Skip to main content
SpringerLink
Log in

Spreading rates, rift propagation, and fracture zone offset histories during the past 5 my on the Mid-Atlantic Ridge; 25°–27°30′ S and 31°–34°30′ S

  • Published:
Marine Geophysical Researches Aims and scope Submit manuscript

Abstract

The southern Mid-Atlantic Ridge (MAR) is spreading at rates (34–38 mm yr−1) that fall within a transitional range between those which characterize slow and intermediate spreading center morphology. To further our understanding of crustal accretion at these transitional spreading rates, we have carried out analysis of magnetic anomaly data from two detailed SeaBeam surveys of the MAR between 25°–27°30′S and 31°–34°30′S. Within these areas, the MAR is subdivided into 9 ridge segments bounded by large- and short-offset discontinuities of the ridge axis. From two-dimensional Fourier inversions of the magnetic anomaly data we establish the history of spreading within each ridge segment for the past 5 my and the evolution of the bounding ridge-axis discontinuities. We see evidence for the initiation and diminishment of small-offset discontinuities, and for the transition of rigid large-offset transform faults to less stable short-offset features. Individual ridge segments display independent spreading histories in terms of both the sense and amount of asymmetric spreading within each which have given rise to changes through time in the lengths of bounding ridge-axis discontinuities. Over the past 3–5 my, the short-offset discontinuities within the area have lengthened/shortened by approximately the same amount (∼ 10 km). During this same time period, larger-offset transform faults have remained comparatively constant in length. A shift in plate motion at anomaly 3 time may have given rise to change in the length of short-offset second-order discontinuities. However, the pattern of lengthening/shortening short-offset discontinuities we see is not simply related to the geometry of the plate boundary in these regions which precludes a simply relationship between plate motion changes and response at the plate boundary. We document a case of rapid (minimum 60 mm yr−1) small-scale rift propagation, occurring between 2.5 and 1.8 my, associated with transition of the Moore transform fault to an oblique-trending ridge-axis discontinuity. Propagation across the Moore discontinuity and similar propagation within the 31°–34°30’S area may be associated with the reduced age contrast in lithosphere across second-order discontinuities.

Total opening rates within our northern survey area decreased from anomaly 4′ to 2 time and rates within both areas have increased since the Jaramillo. Total opening rates measured for anomaly intervals differ along the plate boundary significantly, more than expected with changing distance to the pole of rotation. These differences imply a degree of short-term non-rigid plate behaviour which may be associated with ridge segments acting as independent spreading cells. Magnetic polarity transition widths from our inversion studies may be used to infer a zone of crustal accretion which is 3–6 km wide, within the inner floor of the rift valley. A systematic increase of transition width with age would be expected if deeper crustal sources dominate the magnetic signal in older crust but this is not observed. We present results from three-dimensional analysis of magnetic anomaly data which show magnetization highs located at the intersection of the MAR with both large- and short-offset discontinuities. Within the central anomaly the highs exceed 15 A m−1 compared with a background of approximately 8–10 A m−1 and they persist for at least 2.5 my. The highs may be caused by eruption of fractionated strongly magnetized basalts at ridge-axis discontinuities with both large and small offsets.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Atwater, T. M. and Mudie, J. D., 1973, Detailed Near-Bottom Geophysical Study of the Gorda Rise,J. Geophys. Res. 78, 8665–8686.

    Google Scholar 

  • Batiza, R., Melson, W. G., and O’Hearn, T., 1988, Simple Magma Supply Geometry Inferred Beneath a Segment of the Mid-Atlantic Ridge,Nature 335, 428–431.

    Article  Google Scholar 

  • Blackman, D. and Forsyth, D. W., Gravity and Tectonics of the Mid-Atlantic Ridge 25°–27°30′ S,J. Geophys. Res. (in review).

  • Blakely, R. J. and Lynn, W. S., 1977, Reversal Transition Widths and Fast Spreading Centers,Earth Planet. Sci. Lett. 33, 321–330.

    Article  Google Scholar 

  • Brozena, J. M., 1986, Temporal and Spatial Variability of Seafloor Spreading Processes in the Northern South Atlantic,J. Geophys. Res. 91, 497–510.

    Google Scholar 

  • Cande, S. C., Vogt, P. R., and Fox, P. J., 1987, Detailed Investigations of a Flowline Corridor in the South Atlantic: Part II a Survey of 50 to 70 m.y. Old Crust on the West Flank,EOS 68, 1491.

