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T. Mark Harrison - One of the best experts on this subject based on the ideXlab platform.
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Proposed Sources of Hadean Zircons
Hadean Earth, 2020Co-Authors: T. Mark HarrisonAbstract:Any successful geodynamic or environmental model for early Earth must be consistent with ten robust lines of evidence derived from geochemical and petrologic observations of Hadean Jack Hills zircons. These are: (1) a zircon sub-population enriched in 18O and depleted in 30Si relative to mantle values; (2) low crystallization temperatures; (3) the presence of primary hydrous mineral inclusions; (4) the predominance of magmatic muscovite, quartz, and biotite inclusions; (5) zircon formation in relatively low heat flow environments; (6) sub-chondritic initial 176Hf/177Hf ratios consistent with source isolation as early as 4.50 Ga; (7) fission Xe isotope compositions indicating variable fractionation of Pu from U; (8) the absence of ultra-high pressure mineral inclusions; (9) zircon formation under a wide range of redox conditions; and (10) geochemical signatures diagnostic of felsic continental crust. Numerous models have been proposed to explain these characteristics, including an origin similar to Icelandic rhyolites or lunar KREEP terranes, crystallization from mafic igneous rocks, formation in impact melts or sagduction, plate boundary and heat pipe tectonic environments, and multi-stage scenarios involving several of these mechanisms. While an origin of Jack Hills Hadean zircons in felsic and intermediate granitoids in a plate-boundary-type setting is consistent with all ten geochemically-derived constraints, competitor models are either only partially consistent or inconsistent with the evidence.
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Hadean Jack Hills Zircon Geochemistry
Hadean Earth, 2020Co-Authors: T. Mark HarrisonAbstract:Geochemical analysis of zircons older than 4 billion years, found in Early Archean metasediments at Jack Hills, Western Australia, provide insights into the nature of Hadean Earth. Oxygen isotopes have been interpreted as indicating that protoliths of magmas from which Hadean zircons crystallized were formed in the presence of water at or near Earth’s surface. Apparent crystallization temperatures of Hadean zircons cluster at 680 °C. Given the low porosity expected in rocks under anatectic conditions, dehydration melting of micas as the principal source of the melts from which these zircons crystallized can be ruled out. Instead, a regulated mechanism producing near minimum-melting conditions during the Hadean is inferred. Combined, these results have been interpreted to reflect chemical weathering and sediment cycling in the presence of liquid water shortly after Earth accretion. 176Hf/177Hf ratios of Hadean Jack Hills zircons show large heterogeneities indicating a major differentiation of the silicate Earth by 4.50 Ga. A possible consequence of this differentiation is the formation of continental crust of similar order to the present. Studies of mineral inclusions within Hadean zircons indicate their crystallization from hydrous, granitoid magmas at pressures greater than 6 kbars, implying low near-surface geothermal gradients which in turn suggests their origin in underthrust environments. Given general agreement that life could not have emerged until liquid water appeared at or near Earth’s surface, a significant implication is that our planet may have been habitable as much as 500 Ma earlier than previously thought. Indeed, carbon isotopic evidence obtained from inclusions in a Hadean zircon is consistent with life having emerged by 4.1 Ga, or several 100 million years earlier that the hypothesized lunar cataclysm. Trace element analyses of aluminum, halogens, sulfur, phosphorus, rare earth elements in Hadean zircons are consistent with their origin in a range of granitoid magma types and redox conditions. Although some of the above interpretations remain subject to debate, there is now a widespread consensus that molecular water was present at or near Earth’s surface since at least 4.3 Ga. Perhaps the most remarkable feature of inferences drawn from investigations of these ancient zircons is that none were predicted from theory, underscoring the importance of observations in testing models of early Earth.
