Abstract
ALVIN investigations have defined the fine-scale structural and volcanic patterns produced by active rift and spreading center propagation and failure near 95.5° W on the Galapagos spreading center. Behind the initial lithospheric rifting, which is propagating nearly due west at about 50 km m.y.−1, a triangular block of preexisting lithosphere is being stretched and fractured, with some recent volcanism along curving fissures. A well-organized seafloor spreading center, an extensively faulted and fissured volcanic ridge, develops ~ 10 km (~ 200,000 years) behind the tectonic rift tip. Regional variations in the chemical compositions of the youngest lavas collected during this program contrast with those encompassing the entire 3 m.y. of propagation history for this region. A maximum in degree of magmatic differentiation occurs about 9 km behind the propagating rift tip, in a region of diffuse rifting. The propagating spreading center shows a gentle gradient in magmatic differentiation culminating at the SW-curving spreading center tip. Except for the doomed rift, which is in a constructional phase, tectonic activity also dominates over volcanic activity along the failing spreading system. In contrast to the propagating rift, failing rift lavas show a highly restricted range of compositions consistent with derivation from a declining upwelling zone accompanying rift failure. The lithosphere transferred from the Cocos to the Nazca plate by this propagator is extensively faulted and characterized by ubiquitous talus in one of the most tectonically disrupted areas of seafloor known. The pseudofault scarps, where the preexisting lithosphere was rifted apart, appear to include both normal and propagator lavas and are thus more lithologically complex than previously thought. Biological communities, probably vestimentiferan tubeworms, occur near the top of the outer pseudofault scarp, although no hydrothermal venting was observed.
Similar content being viewed by others
References
Acton, G., Stein, S., and Engeln, J. F., 1988, Formation of Curved Seafloor Fabric by Changes in Rift Propagation Velocity and Spreading Rate: Application to the 95.5° W Galapagos Propagator,J. Geophys. Res. 93, 11845–11862.
Byerly, G. R., 1980, The Nature of Differentiation Trends in Some Volcanic Rocks from the Galapagos Spreading Center,J. Geophys. Res. 25 3797–3810.
Byerly, G. R., Melson, W. G., and Vogt, P. R., 1976, Rhyodacites, Andesite, Ferrobasalts, and Ocean Tholeiites from the Galapagos Spreading Center,Earth Planet. Sci. Lett. 30, 215–221.
Christie, D. M. and Sinton J. M., 1981, Evolution of Abyssal Lavas along Propagating Segments of the Galapagos Spreading Center,Earth Planet. Sci. Lett. 56, 321–335.
Cooper, P., Milholland, P., and Duennebier, F. K., 1987, Seismicity of the Galapagos 95.5° W Propagating Rift,J. Geophys. Res. 92 14091–14112.
Cyaden Scientific Team: Choukroune, P., Auvray, B., Francheteau, J., Lepine, J. C., Arthaud, F., Brun, J. P., Auzende, J. M. Sichler, B., and Khobar, Y., 1986, Tectonics of the Westernmost Gulf of Aden and the Gulf of Tadjoura from Submersible Observations,Nature,319, 396–399.
Hey, R. N., 1977, Tectonic Evolution of the Cocos-Nazca Spreading Center,Geol. Soc. Am. Bull. 88, 1404–1420.
Hey, R. N. and Vogt, P. R., 1977, Spreading Center Jumps and Sub-Axial Asthenosphere Flow near the Galapagos Hotspot,Tectonophysics 37, 41–52.
Hey, R. N., Duennebier, F. K., and Morgan, W. J., 1980, Propagating Rifts on Mid-Ocean Ridges,J. Geophys. Res. 85, 2647–2658.
Hey, R. N., Kleinrock, M. C., Miller, S. P., Atwater, T. M., and Searle, R. C., 1986, Sea Beam/Deep Tow Investigation of an Active Oceanic Propagating Rift System, Galapagos 95.5° W,J. Geophys. Res. 91 3369–3393; 3884–3886.
Hey, R. N., Sinton, J. M., and Duennebier, F. K., 1989, Propagating Rifts and Spreading Centers, in Winterer, E. L., Hussong, D. M., and Decker, R. W. (eds.),The Eastern Pacific Ocean and Hawaii, Boulder, Colorado, Geological Society of America, v. N, 161–176.
Jones, M. L., 1985, On the Vestimentifera, New Phylum: Six New Species, and Other Taxa from Hydrothermal Vents and Elsewhere,Biol. Soc. Wash. Bull. No. 6, 117–158.
Kleinrock, M. C. and Hey, R. N., 1989a, Detailed Tectonics near the Tip of the Galapagos 95.5°W Propagator: How the Lithosphere Tears and a Spreading Axis Develops,J. Geophys. Res. 94 13801–13838.
Kleinrock, M. C. and Hey, R. N., 1989b, Migrating Transform Zone and Lithospheric Transfer at the Galapagos 95.5° W Propagator,J. Geophys. Res. 94 13859–13878.
Kleinrock, M. C., Searle, R. C., and Hey, R. N., 1989, Tectonics of the Failing Spreading System Associated with the Galapagos 95.5° W propagator,J. Geophys. Res. 94 13839–13858.
