The morphology and tectonics of the Mark area from Sea Beam and Sea MARC I observations (Mid-Atlantic Ridge 23° N)

  • Laura S. L. Kong
  • Robert S. Detrick
  • Paul J. Fox
  • Larry A. Mayer
  • W. B. F. Ryan
Part II: The Kane Fracture Zone


High-resolution Sea Beam bathymetry and Sea MARC I side scan sonar data have been obtained in the MARK area, a 100-km-long portion of the Mid-Atlantic Ridge rift valley south of the Kane Fracture Zone. These data reveal a surprisingly complex rift valley structure that is composed of two distinct spreading cells which overlap to create a small, zero-offset transform or discordant zone. The northern spreading cell consists of a magmatically robust, active ridge segment 40–50 km in length that extends from the eastern Kane ridge-transform intersection south to about 23°12′ N. The rift valley in this area is dominated by a large constructional volcanic ridge that creates 200–500 m of relief and is associated with high-temperature hydrothermal activity. The southern spreading cell is characterized by a NNE-trending band of small (50–200 m high), conical volcanos that are built upon relatively old, fissured and sediment-covered lavas, and which in some cases are themselves fissured and faulted. This cell appears to be in a predominantly extensional phase with only small, isolated eruptions. These two spreading cells overlap in an anomalous zone between 23°05′ N and 23°17′ N that lacks a well-developed rift valley or neovolcanic zone, and may represent a slow-spreading ridge analogue to the overlapping spreading centers found at the East Pacific Rise. Despite the complexity of the MARK area, volcanic and tectonic activity appears to be confined to the 10–17 km wide rift valley floor. Block faulting along near-vertical, small-offset normal faults, accompanied by minor amounts of back-tilting (generally less than 5°), begins within a few km of the ridge axis and is largely completed by the time the crust is transported up into the rift valley walls. Features that appear to be constructional volcanic ridges formed in the median valley are preserved largely intact in the rift mountains. Mass-wasting and gullying of scarp faces, and sedimentation which buries low-relief seafloor features, are the major geological processes occurring outside of the rift valley. The morphological and structural heterogeneity within the MARK rift valley and in the flanking rift mountains documented in this study are largely the product of two spreading cells that evolve independently to the interplay between extensional tectonism and episodic variations in magma production rates.