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Hadean Zircons Elsewhere in the Solar System
Hadean Earth, 2020Co-Authors: T. Mark HarrisonAbstract:Hadean zircons have been documented from fifteen terrestrial localities in Australia, Asia, Africa, and North and South America, in stony and martian meteorites, and in lunar rocks. Extraterrestrial zircons are characterized by the absence of the positive Ce anomaly, seen in virtually all terrestrial zircons, much higher formation temperatures, and a unique suite of mineral inclusions. Remarkably little effort has been directed toward characterizing the geochemical nature of Hadean zircons from terrestrial localities beyond the Jack Hills region and thus it remains unclear how representative it is of the Hadean world. A massive analysis campaign is indicated to better understand Earth’s last true ‘dark age’.
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Could the Hadean Eon Have Been Habitable
Hadean Earth, 2020Co-Authors: T. Mark HarrisonAbstract:Given the absence of a macroscopic Hadean rock record, evaluating terrestrial habitability is largely a thought experiment, but data from Hadean zircons can provide some constraints. We are certain that life as we know it would not be possible without four requirements; soluble bioactive elements (carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorous), free energy, liquid water, and time. Beyond these essential ingredients, there is broad agreement that there are ten secondary factors that separate us from the other, uninhabited terrestrial planets and maintain our planet’s homeostasis. They are: (1) a galactic and planetary sanctuary for life; (2) liquid water at the planetary surface to mediate biochemistry and efficiently cool the planet; (3) dissolved water in the deep planetary interior to enhance mantle circulation and catalyze the eclogite transition; (4) a broadly solar chemical composition to provide sufficient metallicity for a stable surface platform; (5) sufficient planetary mass to retain an atmosphere and heat; (6) planetary satellite(s) to stabilize climate zones; (7) extra-planetary impactors to introduce organic building blocks and water and to create satellites; (8) long-term interior heat generation to maintain mantle circulation and the geodynamo; (9) a self-sustaining dynamo to protect the atmosphere is erosion; and (10) a mechanism to recycle surface carbon into the interior and back. Evaluating how these various factors interact is complicated but our speculations can be guided by inferences from Hadean zircon geochemistry which potentially bear on six of the ten ingredients for life—the presence of surface and interior water, the role of impacts on early Earth, internal heat generation, surface recycling, and the existence of a Hadean geodynamo. Knowledge of the geochemistry and inclusion population of Hadean zircons also permits constraints to be placed on whether mineral phases and trace elements key to biopoiesis were present during the Hadean eon.
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Stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis of microfractured Hadean zircon
Geochronology, 2019Co-Authors: C. Brenhin Keller, Blair Schoene, Patrick Boehnke, T. Mark HarrisonAbstract:Abstract. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high-spatial-resolution high-throughput in situ isotopic and elemental analysis techniques, such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision ( % two-sigma) thermal ionization mass spectrometry (TIMS). In order to better understand the lead loss and alteration history of terrestrial Hadean zircons, we conduct stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis (CA-ID-TIMS-TEA) on manually microfractured Hadean Jack Hills zircon fragments previously dated by SIMS. We conducted three successive HF leaching steps on each individual zircon fragment, followed by column chromatography to isolate U–Pb and trace element fractions. Following isotopic and elemental analysis, the result is an independent age and trace element composition for each leachate of each zircon fragment. We observe ∼50 Myr of age heterogeneity in concordant residues from a single zircon grain, along with a protracted history of post-Hadean Pb loss with at least two modes circa ∼0 and 2–4 Ga. Meanwhile, stepwise leachate trace element chemistry reveals enrichments of light rare earth elements, uranium, thorium, and radiogenic lead in early leached domains relative to the zircon residue. In addition to confirming the efficacy of the LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggest that Pb loss is largely driven by low-temperature aqueous recrystallization and that regional thermal events may act to halt – not initiate – Pb loss from metamict domains in the Hadean Jack Hills zircons.
Patrick Boehnke - One of the best experts on this subject based on the ideXlab platform.