    Google Scholar 

  • Cande, S. C., LaBrecque, J. L., and Haxby, W. F., 1988, Plate Kinematics of the South Atlantic: Chron C34 to Present,J. Geophys. Res. 93, 13,479–13,492.

    Google Scholar 

  • Castillo, P. and Batiza R., 1989, Strontium, Neodymium and Lead Isotope Constraints on Near-Ridge Seamount Production Beneath the South Atlantic,Nature 343, 262–265.

    Article  Google Scholar 

  • Crane, K., 1985, The Spacing of Rift Axis Highs: Dependence upon Diapiric Processes in the Underlying Lithosphere?Earth Planet. Sci. Lett. 72, 405–414.

    Article  Google Scholar 

  • Detrick, R. S., Mudie, J. D., Luyendyk, B. P., and Macdonald, K. C., 1973, Near Bottom Observations of an Active Transform Fault (Mid-Atlantic Ridge at 37°N),Nature 246, 59–61.

    Google Scholar 

  • Fox, P. J. and Gallo, D. G., 1984, A Tectonic Model for RidgeTransform-Ridge Plate Boundaries: Implications for the Structure of Oceanic Lithosphere,Tectonophysics 104, 205–242.

    Article  Google Scholar 

  • Fox, P. J., Grindlay, N. R., Macdonald, K. C., Bicknell, J., and Forsyth, D. W., 1985, The Morphotectonic Character of the Mid-Atlantic Ridge Between 31°–34°30′ S: Implications for Plate Accretion,EOS Trans. Amer. Geophys. Union 66, 1078.

    Google Scholar 

  • Fox, P. J., Grindlay, N. R., Macdonald, K. C., Carbotte, S. M., Forsyth, D. W., and Kuo, B. Y., 1991, The Mid-Atlantic Ridge (31°–34°30′ S): Temporal and Spatial Variations of Accretionary Processes,Marine Geophys. Res. 13, 1–20 (this issue).

    Google Scholar 

  • GEBCO-General Bathymetric Chart of the Oceans, South Atlantic Chart, 1978, Canadian Hydrographic Service, Ottawa, Ont.

  • Grindlay, N. R., Fox, P. J., Macdonald, K. C., Cande, S., Forsyth, D., and Vogt, P., 1987, Ridge Axis Discordant Zones in the South Atlantic: Morphology, Structure, Evolution and Significance,EOS Trans. Amer. Geophys. Union 68, 1491.

    Google Scholar 

  • Grindlay, N. R., Fox, P. J., and Macdonald, K. C., 1991, Second-order Ridge Axis Discontinuities in the South Atlantic: Morphology, Structure, Evolution and Significance,Marine Geophys. Res. 13, 21–49 (this issue).

    Google Scholar 

  • Heirtzler, J. R., 1985, Relief of the Surface of the Earth, Report MGG-2, published by National Geophysical Data Center, Boulder, Co.

  • Hey, R. N., Duennebier, F. K., and Morgan, W. J., 1980, Propagating Rifts on Mid-Ocean Ridges,J. Geophys. Res. 85, 3658–3677.

    Google Scholar 

  • Karson, J. A., Thompson, G., Humphris, S. E., Edmond, J. M., Bryan, W. B., Brown, J. R., Winters, A. T., Pockalny, R. A., Casey, J. F., Campbell, A. C., Klinkhammer, G., Palmer, M. R., Kinzler, R. J., and Sulanowska, M. M., 1987, Along-Axis Variations in Seafloor Spreading in the MARK Area,Nature 328, 681–685.

    Article  Google Scholar 

  • Kent, D. and Gradstein, F. M., 1986, A Jurassic to Recent Chronology, in Vogt, P. R., and Tucholke, B. E. (eds.),The Geology of North America, Volume M, The Western North Atlantic Region: Geological Society of America, pp. 45–50.

  • Klitgord, K. D. and Mudie, J. D., 1974, The Galapagos Spreading Center: A Near Bottom Geophysical Survey,Geophys. J. R. Astron. Soc. 38, 536–586.

    Google Scholar 

  • Kuo, B. -Y. and Forsyth, D. W., 1988, Gravity Anomalies of the Ridge-Transform System in the South Atlantic Between 31° and 34.5° S: Upwelling Centers and Variations in Crustal Thickness,Marine Geophys. Res. 10, 205–232.

    Article  Google Scholar 

  • Lachenbruch, A. H., 1976, Dynamics of Passive Spreading Centers,J. Geophys. Res. 81, 1883–1902.

    Google Scholar 

  • LaBrecque, J. L., Kent, D. V., and Cande, S. C., 1977, Revised Magnetic Polarity Time Scale for the Late Cretaceous and Cenozoic Time,Geology 5, 330–335.

