Michael Broadley

@article{Ardoin_etal2022,

title = {The end of the isotopic evolution of atmospheric xenon},

author = {L. Ardoin and M. W. Broadley and M. Almayrac and G. Avice and D. J. Byrne and A. Tarantola and A. Lepland and T. Saito and T. Komiya and T. Shibuya and B. Marty},

doi = {10.7185/geochemlet.2207},

year  = {2022},

date = {2022-01-01},

journal = {Geochemical Perspectives Letters},

volume = {40},

abstract = {Noble gases are chemically inert and, as such, act as unique tracers of physical processes over geological timescales. The isotopic composition of atmospheric xenon, the heaviest stable noble gas, evolved following mass-dependent fractionation throughout the Hadean and Archaean aeons. This evolution appears to have ceased between 2.5 and 2.1 Ga, around the time of the Great Oxidation Event (GOE). The coincidental halting of atmospheric Xe evolution may provide further insights into the mechanisms affecting the atmosphere at the Archaean-Proterozoic transition. Here, we investigate the isotopic composition of Xe trapped in hydrothermal quartz from three formations around the GOE time period : Seidorechka and Polisarka (Imandra-Varzuga Greenstone Belt, Kola Craton, Russia) with ages of 2441thinspacetextpmthinspace1.6 Ma and 2434thinspacetextpmthinspace6.6 Ma, respectively, and Ongeluk (Kaapvaal Craton, South Africa) dated at 2114thinspacetextpmthinspace312 Ma (Ar-Ar age) with a host formation age of 2425.6thinspacetextpmthinspace2.6 Ma (upper bound). From these analyses we show that Xe isotope fractionation appears to have ceased during the time window delimited by the ages of the Seidorechka and Polisarka Formations, which is concomitant with the disappearance of mass-independent fractionation of sulfur isotopes (MIF-S) in the Kola Craton. The disappearance of Xe isotope fractionation in the geological record may be related to the rise in atmospheric oxygen and, thus, can provide new insights into the triggering mechanisms and timing of the GOE.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Okazaki_etal2022,

title = {Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution},

author = {R. Okazaki and B. Marty and H. Busemann and K. Hashizume and J. D. Gilmour and A. Meshik and T. Yada and F. Kitajima and M. W. Broadley and D. Byrne and E. and F\"{u}ri},

doi = {10.1126/science.abo0431},

year  = {2022},

date = {2022-01-01},

journal = {Science},

number = {8},

pages = {abo0431},

abstract = {The near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth’s volatiles. Samples of Ryugu were retrieved by the Hayabusa2 spacecraft. We measure noble gas and nitrogen isotopes in Ryugu samples, finding they are dominated by pre-solar and primordial components, incorporated during Solar System formation. Noble gas concentrations are higher than those in Ivuna-type carbonaceous (CI) chondrite meteorites. Several host phases of isotopically distinct nitrogen have heterogeneous abundances between the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating textasciitilde5 Myr exposure, and from implanted solar wind, record the recent irradiation history of Ryugu after it migrated to its current orbit.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Almayrac_etal2022,

title = {The EXCITING experiment exploring the behavior of nitrogen and noble gases in interstellar ice analogs},

author = {M. G. Almayrac and D. V. Bekaert and M. W. Broadley and D. J. Byrne and L. Piani and B. Marty},

doi = {10.3847/PSJ/ac98b0},

year  = {2022},

date = {2022-01-01},

journal = {The Planetary Science Journal},

volume = {3},

pages = {252},

abstract = {Comets represent some of the most pristine bodies in our solar system and can provide a unique insight into the chemical makeup of the early solar system. Due to their icy volatile-rich nature, they may have played an important role in delivering volatile elements and organic material to the early Earth. Understanding how comets form can therefore provide a wealth of information on how the composition of volatile elements evolved in the solar system from the presolar molecular cloud up until the formation of the terrestrial planets. Because noble gases are chemically inert and have distinct condensation temperatures, they can be used to infer the temperatures of formation and thermal history of cometary ices. In this work, we present a new experimental setup called EXCITING to investigate the origin and formation conditions of cometary ices. By trapping nitrogen and noble gases in amorphous water ice, our experiment is designed to study the elemental and isotopic behavior of volatile elements in cometary ice analogs. We report new results of noble gas and nitrogen enrichment in cometary ice analogs and discuss the limitations of the experimental conditions in light of those supposed for comets. We show that forming ice analogs at \^{a}`u70 K best reproduce the noble gas and N2 abundances of comet 67P/Churyumov--Gerasimenko, considering a solar-like starting composition. This formation temperature is higher than previous estimates for cometary ices and suggests that the formation of cometary building blocks may have occurred in the protosolar nebula rather than in the colder molecular cloud.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2022,

