Skip to main content

Study of the Saldanha Massif (MAR, 36°34′ N): Constrains from rock magnetic and geophysical data

Abstract

We present a study of the magnetic properties of a group of basalt samples from the Saldanha Massif (Mid-Atlantic Ridge – MAR – 36° 33′ 54′′ N, 33° 26′ W), and we set out to interpret these properties in the tectono-magmatic framework of this sector of the MAR. Most samples have low magnetic anisotropy and magnetic minerals of single domain grain size, typical of rapid cooling. The thermomagnetic study mostly shows two different susceptibility peaks. The high temperature peak is related to mineralogical alteration due to heating. The low temperature peak shows a distinction between three different stages of low temperature oxidation: the presence of titanomagnetite, titanomagnetite and titanomaghemite, and exclusively of titanomaghemite. Based on established empirical relationships between Curie temperature and degree of oxidation, the latter is tentatively deduced for all samples. Finally, swath bathymetry and sidescan sonar data combined with dive observations show that the Saldanha Massif is located over an exposed section of upper mantle rocks interpreted to be the result of detachment tectonics. Basalt samples inside the detachment zone often have higher than expected oxidation rates; this effect can be explained by the higher permeability caused by the detachment fault activity.

This is a preview of subscription content, access via your institution.

References

  1. Akimoto, S., 1962, Magnetic properties of Fe-Fe2O3 system as a basis of rock magnetism, J. Phys. Soc. Jpn., suppl. B1 707–710.

    Google Scholar 

  2. Alt, J. C., Honnorez, J., Laverne, C. and Emmermann, R., 1986, Hydrothermal alteration of a 1-km section valley of the upper oceanic crust, Deep Sea drilling Project Hole 504B: Mineralogy, chemistry, and evolution of seawater-basalt interactions, J. Geophys. Res. 91, 10,309–10,335.

    Google Scholar 

  3. Barriga, F., Fouquet, Y., Almeida, A., Biscoito, M., Charlou, J. L., Costa, R., Dias, A., Marques, A., Miranda, J. M., Olu, K., Porteiro F., and Queiroz, M. G., 1999, Preliminary results of the Saldanha Cruise (FAMOUS segment of the MAR 36°30´ N), Geophys. Res. Abstr. 1, Eur. Geophys. Soc., Den Haag.

  4. Bideau, D., Hekinian, R., Bolinger, C., Constantin, M., Gracia, E., Guivel, G., Sichler, B., Apprioual, R. and Le Gall, R., 1996, Submersible investigation of highly contrasted magmatic activities recorded on two segments of the Mid-Atlantic Ridge near 34°52? N and 33°55? N, Interridge News 5, 9–14.

    Google Scholar 

  5. Bina, M. M., 1990, Magnetic properties of basalts from ODP Hole 648B on the Mid-Atlantic Ridge near 23 °N, Proc. Ocean Drill Prog. Sci. Res. 106/109, 297–302.

    Google Scholar 

  6. Bina, M. M. and Prévot, M., 1989, Thermomagnetic investigations of titanomagnetite in submarine basalts: Evidence for differential maghemitization, Phys. Earth Planet. Int. 54, 169–179.

    Google Scholar 

  7. Blackman, D. K., Cann, J. R., Janssen, B. and Smith, D. K., 1998, Origin of extensional core complexes: Evidences from the Mid-Atlantic Ridge, Atlantis Fracture Zone, J. Geophys. Res. 103, 21315–21333.

    Google Scholar 

  8. Bleil, U. and Petersen, N., 1983, Variations in magnetization intensity and low-temperature titanomagnetite oxidation of ocean floor basalts, Nature 301, 384–388.

    Google Scholar 

  9. Bougault, H., German, C., Miranda, J. M. and Marflux /A T J. 1996, Mid-Atlantic Ridge: Hydrothermal fluxes at the Azores Triple Junction, Interridge News 5(2), 13–17.

