Physical setting and tephrochronology of the summit caldera ice record at Mount Moulton, West Antarctica

Research Article| July 01, 2008 Physical setting and tephrochronology of the summit caldera ice record at Mount Moulton, West Antarctica Nelia W. Dunbar; Nelia W. Dunbar † 1Earth and Environmental Science Department, New Mexico Bureau of Geology, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA †E-mail: nelia@nmt.edu Search for other works by this author on: GSW Google Scholar William C. McIntosh; William C. McIntosh ‡ 1Earth and Environmental Science Department, New Mexico Bureau of Geology, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA ‡E-mail: mcintosh@nmt.edu Search for other works by this author on: GSW Google Scholar Richard P. Esser Richard P. Esser § 2New Mexico Bureau of Geology, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA §E-mail: esser@nmt.edu Search for other works by this author on: GSW Google Scholar GSA Bulletin (2008) 120 (7-8): 796–812. https://doi.org/10.1130/B26140.1 Article history received: 07 Nov 2006 rev-recd: 30 Jul 2007 accepted: 19 Sep 2007 first online: 02 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 Nelia W. Dunbar, William C. McIntosh, Richard P. Esser; Physical setting and tephrochronology of the summit caldera ice record at Mount Moulton, West Antarctica. GSA Bulletin 2008;; 120 (7-8): 796–812. doi: https://doi.org/10.1130/B26140.1 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 SocietyGSA Bulletin Search Advanced Search Abstract A site on the shoulder of the ice-filled summit crater of Mount Moulton, located at an elevation of 2800 m in West Antarctica, exhibits a 400-m-long section of exposed blue ice and intercalated tephra layers. A total of 48 tephra layers are observed. Many are thick (up to 10 cm) and coarse (pumice up to 3 cm). Detailed dip measurements and global positioning system (GPS) mapping reveals a simple geometry of parallel tephra layers all exhibiting consistent dips. The simple stratigraphy of the tephra layers suggests that although the local ice is thinned, based on the boudinaged appearance of the thicker tephra layers, it is otherwise undeformed. Local measured ice motion and ablation rates are similar, averaging around 3 cm/yr for the 4-yr measurement period. Most of the Mount Moulton tephra layers are trachytic, and are derived from Mount Berlin, a still thermally active volcano located ~30 km away to the west. Eight of the tephra layers at the Mount Moulton site have been directly dated, using 40Ar/39Ar geochronology of potassic feldspar phenocrysts, to (in stratigraphic order from top to base of the blue ice section) 10.5 ± 2.5; 24.7 ± 1.5; 92.1 ± 0.9; 104.9 ± 0.6; 118.1 ± 1.3; 135.6 ± 0.9; 225.7 ± 11.6; and 495.6 ± 9.7 ka. The depth-age curve for the Mount Moulton site, based on these radioisotopic ages, is qualitatively similar to that of the Siple Dome ice core, also in West Antarctica. Although not part of the West Antarctic ice sheet, the Mount Moulton site certainly contains some of the oldest known ice in West Antarctica, and provides a long and detailed climate record. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.