Fulgurites: the Earth’s minute melts and their interaction with the atmosphere
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Keywords: fulgurites, mass independent, atmosphere, experimental melting
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Abstract
Figures
 Figure 1 Generalised internal structure of a fulgurite and its geometrical relationship to the lightning strike. |  Figure 2 Morphological examples of (a) natural (sedimentary/soil) branched fulgurites, (b) igneous rock fulgurite at Mt Thielsen, Oregon (indicated by yellow arrows), (c) tubular fulgurite from the Namibian desert (blue arrow shows lightning direction almost perpendicular to the original stratification and (d) different morphologies of experimental fulgurites derived from phonolitic volcanic ash from the Eifel, Germany. |  Figure 3 (a) Triple oxygen isotopic variations in natural, experimental, and industrial fulgurites of this study as compared to granites, selected tektites, hydrothermally altered rocks (Bindeman, 2021, this work; Tables S-1 to S-2), and air-O2 and meteoric waters. Shown fields and lines: 1) irgizite proximal ejecta (Magna et al. 2017), 2) silicate material evaporation and air exchange experiments from Pack (2021). Effects of very high T evaporation and condensation are shown here and follow the highest 0.5305 fractionation exponent, while thermal diffusion follows a slope of 0.518 (Table S-2). (b) A zoom in of (a), emphasising igneous and experimental fulgurite data points measured in this work. |
| Figure 1 | Figure 2 | Figure 3 |
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Introduction
Fulgurites are natural glassy products formed when lightning strikes the Earth’s or planetary surface, forming instantaneous melts by fusing ground materials (Rakov and Uman, 2003
Rakov, V.A., Uman, M.A. (2003) Lightning: Physics and Effects. Cambridge University Press, New York. https://doi.org/10.1017/CBO9781107340886
). Electrical current in natural lightning channels may exceed 200,000 A, and calculated temperatures can exceed 20,000 K (Paxton et al., 2017Paxton, A.H., Gardner, R.L., Baker, L. (2017) Lightning Return Stoke: A Numerical Calculation of the Optical Radiation. In: Gardner, R.L. (Ed.) Lightning Electromagnetics. Routledge, New York, 47–61. https://doi.org/10.1201/9780203748992-4
), thus exceeding the temperature of melting and vapourisation for most natural materials. The result is typically a glassy tubular structure that follows the branching pattern of the lightning channel underground (Figs. 1a, 2). Although tubular and branched structures are common, fulgurites can also show globular and massive shapes with irregular vesicular patterns (Fig. 1; Pasek et al., 2012Pasek, M.A., Block, K., Pasek, V. (2012) Fulgurite morphology: a classification scheme and clues to formation. Contributions to Mineralogy and Petrology 164, 477–492. https://doi.org/10.1007/s00410-012-0753-5
; Genareau et al., 2020Genareau, K., Gharghabi, P., Klüss, J. (2020) Influence of shock propagation on lightning evidence in volcanic ashfall deposits. Earth and Planetary Science Letters 535, 116124. https://doi.org/10.1016/j.epsl.2020.116124
). Depending on the material and amount melted, the cooling of mm to cm size melt pockets within a rock will continue conductively for many tens of seconds, enabling further compositional and isotopic interdiffusion. Accordingly, textures defined by their degree of melting may vary radially from the core or axis of the fulgurite towards the surrounding pristine material (Fig. 1). Based on substrate and morphology, fulgurites have been classified into soil/sand and hard rock (Fig. 2). In hard bedrock fulgurites formed from any solid igneous or metamorphic rock, the walls consist mostly of pristine country rock invaded by veins of pure glass (Fig. 2b). Soil fulgurites often show a bubbly appearance and thick, melt-rich glassy walls; the glass is generally more heterogeneous, incorporating aluminum silicate clay and feldspar minerals, whilst the carbonate materials do not melt but are preferentially devolatilised (Purdom, 1966Purdom, W.B. (1966) Fulgurites from Mount Thielsen. The Ore Bin 28, 153–159.
).Figure 1 Generalised internal structure of a fulgurite and its geometrical relationship to the lightning strike.
Figure 2 Morphological examples of (a) natural (sedimentary/soil) branched fulgurites, (b) igneous rock fulgurite at Mt Thielsen, Oregon (indicated by yellow arrows), (c) tubular fulgurite from the Namibian desert (blue arrow shows lightning direction almost perpendicular to the original stratification and (d) different morphologies of experimental fulgurites derived from phonolitic volcanic ash from the Eifel, Germany.
