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Magnetic Properties and Redox State of Impact Glasses: a Review and New Case Studies from Siberia

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Magnetic Properties and Redox State of Impact Glasses: a Review and New Case Studies from Siberia geosciences Review Magnetic Properties and Redox State of Impact Glasses: A Review and New Case Studies from Siberia Pierre Rochette 1,* , Natalia S. Bezaeva 2,3, Andrei Kosterov 4 ,Jérôme Gattacceca 1, Victor L. Masaitis 5, Dmitry D. Badyukov 6, Gabriele Giuli 7 , Giovani Orazio Lepore 8 and Pierre Beck 9 1 Aix Marseille Université, CNRS, IRD, Coll. France, INRA, CEREGE, 13545 Aix-en-Provence, France; [email protected] 2 Institute of Geology and Petroleum Technologies, Kazan Federal University, 4/5 Kremlyovskaya Str., 420008 Kazan, Russia; [email protected] 3 Institute of Physics and Technology, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia 4 St. Petersburg State University, 199034 St. Petersburg, Russia; [email protected] 5 A.P. Karpinsky Russian Geological Research Institute (VSEGEI), Sredny prospect 74, 199106 St. Petersburg, Russia; [email protected] 6 V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin str., 119991 Moscow, Russia; [email protected] 7 School of Science and Technology-Geology division, University of Camerino, Via Gentile III da Varano, 62032 Camerino (MC), Italy; [email protected] 8 CNR-IOM-OGG c/o ESRF, 71 Avenue des Martyrs CS 40220, F-38043 Grenoble, France; [email protected] 9 Université Grenoble Alpes, CNRS, IPAG, UMR5274, 38041 Grenoble, France; [email protected] * Correspondence: [email protected]; Tel.: +33-442971562 Received: 26 February 2019; Accepted: 11 May 2019; Published: 15 May 2019 Abstract: High velocity impacts produce melts that solidify as ejected or in-situ glasses. We provide a review of their peculiar magnetic properties, as well as a new detailed study of four glasses from Siberia: El’gygytgyn, Popigai, urengoites, and South-Ural glass (on a total of 24 different craters or strewn-fields). Two types of behavior appear: 1) purely paramagnetic with ferromagnetic impurities at most of the order of 10 ppm; this corresponds to the five tektite strewn-fields (including the new one from Belize), urengoites, and Darwin glass. Oxidation state, based in particular on X-ray spectroscopy, is mostly restricted to Fe2+; 2) variable and up to strong ferromagnetic component, up to the 1 wt % range, mostly due to substituted magnetite often in superparamagnetic state. Accordingly, bulk oxidation state is intermediate between Fe2+ and Fe3+, although metallic iron, hematite, and pyrrhotite are sometimes encountered. Various applications of these magnetic properties are reviewed in the field of paleomagnetism, magnetic anomalies, recognition of glass origin, and formation processes. Keywords: magnetic properties; impact glasses; redox state; Popigai impact glasses; El’gygytgyn impact glasses; urengoites; South-Ural glass 1. Introduction Various types of silicate glass occur in nature [1] and may show exotic iron-bearing inclusions representative of a wide range of redox state [2–4]. Impact generated glasses, having often recorded particularly high pressures and temperatures (>10 GPa and >1700 ◦C; see [5]) on a short time scale (seconds) and endured equally fast quenching, may yield original magnetic properties that we will describe in the present review. Geosciences 2019, 9, 225; doi:10.3390/geosciences9050225 www.mdpi.com/journal/geosciences Geosciences 2019, 9, 225 2 of 23 Geosciences 2019, 9, x FOR PEER REVIEW 2 of 25 Hypervelocity impacts on the Earth surface generate deformation, metamorphism, and melting of the targetHypervelocity rocks (e.g., impacts [5]). on The the meltedEarth surface material generate can be deformation, subsequently metamorphism, fragmented and and /meltingor mixed withof the unmelted target rocks material. (e.g., [5]). It may The melted also be material ejected can outside be subsequently the crater as fragmented liquid masses, and/or injected mixed with in the targetunmelted rocks asmaterial. dikes, orIt may remain also in be the ejected crater outside as a melt the sheet. crater They as liquid may masses, be subsequently injected in altered the target by the impact-inducedrocks as dikes, hydrothermalism. or remain in the crater Depending as a melt on these sheet. modalities, They may andbe subsequently especially on altered cooling by rate, the the rockimpact-induced derived from hydrothermalism. this melted material Depending may be a on pure these glass modalities, (case of fully and especially melted material on cooling rapidly rate, cooled the duringrock ballisticderived ejection,from this like melted tektites), material or a may more be or a less pure cryptocrystalline glass (case of fully material melted mixed material with rapidly unmelted material,cooled during with variable