Lonsdale, P., 1978, Near-bottom Reconnaissance of a Fast-Slipping Transform Fault Zone at the Pacific-Nazca Plate Boundary,J. Geol. 86 451–472.
Lonsdale, P., 1989, The Rise Flank Trails Left by Migrating Offsets of the Equatorial East Pacific Rise Axis,J. Geophys. Res. 94 713–743.
Macdonald, K. C., Haymon, R. M., Miller, S. P., Sempere, J.-C., and Fox, P. J., 1988, Deep-Tow and Sea Beam Studies of Duelling Propagating Ridges on the East Pacific Rise near 20°40′S,J. Geophys. Res. 93 2875–2898.
Macdonald, K. C., Fox, P. J., Carbotte, S., Eisen, M., Miller, S., Perram, L., Scheirer, D., Tighe, S., and Weiland, C., 1991, The East Pacific Rise and its Flanks 8°–17° N: History of Segmentation, Propagation and Spreading Direction Based on Sea-MARC II and Sea Beam Studies,Mar. Geophys. Res. (in press).
McKenzie, D. P., 1986, The Geometry of Propagating Rifts,Earth Planet. Sci. Lett. 77, 176–186.
Milholland, P. D., 1984, Seismicity at the Galapagos 95.5° W Propagating Rift (Ph.D. Dissertation), University of Hawaii, Manoa, 239 pp.
Miller, S. P. and Hey, R. N., 1986, Three-Dimensional Magnetic Modeling of a Propagating Rift, Galapagos 95.5° W,J. Geophys. Res. 91, 3395–3406; 3887–3888.
Miller, S. P. and Macdonald, K. C., 1986, ALVIN Magnetic Gradiometer Studies: Propagating Rifts and Tectonic Rotations,EOS Trans. AGU 67, 1185.
Phipps Morgan, J. and Parmentier, E. M., 1985, Causes and Rate-Limiting Mechanisms of Ridge Propagation: A Fracture Mechanics Model,J. Geophys. Res. 90, 8603–8612.
Phipps Morgan, J. and Parmentier, E. M., 1987, A Three-Dimensional Gravity Study of the 95.5° W Propagating Rift in the Galapagos Spreading Center,Earth Planet. Sci. Lett. 81, 289–298.
Phipps Morgan, J., Caress, D. W., and Orcutt, J. A., 1991, Structure and Evolution of the Cocos-Nazca Spreading Center, 94°30′W to 96°30′W,Mar. Geophys. Res. (submitted).
Schubert, G. and Hey, R. N., 1986, Mantle Viscosity Beneath the Galapagos 95.5° W Propagating Rift,Geophys. Res. Lett. 13, 329–332.
Searle, R. C., 1989, Location and Segmentation of the Cocos-Nazca Spreading Center West of 95° W,Mar. Geophys. Res. 11, 15–26.
Searle, R. C. and Hey, R. N., 1983, GLORIA Observations of the Propagating Rift at 95.5° W on the Cocos-Nazca Spreading Center,J. Geophys. Res. 88, 6433–6447.
Shemenda, A. I. and Grokholsky, 1991, Formation and Evolution Model of Overlapping Spreading Centers,Tectonophysics (submitted).
Sinton, J. M. and Detrick, R. S., 1992, Mid-ocean Ridge Magma Chambers,J. Geophys. Res. (submitted).
Sinton, J. M., Wilson, D. S., Christie, D. M., Hey, R. N., and Delaney, J. R., 1983, Petrologic Consequences of Rift Propagation on Oceanic Spreading Ridges,Earth Planet. Sci. Lett. 62, 193–207.
Suess, E., Cason, B., Ritger, S., Moore, J. C., Jones, M. C., Kulm, L. D., and Cochrane, G. R., 1985, Biological Communities at Vent Sites along the Subduction Zone off Oregon,Biol. Soc. Wash. Bull. No. 6, 478–484.
Tunnicliffe, V., Juniper, S. K., and de Burgh, M. E., 1985, The Hydrothermal Vent Community on Axial Seamount, Juan de Fuca Ridge. In M. L. Jones (ed.), The Hydrothermal Vents of the Eastern Pacific: An overview,Bulletin of the Biol. Soc. of Wash., No. 6, 453–464.
van Andel, T. H. and Ballard, R. D., 1979, The Galapagos Rift at 86° W: 2. Volcanism, Structure, and Evolution of the Rift Valley,J. Geophys. Res. 84, 5390–5406.
Yonover, R. N., 1989, Petrological Effects of Rift Failure at the Galapagos Spreading Center near 95.5° W Including Analyses of Glass Inclusions by Laser Mass Spectrometry and Ion Micro-Probe, Ph.D. Dissertation, Univ. Hawaii, Honolulu, 193 pp.
Webb, M., 1969, Lamellibrachia Barhami, Gen. Nov., Sp. Nov. (Pogonophora), from the Northeast Pacific,Bull. Mar. Sci. 19, 18–47.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Hey, R.N., Sinton, J.M., Kleinrock, M.C. et al. ALVIN investigation of an active propagating rift system, Galapagos 95.5° W. Mar Geophys Res 14, 207–226 (1992). https://doi.org/10.1007/BF01270630
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01270630