    Article  Google Scholar 

  • Larson, R. L., 1971, Near-Bottom Geologic Studies of the East Pacific Rise Crest,Geological Society of America Bulletin 82, 823–841.

    Google Scholar 

  • Le Douaran, S., Needham, H. D., and Francheteau, J., 1982, Pattern of Opening Rates Along the Axis of the Mid-Atlantic Ridge,Nature 300, 254–257.

    Article  Google Scholar 

  • Macdonald, K. C., 1977, Near-Bottom Magnetic Anomalies, Asymmetric Spreading, Oblique Spreading, and Tectonics of the Mid-Atlantic Ridge near lat 37°N,Geol. Soc. Am. Bull. 88, 541–555.

    Article  Google Scholar 

  • Macdonald, K. C., 1982, Mid Ocean Ridges: Fine Scale Tectonic, Volcanic and Hydrothermal Processes within the Plate Boundary Zone,Ann. Rev. Earth and Plan. Sci. 10, 155–190.

    Article  Google Scholar 

  • Macdonald, K. C., 1986, The Crest of the Mid-Atlantic Ridge: Models for Crustal Generation Processes and Tectonics,The Geology of North America M, 51–68 Geol. Soc. Amer.

    Google Scholar 

  • Macdonald, K. C. and Luyendyk, B. P., 1977, Deep-tow Studies of the Structure of the Mid-Atlantic Ridge Crest near 37° N,Geol. Soc. Am. Bull. 88, 621–636.

    Article  Google Scholar 

  • Macdonald, K. C., Miller, S. P., Huestis, S. P., and Speiss, F. N., 1980, Three-Dimensional Modelling of a Magnetic Reversal Boundary from Inversion of Deep-Tow Measurements,J. Geophys. Res. 85, 3760–3780.

    Google Scholar 

  • Macdonald, K. C., Sempere, J. C., and Fox, P. J., 1984, East Pacific Rise from Siqueiros to Orozco Fracture Zones: AlongStrike Continuity of Axial Neovoleanic Zone and Structure and Evolution of Overlapping Spreading Centers,J. Geophys Res. 89, 6049–6069.

    Google Scholar 

  • Macdonald, K. C., Fox, P. J., Perram, L. J., Eisen, M. F., Haymon, R. M., Miller, S. P., Carbotte, S. M., Cormier, M.-H., and Shor, A. N., 1988, A new View of the Mid-Ocean Ridge from the Behavior of Ridge-Axis Discontinuities,Nature 335, 217–225.

    Article  Google Scholar 

  • Menard, H. W., 1967, Sea Floor Spreading, Topography, and the Second Layer,Science 157, 923–924.

    Google Scholar 

  • Miller, S. P., 1977, The Validity of the Geologic Interpretation of Marine Magnetic Anomalies,Geophys. J. R. Astron. Soc. 50, 1–22.

    Google Scholar 

  • Miller, S. P., Macdonald, K. C., and Lonsdale, P. F., 1985, Near Bottom Magnetic Profile Across the Red Sea,Marine Geophys. Res. 7, 401–418.

    Article  Google Scholar 

  • Minster, J. B. and Jordan, T. H., 1978, Present-day Plate Motions,J. Geophys. Res. 83, 5331–5354.

    Google Scholar 

  • Ness, G., Levi, S., and Couch, R., 1980, Marine Magnetic Anomaly Timescales for the Cenozoic and Late Cretaceous: A Precis, Critique, and SynthesisRev. Geophys. Space Phys. 18, 753–770.

    Google Scholar 

  • Normark, W. R., 1976, Delineation of the Main Extrusive Zone of the East Pacific Rise at Lat. 21° N,Geology 4, 681–685.

    Article  Google Scholar 

  • Norrell, G. T. and Harper, G. D., 1988, Detachment Faulting and Amagmatic Extension at Mid-Ocean Ridges: the Josephine Ophiolite as an Example,Geology 16, 827–834.

    Article  Google Scholar 

  • Parker, R. L. and Huestis, S. P., 1974, The Inversion of Magnetic Anomalies in the Presence of Topography,J. Geophys. Res. 79, 1587–1593.

    Google Scholar 

  • Peddie, N. W., 1982, International Geomagnetic Reference Field 1980,Geophysics 47, 841–842.

    Article  Google Scholar 

  • Phillips, J. D. and Fleming, H. S., 1978, Multi-Beam Sonar Study of the Mid-Atlantic Rift Valley 36°–37° N: FAMOUS, Geological Society of America, MC-19.