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stepwise chemical abrasion isotope dilution thermal ionization mass spectrometry with trace element analysis of microfractured Hadean zircon
Geochronology, 2019Co-Authors: Brenhin C Keller, Patrick Boehnke, Blair Schoene, Mark T HarrisonAbstract:Abstract. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high-spatial-resolution high-throughput in situ isotopic and elemental analysis techniques, such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision ( % two-sigma) thermal ionization mass spectrometry (TIMS). In order to better understand the lead loss and alteration history of terrestrial Hadean zircons, we conduct stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis (CA-ID-TIMS-TEA) on manually microfractured Hadean Jack Hills zircon fragments previously dated by SIMS. We conducted three successive HF leaching steps on each individual zircon fragment, followed by column chromatography to isolate U–Pb and trace element fractions. Following isotopic and elemental analysis, the result is an independent age and trace element composition for each leachate of each zircon fragment. We observe ∼50 Myr of age heterogeneity in concordant residues from a single zircon grain, along with a protracted history of post-Hadean Pb loss with at least two modes circa ∼0 and 2–4 Ga. Meanwhile, stepwise leachate trace element chemistry reveals enrichments of light rare earth elements, uranium, thorium, and radiogenic lead in early leached domains relative to the zircon residue. In addition to confirming the efficacy of the LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggest that Pb loss is largely driven by low-temperature aqueous recrystallization and that regional thermal events may act to halt – not initiate – Pb loss from metamict domains in the Hadean Jack Hills zircons.
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Stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis of microfractured Hadean zircon
Geochronology, 2019Co-Authors: C. Brenhin Keller, Blair Schoene, Patrick Boehnke, T. Mark HarrisonAbstract:Abstract. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high-spatial-resolution high-throughput in situ isotopic and elemental analysis techniques, such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision ( % two-sigma) thermal ionization mass spectrometry (TIMS). In order to better understand the lead loss and alteration history of terrestrial Hadean zircons, we conduct stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis (CA-ID-TIMS-TEA) on manually microfractured Hadean Jack Hills zircon fragments previously dated by SIMS. We conducted three successive HF leaching steps on each individual zircon fragment, followed by column chromatography to isolate U–Pb and trace element fractions. Following isotopic and elemental analysis, the result is an independent age and trace element composition for each leachate of each zircon fragment. We observe ∼50 Myr of age heterogeneity in concordant residues from a single zircon grain, along with a protracted history of post-Hadean Pb loss with at least two modes circa ∼0 and 2–4 Ga. Meanwhile, stepwise leachate trace element chemistry reveals enrichments of light rare earth elements, uranium, thorium, and radiogenic lead in early leached domains relative to the zircon residue. In addition to confirming the efficacy of the LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggest that Pb loss is largely driven by low-temperature aqueous recrystallization and that regional thermal events may act to halt – not initiate – Pb loss from metamict domains in the Hadean Jack Hills zircons.
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Stepwise chemical abrasion ID-TIMS-TEA of microfractured Hadean zircon
2019Co-Authors: C. Brenhin Keller, Blair Schoene, Patrick Boehnke, T. Mark HarrisonAbstract:Abstract. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high spatial resolution, high throughput in situ isotopic and elemental analysis techniques such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision (
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Stepwise chemical abrasion ID-TIMS-TEA of microfractured Hadean zircon
2019Co-Authors: C. Brenhin Keller, Blair Schoene, Patrick Boehnke, T. Mark HarrisonAbstract:Abstract. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high spatial resolution, high throughput in situ isotopic and elemental analysis techniques such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision ( LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggests that Pb-loss is largely driven by low-temperature aqueous recrystallization, and that regional thermal events may act to halt – not initiate – Pb-loss from metamict domains in the Hadean Jack Hills zircons.
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Origin and significance of Si and O isotope heterogeneities in Phanerozoic, Archean, and Hadean zircon.
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Dustin Trail, Patrick Boehnke, Paul S. Savage, Ming-chang Liu, Martha L. Miller, Ilya N. BindemanAbstract: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.
Dustin Trail - One of the best experts on this subject based on the ideXlab platform.