title = {Origin of life-forming volatile elements in the inner Solar System},

author = {M. W. Broadley and D. V. Bekaert and L. Piani and E. F\"{u}ri and B. Marty},

doi = {10.1038/s41586-022-05276-x},

year  = {2022},

date = {2022-01-01},

journal = {Nature},

volume = {611},

pages = {245--255},

abstract = {Volatile elements such as hydrogen, carbon, nitrogen and oxygen are essential ingredients to build habitable worlds like Earth, but their origin and evolution on terrestrial planets remain highly debated. Here we discuss the processes that distributed these elements throughout the early Solar System and how they then became incorporated into planetary building blocks. Volatiles on Earth and the other terrestrial planets appear to have been heterogeneously sourced from different Solar System reservoirs. The sources of planetary volatiles and the timing at which they were accreted to growing planets probably play a crucial role in controlling planet habitability.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bekaert_etal2020,

title = {Xenon isotopes in Archean and Proterozoic insoluble organic matter: A robust indicator of syngenecity?},

author = {D. V. Bekaert and M. W. Broadley and F. Delarue and Z. Druzhinina and G. Paris and F. Robert and K. Sugitani and B. Marty},

doi = {10.1016/j.precamres.2019.105505},

year  = {2020},

date = {2020-01-01},

journal = {Precambrian Research},

volume = {336},

pages = {105505},

abstract = {Insoluble organic materials (kerogens) isolated from ancient sedimentary rocks provide unique insights into the evolution of early life. However, establishing whether these kerogens are indeed syngenetic with the deposition of associated sedimentary host rocks, or contain contribution from episodes of secondary deposition, is not straightforward. Novel geochemical criterions are therefore required to test the syngenetic origin of Archean organic materials. On the one hand, the occurrence of mass-independent fractionation of sulphur isotopes (MIF-S) provides a tool to test the Archean origin of ancient sedimentary rocks. Determining the isotope composition of sulphur within kerogens whilst limiting the contribution from associated minerals (e.g., nano-pyrites) is however challenging. On the other hand, the Xe isotope composition of the Archean atmosphere has been shown to present enrichments in the light isotopes relative to its modern composition, together with a mono-isotopic deficit in 129Xe. Given that the isotopic composition of atmospheric Xe evolved through time by mass dependent fractionation (MDF) until textasciitilde2.5 to 2.0 Ga, the degree of MDF of Xe isotopes trapped in kerogens could provide a time stamp for the last chemical equilibration between organic matter and the atmosphere. However, the extent to which geological processes could affect the signature of Xe trapped in ancient kerogen remains unclear. In this contribution, we present new Ar, Kr and Xe isotopic data for four kerogens isolated from 3.4 to 1.8 Gy-old cherts and confirm that Xe isotopes from the Archean atmosphere can be retained within kerogens. However, new Xe-derived model ages are lower than expected from the ages of host rocks, indicating that initially trapped Xe components were at least partially lost and/or mixed together with some Xe carried out by younger generations of organic materials, therefore complicating the Xe-based dating method. Whilst non-null $Delta$33S values and 129Xe deficits relative to modern atmosphere constitute reliable imprints from the Archean atmosphere, using Xe isotopes to provide information on the syngenetic origin of ancient organic matter appears to be a promising -- but not unequivocal -- tool that calls for further analytical development.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bekaert_etal2020_2,

title = {The origin and fate of volatile elements on Earth revisited in light of noble gas data obtained from comet 67P/Churyumov-Gerasimenko},

