Stratigraphic and structural evolution of the middle Miocene synvolcanic Oregon-Idaho graben

Abstract

Research Article| May 01, 2000 Stratigraphic and structural evolution of the middle Miocene synvolcanic Oregon-Idaho graben Michael L. Cummings; Michael L. Cummings 1Department of Geology, Portland State University, P.O. Box 751, Portland, Oregon 97207, USA Search for other works by this author on: GSW Google Scholar James G. Evans; James G. Evans 2U.S. Geological Survey, West 904 Riverside, Room 202, Spokane, Washington 99210, USA Search for other works by this author on: GSW Google Scholar Mark L. Ferns; Mark L. Ferns 3Oregon Department of Geology and Mineral Industries, 1831 First Street, Baker City, Oregon 97814, USA Search for other works by this author on: GSW Google Scholar Kate R. Lees Kate R. Lees 4Department of Earth Sciences, Open University, Milton Keynes, UK Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (5): 668–682. https://doi.org/10.1130/0016-7606(2000)112<668:SASEOT>2.0.CO;2 Article history received: 23 Jun 1997 rev-recd: 04 May 1999 accepted: 11 May 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Michael L. Cummings, James G. Evans, Mark L. Ferns, Kate R. Lees; Stratigraphic and structural evolution of the middle Miocene synvolcanic Oregon-Idaho graben. GSA Bulletin 2000;; 112 (5): 668–682. doi: https://doi.org/10.1130/0016-7606(2000)112<668:SASEOT>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 Oregon-Idaho graben is a newly identified north-south–trending synvolcanic graben in southeastern Oregon and southwestern Idaho within the middle Miocene backarc rift system that extends 1100 km from southern Nevada to southeastern Washington. The graben formed along the western margin of the North American craton shortly after the largest volumes of tholeiitic flood basalt erupted (Columbia River Basalt Group, Steens-Pueblo Basalt, basalt of Malheur Gorge, basalt and latite unit of Ekren et al., 1981). Rhyolite flows and ash-flow tuffs (16.1–14.0 Ma) erupted from northeastern Oregon (Dooley Volcanics) to northern Nevada (McDermitt volcanic field) shortly after the flood basalt was emplaced. Subsidence of the Oregon-Idaho graben (15.5–15.3 Ma) coincides with eruption of rhyolite flows and caldera-related ash-flow tuffs from vents along the margins and within the graben. Mafic and silicic intragraben volcanism accompanied sedimentation from about 15.3 to 10.5 Ma. Sedimentary and volcanic rocks from extrabasinal sources, especially southwestern Idaho, were introduced periodically.After initial subsidence, the evolution of the Oregon-Idaho graben is divided into three stages. Stage 1 (15.3–14.3 Ma) followed intragraben caldera collapse and was marked by deposition of fluvial and lacustrine sediment across the graben. Stage 2 (14.3–12.6 Ma) movement on intragraben fault zones divided the graben into distinct subbasins and marked the onset of calc-alkalic volcanism. Fine-grained tuffaceous sediment derived from glassy rhyolite and pyroclastic deposits and basalt tuff cones interbedded with rhyolite ash and lapilli-fall deposits and locally erupted basalt hydrovolcanic deposits predominated during synvolcanic subsidence. Synsedimentary hot-spring alteration and precious-metals mineralization of graben fill were controlled by the same intragraben fault zones that served as magmatic conduits. During stage 3 (12.6–10.5 Ma) the subbasins were filled, and graben-wide fluviatile and lacustrine sedimentation resumed. At about the same time, renewed rhyolitic volcanism occurred on both flanks, and tholeiitic volcanism resumed within the Oregon-Idaho graben. Subsidence in the Oregon-Idaho graben ceased as west-northwest–striking faults related to the formation of the western Snake River plain became active. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.