Deep-tow studies of the structure of the Mid-Atlantic Ridge crest near lat 37°N

Research Article| May 01, 1977 Deep-tow studies of the structure of the Mid-Atlantic Ridge crest near lat 37°N KEN C. MACDONALD; KEN C. MACDONALD 1Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, California 92093 Search for other works by this author on: GSW Google Scholar BRUCE P. LUYENDYK BRUCE P. LUYENDYK 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1977) 88 (5): 621–636. https://doi.org/10.1130/0016-7606(1977)882.0.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 KEN C. MACDONALD, BRUCE P. LUYENDYK; Deep-tow studies of the structure of the Mid-Atlantic Ridge crest near lat 37°N. GSA Bulletin 1977;; 88 (5): 621–636. doi: https://doi.org/10.1130/0016-7606(1977)882.0.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 A detailed study of the structure of the Mid-Atlantic Ridge median valley and rift mountains near lat 37°N (FAMOUS) was conducted using a deep-tow instrument package. The median valley may have either a very narrow inner floor (1 to 4 km) and well-developed terraces or a wide inner floor (10 to 14 km) and narrow or no terraces. The terraces appear to be non–steady-state features of the rift valley. The entire depth and gross morphology of the median valley may be accounted for by normal faulting, while volcanic relief contributes to the short-wavelength topography (<2 km). Most faults dip toward the valley axis an average of 50°, and the blocks are tilted back 2° to 3°. Fault dip is asymmetric about the valley axis. Active crustal extension in the inner floor and inner walls has the same sense of asymmetry as the local spreading rates, reaching a maximum of 18 percent. Thus, asymmetric spreading appears to be accomplished by asymmetric crustal extension on a fine scale as well as by asymmetric crustal accretion. Spreading is 17° oblique to the transform faults and shows no indication of readjusting to an orthogonal system, even on a fine scale. Eighty percent of the decay or transformation of median-valley relief into rift-mountain topography is accomplished by normal faults that dip away from the valley axis. Most of the outward-facing faulting occurs near the median-valley–rift-mountain boundary. Tilting of crustal blocks accounts for only 20 percent of the decay of median-valley relief. Most long-wavelength topography in the rift mountains has a faulted origin. As in the median valley, volcanic relief is short wavelength (<2 km) and appears to be fossil, originating in the median-valley inner floor. Bending of large faulted blocks toward nearby fracture zones suggests that spreading-center tectonics is affected by fracture-zone tectonics throughout the length of the rift in the FAMOUS area. Both the crustal accretion zone and transform fault zone are narrow, only 1 to 2 km wide, over short periods of time. In the course of millions of years, however, they apparently migrate over a zone 10 to 20 km wide. 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.