author = {D. V. Bekaert and M. W. Broadley and B. Marty},

doi = {10.1038/s41598-020-62650-3},

year  = {2020},

date = {2020-01-01},

journal = {Scientific Reports},

volume = {10},

pages = {5796},

abstract = {The origin of terrestrial volatiles remains one of the most puzzling questions in planetary sciences. The timing and composition of chondritic and cometary deliveries to Earth has remained enigmatic due to the paucity of reliable measurements of cometary material. This work uses recently measured volatile elemental ratios and noble gas isotope data from comet 67P/Churyumov-Gerasimenko (67P/C-G), in combination with chondritic data from the literature, to reconstruct the composition of Earthtextquoterights ancient atmosphere. Comets are found to have contributed textasciitilde20% of atmospheric heavy noble gases (i.e., Kr and Xe) but limited amounts of other volatile elements (water, halogens and likely organic materials) to Earth. These cometary noble gases were likely mixed with chondritic ?\u{I} and not solar ?\u{I} sources to form the atmosphere. We show that an ancient atmosphere composed of chondritic and cometary volatiles is more enriched in Xe relative to the modern atmosphere, requiring that 8--12 times the present-day inventory of Xe was lost to space. This potentially resolves the long-standing mystery of Earthtextquoterights textquotelefttextquoteleftmissing xenontextquoterighttextquoteright, with regards to both Xe elemental depletion and isotopic fractionation in the atmosphere. The inferred Kr/H2O and Xe/H2O of the initial atmosphere suggest that Earthtextquoterights surface volatiles might not have been fully delivered by the late accretion of volatile-rich carbonaceous chondrites. Instead, textquotelefttextquoteleftdrytextquoterighttextquoteright materials akin to enstatite chondrites potentially constituted a significant source of chondritic volatiles now residing on the Earthtextquoterights surface. We outline the working hypotheses, implications and limitations of this model in the last section of this contribution},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2020,

title = {Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion},

author = {M. W. Broadley and P. H. Barry and D. Bekaert and D. J. Byrne and A. Caracausi and C. J. Ballentine and B. Marty},

doi = {10.1073/pnas.2003907117},

year  = {2020},

date = {2020-01-01},

journal = {PNAS},

volume = {117},

number = {25},

pages = {13997--14004},

abstract = {Identifying the origin of noble gases in Earthtextquoterights mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of 129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earthtextquoterights history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earthtextquoterights volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2020_2,

title = {Noble gas variations in ureilites and their implications for ureilite parent body formation},

author = {M. W. Broadley and D. V. Bekaert and B. Marty and A. Yamaguchi and J. A. Barrat},

doi = {10.1016/j.gca.2019.11.032},

year  = {2020},

date = {2020-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {270},

pages = {325--337},

abstract = {Ureilites are equilibrated carbon-rich olivine-pyroxene rocks from the partially melted mantle of a large (\>500 km diameter) heterogeneous parent body. Recently the ureilite parent body was interpreted as an incomplete mixture of material from two carbon-rich chondritic reservoirs, one (Mg-rich) with reduced iron, low $Delta$17O and low $delta$13C, and the other with oxidised iron, high $Delta$17O and high $delta$13C. Here we analyse noble gases (Ar, Kr and Xe) in six equilibrated (unbrecciated) ureilites from Northwest Africa (NWA 2236, NWA 7686, NWA 8049, NWA 8172, NWA 11032 and NWA 11368). We observe weak positive and negative correlations of $Delta$17O and Mg# with the elemental ratios of Ar/Xe and Kr/Xe, respectively, as well as a weak positive correlation of Mg# with the heavy isotopes of Xe. These correlations broadly support the idea of the two-component mixing hypothesis. Our analyses further suggest that the Mg-rich endmember was rich in Xe from presolar grains (HL-Xe) while the Mg-poorer component may have contained solar-derived noble gases. The observed correlations are less straightforward to reconcile with a recent model for the origin of the ureilite parent body, involving oxidation of metal by H2O from accreted ice with textquoteleftheavytextquoteright oxygen isotopes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Labidi_etal2020,

title = {Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen},

author = {J. Labidi and P. H. Barry and D. V. Bekaert and M. W. Broadley and B. Marty and T. Giunta and O. Warr and B. S. Sherwood and T. P. Fischer and G. Avice and A. Caracausi and C. J. Ballentine and S. A. Halldorsson and A. Stefansson and M. D. Kurz and I. E. Kohl and E. D. Young},

