Shock Deformation in Zircon, a Comparison of Results from Shock-Reverberation and Single-Shock Experiments

The utility of the mineral zircon, ZrSiO4, as a shock-metamorphic geobarometer and geochronometer, has been steadily growing within the planetary science community. Zircon is an accessory phase found in many terrestrial rock types, lunar samples, lunar meteorites, martian meteorites and various other achondrites. Because zircon is refractory and has a high closure temperature for Pb diffusion, it has been used to determine the ages of some of the oldest material on Earth and elsewhere in the Solar System. Furthermore, major (O) and trace-element (REE, Ti, Hf) abundances and isotope compositions of zircon help characterize the petrogenetic environments and sources from which they crystallized. The response of zircon to impact-induced shock deformation is predominantly crystallographic, including dislocation creep and the formation of planar and sub-planar, low-angle grain boundaries; the formation of mechanical {112} twins; transformation to the high pressure polymorph reidite; the development of polycrystalline microtextures; and dissociation to the oxide constituents SiO2 and ZrO2. Shock microstructures can also variably affect the U- Pb isotope systematics of zircon and, in some instances, be used to constrain the impact age. While numerous studies have characterized shock deformation in zircon recovered from a variety of terrestrial impact craters and ejecta deposits and Apollo samples, experimental studies of shock deformation in zircon are limited to a handful of examples in the literature. In addition, the formation conditions (e.g., P, T) of various shock microstructures, such as planar-deformation bands, twins, and reidite lamellae, remain poorly con-strained. Furthermore, previous shocked-zircon experimental charges have not been analyzed using modern analytical equipment. This study will therefore under-take an new set of zircon shock experiments, which will then be microstructurally characterized using state-of-the-art instrumentation within the Astromaterials Research and Exploration Science Division (ARES), NASA Johnson Space Center

In situ estimation of subsurface hydro-geomechanical properties using the groundwater response to semi-diurnal Earth and atmospheric tides

Subsurface hydro-geomechanical properties crucially underpin the management of Earth\u27s resources, yet they are predominantly measured on core samples in the laboratory while little is known about the representativeness of in situ conditions. The impact of Earth and atmospheric tides on borehole water levels is ubiquitous and can be used to characterise the subsurface. We illustrate that disentangling the groundwater response to Earth (M₂) and atmospheric tidal (S₂) forces in conjunction with established hydraulic and linear poroelastic theories leads to a complete determination of the whole hydro-geomechanical parameter space for unconsolidated systems. Further, the characterisation of consolidated systems is possible when using literature estimates of the grain compressibility. While previous field investigations have assumed a Poisson\u27s ratio from literature values, our new approach allows for its estimation under in situ field conditions. We apply this method to water level and barometric pressure records from four field sites with contrasting hydrogeology. Estimated hydro-geomechanical properties (e.g. specific storage; hydraulic conductivity; porosity; shear, Young\u27s, and bulk moduli; Skempton\u27s and Biot–Willis coefficients; and undrained or drained Poisson\u27s ratios) are comparable to values reported in the literature, except for consistently negative drained Poisson\u27s ratios, which is surprising. Our results reveal an anisotropic response to strain, which is expected for heterogeneous (layered) lithological profiles. Closer analysis reveals that negative Poisson\u27s ratios can be explained by in situ conditions differing to those from typical laboratory core tests and the small strains generated by Earth and atmospheric tides. Our new approach can be used to passively, and therefore cost-effectively, estimate subsurface hydro-geomechanical properties representative of in situ conditions and it improves our understanding of the relationship between geological heterogeneity and geomechanical behaviour

Multifactor analysis of specific storage estimates and implications for transient groundwater modelling

Specific storage (S$_S$) has considerable predictive importance in the modelling of groundwater systems, yet little is known about its statistical distribution and dependency on other hydrogeological characteristics. This study provides a comprehensive overview and compiles 430 values of S$_S$ from 183 individual studies, along with complementary hydrogeological information such as estimation methods, lithology, porosity, and formation compressibility. Further evaluation of different approaches to determine and utilize S$_S$ values for numerical groundwater modelling, along with the scale and source of uncertainty of different measurement methods, was carried out. Overall, S$_S$ values range across six orders of magnitude (from 3.2 × 10$^{–9}$ to 6 × 10$^{–3}$ m$^{–1}$) with a geometric mean of 1.1 × 10$^{–5}$ m$^{–1}$ and the majority (> 67%) of values are in the order of 10$^{–5}$ and 10$^{–6}$ m$^{–1}$. High S$_S$ values of ~10$^{–4}$ m$^{–1}$ were reported for glacial till and sandy lithologies, particularly for shallow and thin strata where leakage may obscure the estimation of S$_S$. A parallel assessment of 45 transient regional-scale groundwater models reveals a disconnect between findings of this study and the way S$_S$ is treated in practice, and that there is a lack of foundational S$_S$ data to conduct quantitative uncertainty analysis. This study provides the first probability density functions of S$_S$ for a variety of lithology types based on the field and laboratory tests collated from the literature. Log transformed S$_S$ values follow a Gaussian/normal distribution which can be applied to evaluate uncertainties of modelling results and therefore enhance confidence in the groundwater models that support decision making

Interpreting U–Pb data from primary and secondary features in lunar zircon

In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U–Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th–U–Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal–plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U–Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal–plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U–Pb isotopic systems

Physical properties of Mesozoic sedimentary rocks from the Perth Basin, Western Australia