With the aim of investigating the physics of lightning–ground interaction and its duration and peak temperatures (Rakov and Uman, 2003
Rakov, V.A., Uman, M.A. (2003) Lightning: Physics and Effects. Cambridge University Press, New York. https://doi.org/10.1017/CBO9781107340886
; Pasek et al., 2012Pasek, M.A., Block, K., Pasek, V. (2012) Fulgurite morphology: a classification scheme and clues to formation. Contributions to Mineralogy and Petrology 164, 477–492. https://doi.org/10.1007/s00410-012-0753-5
), several attempts have been made to experimentally reproduce fulgurites (Elmi et al., 2018Elmi, C., Coleman, N.S., Miu, K., Schruba, E. (2018) Experimental simulation of lightning current discharge on rocks. Applied Sciences 8, 2394. https://doi.org/10.3390/app8122394
; Çalişkanoğlu et al., 2023aÇalişkanoğlu, A.Z., Dingwell, D.B., Cimarelli, C., Camara, A.S.B., Breitzke, H., Buntkowsky, G., Pasek, M.A., Braun, D., Scheu, B., Molaverdikhani, K. (2023b) Reactive phosphorus via simulated lightning discharge: A role for fulgurites in pre-biotic chemistry. Chemical Geology 620, 121343. https://doi.org/10.1016/j.chemgeo.2023.121343
, 2024Çalişkanoğlu, A.Z., Cimarelli, C., Dingwell, D.B., Camara, A.S.B. (2024) Experimental vs. natural fulgurite: A comparison and implications for the formation process. American Mineralogist 109, 1682–1690. https://doi.org/10.2138/am-2023-9192
and references therein). In these experiments, voltage, currents, and discharge duration have been systematically varied to produce fulgurites that are morphologically and chemically similar to the natural ones (Fig. 2d), and thus constrain the above experimental parameters needed for the formation of natural fulgurites. Finally, glassy materials are often found near electrical power lines fallen to the ground. These represent ground high voltage electrification, often leading to the injection of molten wire metal into the molten rock, and the formation of predominantly glassy and highly vesicular fulgurites. We will hereafter call these fulgurites “industrial accident fulgurites”.Whilst being fascinating in their own right as the Earth’s most minute melts, mapping of fulgurites in modern deserts and stratigraphic record is used to understand their origins, and indicator of lightning frequency (Orville et al., 2011
Orville, R.E., Huffines, G.R., Burrows, W.R., Cummins, K.L. (2011) The North American lightning detection network (NALDN) - analysis of flash data: 2001-2009. Monthly Weather Review 139, 1305–1322. https://doi.org/10.1175/2010MWR3452.1
). Interaction of lightning with volcanic ash plumes (Wadsworth et al., 2017Wadsworth, F.B. Vasseur, J., Llewellin, E.W., Genareau, K., Cimarelli, C., Dingwell, D.B. (2017) Size limits for rounding of volcanic ash particles heated by lightning. Journal of Geophysical Research: Solid Earth 122, 1977–1989. https://doi.org/10.1002/2016JB013864
; Genareau et al., 2020Genareau, K., Gharghabi, P., Klüss, J. (2020) Influence of shock propagation on lightning evidence in volcanic ashfall deposits. Earth and Planetary Science Letters 535, 116124. https://doi.org/10.1016/j.epsl.2020.116124
) is a very common occurrence of many volcanic eruptions. Furthermore, the presence of Fe-Si alloys in some fulgurites reflects extremely reducing conditions during oxygen evaporation or carbon compound’s reduction (Pasek and Block, 2009Pasek, M., Block, K. (2009) Lightning-induced reduction of phosphorus oxidation state. Nature Geoscience 2, 553–556. https://doi.org/10.1038/ngeo580
; Pasek et al., 2012Pasek, M.A., Block, K., Pasek, V. (2012) Fulgurite morphology: a classification scheme and clues to formation. Contributions to Mineralogy and Petrology 164, 477–492. https://doi.org/10.1007/s00410-012-0753-5
; Ballhaus et al., 2017Ballhaus, C., Wirth, R., Fonseca, R.O.C., Blanchard, H., Pröll, W., Bragagni, A., Nagel, T., Schreiber, A., Dittrich, S., Thome, V., Hezel, D.C., Below, R., Cieszynski, H. (2017) Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes. Geochemical Perspectives Letters 5, 42–46. https://doi.org/10.7185/geochemlet.1744
). Therefore, on the surfaces of the Earth and other planets, lightning has the potential to locally reduce components such as iron and phosphorus making them biologically available, thus playing a role in the origin of life (Pasek and Block, 2009Pasek, M., Block, K. (2009) Lightning-induced reduction of phosphorus oxidation state. Nature Geoscience 2, 553–556. https://doi.org/10.1038/ngeo580
; Roberts et al., 2019Roberts, S.E., Sheffer, A.A., McCanta, M.C., Dyar, M.D., Sklute, E.C. (2019) Oxidation state of iron in fulgurites and trinitite: implications for redox changes during abrupt high-temperature and pressure events. Geochimica et Cosmochimica Acta 266, 332–350. https://doi.org/10.1016/j.gca.2019.08.021
; Hess et al., 2021Hess, B.L., Piazolo, S., Harvey, J. (2021) Lightning strikes as a major facilitator of prebiotic phosphorus reduction on early Earth. Nature Communications 12, 1535. https://doi.org/10.1038/s41467-021-21849-2
; Bindi et al., 2023Bindi, L., Feng, T., Pasek, M.A. (2023) Routes to reduction of phosphate by high-energy events. Communications Earth & Environment 4, 70. https://doi.org/10.1038/s43247-023-00736-2
; Çalişkanoğlu et al., 2023bÇalişkanoğlu, A.Z., Dingwell, D.B., Cimarelli, C., Camara, A.S.B., Breitzke, H., Buntkowsky, G., Pasek, M.A., Braun, D., Scheu, B., Molaverdikhani, K. (2023b) Reactive phosphorus via simulated lightning discharge: A role for fulgurites in pre-biotic chemistry. Chemical Geology 620, 121343. https://doi.org/10.1016/j.chemgeo.2023.121343
).We here investigate for the first time triple oxygen isotopic variations in a variety of fulgurites. The first motivation of this study is to determine whether atmospheric lightning discharge causes large 17O/18O/16O fractionations in fulgurite melts. Independent of lightning, the UV radiation has been the leading cause of very large mass independent fractionations that lead to +30 to +100 ‰ Δ’17O anomalies in the air-O3 (or ozone, e.g., Thiemens and Lin, 2021
Thiemens, M.H., Lin, M. (2021) Discoveries of Mass Independent Isotope Effects in the Solar System: Past, Present and Future. Reviews in Mineralogy and Geochemistry 86, 35–95. https://doi.org/10.2138/rmg.2021.86.02
), and a negative Δ’17O in the residual atmospheric oxygen. The discovery of mass independent effects in atmospheric oxygen, and oxygen from the planetary cloud in the 1980s has established the whole new subfield in atmospheric science and geoscience. Second, since oxygen is a major element in surface rocks, air, and water, its isotopes can potentially provide further insight into fulgurite genesis and the extent of interaction between these reservoirs. Interaction with atmospheric compounds and waters (at the surface or in the ground) may proceed during the lightning strike and over the time of fulgurite melt cooling. Whilst typical terrestrial rocks have normal δ18O (+5 to +12 ‰) and Δ’17O (−0.10 to +0.02 ‰), atmospheric oxygen is both heavy with respect to δ18O (+24 ‰) and low in Δ’17O0.528 (−0.45‰; Luz et al., 2014Luz, B., Barkan, E., Severinghaus, J.P. (2014) 5.14 - The stable isotopic composition of atmospheric O2. In: Holland, H.D., Turekian, K.K. (Eds.) Treatise on Geochemistry. Second Edition, Elsevier, Amsterdam, 363–383. https://doi.org/10.1016/B978-0-08-095975-7.00419-8
