Kenny Gavin G, Hyde William R, Storey Michael, Garde Adam A, Whitehouse Martin J, Beck Pierre, Johansson Leif, Søndergaard Anne Sofie, Bjørk Anders A, MacGregor Joseph A, Khan Shfaqat A, Mouginot Jérémie, Johnson Brandon C, Silber Elizabeth A, Wielandt Daniel K P, Kjær Kurt H, Larsen Nicolaj K
Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden.
Globe Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark.
Sci Adv. 2022 Mar 11;8(10):eabm2434. doi: 10.1126/sciadv.abm2434. Epub 2022 Mar 9.
The ~31-km-wide Hiawatha structure, located beneath Hiawatha Glacier in northwestern Greenland, has been proposed as an impact structure that may have formed after the Pleistocene inception of the Greenland Ice Sheet. To date the structure, we conducted Ar/Ar analyses on glaciofluvial sand and U-Pb analyses on zircon separated from glaciofluvial pebbles of impact melt rock, all sampled immediately downstream of Hiawatha Glacier. Unshocked zircon in the impact melt rocks dates to ~1915 million years (Ma), consistent with felsic intrusions found in local bedrock. The Ar/Ar data indicate Late Paleocene resetting and shocked zircon dates to 57.99 ± 0.54 Ma, which we interpret as the impact age. Consequently, the Hiawatha impact structure far predates Pleistocene glaciation and is unrelated to either the Paleocene-Eocene Thermal Maximum or flood basalt volcanism in east Greenland. However, it was contemporaneous with the Paleocene Carbon Isotope Maximum, although the impact's exact paleoenvironmental and climatic significance awaits further investigation.
位于格陵兰岛西北部海华沙冰川之下、宽度约31公里的海华沙构造，被认为是一个撞击构造，可能形成于格陵兰冰盖更新世开始之后。为了确定该构造的年代，我们对冰川河流砂进行了氩-氩分析，并对从撞击熔岩层的冰川河流卵石中分离出的锆石进行了铀-铅分析，所有样本均采自海华沙冰川下游紧邻处。撞击熔岩层中未受冲击的锆石年代测定为约19.15亿年，这与当地基岩中发现的长英质侵入岩一致。氩-氩数据表明是古新世晚期重置，受冲击锆石年代测定为57.99 ± 0.54百万年，我们将其解释为撞击年代。因此，海华沙撞击构造远早于更新世冰川作用，与格陵兰岛东部的古新世-始新世极热事件或溢流玄武岩火山活动均无关。然而，它与古新世碳同位素极大值同时期，尽管撞击的确切古环境和气候意义有待进一步研究。
