Evidence of Middle Jurassic magmatism within the Seychelles microcontinent: Implications for the breakup of Gondwana

Abstract

The breakup of East and West Gondwana occurred during the Jurassic, but the exact timing is uncertain due to the limited exposure of rocks suitable for radioisotopic dating. Trachytic rocks from Silhouette Island, Seychelles, yielded a range of zircon ages from Paleoproterozoic to Cenozoic. The 206Pb/238U age of the trachyte is 64.9 ± 1.6 Ma (Danian) but the majority of zircons yielded an age of 163.8 ± 1.8 Ma (Callovian) with a small subset yielding an age of 147.7 ± 4.5 Ma (Tithonian). The Hf isotopes of the Callovian (εHf(t) = +4.1 to +13.4) and Danian (εHf(t) = +1.9 to +7.1) zircons indicate that they were derived from moderately depleted mantle sources whereas the Tithonian zircons (εHf(t) = −7.0 to −7.3) were derived from an enriched source. The identification of middle Jurassic zircons indicates that rifting and magmatism were likely contemporaneous during the initial separation of East and West Gondwana.

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

“…The results from this study are within the range of previously reported ages of the Silhouette/North Island complex 1 , 2 , 14 , 23 . However, we are able to identify a distinct spatial-temporal progression from Silhouette to North Island.…”

“…Ramasse) likely formed the initial volcanic-hypabyssal complex during the early stages (~63 Ma). The only rocks from Silhouette that were found to contain inherited zircons are located in the eastern part of the island where the microgranite and fayalite-absent syenite were collected 23 . Based on the abundance of xenoliths and micro-xenoliths within the trachytic rocks from eastern Silhouette, it is likely that they erupted violently thereby brecciating the country rocks and allowing them to be incorporated into the tuff.…”

“…( a ) Regional topography of the western Indian Ocean and eastern Africa constructed via Generic Mapping Tools (GMT 4.5.14 http://gmt.soest.hawaii.edu/gmt4/ ) from Global Relief Model data of ETOPO1, https://www.ngdc.noaa.gov/mgg/global/relief/ETOPO1/data/18 . M = Madagascar. ( b ) Geological map of the Main Islands of the Seychelles 23 . ( c ) Simplified geological map of Silhouette and the sampling localities for this study 23 .…”

“…M = Madagascar. ( b ) Geological map of the Main Islands of the Seychelles 23 . ( c ) Simplified geological map of Silhouette and the sampling localities for this study 23 . ( d ) Simplified geological map of North Island and the sampling localities for this study 23 .…”

Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius

“…Younger zircons (∼330 and ∼1,600 Ma) have previously been described from Mid-Atlantic Ridge gabbros 36 , and Proterozoic (∼1,800 Ma) 37 and Mesozoic zircons (126–242 Ma) 38 have been found in young Icelandic basalts. Proterozoic zircons (2,430, 1,279, 807 Ma) were recovered in an early Paleogene (64.9 Ma) trachyte from Silhouette Island, Seychelles 39 , a result that is relevant to our work because it further improves our understanding of the nature and distribution of Precambrian continental fragments in the Indian Ocean. We propose that Mauritius and other potential Mauritian continental fragments, collectively named Mauritia 2 ( Fig.…”