^1,2Agata M. Krzesińska,³Richard Wirth,^3,4Monika A. Kusiak
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13296]
¹Centre for Earth Evolution and Dynamics, Department of Geosciences, University of Oslo, Oslo, Norway
²Department of Earth Sciences, Natural History Museum, Cromwell Road, SW7 5BD London, UK
³GeoForschungsZentrum Potsdam, Section 3.5 Surface Geochemistry, D‐14473 Potsdam, Germany
⁴Institute of Geological Sciences Polish Academy of Sciences, ING PAN, Twarda 51/55, PL‐00818 Warszawa, Poland
Published by arrangement with John Wiley & Sons

Zakłodzie is an enstatite meteorite of unknown petrogenesis. Chemically, it resembles enstatite chondrites, but displays an achondrite‐like texture. Here we report on fabric and texture analyses of Zakłodzie utilizing X‐ray computed tomography and scanning electron microscopy and combine it with a nanostructural study of striated pyroxene by transmission electron microscopy. With this approach we identify mechanisms that led to formation of the texture and address the petrogenesis of the rock. Zakłodzie experienced a shock event in its early evolution while located at some depth inside a warm parent body. Shock‐related strain inverted pyroxene to the observed mixture of intercalated orthorhombic and monoclinic polymorphs. The heat that dissipated after the peak shock was added to primary, radiogenic‐derived heat and led to a prolonged thermal event. This caused local, equilibrium‐based partial melting of plagioclase and metal‐sulfide. Partial melting was followed by two‐stage cooling. The first phase of annealing (above 500 °C) allowed for crystallization of plagioclase and for textural equilibration of metal and sulfides with silicates. Below 500 °C, cooling was faster and more heterogeneous at cm scale, allowing retention of keilite and quenching of K‐rich feldspathic glass in some parts. Our study indicates that Zakłodzie is neither an impact melt rock nor a primitive achondrite, as suggested in former studies. An impact melt origin is excluded because enstatite in Zakłodzie was never completely melted and partial melting occurred during equilibrium‐based postshock conditions. Texturally, the rock represents a transition of chondrite and achondrite and was formed when early impact heat was added to internal radiogenic heat.

¹M. Szokaluk,¹R. Jagodziński,¹A. Muszyński,¹W. Szczuciński
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13290]
¹Institute of Geology, Adam Mickiewicz University in Poznań, Bogumiła Krygowskiego 12, 61‐680 Poznań, Poland
Published by arrangement with John Wiley & Sons

Confirmed small impact craters in unconsolidated deposits are rare on Earth, and only a few have been the subjects of detailed investigations. Consequently, our knowledge of indicators permitting unambiguous identification of such structures is limited. In this work, detailed geological mapping was performed in the area of the Morasko craters, of which the largest crater is of about 96 m diameter. These craters were formed in the mid‐Holocene (~5000 yr ago) in unconsolidated sediments of a glacial terminal moraine. Fragments of the impactor—an iron meteorite—have been found in the craters’ vicinity for many decades. Despite numerous studies of the meteorite, no detailed research concerning the geological structure around the craters and of the ejecta deposits has been undertaken. The new data, including evaluation of over 52 sediment cores and 260 shallow drillings, permit the identification of four main sediment types: Neogene clays, diamicton with Neogene clay clasts containing charcoal pieces, diamicton without clasts, and sand with locally preserved paleosoil and charcoal pieces. Based on sedimentological properties, the ejecta deposits are mainly identified as diamicton with Neogene clay clasts, described as lithic impact breccia, covering locally preserved pre‐impact soil. Moreover, crater sections characterized by inverse stratigraphy of sediments are identified as belonging to overturned flaps.

¹Javier Cuadros,¹Christian Mavris,²Joseph R.Michalski,³Jose Miguel Nieto,⁴Janice L.Bishop,⁵Saverio Fiore
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.04.027]
¹Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
²Department of Earth Sciences, Laboratory for Space Research, University of Hong Kong, Pokfulam Road, Hong Kong, China
³Department of Earth Sciences, University of Huelva, 21071 Huelva, Spain
⁴SETI Institute, Mountain View, CA 94043, USA
⁵Institute of Methodologies for Environmental Analysis, CNR, Department of Geoenvironmental and Earth Sciences, University of Bari, Via Orabona 4, 70125 Bari, Italy
Copyright Elsevier

Investigation of Earth analogs and their environments is crucial for the full interpretation of geologic outcrops and processes on Mars. Phyllosilicates are important indicators of aqueous processes and their characterization is a significant piece of the geologic puzzle of Mars. They are chiefly investigated with Near-Infrared (NIR) spectroscopy from orbit. While these studies have revolutionized our understanding of aqueous processes on Mars, they are challenged by the chemical and structural complexity of phyllosilicates, non-linear response to mineral abundance, low penetration of infrared radiation in the target rocks, and spectral modifications caused by rock texture. Phyllosilicate-bearing samples from four locations in the Iberian Pyrite Belt (El Villar, Calañas, Quebrantahuesos, and Tharsis) were investigated using NIR, XRD and thermogravimetry in order to document the effects of acidic alteration under multiple environments and inform orbital detections on Mars. The samples are comprised of chlorite, illite, kaolinite, alunite, jarosite, goethite and interstratified chlorite-vermiculite and kaolinite-smectite. Kaolinite dominates the spectral signature relative to other phyllosilicates from abundances as low as 7 wt%. Only alunite and jarosite display spectral intensities similar to kaolinite. NIR spectra of bulk rock and <2 μm size fractions are very similar, indicating that spectra are dominated by the smaller particles. The octahedral Al-Fe-Mg composition of illite and kaolinite determine the positions of their OH combination band (~2.21 μm), commonly used for phyllosilicate characterization. The range of wavelength variation is narrower for kaolinite-dominated spectra, 2.205–2.216 μm, but wider than the spectral resolution of the orbital probe CRISM (~0.007 μm). Thus, in favorable conditions CRISM spectra can identify variations of kaolinite octahedral composition, a valuable tool to investigate kaolinite origin. A survey of kaolinite-bearing spectra from Mars (Leighton Crater, Mawrth Vallis and Nili Fossae regions) showed that most OH combination bands are within 2.205–2.212 μm. One spectrum displayed this band at 2.215–2.219 μm, and is a good candidate for kaolinite with significant Fe/Mg-substitution.