Shocked quartz in the Alamo breccia, southern Nevada: Evidence for a Devonian impact event

Abstract

Research Article| November 01, 1995 Shocked quartz in the Alamo breccia, southern Nevada: Evidence for a Devonian impact event Hugues Leroux; Hugues Leroux 1Laboratoire de Structure et Propriétés de l'Etat Solide, Université des Sciences et Techniques de Lille, 59655 Villeneuve d'Ascq Cedex, France Search for other works by this author on: GSW Google Scholar John E. Warme; John E. Warme 2Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado 80401 Search for other works by this author on: GSW Google Scholar Jean-Claude Doukhan Jean-Claude Doukhan 1Laboratoire de Structure et Propriétés de l'Etat Solide, Université des Sciences et Techniques de Lille, 59655 Villeneuve d'Ascq Cedex, France Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (11): 1003–1006. https://doi.org/10.1130/0091-7613(1995)023<1003:SQITAB>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hugues Leroux, John E. Warme, Jean-Claude Doukhan; Shocked quartz in the Alamo breccia, southern Nevada: Evidence for a Devonian impact event. Geology 1995;; 23 (11): 1003–1006. doi: https://doi.org/10.1130/0091-7613(1995)023<1003:SQITAB>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A transmission electron microscope (TEM) study of quartz grains strongly implies that the Alamo breccia of southern Nevada resulted indirectly from a Late Devonian hypervelocity impact event. The Alamo breccia is perhaps the most voluminous marine carbonate megabreccia exposed on land. It covers ≈4,000 km2, averages ≈70 m thick, and contains more than 250 km3 of carbonate-platform debris that was deposited by a giant submarine slide. The breccia is a single bed with the characteristics of a chaotic debrite at the base evolving upward to a graded turbidite at the top. The bed is anomalous, compared to other marine megabreccias, because over a large area it is intercalated with cyclic shallow-water carbonate-platform rocks, rather than with deep-water turbidites as expected. Thin sections of peculiar quartz grains, recovered from insoluble residues of the breccia, show one to six sets of imperfect parallel lamellae and other defects suggesting shock tamorphism. When studied by TEM, the grains clearly display planar deformation features (PDFs) and other defects from a high-pressure shock wave. Straight and narrow planar microstructures consist of a high density of dislocations mostly parallel to crystal habit plane {1012}, but {1013}, {1011}, and {1121} orientations were also detected. The PDFs appear identical to those in quartz grains associated with well-known impact structures such as Manicouagan and Manson. We conclude that energy from an impact triggered the epiplatform slide and the consequent sedimentary processes that formed the Alamo breccia. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.