Abstract
Spectral analysis techniques have been applied to data sets of gravity and topography selected across fracture zones with large offset in the Equatorial and Central Atlantic Ocean and processed independently for each fracture zone. Three simple compensation models, two in local isostatic equilibrium (Airy I and II) and one in regional equilibrium (Plate model) have been tested. It is found that the free-air anomalies are primarily controlled by the topography and its isostatic response. For short wavelengths, admittance can be explained either by the effect of uncompensated sea floor topography with high density basement or by the effect of uncompensated sea floor topography with normal oceanic basement density but accompanied by a crust of constant thickness. For intermediate wavelengths, admittance for the Romanche fracture zone agrees best with a local isostatic model in which compensation is achieved by a less dense material in the upper mantle. No such evidence exists for the Vema and Chain fracture zones for which topography could just as well be regionally supported by an elastic plate 3 to 10 km thick. For longer wavelengths, the admittances computed for the three fracture zones are compatible with a thermal compensation of the topography.
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Bonatti, E. and Chermak, A.: 1981, ‘Formally Emerging Blocks in the Equatorial Atlantic’, Tectonophysics 72, 165–180.
Bulot, A., Diament, M., Kogan, M. G., and Dubois, J.: 1984, ‘Isostasy of Aseismic Tectonic Units in the South Atlantic Ocean and Geodynamic Implications’, Earth and Planet. Sci. Lett. 70, 346–354.
Cazenave, A., Lago, B., and Dominh, K.: 1982, ‘Geoid Anomalies over the Northeast Pacific Fracture Zones from Satellite Altimeter Data’, Geophys. J. R. Astron. Soc. 69, 15–31.
Cochran, J. R.: 1973, ‘Gravity and Magnetic Investigations in the Guiana Basin, Western Equatorial Atlantic’, Geol. Soc. Am. Bull. 84, 3249–3268.
Cochran, J. R.: 1979, ‘Analysis of Isostasy in the World's Oceans, 2, Mid-Ocean Ridge crests’, J. Geophys. Res. 84, 4713–4729.
Crough, S. T.: 1979, ‘Geoid Anomalies Across Fracture Zones and the Thickness of the Lithosphere’, Earth and Planet. Sci. Lett. 44, 224–230.
Detrick, R. S.: 1981, ‘An Analysis of Geoid Anomalies Across the Mendocina Fracture Zone: Implications for Thermal Models of the Lithosphere’, J. Geophys. Res. 86, 11751–11762.
Detrick, R. S. and Purdy, G. M.: 1980, ‘The Crustal Structure of the Kane Fracture Zone from Seismic Refraction Studies’, J. Geophys. Res. 85, 3759–3777.
Detrick, R. S., Cormier, M. H., Price, R. A., Forsyth, D. W., and Ambos, E. L.: 1982, ‘Seismic Constraints on the Crustal Structure Within the Vema Fracture Zone’, J. Geophys. Res. 87, 10599–10612.
Diament, M.: 1985, ‘Influence of Method of Data Analysis on Admittance Computation’, Annales Geophysicae 3, 6, 785–792.
Diament, M., Sibuet, J.-C., and Hadaoui, A.: 1986, ‘Isostasy of the Northern Bay of Biscay Continental Margin’, Geophys. J. R. Astron. Soc. (in press).
Dorman, L. M. and Lewis, B. T. R.: 1970, ‘Experimental Isostasy 1. Theory of the Determination of the Earth's Isostatic Response to a Concentrated Load’, H. Geophys. Res. 75, 3357–3365.
Forsyth, D. W.: 1985, ‘Subsurface Loading and Estimates of the Flexural Rigidity of Continental Lithosphere’, J. Geophys. Res. 90, B14, 12623–12632.
Karner, G. D. and Watts, A. B.: 1982, ‘On Isostasy at Atlantic-Type Continental Margins’, J. Geophys. Res. 87, 2923–2948.
Kogan, M. G. and Kostoglodov, V. V.: 1981, ‘Isostasy of Fracture Zones in the Atlantic Ocean’, J. Geophys. Res. 86, 9248–9258.
Le Pichon, X. and Hayes, D. E.: 1971, ‘Marginal Offsets Fracture Zones and the Early Opening of the South Atlantic’, J. Geophys. Res. 76, 6283–6296.
Louden, K. E.: 1981, ‘A Comparison of the Isostatic Response of Bathymetric Features in the North Pacific and Philippine Sea’, Geophys. J. R. Astron. Soc. 64, 393–424.
