier transform infrared spectroscopy using the zircon absorption coefficient epsilon(i) = 36241 cm(-2) per mol H(2)O/L and range from similar to 90 to 200 ppm H(2)O by weight. Crystals grown in the presence of Ti(4+) or Th(4+) do not differ significantly in their H(2)O content. We also synthesized zircons with various concentrations of Lu(2)O(3) and Al(2)O(3) to characterize changes in band positions and hydrogen concentrations related to coupled substitutions in zircon. Trivalent cations correlate in a nearly 1:1 molar fashion with hydrogen highlighting a potentially important coupled substitution in high water activity environments. Bands from undoped and doped zircons in the OH stretching region of the infrared spectrum show broad agreement when compared to spectra from natural samples. Heating experiments at 1 atm and 1000 degrees C produce a decrease in the integrated area; while some bands disappeared entirely, others are particularly stable with little decrease in integrated area after 128 h at 1000 degrees C. Results presented here help eliminate uncertainties that arose from Fourier transform infrared studies of natural zircons and provide further clarification for the origin of band positions in natural samples. In addition to the water activity of the crystallizing medium, the H(2)O content of natural grains will likely be significantly influenced by trivalent cation concentrations. In crustal zircons especially, trivalent atomic contents generally exceed those of phosphorus, meaning that hydrogen may be particularly important for trivalent cation charge compensation. An unanticipated result of this study was the development of a reasonably effective technique that produces relatively homogenous zircons doped with minor impurities. This technique could potentially be utilized in studies aimed at developing zircon standards, because it yields crystals that appear to be more homogenous than those produced by the flux method, and are generally free of inclusions.
Article
Ion microprobe analyses of δ18O in 4400–3900 Ma igneous zircons from the Jack Hills, Western Australia, provide a record of the oxygen isotope composition of magmas in the earliest Archean. We have employed a detailed analysis protocol aimed at correlating spatially related micro-volumes of zircon concordant in U/Pb age with δ18O and internal zoning. Simultaneous analysis of 18O and 16O with dual Faraday cup detectors, combined with frequent standardization, has yielded data with improved accuracy and precision over prior studies, and resulted in a narrower range of what is interpreted as magmatic δ18O in > 3900 Ma zircons. Preserved magmatic δ18O values from individual zircons (Zrc) range from 5.3‰ to 7.3‰ (VSMOW), and increasingly deviate from the mantle range of 5.3 ± 0.3‰ as zircons decrease in age from 4400 to 4200 Ma. Elevated δ18O (Zrc) values up to 6.5‰ occur as early as 4325 Ma, which suggests that evolved rocks were incorporated into magmas within ∼230 Ma of Earth's accretion. Values of magmatic δ18O (Zrc) as high as 7.3‰ are recorded in zircons by 4200 Ma, and are common thereafter. The protoliths of the magmas these zircons crystallized in were altered by low temperature interaction with liquid water near Earth’s surface. These results provide the strongest evidence yet for the existence of liquid water oceans and supracrustal rocks by approximately 4200 Ma, and possibly as early as 4325 Ma. The range of magmatic δ18O values in the 4400–3900 Ma zircons is indistinguishable from Archean igneous zircons, suggesting similar magmatic processes occurred over the first two billion years of recorded Earth history. Zircons with sub-solidus alteration histories, identified by the presence of disturbed internal zoning patterns, record δ18O values both below (4.6‰) and above (10.3‰) the observed range for primary magmatic zircon, and are unreliable indicators of Early Archean magma chemistry.
Article
Diffusion rates for three rare-earth elements (REEs: Sm, Dy, Yb) have been measured in synthetic and natural zircon. REE-phosphate powders were used as the source of diffusant, with Rutherford backscattering spectrometry (RBS) used to measure REE depth profiles.Over the temperature range 1150–1400°C, the following Arrhenius relations were obtained (diffusion coefficients in m2 s−1 ): Results for synthetic: and natural zircons were quite similar, and no evidence of significant anisotropy was observed when comparing transport normal and parallel to the c-axis.The data show a systematic increase in diffusivity with decreasing ionic radius (i.e. faster diffusion rates for the heavier REEs). Given these trends the diffusion rates of Lu and La should differ by over two orders of magnitude. Diffusive fractionation is unlikely in the Sm-Nd system because differences in diffusivities are relatively small, but may be a factor in the Lu-Hf system given the much slower diffusion rates of tetravalent cations.The very slow diffusion rates measured for the REEs suggest that they are essentially immobile under most geologic conditions, thus permitting the preservation of fine-scale chemical zoning and isotopic signatures of inherited cores.
