Neoproterozoic geochronology and palaeogeography of the Seychelles microcontinent: the India link

The geology of the Seychelles Islands in the Indian Ocean is dominated by granitoid rocks and to a lesser extent by basaltic dykes. A U-Pb zircon age from the Takamaka dolerite dyke (Mahe Island) gives an intrusion age of 750.2 +/- 2.5 Ma. The dyke age is considerably older than previous age estimates and suggests that some of the Mahe dolerite dykes are almost coeval with the granitoid rocks. The Mahe: dykes show variable degrees of magnetic overprinting, but the proposed oldest magnetization, component A (Decl. = 001.4 degrees, Incl. = + 49.7 degrees and alpha (95) = 11.2; palaeomagnetic pole: Lat. = 54.8 degreesN and Long. = 057.6 degreesE), is identified as a high unblocking component in most dykes, and compares favorably with palaeomagnetic data from the Mahe granitoids. A new Seychelles-India fit (Euler pole: Lat. = 25.8 degrees, Long. = 330 degrees and rotation angle = 28 degrees) produces a good match of palaeomagnetic poles from ca. 750 Ma magmatic rocks in the Seychelles and NW India (Malani), and places these regions only 600 km apart. Together with Madagascar, this tectonic trio formed an outboard continental terrane of the Rodinia supercontinent during the Neoproterozoic (ca. 750 Ma). The position of the Seychelles at this time marks the incipient formation of a microcontinent because there is no evidence for older continental crust than the 750-755 Ma granitoid rocks. The Seychelles formed at 30 degreesN and most likely as part of an Andean-type are along the western margin of the former Rodinia supercontinent. (C) 2001 Elsevier Science B.V. All rights reserved.