¹P. Oliver,¹M. Ralchenko,¹C. Samson,^1,2R. E. Ernst,³P. J. A. McCausland,⁴G. F. West
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13028]
¹Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
²Faculty of Geology and Geography, Tomsk State University, Tomsk, Russia
³Western Paleomagnetic and Petrophysical Laboratory, Western University, London, Ontario, Canada
⁴Department of Physics, University of Toronto, Toronto, Ontario, Canada
Published by arrangement with John Wiley & Sons

Ordinary chondrites have previously been nondestructively characterized using bulk magnetic susceptibility, broadly reflecting their Fe-Ni alloy content. We seek to expand the information that can be recovered from magnetic susceptibility by using the University of Toronto Electromagnetic Induction Spectrometer (UTEMIS) to measure the complex magnetic susceptibility tensor of 20 ordinary chondrites samples in addition to 16 Gao–Guenie (H5) chondrites at 35 frequencies from 90 Hz to 64 kHz, at variable low applied field strengths <10 A m−1. Following removal of the field-dependent component of susceptibility, frequency dependence, in- and out-of-phase components, and bulk magnetic susceptibility were interpreted. Most meteorites showed no frequency-dependent in-phase responses, but had a frequency-dependent out-of-phase response attributed to eddy currents induced in conductive minerals. Greater in- and out-of-phase frequency dependence correlated with lower fayalite content in olivine and was, in turn, inversely proportional to Fe-Ni alloy content. The uncertainty in the UTEMIS measurements ranges from approximately 0.05% for low-frequency in-phase measurements to a maximum of 3% for low-frequency out-of-phase measurements. This uncertainty level was far lower than the intra-meteorite variability for the Gao–Guenie suite suggesting inhomogeneity at scales of approximately 10 g.

¹C.M.Pieters et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13008]
¹Brown University, Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

The geologic context of red organic-rich materials (ROR) found across an elongated 200 km region on Ceres is evaluated with spectral information from the multispectral framing camera (FC) and the visible and near-infrared mapping spectrometer (VIR) of Dawn. Discrete areas of ROR materials are found to be associated with small fresh craters less than a few hundred meters in diameter. Regions with the highest concentration of discrete ROR areas exhibit a weaker diffuse background of ROR materials. The observed pattern could be consistent with a field of secondary impacts, but no appropriate primary crater has been found. Both endogenic and exogenic sources are being considered for these distinctive organic materials.

^1,2Matthias Ebert,^2,3Astrid Kowitz,²Ralf Thomas Schmitt,^2,4,5Wolf Uwe Reimold,⁶Ulrich Mansfeld,⁶Falko Langenhorst
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12948]
¹Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
²Museum für Naturkunde – Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
³Department of Earth Sciences, Freie Universität, Berlin, Germany
⁴Humboldt Universität zu Berlin, Berlin, Germany
⁵Geochronology Laboratory, University of Brasilia, Brasilia, Brazil
⁶Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
Published by arrangement with John Wiley & Sons

Shock-induced recovery experiments were performed to investigate melt formation in porous sandstones in the low shock pressure regime between 2.5 and 17.5 GPa. The sandstone shocked at 2.5 and 5 GPa is characterized by pore closure, fracturing of quartz (Qtz), and compression and deformation of phyllosilicates; no melting was observed. At higher pressures, five different types of melts were generated around pores and alongside fractures in the sandstone. Melting of kaolinite (Kln), illite (Ill), and muscovite (Ms) starts at 7.5, 12, and 15 GPa, respectively. The larger the amount of water in these minerals (Kln ~14 wt%, Ill ~6–10 wt%, and Ms ~4 wt% H₂O), the higher the shock compressibility and the lower the shock pressure required to induce melting. Vesicles in the almost dry silicate glasses attest to the loss of structural water during the short shock duration of the experiment. The compositions of the phyllosilicate-based glasses are identical to the composition of the parental minerals or their mixtures. Thus, this study has demonstrated that phyllosilicates in shocked sandstone undergo congruent melting during shock loading. In experiments at 10 GPa and higher, iron melt from the driver plate was injected into the phyllosilicate melts. During this process, Fe is partitioned from the metal droplets into the surrounding silicate melts, which induced unmixing of silicate melts with different chemical properties (liquid immiscibility). At pressures between 7.5 and 15 GPa, a pure SiO₂ glass was formed, which is located as short and thin bands within Qtz grains. These bands were shown to contain tiny crystals of experimentally generated stishovite.