AGES AND GEOLOGICAL SIGNIFICANCE OF THE IGNEOUS ROCKS FROM SEYCHELLES

Isotopic age dating of igneous rocks from the Seychelles and its related Gondwana fragments reveals seven major igneous events related to four phases of rifting during the fragmentation of Gondwana. Two phases of rift-related Late Precambrian granitic magmatism occurred on Mahe between similar to 710-680 Ma, followed by the Praslin/La Digue/Felicite granites at similar to 665 Ma, then by basic dykes, which intruded these granites at similar to 620 Ma. The Early Jurassic (similar to 190 Ma) layers of devitrified ash can be correlated with the Karoo flood-basalt volcanism and its equivalents. Five important igneous events are recorded in the Cretaceous/Tertiary: i) similar to 135 Ma: basic dykes temporally equivalent to the Marion hotspot-related Lebombo and Movene volcanics of South Africa and Mozambique. ii) similar to 124-113 Ma: igneous interbeds possibly correlative of the postulated volcanic development of the Saya de Mahla from the Marion hotspot iii) similar to 82-?65 Ma: tholeiitic basalts representing the formation of the Amirante ridge complex iv) similar to 70-60 Ma: representing the Deccan event and divisible into pre-Deccan tholeiitic (similar to 70-68 Ma), main Deccan basic (similar to 68-63 Ma) and post-Deccan acidic magmatism(similar to 63-60 Ma) v) similar to 47 Ma: basalts extruded when the drift of Seychelles/Mascarene coincided with the Deccan-Reunion hotspot at Saya de Mahla. Acid volcanics from the northeast coast of Madagascar, and offshore the Indian west coast are related to the beginning (similar to 96 Ma) and end (similar to 84 Ma) of rifting between Seychelles/India and Madagascar.