Article
The oxygen-isotope composition of the Earth's upper mantle is an important reference for understanding mantle and crust geochemical cycles. Olivine is the most commonly used mineral for determining the influence of crustal processes on the oxygen-isotope ratio (delta(18)O) of primitive rocks, however it is an uncommon mineral in continental crust and readily alters at or near Earth's surface. Here we report the first measurements of oxygen-isotope ratios in zircon from oceanic crust exposed at a mid-ocean ridge. Measurements of delta(18)O and trace elements were made by ion microprobe on zircon in polished rock chips of gabbro and veins in serpentinized peridotite drilled from the Mid-Atlantic Ridge. The zircon grains contain both oscillatory and sector growth zoning, features characteristic of magmatic zircon. Values of delta(18)O (zircon) = 5.3 +/- 0.8 parts per thousand (2 st. dev., n = 68) for the population are consistent with the interpretation that these grains are igneous in origin and formed in high-temperature isotopic equilibrium with mantle oxygen. The delta(18)O values demonstrate that zircon in oceanic crust preserves primitive delta(18)O in spite of sub-solidus alteration of the whole rock. The fact that the primitive delta(18)O (zircon) values fall in a narrow range (5.3 +/- 0.8 parts per thousand) strengthens the use of oxygen isotopes in zircon as a tracer to identify processes of exchange in a wide range of modem and ancient crustal environments, including subducted oceanic crust (eclogite), and also in the oldest known pieces of Earth, >3900 million-year-old detrital zircon grains from Western Australia.
Article
The trace element compositions of Hadean zircons have been used in two ways to argue for the existence of Hadean continental crust. One argument is based on low crystallization temperatures of Hadean zircons that have been determined using a novel geothermometer based on the Ti content of zircons in equilibrium with rutile. The second argument is based on using the trace element abundances in zircons to calculate their parental melt compositions, especially the rare earth elements. Here we demonstrate that zircons that grow from a melt formed by basalt differentiation at modern mid-ocean ridges cannot be unambiguously distinguished from Hadean zircons on either of these grounds. Thus, we conclude that the trace element compositions of Hadean zircons are permissive of models that do not include the generation of continental crust in the Hadean.
Article
Oxygen thermobarometry measurements on spinel peridotite rocks indicate that the oxygen fugacity at the top of the upper mantle falls within ±2 log units of the fayalite-magnetite-quartz (FMQ) oxygen buffer. Measurements on garnet peridotites from cratonic lithosphere reveal a general decrease in fo2 with depth, which appears to result principally from the effect of pressure on the controlling Fe3+/Fe2+ equilibria. Modeling of experimental data indicates that at approximately 8 GPa, mantle fo2 will be 5 log units below FMQ and at a level where Ni-Fe metal becomes stable. Fe-Ni alloy and an Fe2O3-garnet component will be formed as a result of the disproportionation of FeO, which is experimentally demonstrated through observations of high Fe3+/ΣFe ratios in minerals in equilibrium with metallic Fe. In the lower mantle, the favorable coupled substitution of Al and Fe3+ into (Fe,Mg)SiO3 perovskite results in very high perovskite Fe3+/ΣFe ratios in equilibrium with metallic Fe. As a result, the lower mantle sh...
Article
Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y+REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720°C for zircon rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage in its evolution. There is also no compelling evidence for punctuated heat±chemical influxes during the intermediate stages of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir by—or zircon entrainment in—a less evolved melt from the one in which the zircons had previously resided. KeywordsZircon–Ti-in-zircon thermometry–Trace elements–Magma chambers–Bishop Tuff
Article
Zircons from the Apollo 14 polymict breccias 14304, 14305, and 14321 crystallized from highly incompatible-trace-element enriched sources over an extended period of early lunar history from 4.4 to 4.0 Ga. These zircons contain the least radiogenic 176Hf/177Hf yet observed in lunar samples, consistent with their source magmas containing a component (KREEP) that evolved during chemical differentiation of a global lunar magma ocean. The initial 176Hf/177Hf isotopic compositions of the zircons as a function of their crystallization ages suggest separation of the KREEP source, and thus crystallization of the lunar magma ocean, by ~ 4.48 Ga to no later than 4.38 Ga.
