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The Li concentrations in natural zircons vary by over six orders of magnitude, and Li intra-zoning within zircon has been used to model temperature–time histories in the crust, where the inputs to these T–t models presume some initial Li content of intra-zircon domains. This potential wealth of information may be further improved with experimental studies that characterize Li partitioning between zircon and melt. Here we report experiments that systematically quantify Li partitioning between zircon and different silicate melts as a function of temperature. We also explored how Li in zircon is structurally accommodated and the possible element(s) that influence Li incorporation. Zircon–melt partitioning is reported in four different melt compositions, with ASI values (molar ratio of Al 2 O 3 /(Na 2 O + K 2 O + CaO)) ranging from 0.56 to 1.44. The experiments were performed in a piston–cylinder device at 1000, 1100, 1200, and 1300 °C, and at a constant pressure of 1 GPa. Results of experiments show that the zircon–melt Li partition coefficient is not dependent on melt composition, but shows a negative relationship to temperature. This means the large range of Li concentrations in natural zircon is probably due to the combined factors of crystallization temperature and the original melt Li contents. We used our data to derive an empirical equation to describe the relationship of Li partitioning between zircon and melt (D Li ) and temperature ( K ): log 10 (D Li ) = (5918 ± 1479)/  T  − (6.91 ± 1.05). Through experiments with or without P added to the starting rock mix, we found that P-doped experiments yield lower D Li than those without P, which implies that Li competes with P for rare earth element (REE 3+ ) charge balance. To test the influence of H 2 O content of the melt on Li partitioning in zircon, we also explored melts with varying H 2 O contents (nominally 0, 5 wt.%, and 10 wt.%); results indicate that Li partitioning in zircon is not dependent on the H 2 O content of the melt. This method lays the groundwork to estimate the concentration of Li in melt that crystallized zircon, given the concentration of Li in zircon and an independent temperature estimate, provided that no post-crystallization modification of Li in zircon has occurred. We applied this equation to Hadean, Archean, and modern zircons and found that the predicted [Li] melt for Jack Hills zircons, Archean TTG and sanukitoid are one order magnitude higher than the modern crust.

Constraining the lithological diversity and tectonics of the earliest Earth is critical to understanding our planet’s evolution. Here we use detrital Jack Hills zircon (3.7 − 4.2 Ga) analyses coupled with new experimental partitioning data to model the silica content, Si+O isotopic composition, and trace element contents of their parent melts. Comparing our derived Jack Hills zircons’ parent melt Si+O isotopic compositions (−1.92 ≤ δ 30 Si NBS28  ≤ 0.53 ‰; 5.23 ≤ δ 18 O VSMOW  ≤ 9.00 ‰) to younger crustal lithologies, we conclude that the chemistry of the parent melts was influenced by the assimilation of terrigenous sediments, serpentinites, cherts, and silicified basalts, followed by igneous differentiation, leading to the formation of intermediate to felsic melts in the early Earth. Trace element measurements also show that the formational regime had an arc-like chemistry, implying the presence of mobile-lid tectonics in the Hadean. Finally, we propose that these continental-crust forming processes operated uniformly from 4.2 to at least 3.7 Ga. Geochemical analysis indicates a formational regime for Jack Hills zircons that is lithologically diverse and chemically similar to modern arcs. This depicts complicated geodynamics of the early Earth, which is currently proposed by many as stagnant-lid.

Earth's mantle is likely to have reached its present-day oxidation state before 4 billion years ago, according to a determination of the oxidation state of Hadean magmatic melts. On the track of Earth's first atmosphere The composition of Earth's earliest atmosphere, which accumulated more than four billion years ago during the Hadean eon, may have been influenced by magmatic outgassing of volatiles from Earth's interior. This paper reports a redox-sensitive calibration to determine the oxidation state of Hadean magmatic melts based on the incorporation of cerium into zircon crystals. The authors find that the melts have oxygen fugacities that are consistent with the idea that Earth's mantle reached its present-day oxidation state as early as 4.35 billion years ago. The findings suggest that outgassing of Earth's interior about 200 million years into the history of Solar System formation would not have resulted in a reducing atmosphere. 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 1 . 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 2 , 3 , 4 , 9 , 10 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.