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Boron partitioning between zircon and melt: Insights into Hadean, modern arc, and pegmatitic settings
Chemical Geology, 2020Co-Authors: Wriju Chowdhury, Dustin Trail, Elizabeth A. BellAbstract:Abstract There is a lot of debate surrounding the geodynamic environment of the Hadean Earth, and the only definitively known fragments from the first 500 Ma are detrital zircons. This makes the combination of natural and experimentally obtained data a powerful tool to unravel the chemistry of the early Earth. We have used an incompatible marker element, B, to partially derive the chemistry of the parent melts of the Hadean and modern zircons. We report an experimental calibration for temperature dependent B partitioning between zircon and a hydrous weakly peraluminous granitic melt. log 10 D B zrc / melt = − 1027 ± 372 T K − 2.011 ± 0.257 where DBzrc/melt is the zircon-melt partition coefficient for B and T is temperature in K. This calibration has been applied to natural samples, viz., Hadean zircons from the Jack Hills (JH), Australia, Phanerozoic zircons from the Lachlan Fold Belt (LFB), Australia and three pegmatitic zircons from Seiland Igneous province, Norway, Paicoma Canyon, California and Freeman Mine, North Carolina. Our results present direct evidence of B being present in the Hadean crust. The zircons from JH and LFB are rather poor in B (8–80 ppb), but comparable to each other, while the pegmatites have as much as ten times the [B] (~0.35–0.45 ppm). Application of our experimental calibration yields calculated B melt concentrations of 10–90 ppm for the JH and LFB zircons. Such values for melt [B] (concentrations) are similar to the modern upper continental crust (17 ppm) and volcanic arcs, but are high when to compared to OIBs (0.6–1.8 ppm) and MORBs (1.3 ppm). The Lachlan zircons have [B] values that are broadly similar to the detrital Hadean and Archean zircons, and these have been presented as a point of comparison between Hadean and modern zircons. The pegmatite zircons return calculated melt values (244–701 ppm) that are much higher than the parent melts of the Australian zircons. One of the pegmatite zircons show a variation in calculated Ti-in-zircon crystallization T from the core to the rim (716 °C – 916 °C). Two of the other zircons crystallized at 664 ± 14 °C and 598 ± 13 °C (2 s.e.; not taking into consideration a ~50oT uncertainty due to imperfectly constrained silica/titania activities) and show no intracrystalline variation in [B] or T. Finally, B has been proposed to have been a possible stabilizing agent for ribose aqueous solutions and could have played a part in the formation of carbohydrates and proteins which were building blocks for RNA. Our documented presence of B in the Hadean crust at calculated concentrations similar to a modern volcanic arc setting, makes the role of B in ribose stabilization at least possible on the primordial Earth.
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Origin and significance of Si and O isotope heterogeneities in Phanerozoic, Archean, and Hadean zircon.
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Dustin Trail, Patrick Boehnke, Paul S. Savage, Ming-chang Liu, Martha L. Miller, Ilya N. BindemanAbstract: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.
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Aluminum in zircon as evidence for peraluminous and metaluminous melts from the Hadean to present
Geochemistry Geophysics Geosystems, 2017Co-Authors: Dustin Trail, Nicholas D Tailby, T. Mark Harrison, Yanling Wang, Patrick BoehnkeAbstract:Zircon structurally accommodates a range of trace impurities into its lattice, a feature which is used extensively to investigate the evolution of silicate magmas. One key compositional boundary of magmas is defined by whether the molar ratio of Al2O3/(CaO + Na2O + K2O) is larger or smaller than unity. Here we report ∼800 Al in zircon concentrations from 19 different rocks from the Lachlan Fold Belt (southeastern Australia), New England (USA), and Arunachal leucogranites (eastern Himalaya) with Al2O3/(CaO + Na2O + K2O) whole rock values that range from 0.88 to 1.6. Zircons from peraluminous rocks yield an average Al concentration of ∼10 ppm, which distinguishes them from crystals found in metaluminous rocks (∼1.3 ppm). This difference is related to the materials involved in the melting, assimilation, and/or magma differentiation processes; for example, magmas that assimilate Al-rich material such as metapelites are expected to produce melts with elevated alumina activities, and thus zircons with high Al concentrations. These observations are applied to the Archean and Hadean Jack Hills detrital zircon record. Detrital Archean zircons, with ages from about 3.30 to 3.75 Ga, yield Al in zircon concentrations consistent with origins in peraluminous rocks in ∼8% of the cases (n = 236). A single zircon from the pre-3.9 Ga age group (n = 39) contains elevated Al contents, which suggests that metaluminous crustal rocks were more common than peraluminous rocks in the Hadean. Weathered material assimilated into these Hadean source melts was not dominated by Al-rich source material.