doi = {10.1038/s41586-020-2173-4},

year  = {2020},

date = {2020-01-01},

journal = {Nature},

volume = {580},

pages = {367--371},

abstract = {Nitrogen is the main constituent of the Earthtextquoterights atmosphere, but its provenance in the Earthtextquoterights mantle remains uncertain. The relative contribution of primordial nitrogen inherited during the Earthtextquoterights accretion versus that subducted from the Earthtextquoterights surface is unclear1,2,3,4,5,6. Here we show that the mantle may have retained remnants of such primordial nitrogen. We use the rare 15N15N isotopologue of N2 as a new tracer of air contamination in volcanic gas effusions. By constraining air contamination in gases from Iceland, Eifel (Germany) and Yellowstone (USA), we derive estimates of mantle $delta$15N (the fractional difference in 15N/14N from air), N2/36Ar and N2/3He. Our results show that negative $delta$15N values observed in gases, previously regarded as indicating a mantle origin for nitrogen7,8,9,10, in fact represent dominantly air-derived N2 that experienced 15N/14N fractionation in hydrothermal systems. Using two-component mixing models to correct for this effect, the 15N15N data allow extrapolations that characterize mantle endmember $delta$15N, N2/36Ar and N2/3He values. We show that the Eifel region has slightly increased $delta$15N and N2/36Ar values relative to estimates for the convective mantle provided by mid-ocean-ridge basalts11, consistent with subducted nitrogen being added to the mantle source. In contrast, we find that whereas the Yellowstone plume has $delta$15N values substantially greater than that of the convective mantle, resembling surface components12,13,14,15, its N2/36Ar and N2/3He ratios are indistinguishable from those of the convective mantle. This observation raises the possibility that the plume hosts a primordial component. We provide a test of the subduction hypothesis with a two-box model, describing the evolution of mantle and surface nitrogen through geological time. We show that the effect of subduction on the deep nitrogen cycle may be less important than has been suggested by previous investigations. We propose instead that high mid-ocean-ridge basalt and plume $delta$15N values may both be dominantly primordial features.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marty_etal2020,

title = {An evaluation of the C/N ratio of the mantle from natural CO2-rich gas analysis : Geochemical and cosmochemical implications},

author = {B. Marty and M. Almayrac and P. H. Barry and D. Bekaert and M. W. Broadley and D. J. Byrne and C. J. Ballentine and A. Caracausi},

doi = {10.1016/j.epsl.2020.116574},

year  = {2020},

date = {2020-01-01},

journal = {Earth and Planetary Science Letters},

volume = {551},

pages = {116574},

abstract = {The terrestrial carbon to nitrogen ratio is a key geochemical parameter that can provide information on the nature of Earthtextquoterights precursors, accretion/differentiation processes of our planet, as well as on the volatile budget of Earth. In principle, this ratio can be determined from the analysis of volatile elements trapped in mantle-derived rocks like mid-ocean ridge basalts (MORB), corrected for fractional degassing during eruption. However, this correction is critical and previous attempts have adopted different approaches which led to contrasting C/N estimates for the bulk silicate Earth (BSE) (Marty and Zimmermann, 1999 ; Bergin et al., 2015). Here we consider the analysis of CO2-rich gases worldwide for which a mantle origin has been determined using noble gas isotopes in order to evaluate the C/N ratio of the mantle source regions. These gases experienced little fractionation due to degassing, as indicated by radiogenic ⁎ values (where 4He and 40Ar* are produced by the decay of U+Th, and 40K isotopes, respectively) close to the mantle production/accumulation values. The C/N and ratios of gases investigated here are within the range of values previously observed in oceanic basalts. They point to an elevated mantle C/N ratio (�`u350-470, molar) higher than those of potential cosmochemical accretionary endmembers. For example, the BSE C/N and ratios (160-220 and , respectively) are higher than those of CM-CI chondrites but within the range of CV-CO groups. This similarity suggests that the Earth accreted from evolved planetary precursors depleted in volatile and moderately volatile elements. Hence the high composition of the BSE may be an inherited feature rather than the result of terrestrial differentiation. The and ratios of the surface (atmosphere plus crust) and of the mantle cannot be easily linked to any known chondritic composition. However, these compositions are consistent with early sequestration of carbon into the mantle (but not N and noble gases), permitting the establishment of clement temperatures at the surface of our planet.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bekaert_etal2019,

title = {Novel insights into the degassing history of Earthtextquoterights mantle from high precision noble gas analysis of magmatic gas},

