Igneous rocks of the northern Big Belt Range, Montana

Research Article| April 01, 1944 Igneous rocks of the northern Big Belt Range, Montana JOHN B. LYONS JOHN B. LYONS Search for other works by this author on: GSW Google Scholar GSA Bulletin (1944) 55 (4): 445–472. https://doi.org/10.1130/GSAB-55-445 Article history received: 09 Jul 1942 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 B. LYONS; Igneous rocks of the northern Big Belt Range, Montana. GSA Bulletin 1944;; 55 (4): 445–472. doi: https://doi.org/10.1130/GSAB-55-445 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 northern end of the Big Belt Range of west-central Montana is underlain chiefly by upper Cretaceous potash-rich basalts which were extruded unconformably on Cretaceous sediments and folded with them into northwesterly trending anticlines and synclines. The western border of the igneous rocks is marked by an imbricate zone of Mississippian to upper Cretaceous rocks. The Lewis overthrust, carrying the Belt series over the upper Cretaceous strata, bounds the fault zone on the west.The trachybasaltic breccias, agglomerates, and flows, 3200 feet thick, are intruded by many chonoliths, sills, and dikes ranging from gabbro to quartz monzonite. Some of the trachybasalts have abundant primary analcime phenocrysts. All evidence favors crystal settling as the cause for the magmatic differentiation within this petrographic province. 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.