Ages and geological significance of the igneous rocks from Seychelles

Abstract

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 Mahé between ∼710-680 Ma, followed by the Praslin/La Digue/Félicité granites at ∼665 Ma, then by basic dykes, which intruded these granites at ∼620 Ma. The Early Jurassic (∼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:- 1. i ∼135 Ma: basic dykes temporally equivalent to the Marion hotspot-related Lebombo and Movene volcanics of South Africa and Mozambique. 2. ii) ∼124-113 Ma: igneous interbeds possibly correlative of the postulated volcanic development of the Saya de Mahla from the Marion hotspot 3. iii) ∼82–?65 Ma: tholeiitic basalts representing the formation of the Amirante ridge complex 4. iv) ∼70-60 Ma: representing the Deccan event and divisible into pre-Deccan tholeiitic (∼70-68 Ma), main Deccan basic (∼68-63 Ma) and post-Deccan acidic magmatism(∼63-60 Ma) 5. v) ∼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 (∼96 Ma) and end (∼84 Ma) of rifting between Seychelles/ India and Madagascar.