    Google Scholar 

  10. Bougault, H., Aballéa, M., Radford-Knoery, J., Charlou, J. L., Jean Baptiste, P., Appriou, P., Needham, H. D., German, C. and Miranda, J. M., 1998, FAMOUS and AMAR segments on the Mid-Atlantic Ridge: ubiquitous hydrothermal Mn, CH4, δ3He signals along the rift through walls and rift offsets, Earth Planet. Sci. Lett. 161, 1–17.

    Google Scholar 

  11. Bonnati, E., 1976, Serpentinite intrusions in the oceanic crust, Earth and Planet. Sci. Lett. 32, 107–113.

    Google Scholar 

  12. Brown, K. and O'Reilly, W., 1988, The effect of low-temperature oxidation on the remanence of TRM-carrying titanomagnetite Fe2.4Ti0.6O4, Phys. Earth Planet. Int. 52, 108–116.

    Google Scholar 

  13. Cann, J. R., Blackman, D. K., Smith, D. K., McAllister, E., Janssen, B., Mello, S., Avegerinos, E., Pascoe, A. R. and Escartin, J., 1997, Corrugated slip surfaces formed at North Atlantic Ridge-transform intersections, Nature 385, 329–332.

    Google Scholar 

  14. Cannat, M., 1993, Emplacement of mantle rocks in the seafloor at the Mid-Atlantic ridge, J. Geophys. Res. 98, 4163–4172.

    Google Scholar 

  15. Cannat, M., Briais, A., Deplus, C., Escartín, J., Georgen, J., Lin, J., Mercouriev, S., Meyzen, C., Muller, M., Pouliquen, G., Rabain, A. and Silva, P. 1999, 'Mid-Atlantic Ridge-Azores hotspot interactions: along-axis migration of a hotspot-derived event of enhanced magmatism 10 to 40 Ma ago', Earth Planet. Sci. Lett. 173, 257–269.

    Google Scholar 

  16. Canon-Tapia E., Walker G. P. L. and Herrero-Bervera E., 1995, Magnetic fabric and flow direction in basaltic Pahoehoe lava of Xitle Volcano, Mexico, J. Volcanol. Geotherm. Res. 65, 249–263.

    Google Scholar 

  17. Charlou J. L., Bougault, H., Donval, J. P., Pellé, H., Langmuir C. H. and C. F. S. Team. 1993, Seawater CH4 concentration over the Mid-Atlantic Ridge, from Hayes F. Z. to the Azores Triple Junction, EOS 74, 380.

    Google Scholar 

  18. Chevallier, R. and Pierre, J., 1932, Propriétés magnétiques des roches volcaniques, Ann. Phys. 18, 383–477.

    Google Scholar 

  19. Day, R., Fuller, M. and Schmidt, V. A., 1977, Hysteresis properties of titanomagnetites: Grain size and compositional dependence, Phys. Earth Planet. Inters. 13, 260–267.

    Google Scholar 

  20. DeMets, C., Gordon, R. G., Argus, D. F. and Stein, S., 1994, Effects of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions, Geoph. Res. Lett. 21, 2191–2194.

    Google Scholar 

  21. Dick, H. J. B., Thompson, G. and Bryan, W. B., 1981, Low-angle faulting and steady-state emplacement of plutonic rocks at ridge transform intersections, Am. Geophys. Union Trans. EOS 62, 406.

    Google Scholar 

  22. Dunlop, D. J., 1981, The rock magnetism of fine particles, Phys. Earth Planet. Inter. 26, 1–26.

    Google Scholar 

  23. Dunlop, D. J., 1986a, Hysteresis properties of magnetite and their dependence on particle size: A test of pseudo-single-domain remanence models, J. Geophys. Res. 91, 9569–9584.

    Google Scholar 

  24. Dunlop, D. J., 1986b, Coercive force and coercivity spectra for submicron magnetites, Earth Planet. Sci. Lett. 78, 288–295.

    Google Scholar 

  25. Dunlop, D. J. and Ozdemir, O., 1997, Rock Magnetism: Fundamentals and frontiers, Cambridge University Press, 573 pp.

  26. Fouquet, Y. and Scientific Party, 1997, Cruise report, FLORES cruise, AMORES project of the European MAST III programme Plouzané, IFREMER, DRO/GM.

