Rockmagnetism and palaeomagnetism of an Early Cretaceous/Late Jurassic dike swarm in Rio Grande do Norte, Brazil

Main Article Content

C. Bucker
A. Schult
W. Bloch
S.D.C. Guerreiro


Ten sites from a dike swarm of early Cretaceous/Late Jurassic age in northeast Brazil (5.7°S, 36.6°W) yielded a pole at 80.6°N, 95°E with A95 = 9.5°, K = 26.7 after AF cleaning. Rock-magnetic investigations and chemical analyses revealed titanomagnetites and maghemites, both with low titanium content showing ilmenite exsolution lamellae (oxidation class III). These are due to an internal high-temperature oxidation during cooling of the large dikes, follwed by low-temperature oxidation and/or hydrothermal alterations. There is evidence that with low-temperature oxidation the Ti-to-Fe ratio increases, a finding that is consistent with previous studies. Hysteresis parameters and susceptibility versus temperature curves can be interpreted in terms of pseudosingle-domain behavior with a trend toward multidomain behavior in accordance with moderate-to-weak stability of the remanence.

Google Scholar           ARK:



Article Details

How to Cite
Bucker, C., Schult, A., Bloch, W., & Guerreiro, S. (1986). Rockmagnetism and palaeomagnetism of an Early Cretaceous/Late Jurassic dike swarm in Rio Grande do Norte, Brazil. Journal of Geophysics, 60(1), 129-135. Retrieved from


Ade-Hall, J.M., Palmer, H.C., Hubbard, T.P. (1971) The magnetic and opaque petrological response of basalts to regional hydrothermal alteration. Geophys. J. R. Astron. Soc 24:137-174

Bleil, U., Petersen, N. (1982) Magnetic properties of natural minerals. In: Landolt-Bornstein, New Series, Group V, Vol. 1 b, G. Angenheister ed.: pp. 308-365. Heidelberg, Springer, New York

Buddington, A.F., Lindsley, D.H. (1964) Iron-titanium oxide minerals and synthetic equivalents. J. Petrol. 5:310-357

Collinson, D.W., Creer, D.M., Runcorn, S.K. (1967) Methods in paleomagnetism. Amsterdam: Elsevier

Day, R., Fuller, M., Schmidt, V.A. (1977) Hysteresis properties oftitanomagnetites: grain-size and compositional dependence. Phys. Earth Planet. Interiors 13:260-267

Dunlop, D.J. (1974) Thermal enhancement of magnetic susceptibility. J. Geophys. 40:439-451

Furuta, T., Otsuki, M., Akimoto, T. (1985) Quantitative electron probe microanalysis of oxygen in titanomagnetites with implications for oxidation process. J. Geophys. Res. 90:3145-3150

Guerreiro, S.D.C., Schult, A. (1983) Palaeomagnetismo de um enxame de diques toleiticos de idade meso-cenozoica, localizados no Rio Grande do Norte. Rev. Bras. Geofis 1:89-98

Guerreiro, S.D.C., Schult, A. (1986) Palaeomagnetism of Jurassic tholeiitic intrusions in the Amazon Basin. Veroffentlichung des Geophysikalischen Observatoriums Furstenfeldbruck, Munchner Universitatsschriften, Serie B, Nr. 10:61-72

Mapa Geologico do Brazil (1981) Ministerio das Minas e Energia, DNPM

Marshall, M., Cox, A. (1972) Magnetic changes in pillow basalt due to sea floor weathering. J. Geophys. Res. 77:6459-6469

Petersen, N., Eisenach, P., Bleil, U. (1979) Low temperature alteration of the magnetic minerals in ocean floor basalts. In: Talwani, M., Harrison, C.G., Hayes, D.E. (Eds.) Maurice Ewing Series 2,
pp. 169-209. American Geophysical Union

Readman, P.W., O'Reilly, W. (1972) Magnetic properties of oxidized (cation-deficient) titanomagnetites (Fe, Ti)3O4. J. Geomagn. Geoelectr. 24:69-90

Schult, A., Guerreiro, S.D.C. (1979) Palaeomagnetism of Mesozoic igneous rocks from the Maranhao Basin, Brazil and the time of opening the South Atlantic. Earth Planet. Sci. Lett. 42:427-436

Schult, A., Guerreiro, S.D.C. (1980) Palaeomagnetism of Upper Cretaceous volcanic rocks from Cabo de Sto. Agostinho, Brazil. Earth Planet. Sci. Lett. 50:311-315

Schult, A., Hussain, A.G., Soffel, H.C. (1981) Palaeomagnetism of Upper Cretaceous volcanics and Nubian sondstones of Wadi Natash, SE Egypt and implications for the polar wander path for Africa in the Mesozoic. J. Geophys. 50:16-22

Sial, A.N. (1974) Petrology and tectonic significance of the post-Palaeozoic basaltic rocks of northeast Brazil. Ph.D. Thesis, University of Columbia, 403 pp.

Sial, A.N. (1976) The post-Palaeozoic volcanism of northeast Brasil and its tectonic significance. Ann. Acad. Bras. Cienc. [Suppl], 48:299-311

Wilson, R.W., Watkins, N.D. (1967) Correlation of petrology and natural magnetic polarity in Columbia Plateau basalts. Geophys. J. R. Astron. Soc. 12:405-424