Physics
Scientific paper
Jun 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976e%26psl..31..101m&link_type=abstract
Earth and Planetary Science Letters, Volume 31, Issue 1, p. 101-112.
Physics
9
Scientific paper
Palaeomagnetic results are reported from the predominantly green sediments of the Upper Permian to Lower Triassic Sakamena Group and the Upper Carboniferous to Lower Permian Sakoa Group of Madagascar. Secondary magnetizations could only be removed successfully through thermal demagnetization procedures and then only if the cleaning process was completed by 450°C. Heating in air caused extensive magnetochemical changes to occur above this temperature. Coercivity spectrum analysis and low-temperature characteristics of the heated and unheated green sediments indicate that considerable amounts of fine-grained single-domain magnetite are formed at 500°C or more from some non-magnetic mineral, probably the iron silicates. For this reason consistent palaeomagnetic data could only be obtained from about half the samples collected. Results from 4 sites (19 samples) of the Lower Sakamena Group give a palaeomagnetic pole at 64.9S, 113.9E (A95 = 5.6°) and 3 sites (16 samples) from the Glacial Series of the Sakoa Group give a pole at 47.9S, 84.1E (A95 = 8.1°). When compared with corresponding data from Africa these results confirm and strengthen our previous conclusions from the Triassic-Jurassic Isalo Group regarding the palaeoposition of Madagascar. All three poles are only consistent with the Smith and Hallam reconstruction which places Madagascar off the eastern coast of Africa adjacent to Kenya and Tanzania. Now at: Division of Mineral Physics, C.S.I.R.O. Minerals Research Laboratories, P.O. Box 136, North Ryde, N.S.W. 2113, Australia.
Embleton Brian J. J.
McElhinny Michael W.
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