Abstract
This paper is a report of geological observations made using the submersible ALVIN on the crest of the East Pacific Rise near 21°N. The profile is 6 km long and crosses a 5–10 km wide plateau which rises 100 m±above the rise flanks. At the axis are exposed fresh glassy pillow lavas with no sediment accumulation in a region termed the neovolcanic zone. This zone is about one kilometer wide and includes elongate ridges of pillow lavas and seventeen hydrothermal vent fields in the study area. Outside the neovolcanic zone the seafloor is extensively fissured in another zone which is up to two kilometers wide. The neovolcanic zone and the fissured zone are included within a rift valley or graben about 3 to 5 km wide and 50 m±deep. This rift valley is asymmetrically located on the west side of the axial plateau; the neovolcanic zone in the study area is asymmetrically located on the east side of the rift graben. Fissured crust is not common outside the rift graben or in the neovolcanic zone; similarly, large throw faults such as those which form the edges of the graben are not found outside of it. These observations can be interpreted according to a volcanic-tectonic cycle in which volcanic eruptions and hydrothermal circulation are followed by a tectonic phase which includes fissuring and vertical movements. When a new cycle starts it may involve a lateral shift of the spreading axis. Lavas along the dive profile are suggested to be no older than a few thousand years based on sediment accumulation. In contrast, seafloor spreading rates here predict crust up to 105 yr old. This observation suggests that lavas from the neovolcanic zone can spread laterally about a kilometer or more and overlap on older crust.
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References
BallardR. D., FrancheteauJ., JuteauT., RanginC., and NormarkW.: 1981, ‘East Pacific Rise at 21°N: The Volcanic, Tectonic, and Hydrothermal Processes of the Central Axis’, Earth Planet. Sci. Lett. 55, 1–10.
BallardR. D. and vanAndelTj. H.: 1977, ‘Morphology and Tectonics of the Inner Rift Valley at lat. 36° 50′ N on the Mid-Atlantic Ridge’, Geol. Soc. Amer. Bull. 88, 507–530.
BallardR. D., vanAndelTj. H., and HolcombeT. T.: 1982, ‘The Galapagos Rift at 86° W, 5, Variations in Volcanism, Structure and Hydrothermal Activity along a 30-km Segment of the Rift Valley’, J. Geophys. Res. 87, 1149–1162.
CorlissJ. B., DymondJ., GordonL. I., EdmondJ. M., VonHerzenR. P., BallardR. D., GreenK., WilliamsD., BainbridgeA., CraneK., and vanAndelT. H.: 1979, ‘Submarine Thermal Springs on the Galapagos Rift’, Science 203, 1073–1083.
CYAMEX Scientific Team: 1981, ‘First Manned Submersible Dives on the East Pacific Rise at 21° N (Project RITA): General Results’, Mar. Geophys. Res. 4, 345–379.
EdmondJ.: 1980, ‘Ridge Crest Hot Springs: The Story so Far’, EOS 61, 129–131.
FrancheteauJ. and BallardR. D.: 1983, ‘The East Pacific Rise near 21° N, 13° N and 20° S: Inferences for Along Strike Variability of Axial Processes of the Mid-Ocean Ridge‘, Earth Planet Sci. Lett. 64, 93–116.
HaymonR. M. and KastnerM.: 1981, ‘Hot Spring Deposits on the East Pacific Rise at 21° N: Preliminary Description of Mineralogy and Genesis’, Earth Planet. Sci. Lett. 53, 363–381.
Hess, G. R., Lawhead, B., Lichtman, G. S., Macdonald, K. C., Miller, S. P., Normark, W. R., and Spiess, F. N.: 1980, ‘Fine-Scale Bathymetry Used for Submersible Studies of the East Pacific Rise’, U.S. Geol. Survey Open File Rep. 80-542 MAP.
KlitgordK. D. and MammerickxJ.: 1982, ‘Northern East Pacific Rise: Magnetic Anomaly and Bathymetric Framework’, J. Geophys. Res. 87, 6725–6750.
LarsonR. L.: 1971, ‘Near-Bottom Geologic Studies of the East Pacific Rise Crest’, Geol. Soc. Am. Bull. 82, 823–842.
LarsonR. L. and SpiessF. N.: 1969, ‘East Pacific Rise Crest: A near Bottom Geophysical Profile’, Science 163, 68–71.
