Temporal and structural evolution of the Early Palæogene rocks of the Seychelles microcontinent

Abstract

The Early Palæogene Silhouette/North Island volcano-plutonic complex was emplaced during the rifting of the Seychelles microcontinent from western India. The complex is thought to have been emplaced during magnetochron C28n. However, the magnetic polarities of the rocks are almost entirely reversed and inconsistent with a normal polarity. In this study we present new in situ zircon U/Pb geochronology of the different intrusive facies of the Silhouette/North Island complex in order to address the timing of emplacement and the apparent magnetic polarity dichotomy. The rocks from Silhouette yielded weighted mean 206Pb/238U ages from 62.4 ± 0.9 Ma to 63.1 ± 0.9 Ma whereas the rocks from North Island yielded slightly younger mean ages between 60.6 ± 0.7 Ma to 61.0 ± 0.8 Ma. The secular latitudinal variation from Silhouette to North Island is consistent with the anticlockwise rotation of the Seychelles microcontinent and the measured polarities. The rocks from Silhouette were emplaced across a polarity cycle (C26r-C27n-C27r) and the rocks from North Island were emplaced entirely within a magnetic reversal (C26r). Moreover, the rocks from North Island and those from the conjugate margin of India are contemporaneous and together mark the culmination of rift-related magmatism.

Mineralogy, geochemistry and40Ar–39Ar geochronology of the Barda and Alech complexes, Saurashtra, northwestern Deccan Traps: early silicic magmas derived by flood basalt fractionation

“…As in many other rifted-margin CFB provinces like the Karoo (Melluso et al 2008), silicic magmatism in the Deccan generally postdates thick flood basalt sequences (e.g. Sheth & Melluso, 2008;Owen-Smith et al 2013;Sheth & Pande, 2014;Shellnutt et al 2017).…”

The Magmatic Architecture of Continental Flood Basalts I: Observations From the Deccan Traps

“…(2017) for discussion of isotopic evidence). The present‐day subaerial volume of the DT lava flows is about 600,000 km 3 (Jay & Widdowson, 2008; Richards et al., 2015) along with a significant volume offshore in the Arabian Sea (G. Bhattacharya & Yatheesh, 2015; Calvès et al., 2011; Fainstein et al., 2019; Gombos Jr et al., 1995; P. Kumar & Chaubey, 2019; D. Pandey et al., 2011), and some small‐volume Deccan‐related intrusions in Seychelles (Devey & Stephens, 1991; Ganerød et al., 2011; T. M. Owen‐Smith et al., 2013; Shellnutt et al., 2017). Estimates of the total pre‐erosional DT lava flow volume range from 1 to 2 × 10 6 km 3 (Colleps et al., 2021; Jay & Widdowson, 2008; G. Sen, 2001; Sukheswala, 1981).…”

“…Pandey et al, 2011), and some small-volume Deccan-related intrusions in Seychelles (Devey & Stephens, 1991;Ganerød et al, 2011;T. M. Owen-Smith et al, 2013;Shellnutt et al, 2017). Estimates of the total pre-erosional DT lava flow volume range from 1 to 2 × 10 6 km 3 (Colleps et al, 2021;G.…”

Crustal Structure and Stratigraphy of the South Mozambique Margin to South Mozambique Ridge From Combined Wide‐Angle and Reflection Seismic and Drill Hole Data

“…This sequence is topped by the thick lower Grudja claystone and Grudja shaly marl. The Early Eocene unconformity corresponds to a stop of accretion in the Mascarene basin at C27, and a ridge jump to initiate seafloor spreading between Seychelles and India at C27 with the arrival of the Reunion hotspot initiating the Deccan Traps of India (66 Ma) and the basalts on the Seychelles micro‐continent (62.4 ± 0.9 Ma, Shellnutt et al., 2017).…”