Tag: ta2.10

22-EPN3-010: The Cosmic Dust Flux Over Geological Time – How Extraterrestrial Signals Become Preserved in Earth’s Marine Rock Record

Visit by Martin D. Suttle of the Open University (UK) to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France). Isabelle Mattia (Imperial College London) also took part in the visit, supported through other funding.
Dates of visit: 18 – 27 October 2023

Report Summary:

Fossil micrometeorites (MMs) recovered from sedimentary rocks are mostly <2mm-sized I-type cosmic spherules (CSs): iron-rich cosmic particles that have experienced high degrees of melting and oxidation during atmospheric entry. Since extraterrestrial ³He is implanted into cosmic dust by solar and cosmic rays in interplanetary space, fossil I-types could play a significant role as carriers of ³He in sedimentary archives. This project aimed to test this hypothesis by systematically examining the ³He/⁴He ratios of various types of MMs at different stages of preservation.

Measurements of He isotopes using the Helix SFT mass-spectrometer at CRPG, Nancy revealed variable 3He/4He values, with only 8 of the 36 measurements yielding results above the solar energetic particle (SEP) ratio of 2.17E-04  – most of these were, expectedly, scoriaceous Antarctic MMs which experienced the least atmospheric heating. Two urban CSs and a fossil I-type were also enriched in 3He, suggesting preservation of some implanted nobles gases, although rare, is possible for particles that have experienced high degrees of entry heating and/or alteration during diagenesis. A host chalk enriched in fossil I-types returned a low ratio of 1.00E-06, which could imply ³He may be preferentially removed by secondary fluids peculating within the lithifying sediment, or the source of cosmic dust was not sufficiently saturated in extraterrestrial 3He.The main conclusions from this work are that the ³He signal and the abundance of fossil (I-type) micrometeorites in Earth’s sedimentary rocks are uncoupled. This implies that these two proxies (³He and fossil micrometeorite abundance) record separate size distributions of the extraterrestrial dust flux.

22-EPN3-113: Isotopic constraints on deformation of olivine: a preliminary study on mantle peridotites from Mt. Melbourne, northern Victoria Land, Antarctica

Visit by Daeyeong Kim and Jung Hun Seo of the Korea Polar Research Institute (KOPRI, Korea) to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 17 August – 06 September 2023

Report Summary: Microstructures of olivine-rich rocks record tectonic events in mantle, due to their diverse slip systems associated with the various deformation conditions. There have been, however, no time constraints on the slip systems that generate the microstructures of olivine. This study first investigates the temporal relationship of various microstructures of olivine based on the Re-Os geochronology of included sulphides. Mantle xenoliths of one lherzolite and two harzburgites were collected near Mt. Melbourne, northern Victoria Land, Antarctica, which suffered several tectonic events during the Proterozoic and Phanerozoic eons. Sulphide grains are texturally associated with olivine deformation fabrics in mantle rocks. The Re-Os isotopes of the 18 sulphide grains collected from the mantle xenoliths were analysed by using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and negative-ion thermal ionization mass spectrometry (TIMS) at CRPG Nancy, France.

The measured Os quantities are 0.9–4789.3 pg and Re quantities are 4.3–7.0 pg in the sulphides. ¹⁸⁷Os/¹⁸⁸Os in the sulphide are 0.1250–0.1298 for J04-A, 0.1130–0.1185 and 0.1286 for J04-B, and 0.1203–0.1216 for J04-D1. The corresponding depleted mantle ages (T_RD) are calculated to be 0.26–0.63 Ga for J04-A, 1.5–2.3 and 0.14 Ga for J04-B, and 1.1–1.3 Ga for J04-D1. The ages correspond to the tectonic evolution of suturing, subducting, and rifting events of the studied area, implying that the various structural events preserved in the mantle xenoliths can be temporally constrained by the sulphide Re-Os geochronology.

22-EPN3-025: Isotope Geochemistry Traces Magma–Shale Interaction

Visit by Manfredo Capriolo, University of Oslo (Norway), to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 17 – 28 April 2023

Report Summary: The research project aims to constrain and quantify magma–shale interaction via rhenium-osmium isotope analyses of whole rock samples from different geological settings in the Oslo Rift (about 300 Ma). Magma–shale interaction can produce massive amounts of greenhouse gases when magmas are injected into sedimentary basins, with potential implications for sulphur sequestration as sulphides. Here, 8 magmatic rock samples (of both intrusive and effusive origin) and 2 host shales were analysed in the laboratories of the Stable Rare Gas and Radiogenic Isotope Facility (CRPG, Nancy, France).