  • 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.

    Google Scholar 

  • Pockalny, R. A., Detrick, R. S., and Fox, P. J., 1988, Morphology and Tectonics of the Kane Fracture Zone from Seabeam Bathymetry Data,J. Geophys. Res. 93, 3179–3193.

    Google Scholar 

  • Renard, V., Schrumpf, B., Sibuet, J. C., and Carre, D., 1975, Bathymetrie Detaille d’une Partie de Valle du Rift et de Faille Transformante, Pres de 36°50′N dans l’Ocean Atlantique, Centre National pour l’Exploitation des Ocean, Paris.

    Google Scholar 

  • Rona, P. A. and Gray D. F., 1980, Structural Behavior of Fracture Zones Symmetric and Asymmetric about a Spreading Axis: Mid-Atlantic Ridge (Latitude 23°N to 27°N),Geological Society of America Bull. 91, 485–494.

    Article  Google Scholar 

  • Schouten, H. and Denham C. R., 1979, Modeling the Oceanic Magnetic Source Layer, inDeep Drilling Results in the Atlantic Ocean: Ocean Crust, Maurice Ewing Ser., vol. 2, ed. by M. Talwani C. G. Harrison, and D. E. Hayes, pp. 151–159.

  • Schouten, H. and White, R. S., 1980, Zero-Offset Fracture Zones,Geology 8, 175–179.

    Article  Google Scholar 

  • Searle, R. C. and Laughton, A. S., 1977, Sonar Studies of Mid-Atlantic Ridge and Kurchatov Fracture Zone,J. Geophys. Res. 82, 5313–5328.

    Article  Google Scholar 

  • Sempere, J.-C., Macdonald, K. C., and Miller, S. P., 1987, Detailed Study of the Brunhes/Matuyama Reversal Boundary on the East Pacific Rise at 19°30′ S: Implications for Crustal Emplacement Processes at an Ultra Fast Spreading Center,Marine Geophys. Res. 9, 1–23.

    Google Scholar 

  • Sempere, J.-C., Meshkov, A., Thommeret, M., and Macdonald, K. C., 1988, Magnetic Properties of Some Young Basalts from the East Pacific Rise,Marine Geophys. Res. 9, 131–146.

    Article  Google Scholar 

  • Severinghaus, J. P. and Macdonald, K. C., 1988, High Inside Corners at Ridge-Transform Intersections,Marine Geophys. Res. 9, 353–367.

    Article  Google Scholar 

  • 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 Plant. Sci. Lett. 62, 193–207.

    Article  Google Scholar 

  • paVan Andel, T. H. and Heath, G. R., 1970, Tectonics of the Mid-Atlantic Ridge, 6°–8° South Latitude,Marine Geophys. Res. 1,. 5–36.

    Article  Google Scholar 

  • Van Andel, T. H. and Moore, T. C., 1970, Magnetic Anomalies and Seafloor Spreading Rates in the Northern South Atlantic,Nature 226, 328–330.

    Article  Google Scholar 

  • Vogt, P. R., Cande, S. C., and Fox, P. J., 1987, Detailed Investigation of a Flowline Corridor in the South Atlantic: Part I Mid-Atlantic Ridge crestal area,EOS Trans. Amer. Geophys. Union 68, 1491.

    Google Scholar 

  • Welch, S., Macdonald, K. C., Miller, S. P., and Fox, P. J., 1986, Magnetic Analysis of Slow Spreading in the South Atlantic,EOS Trans. Amer. Geophys. Union 67, 1227.

    Google Scholar 

  • Whitehead, Jr., J. A., Dick, H. J. B., and Schouten, H., 1984, A Mechanism for Magmatic Accretion Under Spreading Centers,312, 146–147.

    Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Marine Science Institute, University of California, 93106, Santa Barbara, CA, USA

    S. Carbotte, S. M. Welch & K. C. MacDonald

Authors
  1. S. Carbotte
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. S. M. Welch
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. K. C. MacDonald
    View author publications

    You can also search for this author in PubMed Google Scholar

Rights and permissions

Reprints and permissions

About this article

Cite this article

Carbotte, S., Welch, S.M. & MacDonald, K.C. Spreading rates, rift propagation, and fracture zone offset histories during the past 5 my on the Mid-Atlantic Ridge; 25°–27°30′ S and 31°–34°30′ S. Mar Geophys Res 13, 51–80 (1991). https://doi.org/10.1007/BF02428195

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF02428195

Key words

Search

Navigation