  27. Francis, T. J. G., 1981, Serpentinization faults and their role in the tectonics of slow-spreading ridges, J. Geophys. Res. 86, 11616–11622.

    Google Scholar 

  28. Gallagher, K. J., Feitknecht, W. and Mannweiler, U., 1968, Mechanism of oxidation of magnetite to ?-Fe2O3, Nature 217, 1118–1121.

    Google Scholar 

  29. German C. R., Parson, L. M. and the HEAT Scientific Team, 1996, Hydrothermal exploration at the Azores Triple Junction: Tectonic control of venting at slow spreading ridges? Earth. Planet. Sci. Lett. 138, 93–104.

    Google Scholar 

  30. German C., Richards K., Rudnicki M. D., Lam M. M., Charlou J. L. and the FLAME Scientific Party, 1998, Topographic control of a dispersing hydrothermal plume, Earth Planet. Sci. Lett. 156, 267–273.

    Google Scholar 

  31. Gracia, E., Charlou, J. L., Radford-Knoery, J. and Parson, L., 2000, Non-transform offsets along the Mid-Atlantic Ridge south of the Azores (38°-34° N): Ultramafic exposures and hosting of hydrothermal vents, Earth Planet. Sci. Lett. 177, 89–103.

    Google Scholar 

  32. Gracia, E., Bideau, D., Hekinian, R., Lagabrielle, Y., Parson, L. M., 1997, Along-axis magmatic oscillations and exposures of ultramafic rocks in a second-order segment of the Mid-Atlantic Ridge (33°43? N to 34°07? N), Geology 25(12), 1059–1062.

    Google Scholar 

  33. Goud, M. R., Karson, J. A., 1985, Tectonics of short-offset. Slow slipping transform zones in the FAMOUS area, Mid-Atlantic Ridge, Marine Geophys. Res. 7, 489–514.

    Google Scholar 

  34. Grommé, C. S., Wright, T. L. and Peck, D. L., 1979, Magnetic properties and oxidation of iron-titanium oxide minerals in Alae and Makaopuhi lava lakes, Hawaii, J. Geophys. Res. 74, 5277–5293.

    Google Scholar 

  35. Honnorez, J., Honnorez-Guerstein, B. M., Worm, H.-U. and Laverne, C., 1996, Correlation among the changes with alteration in mineralogical, chemical, and magnetic properties of upper ocean crust, Hole 896A, Proc. Ocean Drill. Prog. Sci. Res. 148, 171–190.

    Google Scholar 

  36. Horen, H. and Fleutelot, C., 1998, Highly magnetised and differentiated basalts at 18-19 S propagating spreading centre in the North Fiji Basin, Mar. Geophys. Res. 20, 129–137.

    Google Scholar 

  37. Irving, E., 1970, The Mid-Atlantic Ridge at 45 N, XVI. Oxidation and magnetic properties of basalts; review and discussion, Can. J. Earth Sci. 7, 1528–1538.

    Google Scholar 

  38. Jelinek V., 1977, The statistical theory of measuring anisotropy of magnetic susceptibility of rocks and its application, Brno, Geofyzika, 1-88.

  39. Jelinek V., 1981, Characterization of the magnetic fabric of rocks, Tectonophysics 79, 63–67.

    Google Scholar 

  40. Johnson, H. P. and Hall, J. M., 1978, A detailed rock magnetic and opaque mineralogy study of the basalts from the Nazca plate, Geophys. J. R. Astr. Soc. 52, 45–64.

    Google Scholar 

  41. Johnson, H. P. and Pariso, J. E., 1993, Variations in oceanic crustal magnetization: Systematic changes in the last 160 million years, J. Geophys. Res. 98, 435–445.

    Google Scholar 

  42. Karson, J. A., 2000, Internal structure of oceanic lithosphere: A perspective from tectonic windows. In: Faulting and magmatism at Mid-Ocean Ridges. AGU Geophysical Monograph 106, 177–218.

    Google Scholar 

  43. 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.

