A geochemical record of the magmatic activity at Bouvet Island
Sitting atop old oceanic crust of 7 Ma, Bouvet (Lat. 54°26’S, long. 3°24’E) is a solitary, ice-capped and pint sized (55 km2) volcanic island in the Southernmost Atlantic Ocean. It is located off-axis the Southwest Indian Ridge in the vicinity of the triple point joining the African, South American,...
| Published in: | Rendiconti Online della Società Geologica Italiana |
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| Main Authors: | , , , |
| Other Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2014
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| Subjects: | |
| Online Access: | http://hdl.handle.net/11577/3017340 https://doi.org/10.3301/ROL.2014.140 http://www.geoscienze2014.it/ |
| Summary: | Sitting atop old oceanic crust of 7 Ma, Bouvet (Lat. 54°26’S, long. 3°24’E) is a solitary, ice-capped and pint sized (55 km2) volcanic island in the Southernmost Atlantic Ocean. It is located off-axis the Southwest Indian Ridge in the vicinity of the triple point joining the African, South American, and Antarctic plates. As early as the seventies, this island has been regarded as being the surface expression of a mantle plume, which triggered the break-up of the Gondwanaland supercontinent. However, the detailed lower mantle structure of the Bouvet hotspot is largely unknown, because seismic ray coverage of the lowermost mantle under the southwestern Indian Ocean is weak. Surface wave tomography lacks the lateral resolution to image small-scale structures such as hotspots, expected to generate anomalies only a few hundred kilometers wide. The geology of the island is also poorly known because of the presence of a permanent ice cap. Previous studies (e.g. Verwoerd et al., 1990) have established the presence of solely two geological formations: a lower hydrothermally altered sequence of mainly pyroclastic rocks and an upper formation of predominantly subaerial lava flows. This latter unit consists of mainly mildly alkaline basalts, and carries minor amounts of intermediate and acid lavas, ranging in age from 1.39 Ma to < 0.1 Ma. The early magmatic evolution of the island is virtually unknown. The geochemical data presented here are based on a suite of about 25 samples collected from the coastlines of Bouvet Island. The serie extends from basic (mildly alkaline basalts) to intermediate (benmoreites) and acid rocks (rhyolites). None of our samples (MgO < 4.84 wt. %) can be regarded as a primary product of mantle melting. The alkali basalt lavas are chemically homogeneous in spanning a narrow range of major and trace element variability. These lavas all show strong light Rare Earth Element (REE) enrichment typical of ocean island basalts and the overall parallel REE trends show increasing enrichment in all the ... |
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