The Perth Basin (PB) hosts important aquifers within the Yarragadee Formation and adjacent geological formations with potential for economic exploitation by both geothermal energy and carbon capture and sequestration. Published studies on the reservoir quality of the sedimentary units of the PB are very few. This study reports some petrophysical and lithological characteristics of the sedimentary units of interest for geothermal and geosequestration scenarios and help interpolation toward non-sampled intervals. A new fluvial-dominated lithofacies scheme was developed for the Mesozoic stratigraphy from four wells drilled in the central PB (Pinjarra-1, Cockburn-1, Gingin-1 and Gingin-2) based on grainsize, sorting, sedimentary structures and colour that relate to the environment of deposition. Systematic laboratory measurements of permeability, porosity, and thermal conductivity were conducted on core samples to investigate a variety of lithofacies and depths from these wells. Empirical correlations are established among the different physical properties, indicating encouraging relationships for full PB basin interpolation such as between porosity and permeability, when the samples are grouped into ‘hydraulic units’ defined by a ‘flow zone indicator’ parameter. The common principal controls on the PB thermal conductivity are the pore space arrangement and mineralogical content, which are strongly lithofacies-specific. Therefore, the lithofacies type could be a good first-order discriminator for describing spatial variations of thermal conductivity and then estimate their flow zone indicator

Spherical harmonic based noise rejection and neuronal sampling with multi-axis OPMs

In this study we explore the interference rejection and spatial sampling properties of multi-axis Optically Pumped Magnetometer (OPM) data. We use both vector spherical harmonics and eigenspectra to quantify how well an array can separate neuronal signal from environmental interference while adequately sampling the entire cortex. We found that triaxial OPMs have superb noise rejection properties allowing for very high orders of interference (L=6) to be accounted for while minimally affecting the neural space (2dB attenuation for a 60-sensor triaxial system). We show that at least 11th order (143 spatial degrees of freedom) irregular solid harmonics or 95 eigenvectors of the lead field are needed to model the neural space for OPM data (regardless of number of axes measured). This can be adequately sampled with 75-100 equidistant triaxial sensors (225-300 channels) or 200 equidistant radial channels. In other words, ordering the same number of channels in triaxial (rather than purely radial) configuration may give significant advantages not only in terms of external noise rejection but also by minimizing cost, weight and cross-talk

Effects of prenatal exposure to xenobiotic estrogen and the development of endometriosis in adulthood

Abstract only availableEndometriosis is an estrogen-dependent disease that affects millions of women worldwide, causing pain and infertility. While it is known that retrograde menstruation places endometrial tissue in the peritoneal cavity, it is unclear why it invades and proliferates in women with endometriosis. Studies have shown that other hormone-dependent diseases have a fetal basis (e.g. breast cancer), suggesting that the presence of different hormones before birth may alter the incidence of endometriosis in adulthood. For example, women whose mothers took the synthetic estrogen diethylstilbestrol (DES) during pregnancy had an eighty percent increased incidence of endometriosis. Thus, our hypothesis is that prenatal exposure to xenobiotic estrogen will increase the severity of endometriosis in adulthood in a mouse model of surgically-induced endometriosis. To test this hypothesis, mice were time mated and dosed with vehicle control, 100 ng/kg DES or 10,000 ng/kg DES from days 11-17 of gestation. Surgical induction of endometriosis was performed in adulthood by autotransplantation of one uterine horm. The horn was removed, opened, divided into three pieces, and sutured to the arterial cascade of the intestinal mesentery. The implants became vascularized and formed endometriotic lesions. The mice were then collected at 2 or 4 weeks post-surgery, and the following endpoints were measured: 1) uterine weight; 2) implant size; and 3) implant weight. Additionally, implants were set aside for further analysis of 1) histology; 2) estrogen receptor indicator reporter gene activity; and 3) endometriosis-related gene expression. At the conclusion of this ongoing study, we expect to show whether there is an estrogen-mediated fetal component to endometriosis.Life Sciences Undergraduate Research Opportunity Progra

Atomic kinetic energy, momentum distribution and structure of solid neon at zero-temperature

We report on the calculation of the ground-state atomic kinetic energy, $E_{k}$, and momentum distribution of solid Ne by means of the diffusion Monte Carlo method and Aziz HFD-B pair potential. This approach is shown to perform notably for this crystal since we obtain very good agreement with respect to experimental thermodynamic data. Additionally, we study the structural properties of solid Ne at densities near the equilibrium by estimating the radial pair-distribution function, Lindemann's ratio and atomic density profile around the positions of the perfect crystalline lattice. Our value for $E_{k}$ at the equilibrium density is $41.51(6)$ K, which agrees perfectly with the recent prediction made by Timms {\it et al.}, $41(2)$ K, based on their deep-inelastic neutron scattering experiments carried out over the temperature range $4 - 20$ K, and also with previous path integral Monte Carlo results obtained with the Lennard-Jones and Aziz HFD-C2 atomic pairwise interactions. The one-body density function of solid Ne is calculated accurately and found to fit perfectly, within statistical uncertainty, to a Gaussian curve. Furthermore, we analyze the degree of anharmonicity of solid Ne by calculating some of its microscopic ground-state properties within traditional harmonic approaches. We provide insightful comparison to solid $^4$He in terms of the Debye model, in order to size the relevance of anharmonic effects in Ne.Comment: 20 pages, 7 figures. To be published in Physical Review