Key words

Mid-Atlantic Ridge seafloor spreading rift valley oceanic crust 


  1. Abrams, L. J., Detrick, R. S., and Fox, P. J., 1988, Morphology and Crustal Structure of the Kane Fracture Zone Transverse Ridge,J. Geophys. Res. 93, 3195–3210.Google Scholar
  2. Ballard, R. D. and van Andel, T. H., 1977, Morphology and Tectonics of the Inner Rift Valley at Latitude 36°50′ N on the Mid-Atlantic Ridge,Geol. Soc. Amer. Bull. 88, 507–530.CrossRefGoogle Scholar
  3. Brown, J. R. and Karson, J. A., 1989, Variations in Axial Processes on the Mid-Atlantic Ridge: the Neovolcanic Zone of the MARK Area,Mar. Geophys. Res. (in press).Google Scholar
  4. Bryan, W. B., Thompson, G., and Ludden, J. N., 1981, Compositional Variation in Normal MORB from 22–25° N; Mid-Atlantic Ridge and Kane Fracture Zone,J. Geophys. Res. 86, 11815–11836.Google Scholar
  5. Casey, J. F., 1986, Ultramafic Rocks from the MAR at 23° N: Evidence for High Temperature Hydration and High Temperature - low to Moderate Stress Deformation of Mantle Tectonites beneath the Median Valley,EOS (Trans. Amer. Geophys. Union) 67, 1214.Google Scholar
  6. Chayes, D. N., 1983, Evolution of Sea MARC I,IEEE Proceedings of the 3rd Working Symposium on Oceanographic Data Systems, IEEE Computer Society, 103–108.Google Scholar
  7. Cormier, M. H., Detrick, R. S., and Purdy, G. M., 1984, Anomalously Thin Crust in Oceanic Fracture Zones: New Constraints from the Kane Fracture Zone,J. Geophys. Res. 89, 10249–10266.Google Scholar
  8. Crane, K. and Ballard, R. D., 1981, Volcanics and Structure of the FAMOUS Narrowgate Rift: Evidence for Cyclic Evolution: AMAR I,J. Geophys. Res. 86, 5112–5124.Google Scholar
  9. de Moustier, C. and Kleinrock, M. C., 1986, Bathymetric Artifacts in Sea Beam Data: How to Recognize Them and What Causes Them,J. Geophys. Res. 91, 3407–3424.Google Scholar
  10. Detrick, R. S., Fox, P. J., Kastens, K., Ryan, W. B. F., Mayer, L., and Karson, J., 1984, A Sea Beam Survey of the Kane Fracture Zone and Adjacent Mid-Atlantic Ridge Rift Valley,EOS (Trans. Amer. Geophys. Union) 65, 1006.Google Scholar
  11. Detrick, R., Honnorez, J., Bryan, W. B., Juteauet al., 1988,Proc. ODP Init. Repts. (Pt. A), 106/109, College Station, TX (Ocean Drilling Program).Google Scholar
  12. Farre, J. A., Ryan, W. B. F., Koch, W., and Brosius, A. M., 1983, Applying Thyristor Technology to Deep Sea Photography,Functional Photography, March/April, 16–21.Google Scholar
  13. Fox, P. J., 1972, The Geology of Some Atlantic Fracture Zones, Caribbean Escarpments and the Nature of Oceanic Basement and Crust, [Ph.D. dissertation], Columbia University, New York.Google Scholar
  14. Fox, P. J. and Gallo, D.: 1984, A Tectonic Model for Ridge-Transform-Ridge Boundaries: Implications for the Structure of Oceanic Lithosphere,Tectonophysics 104, 205–242.CrossRefGoogle Scholar
  15. Fox, P. J., Pitman, W. C., III, and Shepard, F., 1969, Crustal Plates in the Central Atlantic: Evidence for a Least two Poles of Rotation,Science 165, 487–489.Google Scholar
  16. Francheteau, J. F. and Ballard, R. 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.CrossRefGoogle Scholar
  17. Humphris, S. E. and Bryan, W. B., 1986, Anatomy of Serocki Volcano,EOS (Trans. Amer. Geophys. Union) 67, 1213.Google Scholar
  18. Kappel, E. S. and Ryan, W. B. F., 1986, Volcanic Episodicity and a Non-Stready State Rift Valley along Northeast Pacific Spreading Centers: Evidence from Sea MARC I,J. Geophys. Res. 91, 13,925–13,940.Google Scholar
