Rapid extension in an Eocene volcanic arc: Structure and paleogeography of an intra-arc half graben in central Idaho

Abstract

Research Article| March 01, 1997 Rapid extension in an Eocene volcanic arc: Structure and paleogeography of an intra-arc half graben in central Idaho Susanne U. Janecke; Susanne U. Janecke 1Department of Geology, Utah State University, Logan, Utah 84322-4505 Search for other works by this author on: GSW Google Scholar Brian F. Hammond; Brian F. Hammond 1Department of Geology, Utah State University, Logan, Utah 84322-4505 Search for other works by this author on: GSW Google Scholar Lawrence W. Snee; Lawrence W. Snee 2U.S. Geological Survey, M.S. 963, Box 25046, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar John W. Geissman John W. Geissman 3Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-1116 Search for other works by this author on: GSW Google Scholar Author and Article Information Susanne U. Janecke 1Department of Geology, Utah State University, Logan, Utah 84322-4505 Brian F. Hammond 1Department of Geology, Utah State University, Logan, Utah 84322-4505 Lawrence W. Snee 2U.S. Geological Survey, M.S. 963, Box 25046, Federal Center, Denver, Colorado 80225 John W. Geissman 3Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-1116 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1997) 109 (3): 253–267. https://doi.org/10.1130/0016-7606(1997)109<0253:REIAEV>2.3.CO;2 Article history First Online: 01 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 Susanne U. Janecke, Brian F. Hammond, Lawrence W. Snee, John W. Geissman; Rapid extension in an Eocene volcanic arc: Structure and paleogeography of an intra-arc half graben in central Idaho. GSA Bulletin 1997;; 109 (3): 253–267. doi: https://doi.org/10.1130/0016-7606(1997)109<0253:REIAEV>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 SocietyGSA Bulletin Search Advanced Search Abstract A study of extension, volcanism, and sedimentation in the middle Eocene Panther Creek half graben in central Idaho shows that it formed rapidly during an episode of voluminous volcanism. The east-southeast–tilted Panther Creek half graben developed across the northeast edge of the largest cauldron complex of the Challis volcanic field and along the northeast-trending Trans-Challis fault zone. Two normal fault systems bound the east side of the half graben. One fault system strikes northeast, parallel to the Trans-Challis fault zone, and the other strikes north to northwest. The geometry of the basin-fill deposits shows that movement on these two normal fault systems was synchronous and that both faults controlled the development of the Panther Creek half graben. Strikes of the synextension volcanic and sedimentary rocks are similar throughout the half graben, whereas dips decrease incrementally upsection from as much as 60° to less than 10°. Previous K-Ar dates and a new 40Ar/39Ar plateau date from the youngest widespread tuff in the basin suggest that most of basin formation spanned 3 m.y. between about 47.7 Ma and 44.5 Ma. As much as 6.5 km of volcanic and sedimentary rocks were deposited during that time. Although rates of extension and subsidence were very high, intense volcanic activity continually filled the basin with ash-flow tuffs, outpacing subsidence and sedimentation, until the end of basin development.After the abrupt end of Challis volcanism, locally derived pebble to boulder conglomerate and massive, reworked ash accumulated in the half graben. These sedimentary rocks make up a small part of the basin fill in the Panther Creek half graben and were derived mainly from Proterozoic metasedimentary rocks uplifted in the footwall of the basin. The east-southeast tilt of the sedimentary rocks, their provenance and coarse grain size, and the presence of a gravity slide block derived from tilted volcanic rocks in the hanging wall attest to continued tectonism during conglomerate deposition. Provenance data from the sedimentary rocks imply that the highland in the footwall of the Panther Creek half graben was never thickly blanketed by synextension volcanic rocks, despite intense volcanic activity. Analysis of the Panther Creek half graben and other intra-arc rift basins supports previous interpretations that relative rates of volcanism and subsidence control the proportion of volcanic rocks deposited in intra-arc rifts. 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.