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

The geology of the Seychelles Islands in the Indian Ocean is dominated by g ranitoid 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 estimat es and suggests that some of the Mahe dolerite dykes are almost coeval with the granitoid rocks. The Mahe: dykes show variable degrees of magnetic ove rprinting, but the proposed oldest magnetization, component A (Decl. = 001. 4 degrees, Incl. = + 49.7 degrees and alpha (95) = 11.2; palaeomagnetic pol e: Lat. = 54.8 degreesN and Long. = 057.6 degreesE), is identified as a hig h unblocking component in most dykes, and compares favorably with palaeomag netic 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 roc ks in the Seychelles and NW India (Malani), and places these regions only 6 00 km apart. Together with Madagascar, this tectonic trio formed an outboar d continental terrane of the Rodinia supercontinent during the Neoproterozo ic (ca. 750 Ma). The position of the Seychelles at this time marks the inci pient formation of a microcontinent because there is no evidence for older continental crust than the 750-755 Ma granitoid rocks. The Seychelles forme d at 30 degreesN and most likely as part of an Andean-type are along the we stern margin of the former Rodinia supercontinent. (C) 2001 Elsevier Scienc e B.V. All rights reserved.