Footwall deformation along Willard thrust, Sevier orogenic belt: Implications for mechanisms, timing, and kinematics

Abstract

Research Article| May 01, 1992 Footwall deformation along Willard thrust, Sevier orogenic belt: Implications for mechanisms, timing, and kinematics JAMES P. EVANS; JAMES P. EVANS 1Department of Geology, Utah State University, Logan; Utah 84322-4505 Search for other works by this author on: GSW Google Scholar DOUGLAS S. NEVES DOUGLAS S. NEVES 1Department of Geology, Utah State University, Logan; Utah 84322-4505 Search for other works by this author on: GSW Google Scholar Author and Article Information JAMES P. EVANS 1Department of Geology, Utah State University, Logan; Utah 84322-4505 DOUGLAS S. NEVES 1Department of Geology, Utah State University, Logan; Utah 84322-4505 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1992) 104 (5): 516–527. https://doi.org/10.1130/0016-7606(1992)104<0516:FDAWTS>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 JAMES P. EVANS, DOUGLAS S. NEVES; Footwall deformation along Willard thrust, Sevier orogenic belt: Implications for mechanisms, timing, and kinematics. GSA Bulletin 1992;; 104 (5): 516–527. doi: https://doi.org/10.1130/0016-7606(1992)104<0516:FDAWTS>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 Map-, outcrop-, and microstructural-scale examination of the footwall of the Willard thrust sheet in the Sevier fold-and-thrust belt, northern Utah, reveals deformation of footwall rocks before or during emplacement of the Willard thrust sheet. The Willard thrust sheet contains Proterozoic metasedimentary rocks in its hanging wall and has a footwall lateral ramp that cuts up section southward. In the northern part of the study area, Cambrian Maxfield and Ophir Formations were pervasively ductilely deformed at all scales. There, east and northeast-vergent recumbent isoclinal folds with well-developed axial-planar cleavage, kink folds, small shear zones, and solution cleavage are developed in a 100- to 200-m-thick zone of footwall deformation. Calcite deformed by dynamic recrystallization and diffusive mass transfer; rare twinned dolomite crystals deformed by intracrystalline glide. In the central part of the study area, the Cambrian Maxfield, Ophir, and Nounan Formations are complexly folded and faulted below the Willard thrust. Plastic deformation is largely restricted to a 5- to 10-m-thick limestone mylonite in the Maxfield Formation, with cataclastic deformation predominant below the mylonite. Axes of map-scale folds are nearly parallel with the Willard thrust, and a small thrust appears to be cut by the Willard thrust. Southward, the thrust climbs section in its footwall to Devonian and Mississippian strata, and deformation in the footwall is predominantly brittle, superimposed on locally developed ductile structures. The change from pervasive plastic to brittle deformation and accompanying change in structural style of footwall rocks occurs in the Cambrian Ophir and Maxfield Formations. The lateral changes of footwall deformation may be due to (1) lateral variations of footwall rock rheology and thus a variation in bulk strain of the rocks; (2) different temperature or confining or fluid pressure conditions along strike, perhaps due to a pre-existing footwall high; or (3) lateral variations in stress and strain conditions in the footwall. Whatever the cause, the data show that significant amounts of deformation occurred in the footwall of the Willard thrust before and(or) during motion along the thrust. 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.