This investigation focuses on two well-preserved impact structures developed in sedimentary target rocks: the ~23.5 Ma old Haughton structure, Canada, and the ~14.5 Ma old Ries structure, Germany. The aim of this study was to investigate the effects of hypervelocity impact into sedimentary targets. The study reveals that a series of different impactites are present at Haughton, the bulk of which comprise a groundmass of impact-generated melts (calcite + silicate glass ± anhydrite). Thus, carbonates, evaporites, sandstones, and shales underwent shock melting during the Haughton impact event. The shock melting of impure carbonates resulted in the generation of Mg–Ca–Si-rich melts that crystallized calcite during rapid cooling. The residual melt quenched to Mg–Si-rich glass. These impactites should, therefore, be classified as clast-rich impact melt rocks or impact melt breccias, and not clastic matrix breccias as previously held. Ries surficial suevites are reinterpreted as clast-rich impact melt rocks or impact melt breccias. Four main types of impact melt glass are present, in contrast to previous studies that recognized only one type. These results are at odds with the current, generally accepted, definition of suevite. Given that the Ries is the original type occurrence of ‘suevite’, some redefinition of the term suevite may be in order. Furthermore, it is clear that sedimentary rocks, as well as crystalline rocks, were shock melted during the Ries impact event. The results of this study are, therefore, incompatible with previous models in which the zone of melting is restricted to the crystalline basement. It is apparent that impact melting in sedimentary targets is much more common than previously thought. Furthermore, there is no unequivocal evidence for the decomposition of carbonates or evaporites at any terrestrial impact site. Many previous assumptions about the response of sedimentary rocks during hypervelocity impact events are, therefore, incorrect. The products of impact into sedimentary targets may appear very different from those developed in crystalline targets. However, microscopic imaging and analysis suggests that these seemingly different lithologies may be genetically equivalent. Thus, the apparent ‘anomaly’ between the amount of impact melt rocks formed in sedimentary and crystalline targets may be due to a misinterpretation of the rock record.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:UNB.1882/163 |
| Date | January 2004 |
| Creators | Osinski, Gordon Richard |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Format | 120527 bytes, 507497 bytes, 21746 bytes, 751653 bytes, 887490 bytes, 1005428 bytes, 3127726 bytes, 2666510 bytes, 1117911 bytes, 2051339 bytes, 1334418 bytes, 233966 bytes, 307884 bytes, 48375 bytes, 21757779 bytes, 6646977 bytes, application/pdf |
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