Igneous rocks of the Highwood Mountains, Montana: Part III. Dikes and Related Intrusives

Abstract

Research Article| November 01, 1941 Igneous rocks of the Highwood Mountains, Montana: Part III. Dikes and Related Intrusives B. F. BUIE B. F. BUIE Search for other works by this author on: GSW Google Scholar GSA Bulletin (1941) 52 (11): 1753–1808. https://doi.org/10.1130/GSAB-52-1753 Article history received: 26 Mar 1940 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation B. F. BUIE; Igneous rocks of the Highwood Mountains, Montana: Part III. Dikes and Related Intrusives. GSA Bulletin 1941;; 52 (11): 1753–1808. doi: https://doi.org/10.1130/GSAB-52-1753 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The dikes were classified under five field types, which in the order of their intrusion are: (1) amphibole phonolite, (2) pseudoleucite mafic phonolite, (3) augite mafic phonolite, (4) biotite phonolite, and (5) syenite porphyry. The rare amphibole phonolite dikes appear to be related to the quartz latite volcanics. The other four types form a gradational series related to the mafic phonolite volcanics. Types (2) and (3) constitute more than half the dikes of the area, and type (4) approximately one-fourth. Syenite porphyry and a few dikes of nepheline syenite, monzonite, and alnoite constitute the remainder.The dikes vary in width from less than 2 feet to more than 20 feet. Few segments can be traced continuously for as much as a mile. Dikes are most numerous north and east of the mountains, where a radial trend out from the mountains is clearly recognizable. Fractures into which the dikes were intruded were produced by a centrally acting force and developed outward from the central part of the area.An irregular intrusive body composed of alnoite and monticellite peridotite containing 32 per cent of monticellite was mapped 3 miles northeast of Geraldine.A new term, headed dike, is proposed for intrusive bodies like the one found 8 miles southwest of Geraldine. This body is linear in plan and bulbous in cross section narrowing downward to a feeder dike. The top contact is conformable with the bedding of the Cretaceous sandstone. Fergusite and shonkinite are the principal rocks of the headed dike. Differentiation of the two types was gravitative after intrusion. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.