Comment on ‘Unveiling ductile deformation during fast exhumation of a granitic pluton in a transfer zone’ by Richard Spiess, Antonio Langone, Alfredo Caggianelli, Finlay M. Stuart, Martina Zucchi, Caterina Bianco, Andrea Brogi, & Domenico Liotta

In their paper, Spiess et al. (2021) published structural, geochronological, and EBSD data on one of the monzogranite apophyses (Capo Bianco) of the buried Porto Azzurro Pluton (island of Elba, Northern Apennines, Italy), a pluton emplaced in the upper crust (P < 0.2 GPa; e.g. Papeschi et al., 2019). The authors publish a new U/Pb age of 6.4 ± 0.4 Ma, associated to the thermal peak, and a U-Th/He apatite age of 5.0 ± 0.6 Ma, related to a T of 60 °C. Spiess et al. (2021) use these ages to model the exhumation of the pluton controlled by the sub-horizontal Zuccale Fault, a fault with 6 km of horizontal displacement (ZF; Keller & Coward, 1996). Their structural dataset from the macro to the microscale and EBSD analyses relies on a small section (about 100 m wide) in the NE part of the Calamita Peninsula. Based on their documentation of (1) vertical dykes in the monzogranite, (2) vertical to low-angle top-to-the-E extensional faults, and (3) later NW-striking oblique faults, they interpret the Porto Azzurro Pluton as emplaced in an extensional to transcurrent tectonic setting, extrapolating their findings to the entire Eastern Elba.

Widespread reworking of Hadean-to-Eoarchean continents during Earth’s thermal peak

The nature and evolution of Earth’s crust during the Hadean and Eoarchean is largely unknown owing to a paucity of material preserved from this period. However, clues may be found in the chemical composition of refractory minerals that initially grew in primordial material but were subsequently incorporated into younger rocks and sediment during lithospheric reworking. Here we report Hf isotopic data in 3.9 to 1.8 billion year old detrital zircon from modern stream sediment samples from West Greenland, which document successive reworking of felsic Hadean-to-Eoarchean crust during subsequent periods of magmatism. Combined with global zircon Hf data, we show a planetary shift towards, on average, more juvenile Hf values 3.2 to 3.0 billion years ago. This crustal rejuvenation was coincident with peak mantle potential temperatures that imply greater degrees of mantle melting and injection of hot mafic-ultramafic magmas into older Hadean-to-Eoarchean felsic crust at this time. Given the repeated recognition of felsic Hadean-to-Eoarchean diluted signatures, ancient crust appears to have acted as buoyant life-rafts with enhanced preservation-potential that facilitated later rapid crustal growth during the Meso-and-Neoarchean.

Effect of irradiation with high-energy protons and ions on the structure and properties of composite HTSC-2 tapes

The paper considers the effect of radiation defects caused by irradiation with protons (2.5 MeV), heavy ions 132Xe27+ (167, 80, 40 MeV), 86Kr17+(107 MeV), 40Ar8+(48 MeV), on the critical parameters of HTSC-2 tapes based on compounds YBa2Cu3O7 – x and GdBa2Cu3O7 – x. The results of calculations based on the model of the thermal peak of the ion track sizes are presented. The projective ranges of ions and protons in these samples are calculated. The radiation resistance of the studied samples to ion and proton radiation of the indicated energies is determined. The performed studies made it possible to detect, at low fluences of irradiation with heavy ions, an increase in the critical current (Ic), an improvement in the adhesion between the superconducting layer and the substrate, and a decrease in internal stresses in the HTSC layer. At higher values of fluences, the critical current and critical temperature decrease. It is important that the decrease in Ic begins at lower fluences than Tc.