Louden, K. E. and Forsyth, D. W.: 1976, ‘Thermal Conduction Across Fracture Zones and the Gravitational Edge Effect, J. Geophys. Res. 81, 4869–4874.
Louden, K. E. and Forsyth, D. W.: 1982, ‘Crustal Structure and Isostatic Compensation near the Kane Fracture Zone from Topography and Gravity Measurements: Part I: Spectral Analysis Approach’, Geophys. J. R. Astron. Soc. 68, 725–750.
McKenzie, D. P. and Bowin, C.: 1976, ‘The Relationship Between Bathymetry and Gravity in the Atlantic Ocean’, J. Geophys. Res. 81, 1903–1915.
McNutt, M.: 1979, ‘Compensation of Oceanic Topography: An Application of the Response Function Technique to the SURVEYOR Area’, J. Geophys. Res. 84, 7589–7598.
McNutt, M.: 1983, ‘Influence of Plate Subduction on Isostatic Compensation in Northern California’, Tectonics 2, 399–415.
Mulder, Th. F. A. and Collette, B. J.: 1984, ‘Gravity Anomalies over Inactive Fracture Zones in the Central North Atlantic’, Mar. Geophys. Res. 6, 383–394.
Parker, R. L.: 1972, ‘The Rapid Calculation of Potential Anomalies’, Geophys. J. R. Astron. Soc. 31, 447–455.
Parker, R. L. and McNutt, M. K.: 1980, ‘Statistics for the One-Norm Misfit Measure’, J. Geophys. Res. 85, 4429–4430.
Robb, J. M. and Kane, M. F.: 1975, ‘Structure of the Vema Fracture Zone from Gravity and Magnetic Intensity Profiles’, J. Geophys. Res. 80, 4441–4445.
Sandwell, D. T.: 1982, ‘Thermal Isostasy: Response of a Moving Lithosphere to a Distributed Heat Source’, J. Geophys. Res. 87, 1001–1014.
Sandwell, D. T. and Schubert, G.: 1982a, ‘Geoïd Height-age Relation from Seasat Altimeter Profiles Across the Mendocino Fracture Zone’, J. Geophys. Res. 87, 3949–3958.
Sandwell, D. T. and Schubert, G.: 1982b, ‘Lithospheric Flexure at Fracture Zones’, J. Geophys. Res. 87, 4657–4667.
Sclater, J. G. and Francheteau, J.: 1970, ‘The Implications of Terrestrial Heat Flow Observations on Current Tectonic and Geochemical Models of the Crust and Upper Mantle of the Earth’, Geophys. J. R. Astron. Soc. 20, 509–542.
Sibuet, J. C., Le Pichon, X., and Goslin, J.: 1974, ‘Thickness of Lithosphere Deduced from Gravity Edge Effects Across the Mendocino Fault’, Nature 252 (5485), 676–679.
Sibuet, J. C. and Mascle, J.: 1978, ‘Plate Kinematic Implications of Atlantic Equatorial Fracture Zone Trends’, J. Geophys. Res. 83, 3401–3421.
Sibuet, J. C. and Veyrat-Peiney, B.: 1980, ‘Gravimetric Model of the Atlantic Equatorial Fracture Zones’, J. Geophys. Res. 85, 943–954.
Sinha, M. C. and Louden, K. E.: 1983, ‘The Oceanographer Fracture Zone. I. Crustal Structure from Seismic Refraction Studies’, Geophys. J. R. Astron. Soc. 75, 713–736.
Van Andel, T. H., von Herzen, R. P., and Philips, J. D.: 1971, ‘The Vema Fracture Zone and the Tectonics of Transverse Shear Zones in Oceanic Crustal Plates’, Mar. Geophys. Res. 1, 261–283.
Watts, A. B.: 1978, ‘An Analysis of Isostasy in the World's Ocean, 1, Hawaian-Emperor Seamount Chain’, J. Geophys. Res. 83, 5989–6004.
White, R. S. and Matthews, D. H.: 1980, ‘Variations in Oceanic Upper Crustal Structure in a Small Area of the Northeastern Atlantic’, Geophys. J. R. Astron. Soc. 61, 401–435.
White, R. S., Detrick, R. S., Sinha, M. C., and Cormier, M. H.: 1984, ‘Anomalous Seismic Crustal Structure of Oceanic Fracture Zones’, Geophys. J. R. Astron. Soc. 79, 779–798.
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Diament, M., Sibuet, JC. & Dubois, J. Isostatic response of the large-offset Atlantic Equatorial fracture zones. Mar Geophys Res 8, 243–264 (1986). https://doi.org/10.1007/BF00305485
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DOI: https://doi.org/10.1007/BF00305485