Hydrosphere interactions and alteration of the terrestrial crust likely played a critical role in shaping Earth’s surface, and in promoting prebiotic reactions leading to life, before 4.03 Ga (the Hadean Eon). The identity of aqueously altered material strongly depends on lithospheric cycling of abundant and water-soluble elements such as Si and O. However, direct constraints that define the character of Hadean sedimentary material are absent because samples from this earliest eon are limited to detrital zircons (ZrSiO₄). Here we show that concurrent measurements of Si and O isotope ratios in Phanerozoic and detrital pre-3.0 Ga zircon constrain the composition of aqueously altered precursors incorporated into their source melts. Phanerozoic zircon from (S)edimentary-type rocks contain heterogeneous δ18O and δ30Si values consistent with assimilation of metapelitic material, distinct from the isotopic character of zircon from (I)gneous- and (A)norogenic-type rocks. The δ18O values of detrital Archean zircons are heterogeneous, although yield Si isotope compositions like mantle-derived zircon. Hadean crystals yield elevated δ18O values (vs. mantle zircon) and δ30Si values span almost the entire range observed for Phanerozoic samples. Coupled Si and O isotope data represent a constraint on Hadean weathering and sedimentary input into felsic melts including remelting of amphibolites possibly of basaltic origin, and fractional addition of chemical sediments, such as cherts and/or banded iron formations (BIFs) into source melts. That such sedimentary deposits were extensive enough to change the chemical signature of intracrustal melts suggests they may have been a suitable niche for (pre)biotic chemistry as early as 4.1 Ga.

Monazite is an important host of rare earth elements in the lithosphere including redox-sensitive Ce, which may occur as trivalent and tetravalent in terrestrial environments. Here, monazite solubility is explored as a function of oxygen fugacity through a series of dissolution experiments in alkali-rich and H2O fluids at 925 °C and 1.5 GPa. The oxygen fugacity was controlled with seven different solid-state buffers and ranged from about the iron-wustite to above the magnetite-hematite equilibrium reactions. The solubility of natural monazite increases monotonically at oxygen fugacities equal to or higher than the fayalite-magnetite-quartz equilibrium. Electron microscopy reveals incongruent dissolution at Ni-NiO and above, where Ce-oxide is observed with monazite as a stable phase. Solubility experiments were also conducted with synthetic crystals (CePO4, LaPO4, and Th+Si-doped monazite). End-member CePO4 exhibits profound changes to the surface of the crystal under oxidized conditions, with erosion of the crystal surface to depths of ∼100 µm or greater, coupled with precipitation of Ce-oxide. In contrast, the solubility of LaPO4 shows no sensitivity to the redox state of the experiment. The addition of Th (∼3 wt%) and Si (∼0.3 wt%) to monazite promotes crystal stability under oxidizing conditions, though small ThO2-CeO2 (5-10 µm) crystals are present on the surfaces of these crystals, whose abundance increases at higher oxygen fugacities. In aggregate, these experiments show that the stability and solubility of monazite is affected by oxygen fugacity, and that the redox state of a fluid may be partially responsible for redistribution of rare earth elements and phosphorus in the crust. Lithospheric fluids with oxygen fugacities at or above the fayalite-magnetite-quartz equilibrium may contribute to some of the complex textures, variable chemistry, and age relationships observed in natural monazite.

As the only known mineral with confirmed ages >4 Ga, zircon is unmatched in the field of early Earth research. In the past two decades, researchers have continued to establish connections between zircon chemistry and the physical/chemical processes that shaped the early crust. This connection has benefited greatly from the application of high-temperature and high-pressure laboratory experiments. This study presents: (1) new zircon U-Pb geochronology and strategies for characterizing and identifying ancient terrestrial material from the Inukjuak Domain in northern Quebec, and the Jack Hills, Western Australia; and (2) a blend of new laboratory experiments and measurements of isotope ratios and trace impurities of natural zircon. Research directions in need of future exploration, with emphasis on early Earth studies, are also explored. Topics include Hadean hydrous magmatism and the structural accommodation of \"water\" into the zircon lattice, Hadean subaerial crust and the identification of peraluminous or metaluminous source melts, methods to characterize the oxidation state of magmas and fluids, and the complementarity of the Si- and O-isotopic systems as proxies for crustal weathering. Finally, the implications of this work are discussed in the context of a possible transition from prebiotic to biotic chemistry on the early Earth.