; Pack, 2021Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
) because of the Dole effect (Dole et al., 1954Dole, M., Lane, G.A., Rudd, D.P., Zaukelies, D.A. (1954) Isotopic composition of atmospheric oxygen and nitrogen. Geochimica et Cosmochimica Acta 6, 65–78. https://doi.org/10.1016/0016-7037(54)90016-2
), and formation of the ozone in the stratosphere (Young et al., 2014Young, E.D., Yeung, L.Y., Kohl, I.E. (2014) On the Δ17O budget of atmospheric O2. Geochimica et Cosmochimica Acta 135, 102–125. https://doi.org/10.1016/j.gca.2014.03.026
). Meteoric waters, on the other hand, have low δ18O (<−5 ‰) and high Δ’17O (−0.01 to +0.05 ‰) values (Luz and Barkan, 2010Luz, B., Barkan, E. (2010) Variations of 17O/16O and 18O/16O in meteoric waters. Geochimica et Cosmochimica Acta 74, 6276–6286. https://doi.org/10.1016/j.gca.2010.08.016
; Sharp et al., 2018Sharp, Z., Wostbrock, J., Pack, A. (2018) Mass-dependent triple oxygen isotope variations in terrestrial materials. Geochemical Perspective Letters 7, 27–31. https://doi.org/10.7185/geochemlet.1815
).Here we investigate a worldwide collection of natural fulgurites from igneous rocks, desert sand, and soil materials, as well as experimentally generated fulgurites and industrial fulgurites (fallen power lines; Table S-1). In addition, natural tektites were also measured for comparison, as these also represent high temperature melts that cool in the air for a short time formed by meteorite impacts that interacted with the Earth’s atmosphere (Pack, 2021
Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
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Methods
We performed all measurements (Table S-1) using 1–2 mg of glass and rock materials by laser fluorination to produce O2, coupled with a Thermo-Fisher MAT253 mass spectrometer. Oxygen was then run multiple times (32–80 cycles) of comparison against O2 gas of known composition on VSMOW scale. The data is reported relative to the 0.528 exponent of δ17O vs. δ18O, as Δ’17O = δ’17O − 0.528 δ’18O, where primed coordinates are linearised logarithmic equivalents of conventionally defined δ18O and δ17O (Miller et al., 2020
Miller, M.F., Pack, A., Bindeman, I.N., Greenwood, R. (2020) Standardizing the reporting of Δ17O data from high precision oxygen triple-isotope ratio measurements of silicate rocks and minerals. Chemical Geology 532, 119332. https://doi.org/10.1016/j.chemgeo.2019.119332
) and Δ’17Omantle = −0.037 ‰. We also measured total water and δD in these samples by TCEA-MAT253 system (Fig. S-1).Samples of natural and industrial fulgurites were obtained from the Smithsonian Institution of Washington, commercially, and from the University of Oregon collections. Experimental fulgurites were generated in air, in the high voltage laboratory of the Bundeswehr Universität in Munich, Germany. The experimental setup is designed based on recommendations from the lightning research community, derived from studies of natural lightning. The detailed description of the experimental setup is reported in Çalişkanoğlu et al., (2023a
Çalişkanoğlu, A.Z., Dingwell, D.B., Cimarelli, C., Camara, A.S.B., Breitzke, H., Buntkowsky, G., Pasek, M.A., Braun, D., Scheu, B., Molaverdikhani, K. (2023b) Reactive phosphorus via simulated lightning discharge: A role for fulgurites in pre-biotic chemistry. Chemical Geology 620, 121343. https://doi.org/10.1016/j.chemgeo.2023.121343
, 2024Çalişkanoğlu, A.Z., Camara, A.S.B., Cimarelli, C., Dingwell, D.B., Hess, K.-U. (2023a) Experimental generation of fulgurite under realistic lightning discharge conditions. Scientific Reports 13, 11685. https://doi.org/10.1038/s41598-023-38781-8
). In particular, experimental fulgurites were generated by exposing crushed material (variable grain size <500 μm) to electrical discharges produced by a DC source with a trigger pulse. The trigger pulse generates 135 kA for about 100 ms, creating a conductive path between the electrodes and is followed by a DC current of about 200 to 320 A for a duration of up to 500 ms, simulating the long duration of natural lightning discharges (Rakov and Uman, 2003Rakov, V.A., Uman, M.A. (2003) Lightning: Physics and Effects. Cambridge University Press, New York. https://doi.org/10.1017/CBO9781107340886
). The prolonged (continuing) current further promotes the melting of a larger volume of material, forming the fulgurite.top
Results
Experimental fulgurites. Fulgurites of mm size produced by continuing currents lasting 100 to 500 ms return slightly increasing δ18O and a decreasing Δ’17O values (Fig. 3, Table S-1) in all cases, except an apatite fulgurite. Fulgurites from the phonolithic ash of the Holocene Laacher See Volcano, Germany, generated with increasing discharge duration from 100 to 300 and 500 ms, show a progressive decrease in Δ’17O inversely proportional to the duration of the electrical discharges that generated them. The slope of each line in the Δ’17O-δ18O diagram is toward the atmospheric oxygen, but the slopes of the line vary (Fig. 3), likely explained by the influence of variable amount of volatilisation/condensation during fulgurite formation and/or the analytical uncertainty due to the small amount of shift. The overall decrease in Δ’17O is −0.02 ‰ to −0.03 ‰, whilst δ18O changes from −0.5 ‰ to up to +1 ‰. The dunite fulgurite shows the −0.04 ‰ drop, whilst the apatite fulgurite shows a 0 ‰ Δ’17O drop but an increase in δ18O.
Figure 3 (a) Triple oxygen isotopic variations in natural, experimental, and industrial fulgurites of this study as compared to granites, selected tektites, hydrothermally altered rocks (Bindeman, 2021
Bindeman, I.N. (2021) Triple Oxygen Isotopes in Evolving Continental Crust, Granites, and Clastic Sediments. Reviews in Mineralogy and Geochemistry 86, 241–290. https://doi.org/10.2138/rmg.2021.86.08
, this work; Tables S-1 to S-2), and air-O2 and meteoric waters. Shown fields and lines: 1) irgizite proximal ejecta (Magna et al. 2017Magna, T., Žák, K., Pack, A., Moynier, F., Mougel, B., Skála, R., Jonášová, S., Řanda, Z., Mizera, J. (2017) Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere. Nature Communications 8, 227. https://doi.org/10.1038/s41467-017-00192-5
), 2) silicate material evaporation and air exchange experiments from Pack (2021)Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
. Effects of very high T evaporation and condensation are shown here and follow the highest 0.5305 fractionation exponent, while thermal diffusion follows a slope of 0.518 (Table S-2). (b) A zoom in of (a), emphasising igneous and experimental fulgurite data points measured in this work.Natural igneous fulgurites. A similar pattern is observed for all igneous fulgurites (Fig. 3). In the case when we were able to measure the starting material and the final glass (e.g., Bristen Stock in Switzerland; Mt Jefferson in Oregon, USA) they exhibit a drop in Δ’17O of −0.02 ‰ to −0.03‰, whilst δ18O increases from 0 ‰ to +1.5‰. Similarly, where the starting material was not available, it can be inferred to be close to the mantle and igneous array Δ’17O value (5.7–6 ‰ and −0.05 to −0.06 ‰: Little Ararat in Turkey and Mt Thielsen in Oregon, USA). These fulgurites also show a decrease in Δ’17O values by 0.01 to 0.04 ‰. Igneous fulgurites are the least vesicular of all studied fulgurites and appear as massive vein-like obsidianic injections into the country rocks (Fig. 1b).
