Tag: ta2.9

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 TA2.9 Ion Probe Facility (IPF), 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. 

Read the full scientific report, with kind permission from Gordon Bromley.

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 TA2.9 Ion Probe Facility (IPF), 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 form 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.

20-EPN2-072: Dynamics of the early inner solar system inferred from combined 26 Al-26 Mg and Cr–Ti–O isotope systematics of non-carbonaceous chondrules

Visit by Christian Jansen, WWU Münster (Germany) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 03-12 August 2022

Report Summary: The advent of non-traditional isotopic systems (e.g., Ti, Cr, Mo) revealed that chondrites—the most primitive witnesses of the early solar system—display a fundamental isotopic dichotomy, with carbonaceous chondrites (CCs) showing large nucleosynthetic anomalies relative to terrestrial standards that are not observed in non-carbonaceous chondrites (NCs). NC and CC reservoirs may thus represent the primordial inner and outer parts of the solar system, respectively. 

The scientific goal of this project is to combine several isotopic systems (O, Ti, Cr) for deciphering the conditions and chronology of chondrule formation in the NC reservoir. A key parameter of this approach is to also have access to the formation ages of these chondrules. This requires in situ measurements with a secondary ion mass spectrometer for determining the ²⁶Al ages of chondrule crystallisation.

To do so, 16 chondrules were separated from the minimally altered ordinary chondrite NWA 5206. They were split into two pieces for determining their (i) Cr and Ti isotopic compositions (bulk measurements) and (ii) O isotopic compositions and ²⁶Al ages. These chondrules show no ⁵⁴Cr or ⁵⁰Ti excesses and classical oxygen isotopic composition (with ∆¹⁷ O ranging from -1 to + 1 ‰). ²⁶Al ages are coherent with previous estimates showing that NC chondrules formed over several million years during the evolution of the inner disk.

20-EPN2-102: A new source of water from Mars

Visit by Tim Tomkinson, University of Bristol (UK) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 05-09 December 2022

Report Summary: Here we have searched for a source of D-enriched Martian groundwater previously discovered in the Martian meteorite Lafayette (up to δD 4725‰) within olivine defects below the secondary mineral phyllosilicate. These groundwaters which are known flowed through this sample 670 Ma were sourced from the Martian atmosphere, or had equilibrated with it, and diffused up to ~1.5 µm into the olivine via shock-formed defects in vein walls. In this project we want to determine a calibration line to resolve the water content on the Martian olivines and find a potential location of new water within the defects.

Two 1 inch indium mounts were prepared with olivine plus glass standards and paired Martian nakhlite samples (Yamato 593, 802, 749, Lafayette and Nakhla) to confirm this source of Martian ground water. Work was conducted with Dr Johan Villeneuve and Dr Laurette Piani on the Cameca IMS 1270 E7 ion probe at CRPG, Nancy. The new obtained/formed standards provided calibration to measurements of water contents (H₂O%) within the Martian olivines and when combined with standards from CRPG δD values were roughly constrained. Owing to the unique surfaces of each Martian altered olivine it was impossible to confirm pre analyses if defects hosting water would be present in the outer olivine surfaces. Results show a location where an enriched δD was present, further investigations such as Transmission Electron Microscopy (TEM) are required to confirm this.

20-EPN2-067: Hydrogen isotope compositions of matrices in unequilibrated ordinary chondrites

Visit by Helen Grant, University of Manchester (UK) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 10-21 October 2022

Report Summary: One way to study the origin of water and other volatiles which accreted onto rocky planets such as Earth during the formation of the Solar System is to study meteorites that fall from asteroids and other planetary bodies. Hydrogen isotope ratios within meteorites can be used as a tracer for the source of a body’s water, and to an extent spatial and temporal information about the formation of parent bodies. 

Previously, we measured the D/H ratios of bulk powders of a wide range of unequilibrated ordinary chondrites (UOCs), and found wide variations which did not fit into current H-distribution models. Using SIMS, we measured the H, D, C, and Si contents of the fine-grained matrix of 13 of these previously studied UOCs (only falls) ranging from types 3.00 – 3.9. Preliminary results confirm the wide previously observed spread of D/H ratios between samples, including high elevations in a handful of UOCs. C/H ratios will be used to determine the D contribution within samples specific to water, however initial observations confirm contributions from both hydrated and organic components. The results from this visit will be combined with other in-situ studies carried out at the home institution to determine exactly what phases are hosting this highly D-rich material, and how these chondrites affect models of water transport in the early Solar System.