Apatite is widely distributed in terrestrial and extraterrestrial environments and may therefore crystallize in relatively oxidized environments found here on Earth, and in reduced settings such as the Moon. We present a series of oxygen fugacity-buffered apatite stability and apatite-fluid solubility experiments conducted at 1 atm and in a piston cylinder, respectively. The first style of experiments involved enclosing polished slabs of Durango apatite in evacuated silica tubes with a solid-state oxygen fugacity buffer, followed by heating to ~1100 °C for 65 or 90 h. At oxygen fugacities equal to and lower than the Fe-FeO equilibrium, crystals revealed alteration often in the form of convoluted features, which may to be related to the stability of the apatite component P2O5 under reducing conditions. Preferential evaporation of P2O5 from a haplobasalt heated to 1350 °C under reducing conditions – compared to similar experiments conducted under oxidizing conditions – also supports this interpretation. Fifteen solubility experiments were conducted in a piston cylinder device at 900 or 925 °C and 1 GPa, in either ~3.4 N NaCl or 2 N NaOH fluids. The oxygen fugacity was buffered at about 4 log units below the fayalite magnetite quartz equilibrium (FMQ-4) to 8 log units above this buffer (FMQ + 8). Apatite solubilities were determined by crystal weight loss. There is no systematic sensitivity to solubility vs. oxygen fugacity in H2O-NaOH fluid. In the H2O-NaCl fluid, apatite is less soluble by about a factor of 2 under the most oxidizing experimental conditions. This change in solubility is relatively subtle when compared to intensive variables explored in other studies, such as temperature, pressure, and XNaCl in the fluid. Overall, the apatite crystal structure is resilient across a range of different imposed oxygen fugacities, which contrasts with experimental results for another phosphate, monazite.

Zircon Li concentrations and δ 7 Li values may potentially trace crustal recycling because continental and mantle-derived zircons yield distinct values. The usefulness of these differences may depend upon the retentivity of zircon to Li concentrations and isotopic ratios. Given the relatively high Li diffusivities measured by Cherniak and Watson (Contrib Mineral Petrol 160: 383–390, 2010 ), we sought to discover the scenarios under which Li mobility might be inhibited by charge-compensating cations. Toward this end, we conducted “in” diffusion experiments in which Li depth profiles of synthetic Lu-doped, P-doped, and undoped zircon were determined by nuclear reaction analysis. In separate experiments, Li was ion-implanted at depth within polished natural zircon slabs to form a Gaussian Li concentration profile. Diffusively relaxed concentration profiles were measured after heating the slabs to determine diffusivities. In all experiments, which ranged from 920 to 650 °C, calculated diffusivities are in agreement with a previously established Arrhenius relationship calibrated on trace-element-poor Mud Tank zircon. Our revised Arrhenius relationship that includes both datasets is: D Li = 9.60 × 10 - 7 exp - 278 ± 8 kJ mol - 1 RT m 2 s - 1 We also observed that synthetic sector-zoned zircon exhibits near-step-function Li concentration profiles across sectors that correlate with changes in the rare earth element (REE) and P concentrations. This allowed us to examine how Li diffusion might couple with REE diffusion in a manner different than that described above. In particular, re-heating these grains revealed significant Li migration, but no detectable migration of the rare earth elements. Thus, unlike most elements in zircon which are not mobile at the micrometer scale under most time–temperature paths in the crust, Li zoning, relaxation of zoning, or lack of zoning altogether could be used to reveal time–temperature information. Discrete ~10 μm concentration zones of Li within zircon may be partially preserved at 700 °C for tens to hundreds of years, and at 450 °C for millions of years. In this regard, Li zoning in zircon holds significant potential as a geospeedometer, and in some instances as a qualitative indicator of the maximum temperature experienced by the zircon.

This study is focused on mineralogical and chemical characterization of an authigenic carbonate rock (crust) collected at a recently discovered cold seep on the US North Atlantic continental margin. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the carbonate rock is composed of microcrystalline aragonite cement, white acicular aragonite crystals (AcAr), equant quartz crystals, small microcrystalline aluminosilicates, and trace amounts of iron sulfide microcrystals. Element/calcium ratios were measured with laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) using a calcite standard, which was prepared by annealing USGS certified carbonate powder (MACS-3). The occurrence of microscopic, non-carbonate inclusions precluded evaluation of trace elements in the aragonite cement, but allowed for in situ analysis of AcAr crystals. Carbon and oxygen isotopes were analyzed via isotope ratio mass spectrometry (IRMS) and expressed as δ13C and δ18O. Low δ13C values suggest that aragonite grew as a result of anaerobic oxidation of methane and observed δ18O values indicate that the temperature of aragonite crystallization was 1.7–1.9 °C.