    Google Scholar 

  44. Kent, D. V. and Gee, J., 1996, Magnetic alteration of zero-age oceanic basalt, Geology 24(8), 703–706.

    Google Scholar 

  45. Klinkhammer, G. P., Chin, C. S. and Wilson, C. 1992, Surveys of FARA section of the Mid-Atlantic Ridge for hydrothermal activity during FAZAR, EOS 74(16), 380.

    Google Scholar 

  46. Lagabrielle, Y., Bideau, D., Cannat, M., Karson, J.A. and Mével, C. 2000, Ultra-mafic plutonic rock suites exposed along the Mid-Atlantic Ridge (10 N-30 N). Symmetrical-assymetrical distribution and implications for the seafloor spreading processes. In: Faulting and magmatism at Mid-Ocean Ridges. AGU Geophys. Monogr. 106, 153–173.

    Google Scholar 

  47. Langmuir, C. H., Fornari, D., Colodner, D., Chalou, J. L., Costa, I., Desbruyères, D., Desonie, D., Emerson, T., Fiala-Medoni, A., Fouquet, Y., Humphris, S., Saldanha, L., Sours-Page, R., Thatcher, M., Tivey, M., Van Dover, C., Von Damm, K., Wiess, K. and Wilson, C., 1993, Geological setting and characteristics of the Lucky Strike vent field at 37°17? N on theMAR, EOS 74, 99.

    Google Scholar 

  48. Marshal, M. and Cox, A., 1972, Magnetic changes in pillow basalt due to sea floor weathering, J. Geophys. Res. 77, 6459–6469.

    Google Scholar 

  49. Needham, H. D., Voisset, M., Renard, V. and Bougault, H., 1992, Structural and Volcanic Features of the Mid-Atlantic Rift Zone Between 40° N and 33 N, EOS, Trans. AGU, Fall Meeting 552 (Abstract).

  50. Nishitani, T. and Kono, M., 1983, Curie temperature and lattice constant of oxidized titanomagnetite, Geophys. J. R. Astr. Soc. 74, 585–600.

    Google Scholar 

  51. O'Reilly, W., 1984, Rock and Mineral Magnetism. Blackie, Glasgow and London & Chapman and Hall, New York, 220 pp.

    Google Scholar 

  52. Ozdemir, O. and O'Reilly, W., 1982, An experimental study of thermoremanent magnetization acquired by synthetic monodomain titanomaghemites, J. Geomag. Geoelec. 34, 467–478.

    Google Scholar 

  53. Ozdemir, O., 1987, Inversion of titanomaghemites, Phys. Earth Planet. Inter. 46, 184–196.

    Google Scholar 

  54. Ozima, M. and Larson, E. E., 1970, Low-and high-temperature oxidation of titanomagentite in relation to irreversible changes in the magnetic properties of submarine basalts, J. Geophys. Res. 75, 1003–1018.

    Google Scholar 

  55. Parson, L., Grácia, E., Coller, D., German, C. and Needham, D., 2000, Second-order segmentation: the relationship between volcanism and tectonism at the MAR, 38°N-35°40? N, Earth Planet. Sci. Lett. 178, 231–251.

    Google Scholar 

  56. Peterson, N., Eisenach, P. and Bleil, U., 1979, Low temperature alteration of the magnetic minerals in ocean floor basalts. Talwani, M., Harrison, C. G. A. and Hayes, D. E. (eds.) Deep Drilling Results in the Atlantic Ocean: Ocean Crust, Maurice Ewing Series., pp. 169–209, AGU, Washington, D.C., Vol. 2.

    Google Scholar 

  57. Readman, P. W. and O'Reilly, W., 1972, Magnetic properties of oxidized (cation-deficient) titanomagnetites, (Fe, Ti,?)O4, J. Geomag. Geoelec. 24, 69–90.

    Google Scholar 

  58. Shau, Y. H., Peacor, D. R. and Essene, E. J., 1993, Formation of Magnetic Single-Domain magnetite in Ocean Ridge basalts with implications for sea-floor magnetism, Science 261, 343–345.

    Google Scholar 

  59. Schmidbauer, E. and Readman, P. W., 1982, Low temperature magnetic properties of Ti-rich Fe-Ti spinels, J. Magn. Magn. Mater. 27, 114–118.