Natural sedimentary and soil fulgurites. In contrast to the igneous and experimental fulgurites with anhydrous protoliths, the sedimentary fulgurites, including the majority of sand fulgurites and fulgurites that result from soil/weathered material melting, exhibit diverse Δ’17O and δ18O values around the igneous array. Some fulgurites are plotting higher than the igneous array, which potentially indicates interaction with high Δ’17O soil water or meteoric water, or water vapours (even higher Δ’17O). Interaction with water is also confirmed by textural evidence of vesicularity in all soil fulgurites.
Industrial fulgurites. Fulgurites generated by fallen power lines also plot around the igneous array (Fig. 3a), like soil fulgurites. Both soil and industrial fulgurites are generally high δ18O as is typical for starting soils, but the starting bedrock was not available for sampling. Both soil and industrial fulgurites show significant vesicularity, which is greater than for all other fulgurites.
Natural impact related melts. We also measured triple O isotopic composition of three natural impact melts: irgizites, proximal ejecta from the Zhamanzhin crater in Kazakhstan, and an Australasian tektite found in Tasmania from an unknown source. Like fulgurites these materials have been produced by high temperature quenching of superheated silicate melts produced by meteorite impact that interacted with the air and potentially also water. We observe that the cm size Zhamanshin irgizites have very low Δ’17O values (−0.2 ‰) and our measurements are in line with analyses reported by Magna et al., (2017)
Magna, T., Žák, K., Pack, A., Moynier, F., Mougel, B., Skála, R., Jonášová, S., Řanda, Z., Mizera, J. (2017) Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere. Nature Communications 8, 227. https://doi.org/10.1038/s41467-017-00192-5
and Pack (2021)Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
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Discussion
Our initial motivation for this study, to find large Δ’17O shifts, related perhaps to the mass independent signature similar to the one occurring during ozone formation, has returned a clearly negative result. However, because oxygen is a major element in rocks, air, and water, fulgurites provide insight into the genesis and the extent of interaction between these reservoirs.
Similar to molten crusts of meteorites, micrometeorites, and some tektites (Pack et al., 2017
Pack, A., Höweling, A., Hezel, D.C., Stefanak, M., Beck, A.-K., Peters, S.T.M., Sengupta, S., Herwartz, D., Folco, L. (2017) Tracing the oxygen isotope composition of the upper Earth atmosphere using cosmic spherules. Nature Communications 8, 15702. https://doi.org/10.1038/ncomms15702
; Pack, 2021Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
), the natural igneous and experimental fulgurites record shifts toward low Δ’17O atmospheric oxygen values. Despite having a very short duration of formation, high temperature interaction during fulguritic melt cooling shifts the bulk oxygen composition toward that of atmospheric oxygen by 4 to 8 % of the total ∼0.45 ‰ rock-atmospheric Δ’17O range (Fig. 3a). Pack (2021)Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
reported that reaction of a silicate melt with atmospheric oxygen at 1300–1500 °C lasting for only 5–10 sec, already results in a negative −0.1 to −0.2‰ Δ’17O shift, indicating that 20–50 % of oxygen in the melt exchanges with atmospheric oxygen quite quickly. Some natural mm to cm size proximal impact ejecta of silicic composition (irgizites), measured by Magna et al., (2017)Magna, T., Žák, K., Pack, A., Moynier, F., Mougel, B., Skála, R., Jonášová, S., Řanda, Z., Mizera, J. (2017) Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere. Nature Communications 8, 227. https://doi.org/10.1038/s41467-017-00192-5
and in this study (Table S-1) show −0.2 ‰ Δ’17O shifts in the same direction, estimated to reach a high temperature equilibrium of δ18O = +21.5 ‰, 2.5 ‰ lighter due to high temperature isotope equilibria, but at Δ’17O = −0.45 ‰ similar to air (Fig. 3; Pack, 2021Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
), as evaporation-condensation phenomena at very high temperatures are expected to maintain a high 0.529–0.5305 exponents of isotope fractionation. Thermal diffusion experiments (Table S-2) fractionate oxygen kinetically in the opposite direction to the exchange with air-O2, with low-δ18O and high-Δ’17O values at the hot end along the “diffusive” exponent of 0.518 (Fig. 3a).Natural fulgurite glasses contain fully molten individual crystals of quartz, pyroxenes and other minerals. This suggests that the temperature was high enough (likely in excess of 1500–2000 °C) to individually melt these minerals, and that subsequent cooling and interdiffusion between these melts that may last for tens of seconds to perhaps minutes for a typical 0.1–1 cm diameter fulguritic tube (Castro et al., 2020
Castro, J. M., Keller, Y., Feisel, Y., Lanari, P., Helo, C., Mueller, S.P., Schipper, C.I., Thomas, C. (2020) Lightning-induced weathering of Cascadian volcanic peaks. Earth and Planetary Science Letters 552, 116595. https://doi.org/10.1016/j.epsl.2020.116595
). As cooling was sufficient in duration to diffusively homogenise and physically mix diverse melts (but not to diffusively fractionate oxygen), it should also have been slow enough to allow further exchange with oxygen in the air, water, or ground water vapours. By comparing fulgurites and tektites of the same size, fulgurites do not go as low in Δ’17O despite being equally hot or much hotter for a similar period of time, suggesting either a shorter duration of exchange, or a lower availability of atmospheric oxygen. Increasing the duration of discharge from 100 to 500 ms, as in the Laacher See ash experiment, demonstrates that duration of the discharge (time the material is exposed to highest temperature) matters. More work, including experimental, should be done to further quantify this effect.Limited Δ’17O shifts and diverse outcomes for soil and industrial fulgurites likely indicate involvement of meteoric waters in addition to atmospheric oxygen. As meteoric water values are generally high Δ’17O and low but variable in δ18O (Fig. 3), it is also likely that high Δ’17O groundwater or soil water vapours would continue to interact with the cooling melts many tens of seconds and hours after each episode, during melt cooling into ambient temperatures. However, this duration was not enough to hydrate fulgurites as they remain more anhydrous (<0.1 wt. % water) than natural volcanic glasses (Fig. S-1; e.g., Hudak and Bindeman, 2020