ballistic proportionsejection, like oftektites), glass, or crystals a more grown or less fromcryptocrystalline the melt, and material unmelted mixed material. with unmelted material, with variable proportions of glass, crystals grown from the melt, and unmelted In this review on the magnetic properties of impact glasses, the term ‘impact glass’ will be restricted material. In this review on the magnetic properties of impact glasses, the term ‘impact glass’ will be to impact generated rocks (or large pockets within these rocks) that are mainly in a glassy state at restricted to impact generated rocks (or large pockets within these rocks) that are mainly in a glassy a macroscopic scale. Therefore, we will not treat impactites that contain only small or comminuted state at a macroscopic scale. Therefore, we will not treat impactites that contain only small or fraction of glass or former glass (altered by hydrothermalism or crystallized by slow cooling). These comminuted fraction of glass or former glass (altered by hydrothermalism or crystallized by slow impactites may correspond to suevite or other types of breccia, in particular impact melt dikes often cooling). These impactites may correspond to suevite or other types of breccia, in particular impact usedmelt to dikes perform often paleomagnetic used to perform dating paleomagnetic of impact dating craters. of Inimpact fact, crater a recents. In review fact, a onrecent this review subject on has beenthis performed subject has bybeen Gilder performed et al. [ 6by]. Gilder Therefore, et al. we[6]. will Therefore, mostly we restrict will mostly this review restrict to this impact review glasses to withimpact the above glasses definition, with the above still including definition, afew still cases,including where a few the meltcases, has, where partly-to-totally, the melt has, partly-to- crystallized intotally, a microcrystalline crystallized rock.in a microcrystalline rock. FigureFigure 1. 1. MapMap of tektite tektite fields fields (blue (blue contours: contours: A—australasites;A—australasites; B—moldavites;B—moldavites; C—ivoirites;C—ivoirites; D— D—bediasite-georgiaites;bediasite-georgiaites; E—belizites),E—belizites), craters craters of possible of possible origin origin for tektites for tektites (blue (bluestar: 1 star:—Ries;1—Ries; 2— 2—Bosumtwi;Bosumtwi; 3—Chesapeake3—Chesapeake Bay; Bay; 4—Pantasma),4—Pantasma), other other impact impact glasses glasses without without known known source source crater crater (black(black open open star: star:5 —atacamaites;5—atacamaites;6 6—LDG;—LDG; 7—urengoites; 88—Ural—Ural glass) glass) or or with with known known source source crater crater (black(black filled filled star: star:9 —Popigai;9—Popigai; 1010—El’gygytgyn;—El’gygytgyn; 11—irghizites;—irghizites; 1212—Lonar;—Lonar; 1313—Wabar;—Wabar; 14—Kamil;14—Kamil; 15—Aouelloul;15—Aouelloul; 1616—Lapajarvi;—Lapajarvi; 1717—Janisjarvi;—Janisjarvi; 18—Mistastin;18—Mistastin; 19—Monturaqui;19—Monturaqui; 20—Henbury;20—Henbury; 21— 21—DarwinDarwin glass). glass). TheThe most most peculiar peculiar and and studied studied impactimpact glassesglasses areare tektites. These These correspond correspond to to(almost) (almost) pure pure glassesglasses that that have have been been ejected ejected far far away away from from their their impact impact source source (distance (distance largerlarger thanthan 100100 km and up to 11,000to 11,000 km, e.g., km, [ 7e.g.,]). These [7]). These distal distal materials, materials, besides besides showing showing typical typical splash splash forms dueforms to due their to transport their transport in air or vacuum, have quite distinctive properties. This differentiates them from other in air or vacuum, have quite distinctive properties. This differentiates them from other impact glasses impact glasses that are found near or inside their source crater. Only five tektite (and three that are found near or inside their source crater. Only five tektite (and three microtektite) strewn fields microtektite) strewn fields have been identified on Earth (Figure 1), the largest field by far being the have been identified on Earth (Figure1), the largest field by far being the Australasian one [ 1,8]. The Australasian one [1,8]. The latter is the only confirmed strewn field for which a source crater has not latter is the only confirmed strewn field for which a source crater has not been identified. On the other been identified. On the other hand, impact glasses have been found within or around a significant hand,proportion impact of glasses the >190 have impact been craters found identified within or on around the Earth. a significant A few impact proportion glasses ofhave the been>190 found impact Geosciences 2019, 9, 225 3 of 23 craters identified on the Earth. A few impact glasses have been found unrelated to a source crater but on a rather limited
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