Heart Mountain, Wyoming, detachment lineations: Are they in microbreccia or in volcanic tuff?

Abstract

Research Article| September 01, 1991 Heart Mountain, Wyoming, detachment lineations: Are they in microbreccia or in volcanic tuff? WILLIAM G. PIERCE; WILLIAM G. PIERCE 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar WILLIS H. NELSON; WILLIS H. NELSON 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar ANTONI K. TOKARSKI; ANTONI K. TOKARSKI 2Polish Academy of Science, Krakow, Poland 31-002 Search for other works by this author on: GSW Google Scholar EWA PIEKARSKA EWA PIEKARSKA 2Polish Academy of Science, Krakow, Poland 31-002 Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIAM G. PIERCE 1U.S. Geological Survey, Menlo Park, California 94025 WILLIS H. NELSON 1U.S. Geological Survey, Menlo Park, California 94025 ANTONI K. TOKARSKI 2Polish Academy of Science, Krakow, Poland 31-002 EWA PIEKARSKA 2Polish Academy of Science, Krakow, Poland 31-002 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): 1133–1145. https://doi.org/10.1130/0016-7606(1991)103<1133:HMWDLA>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 WILLIAM G. PIERCE, WILLIS H. NELSON, ANTONI K. TOKARSKI, EWA PIEKARSKA; Heart Mountain, Wyoming, detachment lineations: Are they in microbreccia or in volcanic tuff?. GSA Bulletin 1991;; 103 (9): 1133–1145. doi: https://doi.org/10.1130/0016-7606(1991)103<1133:HMWDLA>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 The concept of tectonic denudation followed by deposition of lower middle Eocene Wapiti Formation volcanic rocks on the exposed Heart Mountain detachment has been challenged by Hauge. His "extending allochthon" interpretation requires that the Wapiti Formation be fault emplaced and that lineations in a volcanic tuff overlying the fault north of Jim Smith Peak be fault striae in "microbreccia." Our re-examination of the field evidence in minute detail indicates that these lineations were produced by flowage of volcanic rocks on a thin layer of air-fall tuff. The following lines of evidence indicate that this tuff was deposited on the detachment surface during the brief interval that the denuded surface was exposed. (1) Field relations indicate that the Wapiti volcanic rocks are younger than the detachment, and so they could not have been fault emplaced. (2) Lineations occur only on the upper surface of Wapiti Formation tuff; none were found at the contact of the tuff with the detachment surface. (3) The reported direction of translation indicated by the lineations is not consistent. Many lineations in the tuff indicate north and northeast movement—a direction that is consistent with lineations produced by lava flowing from a known vent but inconsistent with a southeast direction of detachment movement. (4) The lineations are restricted to the northwestern part of the area covered by the Wapiti Formation, which is also consistent with their derivation as volcanic flow lineations from a known vent. If the Wapiti had been tectonically emplaced, fault striae should occur elsewhere on the detachment surface, but none have been observed. (5) The lower contact of the tuff with the detachment surface, as seen in thin sections, is irregular, suggesting that it is a depositional rather than a fault contact. (6) The contact between the tuff and overlying Wapiti, as seen in thin sections, is also irregular, as would be expected if the Wapiti volcanic breccia had been deposited on the tuff. Thin sections of the "microbreccia" suggest that it is a sedimentary rock, not a "fault rock." (7) A remnant of the tectonic carpet of all-carbonate fault breccia lying on the detachment surface, unmixed with the overlying Wapiti volcanic rock, is compatible with the depositional emplacement of the Wapiti but is not compatible with Wapiti Formation being moved many kilometers across the carpet of all-carbonate fault breccia and not removing or becoming mixed with it. 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.