LichtmanG. S., NormarkW. R., and SpiessF. N.: 1984, ‘Photogeologic Study of a Segment of the East Pacific Rise Axis near 21° N Latitude’, Geol. Soc. Amer. Bull. 95, 743–752.
LuyendykB. P.: 1980, ‘On-Bottom Gravity Profile Across the East Pacific Rise at 21° N’, EOS 61, 1099.
Luyendyk B. P.: ‘On-Bottom Gravity Profile Across the East Pacific Rise Crest at 21 Degrees North’, Geophysics 49, 2166–2177.
LuyendykB. P. and MacdonaldK. C.: 1976, ‘Spreading Center Terms and Concepts’, Geology 4, 369–370.
LuyendykB. P. and MacdonaldK. C.: 1977, ‘Physiography and Structure of the Inner Floor of the FAMOUS Rift Valley: Observations with a Deep-Towed Instrument Package’, Geol. Soc. Amer. Bull. 88, 648–663.
MacdonaldK. C.: 1982, ‘Mid-Ocean Ridges: Fine Scale Tectonic, Volcanic and Hydrothermal Processes within the Plate Boundary Zone’, Ann. Rev. Earth Planet, Sci. 10, 155–190.
MacdonaldK. C. and FoxP. J.: 1983, ‘Overlapping Spreading Centers: New Accretion Geometry on the East Pacific Rise’, Nature 302, 55–58.
MacdonaldK. C. and LuyendykB. P.: 1977, ‘Deep-Tow Studies of the Structure of the Mid-Atlantic Ridge Crest Near Lat. 37° N’, Bull. Geol. Soc. Amer. 88, 621–636.
MacdonaldK. C. and LuyendykB. P.: 1981, ‘The Crest of the East Pacific Rise’, Sci. American 244, 110–117.
MacdonaldK. C. and LuyendykB. P.: 1985, ‘Investigation of Faulting and Abyssal Hill Formation on the Flanks of the East Pacific Rise (21° N) Using ALVIN’, Mar. Geophys. Res. 7, 515–535 (this issue).
MacdonaldK. C., BeckerK., SpiessF. N., and BallardR. D.: 1980, ‘Hydrothermal Heat Flux of the “Black Smoker” Vents on the East Pacific Rise’, Earth Planet. Sci. Lett. 48, 1–7.
MacdonaldK. C., MillerS. P., LuyendykB. P., AtwaterT. M., and ShureL.: 1983, ‘Investigation of a Vine-Matthews Magnetic Lineation from a Submersible: The Source and Character of Marine Magnetic Anomalies’, J. Geophys. Res. 88, 3403–3418.
MammerickxJ. and KlitgordK.: 1982, ‘Northern East Pacific Rise: Evolution from 25 m.y. B.P. to the Present’, J. Geophys. Res. 87, 6751–6760.
NormarkW. R.: 1976, ‘Delineation of the Main Extrusion Zone of the East Pacific Rise at 21°N latitude’, Geology 4, 681–685.
SpiessF. N., MacdonaldK. C., AtwaterT., BallardR. D., CarranzaA., CordobaD., CoxC., Diaz GarciaV. M., FrancheteauJ., GuerreroJ., HawkinsJ., HaymonR., HesslerR., JuteauT., KastnerM., LarsonR. L., LuyendykB. P., MacdougallJ. D., MillerS., NormarkW. R., OrcuttJ., and RanginC.: 1980, ‘East Pacific Rise: Hot Springs, and Geophysical Experiments’, Science 207, 1421–1433.
vanAndelTj. H., and BallardR. D.: 1979, ‘The Galapagos Rift at 86° W-2, Volcanism, Structure and Evolution of the Rift Valley’, J. Geophys. Res. 84, 5390–5406.
VonDammK. L., GrantB., and EdmondJ.: 1983, ‘Preliminary Report on the Chemistry of Hydrothermal Solutions at 21° North, East Pacific Rise’, in, RonaP. A. et al. (eds.), Hydrothermal Processes at Seafloor Spreading Centers, Plenum Press, New York, pp. 369–389.
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Luyendyk, B.P., Macdonald, K.C. A geological transect across the crest of the East Pacific Rise at 21°N latitude made from the deep submersible ALVIN. Marine Geophysical Researches 7, 467–488 (1985). https://doi.org/10.1007/BF00368951
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DOI: https://doi.org/10.1007/BF00368951