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pervasive remagnetization of detrital zircon host rocks in the jack hills western australia and implications for records of the early geodynamo
Earth and Planetary Science Letters, 2015Co-Authors: Dustin Trail, Nicholas D Tailby, Bruce E Watson, Mark T Harrison, Benjamin P Weiss, Adam C Maloof, Jahandar Ramezani, Veronica Hanus, Samuel A BowringAbstract:It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this time. With crystallization ages ranging from 3.0–4.38 Ga, these zircons might preserve a record of the missing first billion years of Earth's magnetic field history. However, a key unknown is the age and origin of magnetization in the Jack Hills zircons. The identification of >3.9 Ga (i.e., Hadean) field records requires first establishing that the zircons have avoided remagnetization since being deposited in quartz-rich conglomerates at 2.65–3.05 Ga. To address this issue, we have conducted paleomagnetic conglomerate, baked contact, and fold tests in combination with U–Pb geochronology to establish the timing of the metamorphic and alteration events and the peak temperatures experienced by the zircon host rocks. These tests include the first conglomerate test directly on the Hadean-zircon bearing conglomerate at Erawandoo Hill. Although we observed little evidence for remagnetization by recent lightning strikes, we found that the Hadean zircon-bearing rocks and surrounding region have been pervasively remagnetized, with the final major overprinting likely due to thermal and/or aqueous effects from the emplacement of the Warakurna large igneous province at ∼1070 million years ago (Ma). Although localized regions of the Jack Hills might have escaped complete remagnetization, there currently is no robust evidence for pre-depositional (>3.0 Ga) magnetization in the Jack Hills detrital zircons.
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the oxidation state of Hadean magmas and implications for early earth s atmosphere
Nature, 2011Co-Authors: Dustin Trail, Bruce E Watson, Nicholas D TailbyAbstract: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. 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) ago1. 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–wustite buffer would yield volatile species such as CH4, H2, H2S, NH3 and CO, whereas melts close to the fayalite–magnetite–quartz buffer would be similar to present-day conditions and would be dominated by H2O, CO2, SO2 and N2 (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 lavas2,3,4,9,10 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.
David R. Nelson - One of the best experts on this subject based on the ideXlab platform.
