Juan de Fuca
Click on the above image to see a full-size version of the magnetic anomalies, with caption.
Click on the above image to see a full-size version of various models of propagating rift geometry, with caption.
The oblique magnetic anomaly offsets in the Juan de Fuca area, where magnetic stripes on the seafloor were first discovered by Raff and Mason,
had been a puzzle since before seafloor spreading was discovered. The recognition by Fred Vine that these anomalies could be correlated across
a previously unknown spreading center, and with the magnetic reversal time scale [see color figure at right from Vine (1968)], were important steps
in the acceptance of the seafloor spreading hypothesis. Following the discovery of plate tectonics, these oblique offsets became even more of a puzzle. Although there was complete agreement with Vine, Raff, and Mason that these were faults, there were two schools of thought on their origin. The plate tectonic school said faults occurred at plate boundaries and thus these faults indicated that numerous small microplates were active in this area. The competing school said plate tectonics did not work in this area where the young Juan de Fuca plate was converging with and being subducted under the North American plate, and this was the scale where rigid plate tectonics broke down, with the faults resulting from this deformation. I discovered the correct explanation for these oblique offsets while I was working in a different area, Galapagos, on what I thought was a different problem, that of small-scale spreading center jumps, and that is these offsets are not faults at all. Instead, they are “pseudofaults” and they mark the V-shaped wakes of propagating rifts (see model B at right). This explanation became generally accepted only after I began showing our computer animations (links to .mov file) at conferences in 1980 and Tanya Atwater wrote a Nature News and Views article about our propagating rift hypothesis.
- Hey, R.N., A new class of pseudofaults and their bearing on plate tectonics: A propagating rift model, Earth Planet. Sci. Lett., 37, 321-325, 1977.
Hey, R.N. and D.S. Wilson, Propagating rifts - the motion picture, Eos Trans. AGU, 61, 1104-1105, 1980.
Hey, R.N. and D.S. Wilson, Propagating rift explanation for the tectonic evolution of the Northeast Pacific - The pseudomovie, Earth Planet. Sci. Lett., 58, 167-188, 1982.
- Sinton, J.M., D.S. Wilson, D.M. Christie, R.N. Hey, and J.R. Delaney, Petrologic consequences of rift propagation on oceanic spreading ridges, Earth Planet. Sci. Lett., 62, 193-207, 1983.
- Wilson, D.S., R.N. Hey, and C. Nishimura, Propagation as a mechanism of reorientation of the Juan de Fuca ridge, J. Geophys. Res., 89, 9215-9225, 1984.
- Nishimura, C., D.S. Wilson, and R.N. Hey, Pole of rotation analysis of present-day Juan de Fuca plate motion, J. Geophys. Res., 89, 10283-10290, 1984.
- Hey, R.N., H.W. Menard, T.M. Atwater, and D.W. Caress, Changes in direction of seafloor spreading revisited, J. Geophys. Res., 93, 2803-2811, 1988.
- Caress, D.W., H.W. Menard, and R.N. Hey, Eocene reorganization of the Pacific-Farallon spreading center north of the Mendocino Fracture Zone, J. Geophys. Res., 93, 2813-2838, 1988.
- Fernandez, L.S. and R.N. Hey, Late Tertiary tectonic evolution of the seafloor spreading system off the coast of California between the Mendocino and Murray fracture zones, J. Geophys. Res., 96, 17955-17979, 1991.
- Hey, R.N., Propagating Rifts and Microplates, in Encyclopedia of Ocean Sciences, eds. J.H. Steele, S.A.Thorpe, and K.K. Turekian, Academic Press, London, Volume 4, 2300-2308, 2001.
- Hey, R.N., Propagating Rifts and Microplates at Mid-Ocean Ridges, in Encyclopedia of Geology, eds. R.C. Selley, R. Cocks and I. Plimer, Academic Press, London, 396-405, 2004.
- Hey, R., Seafloor Spreading, in Encyclopedia of Solid Earth Geophysics, ed. H. Gupta, Springer, Dordrecht, ISBN 978-90-481-8701-0, 1055-1059, 2011.
- Hey, R.N., Propagating Rifts and Microplates at Mid-Ocean Ridges, www.sciencedirect.com/science/article/pii/B978012409548903027X, in Elsevier’s Science Direct online Reference Module in Earth Systems and Environmental Sciences, ed. S. Elias, ISBN: 978-0-12-409548-9, 2013.
- Hey, R.N., Tectonics: Propagating Rifts and Microplates at Mid-Ocean Ridges, www.sciencedirect.com/science/article/pii/B978012409548903027X, in Elsevier’s Science Direct online Reference Module in Earth Systems and Environmental Sciences, ed. S. Elias, ISBN: 978-0-12-409548-9, 2015.
- * 1981 April–May: Survey of a propagating rift tip and hotspot along the Pacific-Juan de Fuca spreading center using Sea Beam, Seattle-Seattle, National Ocean Survey, chief scientist S.R. Hammond, USS SURVEYOR.
- * 1984 July–August: Sea Beam investigation of large-scale changes in direction of seafloor spreading, Kodiak-Honolulu, Scripps Institution of Oceanography, chief scientist H.W. Menard, R/V THOMAS WASHINGTON.
- 1984 August–September: Endeavour ridge dredging program and ALVIN taxi service, Seattle-Seattle, University of Washington/Oregon State University, chief scientist M. Goldfarb, R/V WECOMA.
- 1984 September: ALVIN/AII investigation of the Juan de Fuca spreading center/propagating rift system, Seattle- Astoria, University of Washington/Woods Hole Oceanographic Institution, chief scientist J.R. Delaney, R/V ATLANTIS II, DSRV ALVIN.
- ** Chief Scientist
- * Co-Chief Scientist
Students involved in this research
- D. Wilson
- D. Caress
- L. Skaer Fernandez
- C. Nishimura
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