Magma sheets defined with magnetic susceptibility in the Maiden Creek sill, Henry Mountains, Utah, USA

Abstract

Research Article| July 01, 2017 Magma sheets defined with magnetic susceptibility in the Maiden Creek sill, Henry Mountains, Utah, USA Sven Morgan; Sven Morgan 1Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, Michigan 48859, USA Search for other works by this author on: GSW Google Scholar Rebecca Jones; Rebecca Jones 1Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, Michigan 48859, USA Search for other works by this author on: GSW Google Scholar Jeremy Conner; Jeremy Conner 1Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, Michigan 48859, USA Search for other works by this author on: GSW Google Scholar James Student; James Student 1Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, Michigan 48859, USA Search for other works by this author on: GSW Google Scholar Megan Schaner; Megan Schaner 1Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, Michigan 48859, USA Search for other works by this author on: GSW Google Scholar Eric Horsman; Eric Horsman 2Department of Geological Sciences, East Carolina University,Greenville, North Carolina 27858, USA Search for other works by this author on: GSW Google Scholar Michel de Saint Blanquat Michel de Saint Blanquat 3Géosciences Environnement Toulouse, Université de Toulouse, CNES, CNRS, IRD, UPS, 14 avenue Edouard-Belin, 31400 Toulouse, France Search for other works by this author on: GSW Google Scholar Geology (2017) 45 (7): 599–602. https://doi.org/10.1130/G38932.1 Article history received: 31 Aug 2016 rev-recd: 04 Mar 2017 accepted: 07 Mar 2017 first online: 28 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 Sven Morgan, Rebecca Jones, Jeremy Conner, James Student, Megan Schaner, Eric Horsman, Michel de Saint Blanquat; Magma sheets defined with magnetic susceptibility in the Maiden Creek sill, Henry Mountains, Utah, USA. Geology 2017;; 45 (7): 599–602. doi: https://doi.org/10.1130/G38932.1 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 SocietyGeology Search Advanced Search Abstract In the ∼20-m-thick Maiden Creek sill of the Henry Mountains (Utah, USA) intrusive complex, 2 magma sheets are locally separated by a 1.5-m-thick lens of sandstone. We studied the boundary between these sheets at the termination of this sandstone lens, where the upper sheet directly overlies the lower sheet, in order to test the reliability of using magnetic susceptibility in delineating internal magmatic contacts. The contact between these two sheets is along a cliff face and defined by a thin (<1 cm) brittle-ductile shear zone. Measurements of magnetic susceptibility (K) were collected within a grid every 20 cm across this contact. Drill cores (72) were also collected along four traverses across the shear zone. Mapping K across the cliff face reveals an abrupt decrease immediately below the shear zone contact. 1 m below the contact, K unexpectedly increases again to the same levels observed above the contact. This lower boundary coincides with a 1–2-mm-thick minor fracture zone. The 1-m-thick low-K zone (LKZ) is characterized by more intense microfracturing and is bleached compared to the surrounding igneous rock. Plotting the magnetic foliation from the drill cores reveals abrupt changes to the orientation across both the shear zone and fracture zone. We hypothesize that the LKZ was the original magma sheet that intruded the sandstone. The high-K zones above and below the LKZ represent later sheets that intruded above and below the original sheet, fracturing the partially or wholly crystallized original intrusion. These later sheets exsolved fluids that were injected into the original sheet, resulting in more advanced oxidation of magnetite and thus lowering the K. Alternatively, it is possible that the LKZ is simply the altered zone at the top of a thicker older sheet that was modified by the intrusion of a younger overlying sheet. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.