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.
Highlights
Various types of silicate glass occur in nature [1] and may show exotic iron-bearing inclusions representative of a wide range of redox state [2,3,4]
Magnetic mineralogy of these impact glasses is dominated by substituted magnetite [9,10,11,12,51], as expected by their generally oxidized nature indicated for example by XANES or Mössbauer spectroscopy studies
El’gygytgyn while sedimentary target rocks dominate over lavas in Zhamanshin. Magnetic mineralogy of these impact glasses is dominated by substituted magnetite [9,10,11,12,51], as expected by their generally oxidized nature indicated for example by XANES (for Libyan desert glasses (LDG), Aouelloul, μm irghizite, studies Wabar; [27,45]) or Mössbauer spectroscopy c) Wabar; [44])
Summary
Various types of silicate glass occur in nature [1] and may show exotic iron-bearing inclusions representative of a wide range of redox state [2,3,4]. Thesecorrespond correspond pure glasses that have been ejected far away from their impact source (distance larger than km and glasses that have been ejected far away from their impact source (distance larger than 100 km and up up to to 11,000 km, e.g., [7]) These distal materials, besides showing typical splash forms due to their. The purpose of the present paper, besides a summary of early studies, is to present a synthesis review of the magnetic properties of impact glasses, updating [9] using recent publications [10,11,12] as well as new results These include a specific effort on glasses from Siberia (site 7–10 in Figure 1) either associated to a known crater (Popigai and El’gygytgyn) or not (Urengoite and South-Ural glass; [13]). We will review the oxidation state (based on XANES and EXAFS data) and petrography of magnetic minerals in those glasses
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