Among the investigated magmatic ones, 7 rock samples are alkali basalt sills with variableextents of hydrothermal overprint, and 1 rock sample is an evolved lava. The latter has a very low (< 5 ppt) Os concentration, making its magmatic Os isotope ratio prone to overprinting by crustal assimilation. The 7 alkali basalt sills display ¹⁸⁷Os/¹⁸⁸Os_299Ma values ranging from 0.14 to 1.15, reflecting different (from negligible to strong) degrees of shale contamination. Interestingly, the 2 host shales of Cambrian age display ¹⁸⁷Os/¹⁸⁸Os_299Ma values of 1.12 and 1.42. The rhenium-osmium isotope data from this research project indicate that magma–shale interaction via shallow magmatic intrusions in sedimentary basins can vary in intensity, implying a different extent of thermogenic degassing. These results improve the understanding of degassing scenarios from past events, open new perspective on the comparison with present-day atmospheric changes, and suggest interesting implications for economic resources, such as hydrocarbon reservoirs or sulphide ore deposits.

20-EPN2-017: Resolving critical uncertainties in the impact of geomagnetism on in situ cosmogenic nuclide production via long-term calibration

Visit by Gordon Bromley, University of Galway (Ireland), to  TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 17 – 21 October 2022

Report Summary: Cosmogenic nuclide (CN) surface-exposure dating (SED) has revolutionised geomorphology in recent years, enabling the direct determination of both the rate and age of Earth surface-processes. However, SED relies on strict quantification of CN production rates (PRs) for both the time-period and location in question; for many sites and times periods such data is rare. As a result, calculated exposure ages may vary significantly depending upon the assumptions and model schemes employed in calculations. The impact of geomagnetic field variability on nuclide production is particularly uncertain.

The goal of this project is to test explicitly the methods used to calculate exposure ages, and to assess their viability over space and time. To do this, we measured cosmogenic helium-3 within a series of Peruvian lavas of varying age at the Stable Rare Gas and Radiogenic Isotope Facility, CRPG (France). Paired with later Ar/Ar age determination, we are using these new cosmogenic helium data to produce a series of discrete CN production rates from a single geographic region, and so will assess the variability of nuclide production through time. Our preliminary results indicate the research plan is viable: cosmogenic helium data from single lava flows are internally consistent. Lavas analysed range in age from ~1.6 ka to ~175 ka, and so provide a dataset that spans a period sufficient to assess changes in PR and the potential impact of magnetic field variability on CN PRs. We anticipate sharing final project results within a peer-reviewed, open-access publication within the calendar year. 

20-EPN2-053: Noble gas (³He) analyses of iridium poor marine sediments to understand the astronomic process responsible for the late Eocene meteor shower

Visit by Jörg Fritz, ZERIN (Germany), to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 06 – 15 April 2022

Report Summary: The project aims to understand the astronomical processes leading to the late Eocene shower of extraterrestrial (ET) material onto Earth. The ³He-carrier phases responsible for the ~ 2 million years enduring ³He anomaly will be characterised geochemically by producing a combined ³He and Ir dataset.

Here, 23 samples of marine micro-fossil ooze from the ODP 689B core, Maud Rise, Southern Ocean were measured at the CRPG Nancy noble gas laboratory. These samples cover the Eocene Oligocene transition (38 to 33 Ma) and these new data document the amplitude and duration of the  ³He_ET anomaly and confirms that the late Eocene ³He anomaly reported from the Massignano outcrop (Italy) is a global phenomenon. The here-investigated 689B micro-fossil ooze is exceptional because its low terrigenous mineral content and low iridium concentration of 5-15 ppt Ir. These Ir values are close to the expected ET contribution of 12 ppt Ir, as calculated using the current global/annual ET flux and the sedimentation rate and dry density of the 689B deposits.

The ³He data set acquired during the TA visit combined with literature data on Ir concentrations show that the flux of ³He rich ET particles increase by 4 times whereas the Ir concentrations in 689B remain at background values. New Ir data with low detection limits will further constrain the relation between ET ³He and total Ir during the late Eocene shower. ET ³He does not correlate with Ir indicating that the late Eocene ³He anomaly was caused by ³He-rich and Ir poor dust particles. The study illuminates the potential of marine micro-fossil ooze for planetary science.