Shock metamorphism in the Rubielos de la Cérida impact basin (Eocene-Oligocene Azuara multiple impact event, Spain) – reappraisal and photomicrograph image gallery
by Kord Ernstson1 and Ferran Claudin2 (April 2021)
Abstract. – We present a new compilation of previously abundantly studied and published shock effects in minerals and rocks of the Middle Tertiary Rubielos de la Cérida Impact Basin in northeastern Spain. Typologically, we organize by: shock melt – accretionary lapilli – diaplectic glass – planar deformation features (PDF) – deformation lamellae in quartz – isotropic twins in feldspar – kink banding in mica and quartz – micro-twinning in calcite – shock spallation. Included are the newly associated Jiloca-Singra impact in the so-called Jiloca graben and the Torrecilla ring structure, which immediately adjoins the Rubielos de la Cérida basin to the northeast. The compilation and presentation also opposes once more the still existing fundamental rejection of an impact genesis of the Azuara impact event by leading impact researchers of the so-called impact community and by regional geologists from the University of Zaragoza.
Invitation to submit to MINERALS – international peer-reviewed open access journal of natural mineral systems, mineral resources, mining, and mineral processing. Minerals is published monthly online by MDPI.
Research, Review and Short Communication manuscripts are welcome.
Special Issue Editors
Prof. Dr. Kord Ernstson Website Guest Editor Faculty of Philosophy, Julius-Maximilians-Universität Würzburg, 97074 Würzburg, Germany Interests: meteorite impact cratering; meteorite mineralogy; shock metamorphism; impact rocks/impactites; geology and geophysics of impact structures; meteorite impact archeology
Dr. Pavel SvandaWebsite Guest Editor Department of Mechanics, Materials and Machine Parts, University of Pardubice, Pardubice, Czech Republic Interests: microstructure; scanning electron microscopy (SEM); material properties; material engineering
Dr. Ioannis Baziotis. Website1 Website2 SciProfiles Guest Editor “Natural Resources Management & Agricultural Engineering” Agricultural University of Athens, Athens, Greece Interests: shock metamorphism; Martian meteorites; high- and Ultra-high pressure metamorphic rocks; mantle xenoliths; geomaterials
Special Issue Information
The theme of this Special Issue of Minerals, “Iron Silicide Minerals”, explicitly focuses on its occurrence in nature. In industry, the best known is iron monosilicide FeSi, which is used, among other things, for the production of various alloys.
Iron silicides in nature are very rare, little known, and have only become accessible to science in the last few decades. At the same time, much (origin, formation) is still unclear.
Minerals xifengite, Fe5Si3, and gupeiite, Fe3Si, components of the Yanshan meteorite at the type-locality Chengde, Lever in China, which was published in 1984, got their names from Xifengkou and Gubeikou at passages of the Great Wall of China. Somewhat earlier, in 1960, the natural equivalent of industrial FeSi, naquite, was discovered, but the industrial aspect of their origin remained essential for a long time. Other rare iron silicide minerals include the FeSi2 (linzhite), luobusaite (Fe0.84Si2), and nickel- and titanium-bearing iron silicide minerals suessite (Fe,Ni)3Si and zangboite (TiFeSi2). A special role has been given to the mineral hapkeite Fe2Si, which, based on a 1973 prediction by Prof. Bruce Hapke, was first detected on Earth in 2004 in the lunar meteorite Dhofar 280 and officially recognized as a mineral in the same year.
The reason for the rare occurrence of iron silicide minerals on Earth is the formation conditions, which require extreme temperatures and an extremely reducing environment, which is hardly ever present in terrestrial processes. Accordingly, iron silicides have been detected in some fulgurites, including most recently (2020) in a Michigan fulgurite. Eutectic intergrowth texture of two iron silicides revealed naquite and linzhiite or naquite and xifengite. Iron silicide particles found in Southern Urals, Russia, up to 1 m deep in Pleistocene sediments, were studied as a possible new class of meteorites, but in the end, a terrestrial formation from a completely unknown process was favored. Iron silicides, as a new class of meteorites, have also been considered for a while now.