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tourmaline 40ar 39ar geochronology and thermochronology example from Hadean zircon bearing siliciclastic metasedimentary rocks from the yilgarn craton
Geochimica et Cosmochimica Acta, 2020Co-Authors: Eric R. Thern, Eleanore Blereau, Fred Jourdan, David R. NelsonAbstract:Abstract We present 40Ar/39Ar ages and boron isotopes of tourmalines from a quartz-tourmaline intrusion cross-cutting the Hadean detrital-zircon-bearing metasedimentary rocks from the Mt. Alfred and Brooking Hills localities of the Illaara Greenstone Belt, Western Australia. Concordant 40Ar/39Ar plateau ages on the tourmalines at Mt. Alfred give a weighted mean age of 2935 ± 9 Ma (2σ). These results are the first reported Archean 40Ar/39Ar ages directly obtained on tourmaline, and provide a minimum depositional age for this sequence, placing constraints on the depositional timing of detrital Hadean zircons to between 2935 ± 9 Ma and c.a. 3250 Ma (youngest detrital zircon age in sequence). This is the last known occurrence of abundant detrital Hadean zircons having been directly deposited in a sedimentary sequence, and thus suggests that most Hadean zircon sources have been exhausted by this time. The 2935 ± 9 Ma tourmalines occur within a quartz-tourmaline intrusion with associated stratiform layers and veins, inferred to have grown during a hydrothermal fluid circulation event. A younger generation of tourmalines from the Brooking Hills, 30 km south of Mt. Alfred yielded concordant 40Ar/39Ar plateau ages with a weighted mean age of 2624 ± 16 Ma. These tourmalines occur within and along the margins of post-kinematic quartz veins, parallel to the foliation fabric and marks the end stage of high temperature tectono-thermal events within the Illaara Greenstone Belt. The retention of 2935 ± 9 Ma tourmaline ages within the Illaara Greenstone Belt shows that the K/Ar system of tourmaline remained closed throughout repeated upper-greenschist metamorphic events (∼450 °C) between the ages of c.a. 2930 to 2630 Ma in contrast to muscovite recording plateau ages of about 2600 Ma. This is in agreement with an approximate Ar closure temperature between ∼534 and 628 °C experimentally determined in this study.
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Tourmaline 40Ar/39Ar geochronology and thermochronology: Example from Hadean-zircon-bearing siliciclastic metasedimentary rocks from the Yilgarn Craton
Geochimica et Cosmochimica Acta, 2020Co-Authors: Eric R. Thern, Eleanore Blereau, Fred Jourdan, David R. NelsonAbstract:Abstract We present 40Ar/39Ar ages and boron isotopes of tourmalines from a quartz-tourmaline intrusion cross-cutting the Hadean detrital-zircon-bearing metasedimentary rocks from the Mt. Alfred and Brooking Hills localities of the Illaara Greenstone Belt, Western Australia. Concordant 40Ar/39Ar plateau ages on the tourmalines at Mt. Alfred give a weighted mean age of 2935 ± 9 Ma (2σ). These results are the first reported Archean 40Ar/39Ar ages directly obtained on tourmaline, and provide a minimum depositional age for this sequence, placing constraints on the depositional timing of detrital Hadean zircons to between 2935 ± 9 Ma and c.a. 3250 Ma (youngest detrital zircon age in sequence). This is the last known occurrence of abundant detrital Hadean zircons having been directly deposited in a sedimentary sequence, and thus suggests that most Hadean zircon sources have been exhausted by this time. The 2935 ± 9 Ma tourmalines occur within a quartz-tourmaline intrusion with associated stratiform layers and veins, inferred to have grown during a hydrothermal fluid circulation event. A younger generation of tourmalines from the Brooking Hills, 30 km south of Mt. Alfred yielded concordant 40Ar/39Ar plateau ages with a weighted mean age of 2624 ± 16 Ma. These tourmalines occur within and along the margins of post-kinematic quartz veins, parallel to the foliation fabric and marks the end stage of high temperature tectono-thermal events within the Illaara Greenstone Belt. The retention of 2935 ± 9 Ma tourmaline ages within the Illaara Greenstone Belt shows that the K/Ar system of tourmaline remained closed throughout repeated upper-greenschist metamorphic events (∼450 °C) between the ages of c.a. 2930 to 2630 Ma in contrast to muscovite recording plateau ages of about 2600 Ma. This is in agreement with an approximate Ar closure temperature between ∼534 and 628 °C experimentally determined in this study.
Nicholas D Tailby - One of the best experts on this subject based on the ideXlab platform.