Hudak, M.R., Bindeman, I.N. (2020) Solubility, diffusivity, and O isotope systematics of H2O in rhyolitic glass in hydrothermal temperature experiments. Geochimica et Cosmochimica Acta 283, 222–242. https://doi.org/10.1016/j.gca.2020.06.009
). The overall Δ’17O and δ18O relationships should be understood in this context of a three-component mixture: the dominant bedrock, atmospheric oxygen (δ18O = +24 ‰, Δ’17O = −0.45 ‰) and soil waters and vapours (<−10 ‰, 0 to +0.05 ‰). The effects of volatilisation and condensation also play a role but possibly a minor one; these processes can cause a line with a slope of zero in the δ18O-Δ’17O space (Fig. 3). The high Δ’17O fulgurites could only inherit oxygen from meteoric water, as silicate melt evaporation-condensation at high temperature does not change Δ’17O (Fig. 3).This study documents the isotope effects of fulgurite formation and outlines ways to use them as palaeoclimate tools. We suggest that fulgurites that show the maximum shifts in δ18O-Δ’17O space can potentially be recognised in the geologic record, even if the original glass is devitrified. This study also documents that molten rock interacts with atmospheric oxygen and does not represent a pure melt of the target rock.
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Acknowledgements
We thank the Smithsonian Institution of Washington for providing samples of world’s natural fulgurites and Z. Çalışkanoğlu for providing some of the experimental fulgurites analysed in this study. INB thanks AvH foundation for support. CC acknowledges the support of the ERC 2019 COG Grant 864052 (VOLTA).
Editor: Horst M. Marschall
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References
Ballhaus, C., Wirth, R., Fonseca, R.O.C., Blanchard, H., Pröll, W., Bragagni, A., Nagel, T., Schreiber, A., Dittrich, S., Thome, V., Hezel, D.C., Below, R., Cieszynski, H. (2017) Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes. Geochemical Perspectives Letters 5, 42–46. https://doi.org/10.7185/geochemlet.1744
Show in context Furthermore, the presence of Fe-Si alloys in some fulgurites reflects extremely reducing conditions during oxygen evaporation or carbon compound’s reduction (Pasek and Block, 2009; Pasek et al., 2012; Ballhaus et al., 2017).
View in article
Bindeman, I.N. (2021) Triple Oxygen Isotopes in Evolving Continental Crust, Granites, and Clastic Sediments. Reviews in Mineralogy and Geochemistry 86, 241–290. https://doi.org/10.2138/rmg.2021.86.08
Show in context (a) Triple oxygen isotopic variations in natural, experimental, and industrial fulgurites of this study as compared to granites, selected tektites, hydrothermally altered rocks (Bindeman, 2021, this work; Tables S-1 to S-2), and air-O2 and meteoric waters. Shown fields and lines: 1) irgizite proximal ejecta (Magna et al. 2017), 2) silicate material evaporation and air exchange experiments from Pack (2021).
View in article
Bindi, L., Feng, T., Pasek, M.A. (2023) Routes to reduction of phosphate by high-energy events. Communications Earth & Environment 4, 70. https://doi.org/10.1038/s43247-023-00736-2
Show in context Therefore, on the surfaces of the Earth and other planets, lightning has the potential to locally reduce components such as iron and phosphorus making them biologically available, thus playing a role in the origin of life (Pasek and Block, 2009; Roberts et al., 2019; Hess et al., 2021; Bindi et al., 2023; Çalışkanoğlu et al., 2023b).
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Çalışkanoğlu, A.Z., Camara, A.S.B., Cimarelli, C., Dingwell, D.B., Hess, K.-U. (2023a) Experimental generation of fulgurite under realistic lightning discharge conditions. Scientific Reports 13, 11685. https://doi.org/10.1038/s41598-023-38781-8
Show in context The detailed description of the experimental setup is reported in Çalışkanoğlu et al., (2023a, 2024).
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Çalışkanoğlu, A.Z., Dingwell, D.B., Cimarelli, C., Camara, A.S.B., Breitzke, H., Buntkowsky, G., Pasek, M.A., Braun, D., Scheu, B., Molaverdikhani, K. (2023b) Reactive phosphorus via simulated lightning discharge: A role for fulgurites in pre-biotic chemistry. Chemical Geology 620, 121343. https://doi.org/10.1016/j.chemgeo.2023.121343
Show in context With the aim of investigating the physics of lightning–ground interaction and its duration and peak temperatures (Rakov and Uman, 2003; Pasek et al., 2012), several attempts have been made to experimentally reproduce fulgurites (Elmi et al., 2018; Çalışkanoğlu et al., 2023a, 2024 and references therein).
View in article
Therefore, on the surfaces of the Earth and other planets, lightning has the potential to locally reduce components such as iron and phosphorus making them biologically available, thus playing a role in the origin of life (Pasek and Block, 2009; Roberts et al., 2019; Hess et al., 2021; Bindi et al., 2023; Çalışkanoğlu et al., 2023b).
View in article
The detailed description of the experimental setup is reported in Çalışkanoğlu et al., (2023a, 2024).
View in article
Çalışkanoğlu, A.Z., Cimarelli, C., Dingwell, D.B., Camara, A.S.B. (2024) Experimental vs. natural fulgurite: A comparison and implications for the formation process. American Mineralogist 109, 1682–1690. https://doi.org/10.2138/am-2023-9192
Show in context With the aim of investigating the physics of lightning–ground interaction and its duration and peak temperatures (Rakov and Uman, 2003; Pasek et al., 2012), several attempts have been made to experimentally reproduce fulgurites (Elmi et al., 2018; Çalışkanoğlu et al., 2023a, 2024 and references therein).