BURNUP CALCULATIONS OF THE JSI TRIGA REACTOR FUEL AND COMPARISON WITH MEASUREMENTS

Fuel burnup of the JSI TRIGA was calculated by simulating complete operational history consisting of 240 different core configurations from 1966 to 2020. At the moment we are unable to perform burnup measurements, e.g. gamma spectroscopy on burned fuel elements, hence we used weekly measured excess reactivity as a reference point of different core configurations to verify the calculated core reactivity. Changes in reactivity due to burnup were assumed to be linear and this assumption was verified for burnup intervals smaller than 3 MWd/kg(HM). The comparison was performed on 46 different core configurations with different type of fuel elements. The Serpent-2 calculations decently predict the rate of reactivity change on different cases, as 52 % of calculations are withing 1σ and 86.9 % within 2σ of the measurements for total number of 46 cases. Additional analysis was performed by comparing unit cell calculations of different fuel types. Four different types of TRIGA fuel were used to analyse burnup changes in LEU and HEU fuel, where positive reactivity feedback on burnup was observed for HEU fuel due to burnable absorbers. Serpent-2 and WIMSD-5B were compared on unit-cell basis where good agreement within 200 pcm of reactivity change for large burnup was observed. In addition neutron spectrum changes due to burnup were investigated using unit-cell calculations where 4 % increase of the thermal peak and 1 % decrease of fast peak of the spectrum was observed for typical fuel burnups of 20 MWd/kg(HM), which approximately represents JSI TRIGA burnup at this moment.

On the slowing down of 14 MeV neutrons

An experimental procedure is assessed to obtain moderated neutron fields starting from almost monochromatic 14 MeV neutrons generated by means of an accelerator-driven D-T source. The use of a metallic pre-moderator and a standard hydrogen-containing moderator is effective in producing neutron spectra featuring a thermal peak and an epithermal slowing down tail extending up to 14 MeV. The performance of proposed moderation system was investigated by means of MCNP Monte Carlo calculations, benchmarked against experimental measurements using an explorative set up, assembled at the Frascati Neutron Generator. The benchmarked calculations allow at making predictions about the brilliance of a 14 MeV neutron moderator in view of possible applications in neutron science.

Cassini CIRS and ISS opposition effects of Saturn’s rings – I. C ring narrow or broad surge?

We focus on the thermal and optical opposition effects of Saturn’s C ring seen by Cassini CIRS (Composite InfraRed Spectrometer) at 15.7 ${\mu}$m and ISS (Imaging Science Subsystem) at 0.6 ${\mu}$m. The opposition surge is a brightness peak observed at low phase angle (α → 0°). Saturn rings’ opposition surge was recently observed in reflected light and thermal infrared emission by Cassini. There is debate on whether the C ring’s thermal opposition surge width is narrow (≲1°) or broad (≳30°). This surge is important because its width was used to define the scale of ring properties driving the thermal peak. We parametrize the CIRS and ISS phase curves with several morphological models to fit the surge shape. For five of the largest C ring’s plateaus, we find that their thermal surge is 10 times wider than the optical surge and that the thermal surge width (∼4°) is neither narrow, nor broad. We compare radial differences between CIRS and ISS surge morphologies with the optical depth τ (from UVIS, UltraViolet Imaging Spectrograph) and water ice band depth (from VIMS, Visual and Infrared Mapping Spectrometer) profiles. We find that: water ice band depths (microscopic ring signatures) and τ (macroscopic ring signatures) show respectively little and large contrasts between the background and the plateaus. The thermal surge amplitude and τ are correlated, and we found no band depth dependence, contrary to the optical surge amplitude, which shows no correlation with τ. These correlations suggest a macroscopic scale dominance in controlling the C ring’s thermal opposition effect.

Hydrothermal fluid circulations in the western Pyrenees: new data on stable isotopes, in-situ gas analysis and fluid inclusions

Several fluid circulation events are recorded in the Aquitaine Basin and the Chaînons Béarnais in the Pyrenean belt of southwestern France. Different fluid types are found in all locations studied. The main difference comes from the thermal peak event (rifting), which was more intense in the Chaînons Béarnais close to the exhumed mantle zone. In situ gas analysis associated of fluid inclusions and isotopic (C, O, H, S) analyses show that similar fluids are generated in both systems, although separated by deep structures, e.g. the North Pyrenean Frontal Thrust (NPFT). The Pyrenean tectonic history leads to the compartmentalization of fluid circulations.