Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

Abstract

Research Article| December 01, 1997 Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin N. J. Godfrey; N. J. Godfrey 1Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Search for other works by this author on: GSW Google Scholar Mendocino Working Group; Mendocino Working Group Search for other works by this author on: GSW Google Scholar B. C. Beaudoin; B. C. Beaudoin 1Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Search for other works by this author on: GSW Google Scholar Mendocino Working Group; Mendocino Working Group Search for other works by this author on: GSW Google Scholar S. L. Klemperer; S. L. Klemperer 1Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Search for other works by this author on: GSW Google Scholar Mendocino Working Group Mendocino Working Group Search for other works by this author on: GSW Google Scholar Author and Article Information N. J. Godfrey 1Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Mendocino Working Group B. C. Beaudoin 1Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Mendocino Working Group S. L. Klemperer 1Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Mendocino Working Group Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1997) 109 (12): 1536–1562. https://doi.org/10.1130/0016-7606(1997)109<1536:OBTTGV>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 Email Permissions Search Site Citation N. J. Godfrey, B. C. Beaudoin, S. L. Klemperer; Mendocino Working Group, Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin. GSA Bulletin 1997;; 109 (12): 1536–1562. doi: https://doi.org/10.1130/0016-7606(1997)109<1536:OBTTGV>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 The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7–8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11–16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5–7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16–18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, "present-day" continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle. 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.