View in article
Castro, J. M., Keller, Y., Feisel, Y., Lanari, P., Helo, C., Mueller, S.P., Schipper, C.I., Thomas, C. (2020) Lightning-induced weathering of Cascadian volcanic peaks. Earth and Planetary Science Letters 552, 116595. https://doi.org/10.1016/j.epsl.2020.116595
Show in context This suggests that the temperature was high enough (likely in excess of 1500–2000 °C) to individually melt these minerals, and that subsequent cooling and interdiffusion between these melts that may last for tens of seconds to perhaps minutes for a typical 0.1–1 cm diameter fulguritic tube (Castro et al., 2020).
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Clayton, R.N., Mayeda, T.K., Brownlee, D.E. (1986) Oxygen isotopes in deep-sea spherules. Earth and Planetary Science Letters 79, 235–240. https://doi.org/10.1016/0012-821X(86)90181-0
Dole, M., Lane, G.A., Rudd, D.P., Zaukelies, D.A. (1954) Isotopic composition of atmospheric oxygen and nitrogen. Geochimica et Cosmochimica Acta 6, 65–78. https://doi.org/10.1016/0016-7037(54)90016-2
Show in context Whilst typical terrestrial rocks have normal δ18O (+5 to +12 ‰) and Δ’17O (−0.10 to +0.02 ‰), atmospheric oxygen is both heavy with respect to δ18O (+24 ‰) and low in Δ’17O0.528 (−0.45‰; Luz et al., 2014; Pack, 2021) because of the Dole effect (Dole et al., 1954), and formation of the ozone in the stratosphere (Young et al., 2014).
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Elmi, C., Coleman, N.S., Miu, K., Schruba, E. (2018) Experimental simulation of lightning current discharge on rocks. Applied Sciences 8, 2394. https://doi.org/10.3390/app8122394
Show in context With the aim of investigating the physics of lightning–ground interaction and its duration and peak temperatures (Rakov and Uman, 2003; Pasek et al., 2012), several attempts have been made to experimentally reproduce fulgurites (Elmi et al., 2018; Çalışkanoğlu et al., 2023a, 2024 and references therein).
View in article
Genareau, K., Gharghabi, P., Klüss, J. (2020) Influence of shock propagation on lightning evidence in volcanic ashfall deposits. Earth and Planetary Science Letters 535, 116124. https://doi.org/10.1016/j.epsl.2020.116124
Show in context Although tubular and branched structures are common, fulgurites can also show globular and massive shapes with irregular vesicular patterns (Fig. 1; Pasek et al., 2012; Genareau et al., 2020).
View in article
Interaction of lightning with volcanic ash plumes (Wadsworth et al., 2017; Genareau et al., 2020) is a very common occurrence of many volcanic eruptions.
View in article
Hess, B.L., Piazolo, S., Harvey, J. (2021) Lightning strikes as a major facilitator of prebiotic phosphorus reduction on early Earth. Nature Communications 12, 1535. https://doi.org/10.1038/s41467-021-21849-2
Show in context Therefore, on the surfaces of the Earth and other planets, lightning has the potential to locally reduce components such as iron and phosphorus making them biologically available, thus playing a role in the origin of life (Pasek and Block, 2009; Roberts et al., 2019; Hess et al., 2021; Bindi et al., 2023; Çalışkanoğlu et al., 2023b).
View in article
Hudak, M.R., Bindeman, I.N. (2020) Solubility, diffusivity, and O isotope systematics of H2O in rhyolitic glass in hydrothermal temperature experiments. Geochimica et Cosmochimica Acta 283, 222–242. https://doi.org/10.1016/j.gca.2020.06.009
Show in context However, this duration was not enough to hydrate fulgurites as they remain more anhydrous (<0.1 wt. % water) than natural volcanic glasses (Fig. S-1; e.g., Hudak and Bindeman, 2020).
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Luz, B., Barkan, E. (2010) Variations of 17O/16O and 18O/16O in meteoric waters. Geochimica et Cosmochimica Acta 74, 6276–6286. https://doi.org/10.1016/j.gca.2010.08.016
Show in context Meteoric waters, on the other hand, have low δ18O (<−5 ‰) and high Δ’17O (−0.01 to +0.05 ‰) values (Luz and Barkan, 2010; Sharp et al., 2018).
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Luz, B., Barkan, E., Severinghaus, J.P. (2014) 5.14 - The stable isotopic composition of atmospheric O2. In: Holland, H.D., Turekian, K.K. (Eds.) Treatise on Geochemistry. Second Edition, Elsevier, Amsterdam, 363–383. https://doi.org/10.1016/B978-0-08-095975-7.00419-8
Show in context Whilst typical terrestrial rocks have normal δ18O (+5 to +12 ‰) and Δ’17O (−0.10 to +0.02 ‰), atmospheric oxygen is both heavy with respect to δ18O (+24 ‰) and low in Δ’17O0.528 (−0.45‰; Luz et al., 2014; Pack, 2021) because of the Dole effect (Dole et al., 1954), and formation of the ozone in the stratosphere (Young et al., 2014).
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Magna, T., Žák, K., Pack, A., Moynier, F., Mougel, B., Skála, R., Jonášová, S., Řanda, Z., Mizera, J. (2017) Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere. Nature Communications 8, 227. https://doi.org/10.1038/s41467-017-00192-5
Show in context (a) Triple oxygen isotopic variations in natural, experimental, and industrial fulgurites of this study as compared to granites, selected tektites, hydrothermally altered rocks (Bindeman, 2021, this work; Tables S-1 to S-2), and air-O2 and meteoric waters. Shown fields and lines: 1) irgizite proximal ejecta (Magna et al. 2017), 2) silicate material evaporation and air exchange experiments from Pack (2021).
View in article
We observe that the cm size Zhamanshin irgizites have very low Δ’17O values (−0.2 ‰) and our measurements are in line with analyses reported by Magna et al., (2017) and Pack (2021).
View in article
Some natural mm to cm size proximal impact ejecta of silicic composition (irgizites), measured by Magna et al., (2017) and in this study (Table S-1) show −0.2 ‰ Δ’17O shifts in the same direction, estimated to reach a high temperature equilibrium of δ18O = +21.5 ‰, 2.5 ‰ lighter due to high temperature isotope equilibria, but at Δ’17O = −0.45 ‰ similar to air (Fig. 3; Pack, 2021), as evaporation-condensation phenomena at very high temperatures are expected to maintain a high 0.529–0.5305 exponents of isotope fractionation.
