Abstract
Research Article| October 01, 1938 Igneous rocks of the Crazy Mountains, Montana JOHN E. WOLFF JOHN E. WOLFF Search for other works by this author on: GSW Google Scholar GSA Bulletin (1938) 49 (10): 1569–1626. https://doi.org/10.1130/GSAB-49-1569 Article history received: 17 Mar 1937 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 JOHN E. WOLFF; Igneous rocks of the Crazy Mountains, Montana. GSA Bulletin 1938;; 49 (10): 1569–1626. doi: https://doi.org/10.1130/GSAB-49-1569 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 Intruded into the Fort Union sedimentary formations is a remarkable assemblage of igneous rocks. In the southern part of the area, granites, many phases of diorite, gabbro, and peridotite occur as stocks, laccoliths, sills, and countless dikes. In the northern part of the area, super-alkaline rocks occur in profusion in laccoliths, sills, dikes, and three volcanic necks, as well as in a small diorite stock. No effusive rocks occur in the area. The sediments of the northern area have been intensely folded along north and south axes. In the southern area the Fort Union beds form a broad flat syncline plunging gently northward. Where pierced by the diorite stock the beds are arched and dip away on all sides. More than 20 different types of igneous rocks have been determined here. Many chemical analyses, including some mineral analyses, are presented. The rock analyses disclose one common feature—a richness in barium and strontium—pointing to a common magma. Pegmatites are absent. Pneumatolytic agents are not in evidence. The magma was evidently dry. Lateral compression evidently attended emplacement of the intrusives. 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.
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