Impact melt rocks from the Late Paleocene Hiawatha impact structure,northwest Greenland |
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| Authors: | William R Hyde Adam A Garde Nynke Keulen Sebastian N Malkki Steven J Jaret Tod Waight Pierre Beck Iain McDonald Nicolaj K Larsen |
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| Institution: | 1. Globe Institute, University of Copenhagen, Copenhagen K, Denmark;2. Geological Survey of Denmark and Greenland, Copenhagen K, Denmark;3. Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA;4. Department of Geosciences and Natural Resource Management (Geology Section), University of Copenhagen, Copenhagen K, Denmark;5. Université Grenoble Alpes, CNRS, IPAG, Grenoble, France;6. School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK |
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| Abstract: | Impact melt rocks formed during hypervelocity impact events are ideal for studying impact structures. Here, we describe impact melt rock samples collected proximal to the 31 km wide 58 Ma Hiawatha impact structure, northwest Greenland, which is completely covered by the Greenland Ice Sheet. The melt rocks contain diagnostic shock indicators (e.g., planar deformation features PDF] in quartz and shocked zircon) and form three 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 consists of metasedimentary successions and igneous plutons; however, the carbonate-based impactites indicate a mixed target sequence with a significant carbonate-rich component. Well-preserved organic material in some melt rocks indicates that North Greenland at the time of impact was host to abundant organic material, likely a dense high-latitude temperate forest. Geochemical signatures of platinum-group elements in selected samples indicate an extraterrestrial component and support previous identification of a highly fractionated iron impactor in glaciofluvial sand. Our results illustrate the possibility to study impact structures hidden beneath a thick ice sheet based on transported samples and this opens a new avenue for identifying other potential impact craters in Greenland and Antarctica. |
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