author = {D. Bekaert and M. W. Broadley and A. Caracausi and B. Marty},

doi = {10.1016/j.epsl.2019.115766.},

year  = {2019},

date = {2019-01-01},

journal = {Earth and Planetary Science Letters},

volume = {525},

number = {115766},

abstract = {The noble gas isotope composition of the mantle can provide unique insights into the origin and evolution of volatile elements on Earth. Xenon isotopes combine primordial signatures with contributions from extinct and extant radionuclides, therefore offering the potential to set constraints on both the nature of Earthtextquoterights planetary precursor(s) and the timing of their contributions. However, measuring the Xe isotope composition of mantle-derived samples to sufficiently high-precision has proven difficult due to (i) large occurrence of a modern-like atmospheric component in the mantle, and (ii) contribution from shallow and post-eruptive atmospheric contamination. Mantle-derived samples therefore exhibit only small deviations from the modern atmospheric composition, making the identification and deconvolution of mantle-derived Xe signals challenging. Here, we use the Giggenbach sampling method to concentrate magmatic noble gases from the Eifel volcanic area (Germany) into glass bottles in order to conduct high-precision analyses of Ne, Ar and Xe isotopes. The three samples collected from Victoriaquelle and Schwefelquelle wells (South East Eifel) show variable contributions from atmospheric contamination, with the least contaminated sample reaching 40Ar/36Ar �`u8,300. Our data indicate that the mantle beneath the Eifel volcanic area, and by extension the Central European Volcanic Province, resembles the convective upper mantle reservoir with limited evidence for an OIB-like deep plume source contribution. It has a geochemical signature that is similar (e.g. in Ne isotopic composition, 40Ar/36Ar, 129Xe/130Xe and 129Xe/136Xe) to the mantle source of the so-called popping rocks (thought to best represent the upper mantle), with an additional source of 238U-derived Xe and low 3He/4He that we attribute to the influence of an ancient subducted component (HIMU). A dichotomy exists between the main sources of fissiogenic xenon isotopes measured in popping rocks and Eifel gas, which appear to be mainly derived from 244Pu and 238U, respectively. According to their respective ratios of 244Pu- to 238U-derived Xe, the mantle sources for Eifel volcanism and popping rocks would have experienced extensive and limited degassing, respectively. In this regard, high Pu--Xe/(Pu+U)--Xe may no longer be considered as being indicative of a mantle deep origin, therefore calling for the geochemical differences between plume and MORB sources to be redefined, with the possibility that volatile signatures within the solid Earth may be more heterogeneously distributed than previously thought.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2019,

title = {Recycled Components in Mantle Plumes Deduced From Variations in Halogens (Cl, Br, and I), Trace Elements, and 3He/4He Along the Hawaiian‐Emperor Seamount Chain},

author = {M. W. Broadley and H. Sumino and D. W. Graham and R. Burgess and C. J. Ballentine},

doi = {10.1029/2018GC007959},

year  = {2019},

date = {2019-01-01},

journal = {Geochemistry Geophysics Geosystems G3},

volume = {20},

number = {1},

pages = {277--294},

abstract = {Halogens are primarily located within surface reservoirs of the Earth ; as such they have proven to be effective tracers for the identification of subducted volatiles within the mantle. Subducting lithologies exhibit a wide variety of halogen compositions, yet the mantle maintains a fairly uniform signature, suggesting halogens may be homogenized during subduction to the mantle or during eruption. Here we present halogen (Cl, Br, and I), K, noble gas, and major and trace element data on olivines from three seamounts along the Hawaiian‐Emperor seamount chain to determine if the deep mantle source has retained evidence of halogen heterogeneities introduced through subduction. High Ni contents indicate that the Hawaiian‐Emperor mantle source contains a recycled oceanic crust component in the form of pyroxenite, which increases from the 46% in the oldest (Detroit) to 70% in the younger seamount (Koko). Detroit seamount retains mid‐ocean ridge basalts (MORB)‐like Br/Cl and I/Cl, while the Br/Cl and I/Cl of Suiko and Koko seamounts are higher than MORB and similar to altered oceanic crust and dehydrated serpentinite. Helium isotopes show a similar evolution, from MORB‐like values at Detroit seamount toward higher values at Suiko and Koko seamounts. The correlation between pyroxenite contributions, Br/Cl, I/Cl, and 3He/4He indicates that subducted material has been incorporated into the primordial undegassed Hawaiian mantle plume source. The identification of recycled oceanic crustal signatures in both the trace elements and halogens indicates that subduction and dehydration of altered oceanic crust may exert control on the cycling of volatile elements to the deep mantle.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marty_etal2019,

title = {Geochemical evidence for high volatile fluxes from the mantle at the end of the Archaean},

