Kenny Gavin G, Pasek Matthew A
Department of Geosciences, Swedish Museum of Natural History, 104 05, Stockholm, Sweden.
School of Geosciences, University of South Florida, Tampa, FL, 33620, USA.
Sci Rep. 2021 Jan 15;11(1):1560. doi: 10.1038/s41598-021-81043-8.
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 ZrO and rims of vermicular ZrO, 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 ZrO and SiO 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 ZrO record crystallographic evidence for precursor cubic ZrO, demonstrating that cubic ZrO is not unique to hypervelocity impacts. Given the likelihood that this fulgurite experienced pressures of, at most, a few GPa, evidence for cubic ZrO indicates peak temperatures > 2000 °C.
超高速撞击会在锆石中产生一些通常由内生过程无法产生的特征。然而，闪电也能引发极端的压力 - 温度变化，而其对锆石的影响尚未得到研究。为了识别那些因极端压力 - 温度变化而形成但并非超高速撞击所特有的特征，我们对闪电熔岩（一种因雷击形成的由玻璃和熔结碎屑组成的管状体）中的锆石进行了成像和微观结构表征。我们记录了含有粒状ZrO和蠕虫状ZrO边缘的锆石，这些特征的丰度随距闪电熔岩中心空洞距离的增加而变化。这表明这些特征是由雷击形成的。锆石分解为ZrO和SiO是一种高温、相对低压的现象，这与之前的观点一致，即雷击涉及极端温度以及大于地壳通常产生的压力，但很少超过10 GPa。单斜ZrO的边缘记录了前驱体立方ZrO的晶体学证据，表明立方ZrO并非超高速撞击所特有。鉴于这块闪电熔岩可能最多承受了几GPa的压力，立方ZrO的证据表明峰值温度超过了2000°C。