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Miller, M.F., Pack, A., Bindeman, I.N., Greenwood, R. (2020) Standardizing the reporting of Δ17O data from high precision oxygen triple-isotope ratio measurements of silicate rocks and minerals. Chemical Geology 532, 119332. https://doi.org/10.1016/j.chemgeo.2019.119332
Show in context The data is reported relative to the 0.528 exponent of δ17O vs. δ18O, as Δ’17O = δ’17O − 0.528 δ’18O, where primed coordinates are linearised logarithmic equivalents of conventionally defined δ18O and δ17O (Miller et al., 2020) and Δ’17Omantle = −0.037 ‰. We also measured total water and δD in these samples by TCEA-MAT253 system (Fig. S-1).
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Orville, R.E., Huffines, G.R., Burrows, W.R., Cummins, K.L. (2011) The North American lightning detection network (NALDN) - analysis of flash data: 2001-2009. Monthly Weather Review 139, 1305–1322. https://doi.org/10.1175/2010MWR3452.1
Show in context Whilst being fascinating in their own right as the Earth’s most minute melts, mapping of fulgurites in modern deserts and stratigraphic record is used to understand their origins, and indicator of lightning frequency (Orville et al., 2011).
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Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
Show in context Whilst typical terrestrial rocks have normal δ18O (+5 to +12 ‰) and Δ’17O (−0.10 to +0.02 ‰), atmospheric oxygen is both heavy with respect to δ18O (+24 ‰) and low in Δ’17O0.528 (−0.45‰; Luz et al., 2014; Pack, 2021) because of the Dole effect (Dole et al., 1954), and formation of the ozone in the stratosphere (Young et al., 2014).
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In addition, natural tektites were also measured for comparison, as these also represent high temperature melts that cool in the air for a short time formed by meteorite impacts that interacted with the Earth’s atmosphere (Pack, 2021).
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(a) Triple oxygen isotopic variations in natural, experimental, and industrial fulgurites of this study as compared to granites, selected tektites, hydrothermally altered rocks (Bindeman, 2021, this work; Tables S-1 to S-2), and air-O2 and meteoric waters. Shown fields and lines: 1) irgizite proximal ejecta (Magna et al. 2017), 2) silicate material evaporation and air exchange experiments from Pack (2021).
View in article
We observe that the cm size Zhamanshin irgizites have very low Δ’17O values (−0.2 ‰) and our measurements are in line with analyses reported by Magna et al., (2017) and Pack (2021).
View in article
Similar to molten crusts of meteorites, micrometeorites, and some tektites (Pack et al., 2017; Pack, 2021), the natural igneous and experimental fulgurites record shifts toward low Δ’17O atmospheric oxygen values.
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Pack (2021) reported that reaction of a silicate melt with atmospheric oxygen at 1300–1500 °C lasting for only 5–10 sec, already results in a negative −0.1 to −0.2‰ Δ’17O shift, indicating that 20–50 % of oxygen in the melt exchanges with atmospheric oxygen quite quickly.
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Some natural mm to cm size proximal impact ejecta of silicic composition (irgizites), measured by Magna et al., (2017) and in this study (Table S-1) show −0.2 ‰ Δ’17O shifts in the same direction, estimated to reach a high temperature equilibrium of δ18O = +21.5 ‰, 2.5 ‰ lighter due to high temperature isotope equilibria, but at Δ’17O = −0.45 ‰ similar to air (Fig. 3; Pack, 2021), as evaporation-condensation phenomena at very high temperatures are expected to maintain a high 0.529–0.5305 exponents of isotope fractionation.
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Pack, A., Höweling, A., Hezel, D.C., Stefanak, M., Beck, A.-K., Peters, S.T.M., Sengupta, S., Herwartz, D., Folco, L. (2017) Tracing the oxygen isotope composition of the upper Earth atmosphere using cosmic spherules. Nature Communications 8, 15702. https://doi.org/10.1038/ncomms15702
Show in context Similar to molten crusts of meteorites, micrometeorites, and some tektites (Pack et al., 2017; Pack, 2021), the natural igneous and experimental fulgurites record shifts toward low Δ’17O atmospheric oxygen values.
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Pasek, M., Block, K. (2009) Lightning-induced reduction of phosphorus oxidation state. Nature Geoscience 2, 553–556. https://doi.org/10.1038/ngeo580
Show in context Furthermore, the presence of Fe-Si alloys in some fulgurites reflects extremely reducing conditions during oxygen evaporation or carbon compound’s reduction (Pasek and Block, 2009; Pasek et al., 2012; Ballhaus et al., 2017).
View in article
Therefore, on the surfaces of the Earth and other planets, lightning has the potential to locally reduce components such as iron and phosphorus making them biologically available, thus playing a role in the origin of life (Pasek and Block, 2009; Roberts et al., 2019; Hess et al., 2021; Bindi et al., 2023; Çalışkanoğlu et al., 2023b).
View in article
Pasek, M.A., Block, K., Pasek, V. (2012) Fulgurite morphology: a classification scheme and clues to formation. Contributions to Mineralogy and Petrology 164, 477–492. https://doi.org/10.1007/s00410-012-0753-5
Show in context Although tubular and branched structures are common, fulgurites can also show globular and massive shapes with irregular vesicular patterns (Fig. 1; Pasek et al., 2012; Genareau et al., 2020).
View in article
With the aim of investigating the physics of lightning–ground interaction and its duration and peak temperatures (Rakov and Uman, 2003; Pasek et al., 2012), several attempts have been made to experimentally reproduce fulgurites (Elmi et al., 2018; Çalışkanoğlu et al., 2023a, 2024 and references therein).
View in article
Furthermore, the presence of Fe-Si alloys in some fulgurites reflects extremely reducing conditions during oxygen evaporation or carbon compound’s reduction (Pasek and Block, 2009; Pasek et al., 2012; Ballhaus et al., 2017).
View in article
Paxton, A.H., Gardner, R.L., Baker, L. (2017) Lightning Return Stoke: A Numerical Calculation of the Optical Radiation. In: Gardner, R.L. (Ed.) Lightning Electromagnetics. Routledge, New York, 47–61. https://doi.org/10.1201/9780203748992-4
Show in context Electrical current in natural lightning channels may exceed 200,000 A, and calculated temperatures can exceed 20,000 K (Paxton et al., 2017), thus exceeding the temperature of melting and vapourisation for most natural materials.