  19. Karson, J. A., 1988, Seafloor Spreading on the Mid-Atlantic Ridge: Implications for the Structure of Ophiolites and Oceanic Lithosphere Produced in Slow-Spreading Environments,Proceedings of the Symposium on Ophiolites and Oceanic Lithosphere-TROODOS 87, (in press).Google Scholar
  20. Karson, J. A. and Dick, H. J. B., 1983, Tectonics of Ridge-Transform Intersections at the Kane Fracture Zone,Mar. Geophys. Res. 6, 51–98.CrossRefGoogle Scholar
  21. 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.CrossRefGoogle Scholar
  22. Kastens, K. A., Ryan, W. B. F., and Fox, P. J., 1986, The Structural and Volcanic Expressions of a Fast-Slipping Ridge. Transform-Ridge Plate Boundary: Sea MARC I and Photographic Surveys at the Clipperton Transform Fault,J. Geophys. Res. 91, 3469–3488.Google Scholar
  23. Kong, L., Ryan, W. B. F., Mayer, L., Detrick, R., Fox, P. J., and Manchester, K., 1985, Bare-Rock Drill Sites, OPD Legs 106 and 109: Evidence for Hydrothermal Activity at 23° N on the Mid-Atlantic Ridge,EOS (Trans. Amer. Geophys. Union) 66, 936.Google Scholar
  24. Kosalos, J. G. and Chayes, D. N., 1983, A Portable system for Ocean Bottom Imaging and Charting,Proceedings of Offshore Technology Conference, Houston, TX, 649–656.Google Scholar
  25. Leg 106 Scientific Party, 1986, Drilling the Snake-Pit Hydrothermal Sulfide Deposit on the Mid-Atlantic Ridge, lat 23°22′ N,Geology 14, 1004–1007.CrossRefGoogle Scholar
  26. Lewis, B. T. R., 1979, Periodicities in Volcanism and Longitudinal Magma Flow on the East Pacific Rise at 23° N,Geophys. Res. Lett. 6, 753–756.Google Scholar
  27. Lonsdale, P., 1983, Overlapping Rift Zones at the 5.5° Offset of the East Pacific Rise,J. Geophys. Res. 88, 9393–9406.Google Scholar
  28. Macdonald, K. C., 1983, Crustal Processes at Spreading Centers,Rev. Geophysics,21, 1441–1454.Google Scholar
  29. Macdonald, K. C. and Fox, P. J., 1983, Overlapping Spreading Centers: New Accretion Geometry on the East Pacific Rise,Nature 302, 55–57.CrossRefGoogle Scholar
  30. Macdonald, K. C. and Luyendyk, B. P., 1977, Deep-Tow Studies of the Structure of the Mid-Atlantic Ridge Crest near lat. 37° N,Geol. Soc. Amer. Bull. 88, 621–636.CrossRefGoogle Scholar
  31. Mayer, L. A., Ryan, W. B. F., Detrick, R. S., Fox, P. J., Kong, L., and Manchester, K., 1985, Structure and Tectonics of the Mid-Atlantic Ridge South of the Kane Fracture Zone Based on Sea MARC I and Sea Beam Site Surveys,EOS 66, 1092.Google Scholar
  32. Miyashiro, A., Shido, F., and Ewing, M., 1969, Composition and Origin of Serpentinites from the Mid-Atlantic Ridge, 24° and 30° N,Contrib. Mineral. Petrol. 32, 38–52.CrossRefGoogle Scholar
  33. OTTER, 1984, The Geology of the Oceanographer Transform: The Ridge-Transform Intersection,Marine Geophys. Res. 6, 109–141.CrossRefGoogle Scholar
  34. Pockalny, R. A., Detrick, R. S., and Fox, P. J., 1987, A Comparison of Off-Axis Sea Beam Data Collected at Slow, Intermediate and Fast Spreading Center,EOS (Trans. Amer. Geophys. Union) 68, 1491.Google Scholar
  35. Pockalny R. A., Detrick, R. S., and Fox, P. J., 1988, The Morphology and Tectonics of the Kane Fracture Zone from Sea Beam Bathymetry Data,J. Geophys. Res. 93, 3179–3193.Google Scholar
  36. Pockalny, R. A., Fox, P. J., and Detrick, R. S., in preparation, Morphological Comparison of the Abysal Hills Located on the Flanks of Slow, Intermediate and Fast Spreading Mid-Ocean Ridges.Google Scholar
  37. Purdy, G. M. and Detrick, R. S., 1986, the Crustal Structure of the Mid-Atlantic Ridge at 23° N from Seismic Refraction Studies,J. Geophys. Res. 91, 3739–3762.Google Scholar
