Structural, eruptive, and intrusive evolution of the Grizzly Peak caldera, Sawatch Range, Colorado

Abstract

Research Article| September 01, 1991 Structural, eruptive, and intrusive evolution of the Grizzly Peak caldera, Sawatch Range, Colorado C. J. FRIDRICH; C. J. FRIDRICH 1Department of Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar R. P. SMITH; R. P. SMITH 2Idaho National Engineering Laboratory, EG&G Idaho, Inc., P.O. Box 1625, M.S. 2107, Idaho Falls, Idaho 83415 Search for other works by this author on: GSW Google Scholar ED DEWITT; ED DEWITT 3U.S. Geological Survey, M.S. 905, Box 25046, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar E. H. MCKEE E. H. MCKEE 4U.S. Geological Survey, M.S. 941, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information C. J. FRIDRICH 1Department of Geology, Stanford University, Stanford, California 94305 R. P. SMITH 2Idaho National Engineering Laboratory, EG&G Idaho, Inc., P.O. Box 1625, M.S. 2107, Idaho Falls, Idaho 83415 ED DEWITT 3U.S. Geological Survey, M.S. 905, Box 25046, Federal Center, Denver, Colorado 80225 E. H. MCKEE 4U.S. Geological Survey, M.S. 941, 345 Middlefield Road, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1991) 103 (9): 1160–1177. https://doi.org/10.1130/0016-7606(1991)103<1160:SEAIEO>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 C. J. FRIDRICH, R. P. SMITH, ED DEWITT, E. H. MCKEE; Structural, eruptive, and intrusive evolution of the Grizzly Peak caldera, Sawatch Range, Colorado. GSA Bulletin 1991;; 103 (9): 1160–1177. doi: https://doi.org/10.1130/0016-7606(1991)103<1160:SEAIEO>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 Volcanic and shallow intrusive features of the deeply dissected 34 Ma Grizzly Peak caldera in west-central Colorado record evolution of the magmatic center from pre-caldera through post-resurgent stages. Pre-caldera dikes, zones of hydrothermally altered rocks, and lava flows formed along a circular swarm of cone-sheet fractures around the site of the future caldera. Early, largely rhyolitic uppercrustal magmatism culminated in the caldera-forming eruption of the Grizzly Peak Tuff. Intracaldera tuff is zoned from high-silica rhyolite at the base to low-silica rhyolite at the eroded top and, further, contains dacite to mafic latite pumice lumps in two heterogeneous tuff layers in the upper third of the preserved section.Half of the erupted tuff ponded in the 17-by 23-km, >600-km3 caldera, filling the asymmetric depression to a compacted thickness locally >2.7 km, including intercalated rock-avalanche megabreccias shed from ring-fault scarps. The asymmetric caldera has an inner ring-fracture zone that separates two structural segments that collapsed to different depths. Caldera fill buried collapse structures as they formed; the inner ring-fracture zone is a growth (or syn-depositional) fault in the single-cooling-unit tuff. Welded-tuff ring dikes are locally exposed at erosion levels below the caldera fill. These dikes are remnants of fissure vents in the outer ring-fracture zone.Following collapse, the Grizzly Peak caldera was uplifted, forming a complexly faulted resurgent dome. Resurgence resulted partly from emplacement of a composite granodiorite laccolith now exposed in the eroded core of the dome. A belt of mafic latite to rhyolite porphyry dikes and small stocks formed across the center of the domed caldera during the waning of the magmatic center. Latite intrusions in this suite represent the penetration of relatively mafic magma to the surface following solidification of the felsic subcaldera batholith. 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.