author = {B. Marty and D. V. Bekaert and M. W. Broadley},

doi = {10.1038/s41586-019-1745-7},

year  = {2019},

date = {2019-01-01},

journal = {Nature},

volume = {575},

number = {4865},

pages = {485--488},

abstract = {The exchange of volatile species---water, carbon dioxide, nitrogen and halogens---between the mantle and the surface of the Earth has been a key driver of environmental changes throughout Earthtextquoterights history. Degassing of the mantle requires partial melting and is therefore linked to mantle convection, whose regime and vigour in the Earthtextquoterights distant past remain poorly constrained1,2. Here we present direct geochemical constraints on the flux of volatiles from the mantle. Atmospheric xenon has a monoisotopic excess of 129Xe, produced by the decay of extinct 129I. This excess was mainly acquired during Earthtextquoterights formation and early evolution3, but mantle degassing has also contributed 129Xe to the atmosphere through geological time. Atmospheric xenon trapped in samples from the Archaean eon shows a slight depletion of 129Xe relative to the modern composition4,5, which tends to disappear in more recent samples5,6. To reconcile this deficit in the Archaean atmosphere by mantle degassing would require the degassing rate of Earth at the end of the Archaean to be at least one order of magnitude higher than today. We demonstrate that such an intense activity could not have occurred within a plate tectonics regime. The most likely scenario is a relatively short (about 300 million years) burst of mantle activity at the end of the Archaean (around 2.5 billion years ago). This lends credence to models advocating a magmatic origin for drastic environmental changes during the Neoarchaean era, such as the Great Oxidation Event.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rubin_etal2019,

title = {Volatile Species in Comet 67P/Churyumov-Gerasimenko: Investigating the Link from the ISM to the Terrestrial Planets},

author = {M. Rubin and D. Bekaert and M. W. Broadley},

year  = {2019},

date = {2019-01-01},

journal = {ACS Earth and Space Chemistry},

volume = {3},

number = {9},

pages = {1792--1811},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bekaert_etal2018_3,

title = {Archean kerogen as a new tracer of atmospheric evolution: Implications for dating the widespread nature of early life},

author = {D. V. Bekaert and M. W. Broadley and F. Delarue and G. Avice and F. Robert and B. Marty},

doi = {10.1126/sciadv.aar2091},

year  = {2018},

date = {2018-01-01},

journal = {Science Advances},

volume = {4},

number = {2},

pages = {1--8},

abstract = {Understanding the composition of the Archean atmosphere is vital for unraveling the origin of volatiles and the environmental conditions that led to the development of life. The isotopic composition of xenon in the Archean atmosphere has evolved through time by mass-dependent fractionation from a precursor comprising cometary and solar/chondritic contributions (referred to as U-Xe). Evaluating the composition of the Archean atmosphere is challenging because limited amounts of atmospheric gas are trapped within minerals during their formation. We show that organic matter, known to be efficient at preserving large quantities of noble gases, can be used as a new archive of atmospheric noble gases. Xe isotopes in a kerogen isolated from the 3.0--billion-year--old Farrel Quartzite (Pilbara Craton, Western Australia) are mass fractionated by 9.8 textpm 2.1 per mil (texttenthousand) (2$sigma$) per atomic mass unit, in line with a progressive evolution toward modern atmospheric values. Archean atmospheric Xe signatures in kerogens open a new avenue for following the evolution of atmospheric composition through time. The degree of mass fractionation of Xe isotopes relative to the modern atmosphere can provide a time stamp for dating Archean kerogens and therefore narrowing the time window for the diversification of early life during the Archean eon.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2018,

title = {End-Permian extinction amplified by plume-induced release of recycled lithospheric volatiles},

author = {M. W. Broadley and P. H. Barry and C. J. Ballentine and L. A. Taylor and R. Burgess},

