Geology of a Part of the South-Central Cascade Mountains, Washington

Abstract

Research Article| April 01, 1964 Geology of a Part of the South-Central Cascade Mountains, Washington MARTIN L STOUT MARTIN L STOUT Dept. Geology, Los Angeles State College, Los Angeles, Calif. Search for other works by this author on: GSW Google Scholar Author and Article Information MARTIN L STOUT Dept. Geology, Los Angeles State College, Los Angeles, Calif. Publisher: Geological Society of America Received: 31 Jul 1961 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1964, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1964) 75 (4): 317–334. https://doi.org/10.1130/0016-7606(1964)75[317:GOAPOT]2.0.CO;2 Article history Received: 31 Jul 1961 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation MARTIN L STOUT; Geology of a Part of the South-Central Cascade Mountains, Washington. GSA Bulletin 1964;; 75 (4): 317–334. doi: https://doi.org/10.1130/0016-7606(1964)75[317:GOAPOT]2.0.CO;2 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 center of the area investigated is 68 miles southeast of Seattle on the eastern slope of the south-central Cascade Mountains, Washington.The oldest rocks are pre-Tertiary igneous and metamorphic rocks which crop out in two north-westerly trending belts. The southern belt contains synkinematically metamorphosed greenschists, amphibolites and biotite schists which have been intruded by quartz dioritic rocks, and a tectonic complex of serpentinites and miscellaneous metamorphic rocks. The northern belt contains quartz dioritic gneisses, migmatites, and amphibolites which are in tectonic contact with low-grade metamorphic rocks.Unconformably overlying the pre-Tertiary rocks is the Eocene Naches Formation, a complex series of interbedded sedimentary and volcanic rocks at least 8000 feet thick. Feldspathic sandstones and basalts are most common in the lower and middle parts of the formation; rhyolitic rocks are found throughout the formation; andesitic rocks occur in the upper part of the formation.Unconformably overlying the Naches Formation are a variety of Oligocene-Miocene andesitic and basaltic rocks tentatively referred to as the Keechelus Andesitic Series. This in turn is Unconformably overlain by the Miocene-Pliocene Yakima Basalt, a series of basalt flows with local tuffaceous interbeds and palagonite breccias.The pre-Tertiary and Tertiary rocks have been intruded by a variety of magmatic types ranging in composition from rhyolite to gabbro.Structural trends are northwesterly across the northerly topographic alignment of the Cascade Mountains. The Tertiary structures parallel the pre-Tertiary structures and are largely controlled by them. Pre-Tertiary faulting, possibly thrusting, was intense, but exposures are poor, preventing measurement of exact displacement. At least one pre-Tertiary fault, marked by serpentinite lenses, had recurring movement during the Tertiary. 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.