Geology of the rock foundation of Grand Coulee Dam, Washington

Abstract

Research Article| November 01, 1938 Geology of the rock foundation of Grand Coulee Dam, Washington WILLIAM H. IRWIN WILLIAM H. IRWIN Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIAM H. IRWIN Publisher: Geological Society of America Received: 28 Mar 1938 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1938 Geological Society of America GSA Bulletin (1938) 49 (11): 1627–1650. https://doi.org/10.1130/GSAB-49-1627 Article history Received: 28 Mar 1938 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WILLIAM H. IRWIN; Geology of the rock foundation of Grand Coulee Dam, Washington. GSA Bulletin 1938;; 49 (11): 1627–1650. doi: https://doi.org/10.1130/GSAB-49-1627 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 Grand Coulee Dam, under construction on the Columbia River in north-central Washington, is located at the boundary between the essentially horizontal basalt flows of the Columbia Plateau and the complex granitic mountains to the north.The foundation and abutments of the dam, exposed by excavation of glacial and fluvial overburden, are composed of two types of granite. The older, a coarse-grained, massive, biotite granite, is a marginal facies of the Colville granite batholith. The younger, a fine-grained, slightly porphyritic granite, occurs in vertical dikes, which strike approximately north across the older granite, and represents a resurgent phase of the Colville magma. The rock of the west abutment and western half of the foundation is largely fine-grained granite. The rock of the eastern half and the east abutment is predominantly coarse grained. Irregularly-shaped acid and basic masses are interpreted as differentiates of the coarse-grained granite in which they occur although some may be highly metamorphosed xenoliths.Three major systems of joints cut the foundation granites. One vertical system strikes NNE, and another essentially vertical system strikes WNW. The third system is essentially horizontal. The joints of the two vertical systems are locally abnormally close-spaced and cause a sheeted structure along narrow, discontinuous zones. These vertical sheeted zones acted to concentrate the circulation of heated solutions, and the hydrothermally altered rock is confined chiefly to them. The solutions were somewhat alkaline and probably preceded and accompanied the extrusion of the earliest plateau basalts. 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.