Article
The oxygen fugacity of the Dar al Gani 476 martian basalt is determined to be quartz-fayalite-magnetite (QFM) −2.3 ± 0.4 through analysis of olivine, low-Ca pyroxene, and Cr-spinel and is in good agreement with revised results from Fe-Ti oxides that yield QFM −2.5 ± 0.7. This estimate falls within the range of oxygen fugacity for the other martian basalts, QFM −3 to QFM −1. Oxygen fugacity in martian basalts correlates with 87Sr/86Sr, 143Nd/144Nd, and La/Yb ratios, indicating that the mantle source of the basalts is reduced and that assimilation of crust-like material controls the oxygen fugacity. This allows constraints to be placed on the oxidation state of the martian mantle and on the nature of assimilated crustal material. The assimilated material may be the product of early and extensive hydrothermal alteration of the martian crust, or it may be amphibole- or phlogopite-bearing basaltic rock within the crust. In either case, water may play a significant role in the oxidation of basaltic magmas on Mars, although it may be secondary to assimilation of ferric iron-rich material.
Article
Hydrothermal experiments in the temperature range 750–1020°C have defined the saturation behavior of zircon in crustal anatectic melts as a function of both temperature and composition. The results provide a model of zircon solubility given by: In DZrzircon/melt= −3.80−[0.85(M−1)]+12900/T where DZrzircon/melt is the concentration ratio of Zr in the stoichiometric zircon to that in the melt, T is the absolute temperature, and M is the cation ratio (Na + K + 2Ca)/(Al · Si). This solubility model is based principally upon experiments at 860°, 930°, and 1020°C, but has also been confirmed at temperatures up to 1500°C for M = 1.3. The lowest temperature experiments (750° and 800°C) yielded relatively imprecise, low solubilities, but the measured values (with assigned errors) are nevertheless in agreement with the predictions of the model.For M = 1.3 (a normal peraluminous granite), these results predict zircon solubilities ranging from ∼ 100 ppm dissolved Zr at 750°C to 1330 ppm at 1020°C. Thus, in view of the substantial range of bulk Zr concentrations observed in crustal granitoids (∼ 50–350 ppm), it is clear that anatectic magmas can show contrasting behavior toward zircon in the source rock. Those melts containing insufficient Zr for saturation in zircon during melting can have achieved that condition only by consuming all zircon in the source. On the other hand, melts with higher Zr contents (appropriate to saturation in zircon) must be regarded as incapable of dissolving additional zircon, whether it be located in the residual rocks or as crystals entrained in the departing melt fraction. This latter possibility is particularly interesting, inasmuch as the inability of a melt to consume zircon means that critical geochemical “indicators” contained in the undissolved zircon (e.g. heavy rare earths, Hf, U, Th, and radiogenic Pb) can equilibrate with the contacting melt only by solid-state diffusion, which may be slow relative to the time scale of the melting event.
