Rheological controls on the emplacement of extremely high-grade ignimbrites

Abstract

Research Article| September 01, 2013 Rheological controls on the emplacement of extremely high-grade ignimbrites Geneviève Robert; Geneviève Robert 1Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA Search for other works by this author on: GSW Google Scholar Graham D.M. Andrews; Graham D.M. Andrews 2Department of Geology, California State University, Bakersfield, California 93311, USA Search for other works by this author on: GSW Google Scholar Jiyang Ye; Jiyang Ye 1Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA Search for other works by this author on: GSW Google Scholar Alan G. Whittington Alan G. Whittington 1Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA Search for other works by this author on: GSW Google Scholar Geology (2013) 41 (9): 1031–1034. https://doi.org/10.1130/G34519.1 Article history received: 25 Feb 2013 rev-recd: 17 May 2013 accepted: 22 May 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Geneviève Robert, Graham D.M. Andrews, Jiyang Ye, Alan G. Whittington; Rheological controls on the emplacement of extremely high-grade ignimbrites. Geology 2013;; 41 (9): 1031–1034. doi: https://doi.org/10.1130/G34519.1 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 Extremely high-grade, lava-like welded ignimbrites are produced by many large explosive eruptions with volumes typically 101–103 km3. However, understanding of the physical properties of these unusual deposits, and their transport and depositional mechanisms, is incomplete. The lava-like and rheomorphic Grey’s Landing ignimbrite, Idaho (western United States), provides abundant field evidence supporting the upward migration of a transient, <2-m-thick, sub-horizontal ductile shear zone at the interface between the pyroclastic density current and the deposit, through which all of the aggrading pyroclastic material passed. Here we use a combination of rheological experiments and thermo-mechanical modeling to test the syndepositional shear zone model. We show that syndepositional welding and ductile flow are achievable within a very restricted field of likely temperature–strain rate space, where rapid deformation is favored by higher emplacement temperatures (≥850 °C). The field of ductile deformation is broadened significantly by accounting for strain heating, which permits a sustained temperature increase of up to 250 °C within the shear zone and helps to explain the enormous extents of lava-like lithofacies and the intense rheomorphism recorded in extremely high-grade ignimbrites. Recognition of strain heating within rheomorphic ignimbrites suggests that large pyroclastic density currents may travel over a hot substrate, potentially hotter than the density current itself. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.