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Aluminum in zircon as evidence for peraluminous and metaluminous melts from the Hadean to present
Geochemistry Geophysics Geosystems, 2017Co-Authors: Dustin Trail, Nicholas D Tailby, T. Mark Harrison, Yanling Wang, Patrick BoehnkeAbstract:Zircon structurally accommodates a range of trace impurities into its lattice, a feature which is used extensively to investigate the evolution of silicate magmas. One key compositional boundary of magmas is defined by whether the molar ratio of Al2O3/(CaO + Na2O + K2O) is larger or smaller than unity. Here we report ∼800 Al in zircon concentrations from 19 different rocks from the Lachlan Fold Belt (southeastern Australia), New England (USA), and Arunachal leucogranites (eastern Himalaya) with Al2O3/(CaO + Na2O + K2O) whole rock values that range from 0.88 to 1.6. Zircons from peraluminous rocks yield an average Al concentration of ∼10 ppm, which distinguishes them from crystals found in metaluminous rocks (∼1.3 ppm). This difference is related to the materials involved in the melting, assimilation, and/or magma differentiation processes; for example, magmas that assimilate Al-rich material such as metapelites are expected to produce melts with elevated alumina activities, and thus zircons with high Al concentrations. These observations are applied to the Archean and Hadean Jack Hills detrital zircon record. Detrital Archean zircons, with ages from about 3.30 to 3.75 Ga, yield Al in zircon concentrations consistent with origins in peraluminous rocks in ∼8% of the cases (n = 236). A single zircon from the pre-3.9 Ga age group (n = 39) contains elevated Al contents, which suggests that metaluminous crustal rocks were more common than peraluminous rocks in the Hadean. Weathered material assimilated into these Hadean source melts was not dominated by Al-rich source material.
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pervasive remagnetization of detrital zircon host rocks in the jack hills western australia and implications for records of the early geodynamo
Earth and Planetary Science Letters, 2015Co-Authors: Dustin Trail, Nicholas D Tailby, Bruce E Watson, Mark T Harrison, Benjamin P Weiss, Adam C Maloof, Jahandar Ramezani, Veronica Hanus, Samuel A BowringAbstract:It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this time. With crystallization ages ranging from 3.0–4.38 Ga, these zircons might preserve a record of the missing first billion years of Earth's magnetic field history. However, a key unknown is the age and origin of magnetization in the Jack Hills zircons. The identification of >3.9 Ga (i.e., Hadean) field records requires first establishing that the zircons have avoided remagnetization since being deposited in quartz-rich conglomerates at 2.65–3.05 Ga. To address this issue, we have conducted paleomagnetic conglomerate, baked contact, and fold tests in combination with U–Pb geochronology to establish the timing of the metamorphic and alteration events and the peak temperatures experienced by the zircon host rocks. These tests include the first conglomerate test directly on the Hadean-zircon bearing conglomerate at Erawandoo Hill. Although we observed little evidence for remagnetization by recent lightning strikes, we found that the Hadean zircon-bearing rocks and surrounding region have been pervasively remagnetized, with the final major overprinting likely due to thermal and/or aqueous effects from the emplacement of the Warakurna large igneous province at ∼1070 million years ago (Ma). Although localized regions of the Jack Hills might have escaped complete remagnetization, there currently is no robust evidence for pre-depositional (>3.0 Ga) magnetization in the Jack Hills detrital zircons.
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the oxidation state of Hadean magmas and implications for early earth s atmosphere
Nature, 2011Co-Authors: Dustin Trail, Bruce E Watson, Nicholas D TailbyAbstract: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. 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) ago1. 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–wustite buffer would yield volatile species such as CH4, H2, H2S, NH3 and CO, whereas melts close to the fayalite–magnetite–quartz buffer would be similar to present-day conditions and would be dominated by H2O, CO2, SO2 and N2 (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 lavas2,3,4,9,10 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.
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the oxidation state of Hadean magmas and implications for early earth s atmosphere
Nature, 2011Co-Authors: Dustin Trail, Bruce E Watson, Nicholas D TailbyAbstract: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-wustite 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.
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The oxidation state of Hadean magmas and implications for early Earth’s atmosphere
Nature, 2011Co-Authors: Dustin Trail, E. Bruce Watson, Nicholas D TailbyAbstract: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.
