格陵兰岛西北部发现约格陵兰岛西北部发现约 1 Ga 超高速撞击事件的证据

Geology Pub Date : 2024-04-12 DOI:10.1130/g51876.1
William R. Hyde, G. G. Kenny, S. Jaret, Joseph A. MacGregor, Pierre Beck, M J Whitehouse, N. K. Larsen
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摘要

地球上可能有许多未被发现的撞击结构,但有几项挑战阻碍了对它们的探测,包括可能隐藏在大冰盖之下。近年来,越来越多的地球物理、地球化学和微物理证据表明,格陵兰岛西北部的希亚瓦萨冰川下有一个约 58 Ma 的撞击结构。在此,我们报告了该地区第二次更早的超高速撞击事件的证据,记录在从英格尔菲尔德陆地的冰川流沉积物中采集的撞击熔岩样本中。通过对冲击变质锆石颗粒进行二次离子质谱 U-Pb 分析,我们得出了前所未见的新元古代最佳撞击年龄,即 1039 ± 16 Ma(加权偏差的均方差 = 2.9)。根据从未曾受到冲击的锆石颗粒中获得的Archean-Proterozoic目标岩石U-Pb年龄,以及熔岩样本沿冰缘的位置,我们认为该样本来自被格陵兰冰盖掩盖的更内陆的超高速撞击结构。这项研究表明,我们有能力在地球上一些最难以接近的地区发现新的撞击事件,而且在研究原地材料时,我们有可能从一个地点对多个撞击结构进行取样。我们的研究结果对当前和未来的火星和月球返回样本具有重要意义,因为这些样本明显带有复杂的撞击历史。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Evidence for ca. 1 Ga hypervelocity impact event found in northwest Greenland
There are likely many undiscovered impact structures on Earth, but several challenges prevent their detection, including possible concealment beneath large ice sheets. In recent years, geophysical, geochemical, and microphysical evidence has mounted for a ca. 58 Ma impact structure under the Hiawatha Glacier, northwest Greenland. Here, we report evidence for a second, much older hypervelocity impact event in this region, recorded in an impact melt rock sample collected from a glaciofluvial deposit in Inglefield Land. Secondary ion mass spectrometry U-Pb analyses of shock metamorphosed zircon grains yielded a previously unrecorded, Proterozoic best estimate impact age of 1039 ± 16 Ma (mean square of weighted deviates = 2.9). Based on Archean−Proterozoic target rock U-Pb ages obtained from unshocked zircon grains and the location of the melt rock sample along the ice margin, we suggest this sample was derived from a hypervelocity impact structure farther inland, concealed by the Greenland Ice Sheet. This study demonstrates the ability to uncover new impact events in some of the most inaccessible areas on Earth and the possibility of sampling multiple impact structures from one location when examining ex situ material. Our results have implications for current and future Martian and lunar returned samples that demonstrably bear complex impact histories.
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