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Purdom, W.B. (1966) Fulgurites from Mount Thielsen. The Ore Bin 28, 153–159.
Show in context Soil fulgurites often show a bubbly appearance and thick, melt-rich glassy walls; the glass is generally more heterogeneous, incorporating aluminum silicate clay and feldspar minerals, whilst the carbonate materials do not melt but are preferentially devolatilised (Purdom, 1966).
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Rakov, V.A., Uman, M.A. (2003) Lightning: Physics and Effects. Cambridge University Press, New York. https://doi.org/10.1017/CBO9781107340886
Show in context Fulgurites are natural glassy products formed when lightning strikes the Earth’s or planetary surface, forming instantaneous melts by fusing ground materials (Rakov and Uman, 2003).
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With the aim of investigating the physics of lightning–ground interaction and its duration and peak temperatures (Rakov and Uman, 2003; Pasek et al., 2012), several attempts have been made to experimentally reproduce fulgurites (Elmi et al., 2018; Çalışkanoğlu et al., 2023a, 2024 and references therein).
View in article
The trigger pulse generates 135 kA for about 100 ms, creating a conductive path between the electrodes and is followed by a DC current of about 200 to 320 A for a duration of up to 500 ms, simulating the long duration of natural lightning discharges (Rakov and Uman, 2003).
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Roberts, S.E., Sheffer, A.A., McCanta, M.C., Dyar, M.D., Sklute, E.C. (2019) Oxidation state of iron in fulgurites and trinitite: implications for redox changes during abrupt high-temperature and pressure events. Geochimica et Cosmochimica Acta 266, 332–350. https://doi.org/10.1016/j.gca.2019.08.021
Show in context Therefore, on the surfaces of the Earth and other planets, lightning has the potential to locally reduce components such as iron and phosphorus making them biologically available, thus playing a role in the origin of life (Pasek and Block, 2009; Roberts et al., 2019; Hess et al., 2021; Bindi et al., 2023; Çalışkanoğlu et al., 2023b).
View in article
Sharp, Z., Wostbrock, J., Pack, A. (2018) Mass-dependent triple oxygen isotope variations in terrestrial materials. Geochemical Perspective Letters 7, 27–31. https://doi.org/10.7185/geochemlet.1815
Show in context Meteoric waters, on the other hand, have low δ18O (<−5 ‰) and high Δ’17O (−0.01 to +0.05 ‰) values (Luz and Barkan, 2010; Sharp et al., 2018).
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Thiemens, M.H., Lin, M. (2021) Discoveries of Mass Independent Isotope Effects in the Solar System: Past, Present and Future. Reviews in Mineralogy and Geochemistry 86, 35–95. https://doi.org/10.2138/rmg.2021.86.02
Show in context Independent of lightning, the UV radiation has been the leading cause of very large mass independent fractionations that lead to +30 to +100 ‰ Δ’17O anomalies in the air-O3 (or ozone, e.g., Thiemens and Lin, 2021), and a negative Δ’17O in the residual atmospheric oxygen.
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Wadsworth, F.B. Vasseur, J., Llewellin, E.W., Genareau, K., Cimarelli, C., Dingwell, D.B. (2017) Size limits for rounding of volcanic ash particles heated by lightning. Journal of Geophysical Research: Solid Earth 122, 1977–1989. https://doi.org/10.1002/2016JB013864
Show in context Interaction of lightning with volcanic ash plumes (Wadsworth et al., 2017; Genareau et al., 2020) is a very common occurrence of many volcanic eruptions.
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Young, E.D., Yeung, L.Y., Kohl, I.E. (2014) On the Δ17O budget of atmospheric O2. Geochimica et Cosmochimica Acta 135, 102–125. https://doi.org/10.1016/j.gca.2014.03.026
Show in context Whilst typical terrestrial rocks have normal δ18O (+5 to +12 ‰) and Δ’17O (−0.10 to +0.02 ‰), atmospheric oxygen is both heavy with respect to δ18O (+24 ‰) and low in Δ’17O0.528 (−0.45‰; Luz et al., 2014; Pack, 2021) because of the Dole effect (Dole et al., 1954), and formation of the ozone in the stratosphere (Young et al., 2014).
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Supplementary Information
The Supplementary Information includes:
- Figure S-1
- Tables S-1 and S-2
- Supplementary Information References
Download the Supplementary Information (PDF)
Figures
Figure 1 Generalised internal structure of a fulgurite and its geometrical relationship to the lightning strike.
Figure 2 Morphological examples of (a) natural (sedimentary/soil) branched fulgurites, (b) igneous rock fulgurite at Mt Thielsen, Oregon (indicated by yellow arrows), (c) tubular fulgurite from the Namibian desert (blue arrow shows lightning direction almost perpendicular to the original stratification and (d) different morphologies of experimental fulgurites derived from phonolitic volcanic ash from the Eifel, Germany.
Figure 3 (a) Triple oxygen isotopic variations in natural, experimental, and industrial fulgurites of this study as compared to granites, selected tektites, hydrothermally altered rocks (Bindeman, 2021
Bindeman, I.N. (2021) Triple Oxygen Isotopes in Evolving Continental Crust, Granites, and Clastic Sediments. Reviews in Mineralogy and Geochemistry 86, 241–290. https://doi.org/10.2138/rmg.2021.86.08
, this work; Tables S-1 to S-2), and air-O2 and meteoric waters. Shown fields and lines: 1) irgizite proximal ejecta (Magna et al. 2017Magna, T., Žák, K., Pack, A., Moynier, F., Mougel, B., Skála, R., Jonášová, S., Řanda, Z., Mizera, J. (2017) Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere. Nature Communications 8, 227. https://doi.org/10.1038/s41467-017-00192-5
), 2) silicate material evaporation and air exchange experiments from Pack (2021)Pack, A. (2021) Isotopic Traces of Atmospheric O2 in Rocks, Minerals, and Melts. Reviews in Mineralogy and Geochemistry 86, 217–240. https://doi.org/10.2138/rmg.2021.86.07
. Effects of very high T evaporation and condensation are shown here and follow the highest 0.5305 fractionation exponent, while thermal diffusion follows a slope of 0.518 (Table S-2). (b) A zoom in of (a), emphasising igneous and experimental fulgurite data points measured in this work.