Article
The origins of >3900 Ma detrital zircons from Western Australia are controversial, in part due to their complexity and long geologic histories. Conflicting interpretations for the genesis of these zircons propose magmatic, hydrothermal, or metamorphic origins. To test the hypothesis that these zircons preserve magmatic compositions, trace elements [rare earth elements (REE), Y, P, Th, U] were analyzed by ion microprobe from a suite of >3900 Ma zircons from Jack Hills, Western Australia, and include some of the oldest detrital zircons known (4400–4300 Ma). The same ∼20 μm domains previously characterized for U/Pb age, oxygen isotope composition (δ18O), and cathodoluminescence (CL) zoning were specifically targeted for analysis. The zircons are classified into two types based on the light-REE (LREE) composition of the domain analyzed. Zircons with Type 1 domains form the largest group (37 of 42), consisting of grains that preserve evolved REE compositions typical of igneous zircon from crustal rocks. Grains with Type 1 domains display a wide range of CL zoning patterns, yield nearly concordant U/Pb ages from 4400 to 3900 Ma, and preserve a narrow range of δ18O values from 4.7‰ to 7.3‰ that overlap or are slightly elevated relative to mantle oxygen isotope composition. Type 1 domains are interpreted to preserve magmatic compositions. Type 2 domains occur in six zircons that contain spots with enriched light-REE (LREE) compositions, here defined as having chondrite normalized values of LaN > 1 and PrN > 10. A subset of analyses in Type 2 domains appear to result from incorporation of sub-surface mineral inclusions in the analysis volume, as evidenced by positively correlated secondary ion beam intensities for LREE, P, and Y, which are anti-correlated to Si, although not all Type 2 analyses show these features. The LREE enrichment also occurs in areas with discordant U/Pb ages and/or high Th/U ratios, and is apparently associated with past or present radiation damage. The enrichment is not attributed to hydrothermal alteration, however, as oxygen isotope ratios in Type 2 domains overlap with magmatic values of Type 1 domains, and do not appear re-set as might be expected from dissolution or ion-exchange processes operating at variable temperatures. Thus, REE compositions in Type 2 domains where mineral inclusions are not suspected are best interpreted to result from localized enrichment of LREE in areas with past or present radiation damage, and with a very low fluid/rock ratio. Correlated in situ analyses allow magmatic compositions in these complex zircons to be distinguished from the effects of secondary processes. These results are additional evidence for preservation of magmatic compositions in Jack Hills zircons, and demonstrate the benefits of detailed imaging in studies of complicated detrital zircons of unknown origin. The data reported here support previous interpretations that the majority of >3900 Ma zircons from the Jack Hills have an origin in evolved granitic melts, and are evidence for the existence of continental crust very early in Earth’s history.
Article
Single grains of zircon can contain zones indicating several generations of crystal growth, each of which should reflect the chemical and physical conditions occurring at the time of its formation. Trace element analyses have been made of large zircon crystals from rocks of alkaline affinities by ion microprobe. The chondrite-normalised rare earth element (REE) concentrations increase rapidly from La to Lu, as would be expected from the decrease in ionic radius and consequent easier substitution into the Zr site within the zircon lattice. Lanthanum, praseodymium, and neodymium are considerably lower than values observed in bulk analyses of zircon. The partition coefficients for the light rare earth elements (LREEs), between zircon and melt or whole rock, must therefore be significantly lower than those calculated using bulk analyses. Cerium is enriched relative to neighbouring REEs due to the presence of Ce4+. Estimates of partition coefficients of Ce3+ and Ce4+ between zircon and melt demonstrate that although the Ce anomalies are large the ratio is very small (less than 3 × 10−3). The size of the Ce anomaly is variable and should be capable of providing information on oxygen fugacity changes.
Article
Zircon and rutile are common accessory minerals whose essential structural constituents, Zr, Ti, and Si can replace one another to a limited extent. Here we present the combined results of high pressure–temperature experiments and analyses of natural zircons and rutile crystals that reveal systematic changes with temperature in the uptake of Ti in zircon and Zr in rutile. Detailed calibrations of the temperature dependencies are presented as two geothermometers—Ti content of zircon and Zr content of rutile—that may find wide application in crustal petrology. Synthetic zircons were crystallized in the presence of rutile at 1–2 GPa and 1,025–1,450°C from both silicate melts and hydrothermal solutions, and the resulting crystals were analyzed for Ti by electron microprobe (EMP). To augment and extend the experimental results, zircons hosted by five natural rocks of well-constrained but diverse origin (0.7–3 GPa; 580–1,070°C) were analyzed for Ti, in most cases by ion microprobe (IMP). The combined experimental and natural results define a log-linear dependence of equilibrium Ti content (expressed in ppm by weight) upon reciprocal temperature: \log ({\text{Ti}}_{{{\text{zircon}}}}) = (6.01 \pm 0.03) - \frac{{5080 \pm 30}}{{T\;(\hbox{K})}}.
Article
The oxygen fugacity values of lunar samples were measured directly with an improved solid-electrolyte oxygen cell between 1000 and 1200 C with an accuracy mostly better than 0.2 log f(02) unit. The bulk rock f(02) values of basaltic igneous rocks 12009, 12053, 15058, and 15595 ranged from 10 to -15.4 power to 10 to the -15.7 power at 1000 C and from 10 to the -12.3 power to 10 to the -12.8 power at 1200 C. Those of microbreccia 14321 also fell in this range, but the change of oxygen fugacity with temperature was irregular in the first heating cycle in comparison to the smooth changes observed with the basaltic igneous rocks. Two different samples of rock 14310 also showed similar f(02) values below 1170 C, but exhibited irreversible sudden rise in f(02) at this temperature for reasons yet to be determined. The data on the phenocryst olivine and the groundmass of basalt 12009 do not conclusively indicate progressive reduction of the lunar magma during cooling.
