Impact melt rocks from the Late Paleocene Hiawatha impact structure, northwest Greenland

1William R. HYDE,2Adam A. GARDE,2Nynke KEULEN,2Sebastian N. MALKKI,3,4Steven J. JARET,5Tod WAIGHT,6Pierre BECK,7Iain McDONALD,1Nicolaj K. LARSEN
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13987]
1Globe Institute, University of Copenhagen, Copenhagen K, Denmark
2Geological Survey of Denmark and Greenland, Copenhagen K, Denmark
3Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
4Department of Physical Sciences, Kingsborough Community College, City University of New York, Brooklyn, New York, USA
5Department of Geosciences and Natural Resource Management (Geology Section), University of Copenhagen, Copenhagen K,Denmark
6Universit ́e Grenoble Alpes, CNRS, IPAG, Grenoble, France
7School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK
Published by arrangement with John Wiley & Sons

Impact melt rocks formed during hypervelocity impact events are ideal forstudying impact structures. Here, we describe impact melt rock samples collected proximalto the 31 km wide 58 Ma Hiawatha impact structure, northwest Greenland, which iscompletely covered by the Greenland Ice Sheet. The melt rocks contain diagnostic shockindicators (e.g., planar deformation features [PDF] in quartz and shocked zircon) and formthree groups based on melt textures and chemistry: (i) hypocrystalline, (ii) glassy, and (iii)carbonate-based melt rocks. The exposed foreland directly in front of the structure consistsof metasedimentary successions and igneous plutons; however, the carbonate-basedimpactites indicate a mixed target sequence with a significant carbonate-rich component.Well-preserved organic material in some melt rocks indicates that North Greenland at thetime of impact was host to abundant organic material, likely a dense high-latitude temperateforest. Geochemical signatures of platinum-group elements in selected samples indicate anextraterrestrial component and support previous identification of a highly fractionated ironimpactor in glaciofluvial sand. Our results illustrate the possibility to study impact structureshidden beneath a thick ice sheet based on transported samples and this opens a new avenuefor identifying other potential impact craters in Greenland and Antarctica.


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