The response of zircon to the extreme pressures and temperatures of a lightning strike

Abstract

Hypervelocity impacts can produce features in zircon that are not normally produced by endogenic processes. However, lightning can also induce extreme pressure–temperature excursions, and its effect on zircon has not been studied. With the aim to recognise features that form in response to extreme pressure–temperature excursions but are not unique to hypervelocity impacts, we imaged and undertook microstructural characterization of zircon in a fulgurite (a tubular body of glass and fused clasts that formed in response to a lightning strike). We document zircon with granular ZrO2 and rims of vermicular ZrO2, features which vary in abundance with increasing distance from the fulgurite’s central void. This indicates that these features formed in response to the lightning strike. Zircon dissociation to ZrO2 and SiO2 is a high-temperature, relatively low-pressure phenomenon, consistent with previous suggestions that lightning strikes involve extreme temperatures as well as pressures greater than those usually generated in Earth’s crust but rarely > 10 GPa. The rims of monoclinic ZrO2 record crystallographic evidence for precursor cubic ZrO2, demonstrating that cubic ZrO2 is not unique to hypervelocity impacts. Given the likelihood that this fulgurite experienced pressures of, at most, a few GPa, evidence for cubic ZrO2 indicates peak temperatures > 2000 °C.

Iron Silicides in Fulgurites

“…The tube size and morphology of the fulgurite depend on the target mineral composition [3] and physical characteristics, as well as the energy and duration of the discharge event [1,15]. The mineralogy of fulgurites reflects their unusual formation conditions and is characterized by highly reduced phases such as iron silicide minerals and iron phosphides (schreibersite), as well as high-temperature minerals such as cristobalite and baddeleyite, and high-pressure minerals such as shocked quartz and cubic ZrO 2 [10,11,[16][17][18].…”

“…Organic Carbon Reduction [2,3,25,52] Galvanic Reduction [2,53] Shockwave Chemistry [10,11,[16][17][18]54] Vapor deposition of Fe and Si [41] Alternatively, the galvanic reduction of target minerals could occur as the electrons flow from clouds to the ground during a lightning strike. This route has been considered with respect to iron silicide formation [2,53].…”

“…A shockwave associated with a lightning strike may also induce a reducing environment and support the formation of iron silicide [10,11,[16][17][18]54]. However, Cardona et al [25] argues that there is no evidence of shock that has been found in natural fulgurites, which was true at the time.…”

Crystal structure and composition of hiärneite, Ca2Zr4Mn3+SbTiO16, and constitution of the calzirtite group

“…In calzirtite and hiärneite, the ordering of the cations over specific sites leads to a lower symmetry and a tripled a parameter and doubled c parameter (Table 7). More pure variants of cubic ZrO 2 have also been reported to form from shock-metamorphism of zircon (e.g., Kenny and Pasek, 2021). All of the group members belong to the Nickel-Strunz subdivision 4.DL (Strunz and Nickel, 2001).…”

A Semi-Analytical Solution for Shock Wave Pressure and Radius of Soil Plastic Zone Induced by Lightning Strikes

“…Lightning is a dangerous, frequent geophysical phenomenon [ 1 , 2 ], and large amounts of heat and electricity are produced by considerable energy and intense electromagnetic field activities [ 3 , 4 ]. The lightning forms a plasma channel that propagates outward from its starting point with positive and negative charges at each end, known as positive and negative leaders, respectively [ 3 ].…”