Article
Komatiites are volcanic rocks mainly of Archaean age that formed by unusually high degrees of melting of mantle peridotite. Their origin is controversial and has been attributed to either anhydrous melting of anomalously hot mantle or hydrous melting at temperatures only modestly greater than those found today. Here we determine the original Fe(3+)/SigmaFe ratio of 2.7-Gyr-old komatiitic magma from Belingwe, Zimbabwe, preserved as melt inclusions in olivine, to be 0.10 +/- 0.02, using iron K-edge X-ray absorption near-edge structure spectroscopy. This value is consistent with near-anhydrous melting of a source with a similar oxidation state to the source of present-day mid-ocean-ridge basalt. Furthermore, this low Fe(3+)/SigmaFe value, together with a water content of only 0.2-0.3 wt% (ref. 7), excludes the possibility that the trapped melt contained significantly more water that was subsequently lost from the inclusions by reduction to H(2) and diffusion. Loss of only 1.5 wt% water by this mechanism would have resulted in complete oxidation of iron (that is, the Fe(3+)/SigmaFe ratio would be approximately 1). There is also no petrographic evidence for the loss of molecular water. Our results support the identification of the Belingwe komatiite as a product of high mantle temperatures ( approximately 1,700 degrees C), rather than melting under hydrous conditions (3-5-wt% water), confirming the existence of anomalously hot mantle in the Archaean era.
Article
Ideas about atmospheric composition and climate on the early Earth have evolved considerably over the last 30 years, but many uncertainties still remain. It is generally agreed that the atmosphere contained little or no free oxygen initially and that oxygen concentrations increased markedly near 2.0 billion years ago, but the precise timing of and reasons for its rise remain unexplained. Likewise, it is usually conceded that the atmospheric greenhouse effect must have been higher in the past to offset reduced solar luminosity, but the levels of atmospheric carbon dioxide and other greenhouse gases required remain speculative. A better understanding of past atmospheric evolution is important to understanding the evolution of life and to predicting whether Earth-like planets might exist elsewhere in the galaxy.
Article
The history of the oxidation state in the Earth's mantle has been constrained using (a) the whole-rock abundances of Cr and V in ancient volcanics, and (b) the composition of Cr-rich spinels in ancient volcanics. Results indicate that the Earth's mantle has been at-or-near its current oxidation state (+/- 0.5 log-unit fO2) since at least 3600 Ma, and probably since at least 3960 Ma. Volatiles released into the Earth's atmosphere by high-temperature (T > or = 1300 K) volcanism during this time have been dominated by H2O, CO2, and SO2. This blend of volatiles is known to provide smaller yields of prebiotic, organic molecules by atmospheric and surface processes than gas mixtures containing higher concentrations of reduced species such as H2, CO, and H2S (e.g., Miller, 1998; Zolotov and Shock, 2000). The results discussed in this article independently support the conclusion of Canil (1997, 1999). If the atmosphere was reducing (e.g., CH4, H2, H2S, NH3, CO) at any time during the last approximately 3900 Ma, high-temperature volcanic outgassing was not the cause of it.
Article
Ancient zircons from Western Australia's Jack Hills preserve a record of conditions that prevailed on Earth not long after its formation. Widely considered to have been a uniquely violent period geodynamically, the Hadean Eon [4.5 to 4.0 billion years ago (Ga)] has recently been interpreted by some as far more benign—possibly even characterized by oceans like those of the present day. Knowledge of the crystallization temperatures of the Hadean zircons is key to this debate. A thermometer based on titanium content revealed that these zircons cluster strongly at ∼700°C, which is indistinguishable from temperatures of granitoid zircon growth today and strongly suggests a regulated mechanism producing zircon-bearing rocks during the Hadean. The temperatures substantiate the existence of wet, minimum-melting conditions within 200 million years of solar system formation. They further suggest that Earth had settled into a pattern of crust formation, erosion, and sediment recycling as early as 4.35 Ga.