Kjær Kurt H, Larsen Nicolaj K, Binder Tobias, Bjørk Anders A, Eisen Olaf, Fahnestock Mark A, Funder Svend, Garde Adam A, Haack Henning, Helm Veit, Houmark-Nielsen Michael, Kjeldsen Kristian K, Khan Shfaqat A, Machguth Horst, McDonald Iain, Morlighem Mathieu, Mouginot Jérémie, Paden John D, Waight Tod E, Weikusat Christian, Willerslev Eske, MacGregor Joseph A
Centre for GeoGenetics, Natural History Museum, University of Copenhagen, Copenhagen, Denmark.
Department of Geoscience, Aarhus University, Aarhus, Denmark.
Sci Adv. 2018 Nov 14;4(11):eaar8173. doi: 10.1126/sciadv.aar8173. eCollection 2018 Nov.
We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact-related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron asteroid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet.
我们报告了在格陵兰岛西北部的希阿瓦萨冰川之下发现一个大型撞击坑的情况。通过机载雷达探测，我们在厚达一公里的冰层之下识别出一个直径31公里的圆形基岩凹陷。这个凹陷有一个隆起的边缘，它横切了支流冰下河道，还有一个平缓的中央隆起，似乎正在被积极侵蚀。通过对冰消作用后的前陆进行地面调查，我们在冰缘沿线的前寒武纪基岩中识别出了与冰下边缘相切的叠印构造。从流经该撞击坑的最大河流中采集的冰川河流沉积物含有冲击石英和其他与撞击相关的颗粒。对这种沉积物的地球化学分析表明，撞击体是一颗分异的铁小行星，其直径肯定超过一公里才能形成所识别出的撞击坑。撞击坑内冰层的放射性地层学显示，全新世冰层是连续且整合的，但所有更深层和更古老的冰层似乎富含碎屑或受到严重扰动。这个撞击坑的年龄目前未知，但根据我们的地质和地球物理证据，我们得出结论，它不太可能早于格陵兰冰盖的更新世开端。
