Shock impedance amplified impact deformation of zircon in granitic rocks from the Chicxulub impact crater
Shock impedance amplified impact deformation of zircon in granitic rocks from the Chicxulub impact crater
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DOI：
10.1016/j.epsl.2021.117201
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发表时间：
2021-12
影响因子：
5.3
通讯作者：
A. Wittmann;A. Cavosie;N. Timms;L. Ferrière;A. Rae;C. Rasmussen;C. Ross;D. Stockli;M. Schmieder;D. Kring;Jiawei Zhao;Long Xiao;J. Morgan;S. Gulick
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文献类型：
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作者：
A. Wittmann;A. Cavosie;N. Timms;L. Ferrière;A. Rae;C. Rasmussen;C. Ross;D. Stockli;M. Schmieder;D. Kring;Jiawei Zhao;Long Xiao;J. Morgan;S. Gulick
锆石是一种精密的计时器，也是撞击变形的杰出记录者。然而，锆石中许多撞击诱发特征的校准很差，有时是由于实验数据相互矛盾，有时是由于缺乏对撞击变形锆石的系统研究。为了解决冲击岩相学中锆石的使用问题，我们对直径200 km的K-Pg Chicxulub冲击构造峰环中凸起的花岗岩基岩连续钻芯中的429颗锆石颗粒的冲击变形特征进行了分类。在背散射电子（BSE）图像中进行初步鉴定后，拉曼光谱和电子背散射衍射证实了一颗含reidite的锆石颗粒。基于石英的冲击气压测量表明，该锆石-瑞德石颗粒的寄主岩承受的平均冲击压力为17.5 GPa。通过对429颗zrsio4颗粒的BSE图像的调查发现，脆性变形特征普遍存在，23%的锆石颗粒出现1 ~ 5组平面断裂。我们的调查还揭示了锆石平面裂缝的产状与寄主物质类型具有统计学意义的相关性。相对于包覆基性、高密度矿物寄主的锆石，长英质、低密度矿物的锆石具有平面裂缝的发生率要高得多。这一发现表明，由于锆石及其矿物宿主之间的冲击阻抗差异，压力放大。采用阻抗匹配方法，模拟了希克苏鲁伯花岗岩中锆石包裹体的冲击阻抗压力放大效应。我们的模型表明，冲击阻抗可以将希克苏鲁伯花岗岩中石英或长石中的锆石包裹体的平均17.5 GPa冲击压力放大到24±1 GPa，表明这些岩石中的reidite形成于17.5至25 GPa之间。从本质上讲，我们对锆石组合中阻抗诱导的冲击压力放大的研究，包括reidite形成的开始，详细介绍了如何量化矿物组合中的冲击阻抗，以改进冲击压力估计。
Zircon is a precise chronometer and prominent recorder of impact deformation. However, many impact-induced features in zircon are poorly calibrated, sometimes due to contradicting experimental data, in other instances due to the lack of systematic studies of impact-deformed zircon. To resolve issues with the shock petrographic use of zircon, we classified impact deformation features in 429 zircon grains in a continuous drill core of uplifted, granitic bedrock in the peak ring of the 200-km-diameter K-Pg Chicxulub impact structure. Following initial identification in backscattered electron (BSE) images, Raman spectroscopy and electron backscatter diffraction confirmed one reidite-bearing zircon grain. Quartz-based shock barometry indicates the host rock of this zircon-reidite grain experienced an average shock pressure of 17.5 GPa. A survey of BSE images of 429 ZrSiO4grains found brittle deformation features are ubiquitous, with planar fractures in one to five sets occurring in 23% of all zircon grains. Our survey also reveals a statistically significant correlation of the occurrence of planar fractures in zircon with the types of host materials. Compared to zircon enclosed in mafic, higher density mineral hosts, felsic, low-density minerals show a much higher incidence of zircon with planar fractures. This finding suggests amplification of pressure due to shock impedance contrasts between zircon and its mineral hosts. Using the impedance matching method, we modeled the shock impedance pressure amplification effect for zircon inclusions in Chicxulub granitic hosts. Our modeling indicates shock impedance could have amplified the average 17.5 GPa shock pressure in a zircon inclusion in quartz or feldspar in the Chicxulub granitic rocks to 24 ± 1 GPa, suggesting that reidite in these rocks formed between 17.5 and 25 GPa. In essence, our study of impedance-induced shock pressure amplification in zircon assemblages, including the onset of reidite formation, details how shock impedance in mineral associations can be quantified to refine shock pressure estimates.