    Google Scholar 

  60. Smith, G. M. and Banerjee, S. K., 1986, Magnetic structure of the upper kilometer of the marine crust at Deep Sea Drilling Project Hole 504B, Eastern Pacific Ocean, J. Geophys. Res. 91(B10), 10337–10354.

    Google Scholar 

  61. Smith, B. M., 1987, Consequences of the maghemitization on the magnetic properties of submarine basalts: Synthesis of previous works and results concerning basement rocks from mainly DSDP legs 51 and 52, Phys. Earth Planet. Inter. 46, 206–226.

    Google Scholar 

  62. Smith-Daignières, B., 1984, Propriétés magnétiques de roches basaltiques provenant de la couche 2 de la croûteocéanique. Effets du degré de cristallisation et de l'altération a basse temperature. PhD thesis, University of Paris VI, France.

    Google Scholar 

  63. Tucker, P. and O'Reilly, W., 1980, The laboratory simulation of deuteric oxidation of titanomagnetites: Effect on magnetic properties and stability of thermoremanence, Phys. Earth Planet. Inter. 23, 112–133.

    Google Scholar 

  64. Tucholke, B. E., Lin, J. and Kleinrock, M. C., 1998, Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge, J. Geophys. Res. 103, 9857–9866.

    Google Scholar 

  65. Tucholke, B. E., Fujioka, K., Ishihara, T., Hirth, G. and Kinoshita, M., 2001, Submersible study of an oceanic megamullion in the Central North Atlantic, J. Geophys. Res. 106, 16145–16161.

    Google Scholar 

  66. Uyeda, S., 1958, Thermo-remanent magmetism as a medium of paleomagnetism, with special reference to reverse thermoremanent magnetism, Jpn. J. Geophys. 2, 1–23.

    Google Scholar 

  67. Xu, W., Peacor, D. R., Dollase, W. A., Van Der Voo, R. and Beaubouf, R., 1997a, Transformation of titanomagnetite to titanomaghemite: A slow, two-step, oxidation-ordering process in MORB, Am. Miner. 82, 1101–1110.

    Google Scholar 

  68. Xu, W., Van Der Voo, R., Peacor, D. R. and Beaubouf, R., 1997b, Alteration of fine-grained magnetite and its effects on the magnetization of the ocean floor, Earth Planet. Sci. Lett. 151, 279–288.

    Google Scholar 

  69. Zhou, W., Van Der Voo, R. and Peacor, D. R., 1997, Single-domain and superparamagnetic titanomagnetite with variable Ti content in young ocean-floor basalts: No evidence for rapid alteration, Earth Planet. Sci. Lett. 150, 353–362.

    Google Scholar 

  70. Zhou, W., Peacor, D. R., Van Der Voo, R. and Mansfield, J., 1999, Determination of lattice parameter, oxidation state, and composition of individual titanomagnetite/titanomaghemite grains by TEM, J. Geophys. Res. 104, 17689–17702.

    Google Scholar 

  71. Zhou,W., Van Der Voo, R., Peacor, D. R. and Zhang, Y., 2000, Variable Ti-content and grain size of titanomagnetite as a function of cooling rate in very young MORB, Earth Planet. Sci. Lett. 179, 9–20.

    Google Scholar 

  72. Zhou, W., Van Der Voo, R., Peacor, D. R., Wang, D. and Zhang, Y., 2001, Low-temperature oxidation in MORB of titanomagnetite to titanomaghemite: A gradual process with implications for marine magnetic anomaly amplitudes, J. Geophys. Res. 106(B4), 6409–6421.

    Google Scholar 

Download references

Author information

Affiliations

Authors

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Miranda, J., Silva, P., Lourenço, N. et al. Study of the Saldanha Massif (MAR, 36°34′ N): Constrains from rock magnetic and geophysical data. Marine Geophysical Researches 23, 299–318 (2002). https://doi.org/10.1023/A:1025711502122

Download citation

  • detachment fault
  • NTO tectonics
  • rock magnetism