  38. Purdy, G. M., Rabinowitz, P. D., and Schouten H., 1978, The Mid-Atlantic Ridge at 23° N: Bathymetry and Magnetics, in W. C. Melsonet al. (eds.),Initial Reports of the Deep Sea Drilling Project,45, pp. 119–128.Google Scholar
  39. Purdy, G. M., Rabinowitz, P. D., and Veltrop, J. J. A., 1979, The Kane Fracture Zone in the Central North Atlantic,Earth Planet. Sci. Lett. 45, 429–434.CrossRefGoogle Scholar
  40. Rabinowitz, P. D., Purdy, G. M., and Veltrop, J. J. A., 1977, The Kane Fracture Zone in the Central North Atlantic Ocean,EOS (Trans. Amer. Geophys. Union) 58, 511.Google Scholar
  41. Renard, V. and Allenou, 1979, Sea Beam Multibeam Echosounding in Jean Charcot: Description, Evaluation and First Results,Int. Hydrog. Rev.,56, 35–67.Google Scholar
  42. Schouten, H. and White, R. S., 1980, Zero Offset Fracture Zones,Geology 8, 175–179.CrossRefGoogle Scholar
  43. Schouten, H., Cande, S. C., and Klitgord, K. D., 1985, Magnetic Anomaly Profiles South (22° N to 28° N), inOcean Margin Drilling Program Regional Data Synthesis Series, Atlas 11, Mid-Atlantic Ridge between 22° and 38° N, Marine Science International, Woods Hole.Google Scholar
  44. Schulz, N. J., Detrick, R. S., and Miller, S. P., 1988, Two and Three Dimensional Inversions of Magnetic Anomalies in the MARK Area (Mid-Atlantic Ridge 23° N),Mar. Geophys. Res. 10, 41–57 (this issue).Google Scholar
  45. Severinghaus, J. and Macdonald, K. C., 1986, High Inside Corners at Ridge Transform Intersections,EOS (Trans. Amer. Geophys. Union) 67, 1232.Google Scholar
  46. Stakes, D. S., Shervais, J. W., and Hopson, C. A., 1984, The Volcano-Tectonic Cycle of the FAMOUS and AMAR Valleys, Mid-Atlantic Ridge (36°47′ N): Evidence from Basalt Glass and Phenocryst Variations for a Steady-State Magma Chamber Beneath Valley Mid-Sections, AMAR 3,J. Geophys. Res. 89, 6995–7028.Google Scholar
  47. Stroup, J. B. and Fox, P. J., 1981, Geologic Investigations in the Cayman Trough: Evidence for Thin Crust along the Mid-Cayman Rise,J. Geol. 89, 395–420.CrossRefGoogle Scholar
  48. Thompson, G., Humphris, S. E., Schroeder, B., Sulanowska, M., and Rona, P., 1988, Hydrothermal Mineralization on the Mid-Atlantic Ridge,Canadian Mineralogist, Special Publication, (in press).Google Scholar
  49. Toomey, D. R., Solomon, S. C., and Purdy, G. M., 1988, Microearthquakes Beneath the Median Valley of the Mid-Atlantic Ridge near 23° N: Tomography and Tectonics,J. Geophys. Res. 93, 9093–9112.Google Scholar
  50. Toomey, D. R., Solomon, S. C., Purdy, G. M., and Murray, M. H., 1985, Micro-Earthquakes beneath the Median Valley of the Mid-Atlantic Ridge near 23° N: Hypocenters and Focal Mechanisms,J. Geophys. Res. 90, 5443–5458.CrossRefGoogle Scholar
  51. van Andel, T. J. and Bowin, C. O., 1968, Mid-Atlantic Ridge between 22° and 23° North Latitude and the Tectonics of Mid-Ocean Rises,J. Geophys. Res. 73, 1279–1298.Google Scholar

Copyright information

© Kluwer Academic Press 1988

Authors and Affiliations

  • Laura S. L. Kong
    • 1
  • Robert S. Detrick
    • 2
  • Paul J. Fox
    • 2
  • Larry A. Mayer
    • 3
  • W. B. F. Ryan
    • 4
  1. 1.Woods Hole Oceanographic InstitutionMIT/WHOI Joint Program in OceanographyWoods HoleUSA
  2. 2.Graduate School of OceanographyUniversity of Rhode IslandKingstonUSA
  3. 3.Department of OceanographyDalhousie UniversityHalifax
  4. 4.Lamont-Doherty Geological ObservatoryPalisadesUSA

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