Read the full scientific report, with kind permision from Helen Grant.

20-EPN-031: Investigating volatiles in the early Solar System through analysis of halogens in chondrules

Visit by Edward Baker, University of Manchester (UK) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 13-17 December 2021

Report Summary: We have measured the concentration of halogens in the glasses of chondrules from enstatite chondrites. There is a clear correlation between Chlorine and Bromine abundances, but no clear relationship between Cl or Br and F. Iodine was not measured. In the main S is well correlated with Cl: this trend may have been modified by unintended analysis of micron scale blebs on sulphide.  Halogen profiles have been taken across a number of suitable target chondrules, for diffusion modelling, which will be presented and published in due course. The array of data for F/Cl is sub-chondritic while the Br/Cl array is super-chondritic.

Evaporation and condensation may play important roles in controlling halogen behaviour, along with partitioning between other significant reservoirs in chondrites because fluorine is likely to be compatible in a number of silicate minerals. More will be known after diffusion modelling and after the experimental partition coefficients have been determined. 

Read the full scientific report, with kind permision from Edward Baker and Rhian Jones.

21-EPN-FT1-005: Reading the sedimentary archive of discontinuity surfaces

Visit by Simon Andrieu, Aarhus University (Denmark) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 18-22 October 2021

Report Summary: Discontinuity surfaces, associated with seafloor cementation, are hence of primordial importance for fully apprehending the geological record, yet they have received far less attention than the sedimentary rocks surrounding them. Fundamental problems that are still not sufficiently understood concern the lateral change of discontinuities. In this project, we tackle this issue by studying the lateral variation of five distinct discontinuity horizons present in the Middle Jurassic of the High Atlas (Morocco), where outstanding exposures permit to track these surfaces over tens of kilometres. Hence, the purpose of this work is to characterise at a high-resolution the large-scale variation of petrographic and geochemical (C, O and Sr-isotopes) properties of discontinuities (matrix and cement phases) along dip and strike of a Jurassic moderately deepening ramp. δ¹⁸O (176 values) and δ¹³C (105 values) signatures were obtained on twenty-one cements and grain types, including 14 different early calcite cements and fabrics corresponding to dogtooth cements (7), turbid synaxial cements (1) and micritic/microsparitic fabrics (6).

Data confirm that dogtooth cements can precipitate in marine phreatic, meteoric phreatic and shallow burial environments. The highly negative δ¹⁸O values of micritic fabrics and turbid synaxial cements, which form in seawater, indicate that they transformed during subsequent diagenesis (i.e during meteoric water circulation or shallow burial). It indicates that they precipitate initially with an unstable mineralogy (aragonite or high-magnesium calcite). δ¹⁸O and δ¹³C data on early cements suggest that a same discontinuity can change laterally from a subaerial exposure surface to a marine surface.

Read the full scientific report, with kind permision from Simon Andrieu.

20-EPN-034: Calibration of the Al-in-olivine thermometer: Insight into the thermal history of type II chondrules

Visit by Thomas van Gerve and Kat Shepherd, KU Leuven (Belgium) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 18-22 October 2021

Report Summary: Chondrites are the most primitive agglomerates formed in the solar system. In this project, we want to develop a thermometer based on Al-in-olivine/spinel equilibrium to calculate the temperature of formation of chondrites. or this project, we have performed a large number of new low- to high-pressure (1 atm – 10 GPa) experiments relevant to chondrule formation at the KU Leuven.

Experiments were run at high temperature (1200-1800°C), under variable oxygen fugacity conditions (IW+1 to IW+5, IW = iron-wustite). From 18-22 October 2021, Thomas van Gerve and Kat Shepherd (KU Leuven) worked with the Cameca IMS 1270 E7 ion probe at CRPG, Nancy, under the supervision of Dr. Johan Villeneuve and M. Nordine Bouden. We have measured the following masses: ¹²C, ¹⁶O¹H, ¹⁸O, ¹⁹F, ²⁷Al, ³⁰Si, ³²S and ³⁵Cl in olivine, glass and glass inclusions. During our analytical session, we measured ~ 150 points in olivine and glass in addition to the standards. Results are extremely reproducible and show a trend of slightly increasing Al content in olivine as a function of the Fo content (molar Mg/(Mg+Fe)) of olivine. Using our new SIMS results, we are in the process of developing a thermodynamically rooted model taking into account major components in spinel and olivine.

Read the full scientific report, with kind permision by Thoma van Gerve and Kat Shepherd.