Cenozoic active margin and shallow Cascades structure: COCORP results from western Oregon

Research Article| June 01, 1989 Cenozoic active margin and shallow Cascades structure: COCORP results from western Oregon R. WILLIAM KEACH, II; R. WILLIAM KEACH, II 1Cornell University, Ithaca, New York 14853-1504 Search for other works by this author on: GSW Google Scholar J. E. OLIVER; J. E. OLIVER 2Institute for the Study of the Continents, 3122 Snee Hall, Ithaca, New York 14853-15043Department of Geological Sciences, Cornell University, Ithaca, New York 14853-1504 Search for other works by this author on: GSW Google Scholar L. D. BROWN; L. D. BROWN 2Institute for the Study of the Continents, 3122 Snee Hall, Ithaca, New York 14853-15043Department of Geological Sciences, Cornell University, Ithaca, New York 14853-1504 Search for other works by this author on: GSW Google Scholar S. KAUFMAN S. KAUFMAN 2Institute for the Study of the Continents, 3122 Snee Hall, Ithaca, New York 14853-15043Department of Geological Sciences, Cornell University, Ithaca, New York 14853-1504 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1989) 101 (6): 783–794. https://doi.org/10.1130/0016-7606(1989)101<0783:CAMASC>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. WILLIAM KEACH, J. E. OLIVER, L. D. BROWN, S. KAUFMAN; Cenozoic active margin and shallow Cascades structure: COCORP results from western Oregon. GSA Bulletin 1989;; 101 (6): 783–794. doi: https://doi.org/10.1130/0016-7606(1989)101<0783:CAMASC>2.3.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 Two deep seismic reflection profiles totaling 98 km were recorded by the Consortium for Continental Reflection Profiling (COCORP) in western Oregon in 1984, providing some of the first onshore deep seismic reflection data from the forearc and arc of an active convergent margin. These data are of lower quality than most COCORP data, but when combined with other geological and geophysical data, they provide some useful insights into the subduction zone beneath Oregon and into extensional structures in the Cascades.Line 1 crossed the Eocene sediments and underlying pillow basalts of the Coast Range and western Willamette Valley. Reflections from the Willamette Valley clearly define the lower and western boundary of flat-lying, rhythmically bedded Eocene sediments. These sediments appear to be underlain by as much as 8 km of seismically transparent Eocene pillow basalts. Layered reflections at depths of 8-16 km may indicate a remnant crust upon which the Eocene pillow basalts were erupted. East-dipping reflections at depths of 35-40 km may represent the décollement above the subducting Juan de Fuca plate.Oregon line 2 crosses the Cenozoic volcanic arc terrains of the Western and High Cascades. Interpretation of COCORP seismic data suggests modification of existing models for normal faulting that postulate a symmetric graben or grabens in the Cascades of Oregon. In the High Cascades along COCORP Oregon line 2, reflections suggest a large, gently west-dipping half-graben with major offset only on the west side of the range. The seismic reflection data along with other geological and geophysical data suggest that the High Cascades were built on a series of blocks, rather than a single graben. The blocks were differentially faulted during the Pliocene. Seismic data from the Western Cascades indicate several normal faults with down-to-the-east offset, including a major, previously unidentified fault of probable Miocene age. 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.