Let us return to the cosmic connections. Recently, hapkeite (1–2 μm) was found in a meteorite from Koshava, Bulgaria and discovered in the meteorite DAG 1066; it also occurs in a grain from the FRO 90228 ureilite. Fe2Si reported for magnetic spherules in Hungary could be related to cosmic dust or a meteorite impact. Hapkeite was found also in a 7 μm Supernova graphite (OR1d3m-18) from the Orgueil meteorite. A few years ago, naquite, suessite, and xifengite were identified in the Khatyrka CV3 carbonaceous chondrite. An interesting discussion was also triggered on the origin and formation of various iron silicide phases in the aerogel of the Stardust mission. For this Special Issue, we invite recent advances in the investigation of natural iron silicides and their relations to mineralogy. Studies on industrial iron silicides will only be considered if there are direct and informative links to natural minerals.
Insights into the following topics are especially welcome:
Physical and optical properties
Terrestrial iron silicides
Iron silicide in meteorites
Shock metamorphism in iron silicide
Unnamed iron silicides
Deep Earth mantle iron silicides
Earth planets and iron silicides
Prof. Dr. Kord Ernstson Dr. Pavel Svanda Dr. Ioannis Baziotis Guest Editors
Manuscript Submission Information
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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.
The Steinheim Basin, the Ries crater “double disaster” and the mistaken Steinheim crater diameter
by Kord Ernstson1 & Ferran Claudin2 (Febr. 2021)
Abstract. – The article, which we comment here, interprets sedimentological findings (seismite horizons) at a distance of 80 – 180 km from the two impact structures, the Ries crater and the Steinheim basin, to the effect that, contrary to the impacts at a distance of only 40 km from each other, which have always been assumed to be synchronous, the Steinheim basin is supposed to be several 10 000 years younger than the Ries impact. This is against all probability, but because of the purely statistical impact events, it cannot be completely ruled out. This article therefore does not criticize the statement itself, but refers to equally probable alternatives that have not been considered, as well as to a lack of literature citations. The article loses its fundamental significance to the point of the simple alternative: it may be, but it also may not be, a finding without recognizable importance. A major point of criticism of the article is the common practice in the impact literature of suppressing the diameter of the Steinheim impact structure, which at around 7-8 km is actually twice as large, as it was proven almost 40 years ago by detailed morphological analyses and gravimetric measurements and published in a renowned journal. Since the size of the Steinheim Basin is included in the estimates for the formation of the seismites, it must be stated that the authors started from partly false premises. Here, the findings on the much larger Steinheim impact structure, which cannot be explained away, are presented again, combined with the wish to deal with scientific findings more honestly.
1 University of Würzburg, 97074 Würzburg (Germany); email@example.com; 2 Associate Geological Museum Barcelona (Spain); firstname.lastname@example.org
Shock effect in calcite. Multiple sets of closely spaced planar features (micro twins). The width of the twins is of the order of only one micrometer. Thin section micrograph, crossed polarizers. From a polymictic breccia, rim region of the Rubielos de la Cérida impact basin crater chain.
Rock fluidization, Azuara Impact Structure (Spain)
Rock fluidization in strongly competent limestones/dolostones (Muschelkalk Fm.); Monforte de Moyuela, Azuara impact structure, Spain. See article Rock fluidization during peak-ring formation of large impact structures by U. Riller et al. Also focus on Acoustic fluidization (H.J. Melosh). Enlarged image.
Impact spallation – completely underestimated by impact researchers.
Left, from the top down: Shock spallation experiment producing typical open tensile fractures. – Spallation fractures in shocked quartzite cobble, Azuara/Rubielos de la Cérida impact event (Spain). Microscopic shock spallation in sandstone quartz grains, Rubielos de la Cérida impact basin. – To the right: Local megascopic impact spallation in well-bedded Jurassic limestones; Azuara (Spain) impact structure northern rim region south of Fuendetodos. Link to a full article on impact spallation.