PALEOMAGNETIC AND PETROLOGICAL RECONSTRUCTION OF THE SEYCHELLES

The geology of Mahe-Island and adjoining islets, Seychelles, consists of three types of late Precambrian granitic rock series: (1) a gneisso se granodiorite-gneissose tonalite and amphibolite-leucogranodiorite s eries, (2) a porphyritic granite-pink granite series, and (3) a grey g ranite-gneissose grey granite series. All these granitic rocks are cut by dykes of doleritic compositions, mostly with a WNW-ESE trend. The gneissose granodiorite is a calc-alkaline I-type granite with normativ e Ab >> Or, the porphyritic granite is a sub-alkaline A-type granite w ith normative Ab > Or, and the grey granite is an alkaline A-type gran ite with normative Ab > Or. Rb-Sr radiometric analyses yielded ages of 713 +/- 19 Ma for the gneissose granodiorite, 683 +/- 16 Ma for the p orphyritic granite and 570 +/- 5 Ma for the grey granite. Petrological , geological, geochronological and geochemical studies suggest that th e late Precambrian granitic racks of the Seychelles are very similar t o, and are well correlated with those of the Arabian-Nubian shield. 40 8 late Precambrian granite specimens were collected from the Mahe isla nd group, Seychelles. Progressive alternating field demagnetization an d thermal demagnetization have been successfully performed to isolate stable remanence with well-grouped direction from natural remanent mag netization of the granites. The stable remanences of the granite fall around a northerly mean direction, of which the declination is 348.5 d egrees and the inclination +48.7 degrees. The stable remanences of the Mahe island group granite yield a palaeomagnetic pole at 54.0 degrees N, 38.2 degrees E. From the above data, in conjunction with reported polar wander path and plate rotation poles, it is concluded that the S eychelles were originally located near the eastern end of the Kern of Africa and have drifted to the present position since continental brea k-up.