doi = {10.1038/s41561-018-0215-4},

year  = {2018},

date = {2018-01-01},

journal = {Nature Geoscience},

volume = {11},

number = {9},

pages = {682--687},

abstract = {Magmatic volatile release to the atmosphere can lead to climatic changes and substantial environmental degradation including the production of acid rain, ocean acidification and ozone depletion, potentially resulting in the collapse of the biosphere. The largest recorded mass extinction in Earthtextquoterights history occurred at the end of the Permian, coinciding with the emplacement of the Siberian large igneous province, suggesting that large-scale magmatism is a key driver of global environmental change. However, the source and nature of volatiles in the Siberian large igneous province remain contentious. Here we present halogen compositions of sub-continental lithospheric mantle xenoliths emplaced before and after the eruption of the Siberian flood basalts. We show that the Siberian lithosphere is massively enriched in halogens from the infiltration of subducted seawater-derived volatiles and that a considerable amount (up to 70%) of lithospheric halogens are assimilated into the plume and released to the atmosphere during emplacement. Plume--lithosphere interaction is therefore a key process controlling the volatile content of large igneous provinces and thus the extent of environmental crises, leading to mass extinctions during their emplacement.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2018_2,

title = {Plume-lithosphere interaction, and the formation of fibrous diamonds},

author = {M. W. Broadley and H. Hagi and R. Burgess and D. Zedgenizov and S. Mikhail and M. Almayrac and A. Ragozin and B. Pomazansky and H. Sumino},

doi = {10.7185/geochemlet.1825},

year  = {2018},

date = {2018-01-01},

journal = {Geochemical Perspectives Letters},

volume = {2018},

number = {8},

pages = {26--30},

abstract = {Fluid inclusions in diamond provide otherwise inaccessible information on theorigin and nature of carbonaceous fluid(s) in the mantle. Here we evaluate therole of subducted volatiles in diamond formation within the Siberian cratoniclithosphere. Specifically, we focus on the halogen (Cl, Br and I) and noble gas(He, Ne and Ar) geochemistry of fluids trapped within cubic, coated and cloudyfibrous diamonds from the Nyurbinskaya kimberlite, Siberia. Our data show Br/Cl and I/Cl ratios consistent with involvement of altered oceanic crust, suggestingsubduction-derived fluids have infiltrated the Siberian lithosphere. 3He/4Heranging from 2 to 11 RA, indicates the addition of a primordial mantle componentto the SCLM. Mantle plumes may therefore act as a trigger to re-mobilisesubducted carbon-rich fluids from the sub-continental lithospheric mantle, andwe argue this may be an essential process in the formation of fluid-rich diamonds,and kimberlitic magmatism.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marty_etal2018,

title = {Salinity of the Archaean oceans from analysis of fluid inclusions in quartz},

author = {B. Marty and G. Avice and D. V. Bekaert and M. W. Broadley},

doi = {10.1016/j.crte.2017.12.002},

year  = {2018},

date = {2018-01-01},

journal = {Comptes Rendus Geoscience},

volume = {350},

pages = {154--163},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Broadley_etal2017,

title = {Halogen variations through the quenched margin of a MORB lava: Evidence for direct assimilation of seawater during eruption},

author = {M. W. Broadley and R. Burgess and H. Kumagai and N. M. Curran and C. J. Ballentine},

doi = {10.1002/2016GC006711},

year  = {2017},

date = {2017-01-01},

journal = {Geochemistry, Geophysics, Geosystems G3},

volume = {18},

pages = {2413--2428},

abstract = {Halogens and noble gases within submarine basaltic glasses are critical tracers of interactions between the surface volatile reservoirs and the mantle. However, as the halogens and noble gases are concentrated within seawater, sediments, and the oceanic crust this makes the original volatile signature of submarine basaltic lavas susceptible to geochemical overprinting. This study combines halogen (Cl, Br, and I), noble gas, and K concentrations within a single submarine basaltic quenched margin to quantify the amount of seawater assimilation during eruption, and to further elucidate the mechanisms of overprinting. The outer sections of the glass rim are enriched in Cl compared to the interior of the margin, which maintains mantle‐like Br/Cl, I/Cl, and K/Cl ratios. Low Br/Cl and K/Cl in the outer sections of the basaltic glass margin indicate that the Cl enrichment in the outer glass is derived from the assimilation of a saline brine component with up to 70% of the Cl within the glass being derived from brine assimilation. Atmospheric noble gas contamination is decoupled from halogen contamination with contaminated outer sections maintaining MORB‐like 40Ar/36Ar, suggesting seawater‐derived brine assimilation during eruption is not the dominant source of atmospheric noble gases in submarine basalts. Volatile heterogeneities in submarine basalts introduced during and after eruption, as we have shown in this study, have the potential to expand the range of mantle halogen compositions and only by better understanding these heterogeneities can the Br/Cl and I/Cl variance in mantle derived samples are determined accurately.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}