Insight into the shallow lithosphere structure and magmatic plumbing system beneath the Tristan da Cunha hot spot from geophysical and petrological studies


Contact
Wolfram.Geissler [ at ] awi.de

Abstract

According to classical plume theory, the Tristan da Cunha plume is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge by impinging at the base of the continental lithosphere shortly before or during the breakup of the South Atlantic margins. However, Tristan da Cunha is enigmatic as it cannot be clearly identified as a deep-rooted hot spot, but may instead be related to a more shallow feature in the mantle that could actually have been caused by the opening of the South Atlantic. The equivocal character of Tristan da Cunha is largely due to a lack of geophysical and petrological data in this region. We therefore staged a multi-disciplinary geophysical study of the region by acquiring passive marine electromagnetic and seismic data, and bathymetric data within the framework of the SPP1375 South Atlantic Margin Processes and Links with onshore Evolution (SAMPLE) funded by the German Science foundation. The experiment included two expeditions onboard the German R/V MARIA S. MERIAN in 2012 and 2013. In addition to the geophysical work, a landing party collected samples for petrological studies. In our contribution we present first results on the shallow lithosphere structure beneath the Tristan da Cunha archipelago derived from geophysical studies. These results are combined with results from thermobarometric analyses of basanitic/ankaramitic rocks that represent the main rock type on the island. The more evolved products of the eruption in 1962, (trachyandesites), were also studied to include the full range of magma compositions. Clinopyroxene-melt thermobarometry yielded crystallization pressures between 4 and 14 kbar, corresponding to depths of 12-42 km, whereby the youngest and most evolved rocks erupted from the shallowest depth. Olivine-, clinopyroxene-, and plagioclase-melt thermometry yielded magmatic temperatures of 1100° - 1320°C. The Moho below the archipelago is at approximately 11-12 km depth based on the receiver function method at two island stations and ocean-bottom seismometers. Therefore the petrologic depth estimates demonstrate that magmas erupted from a plumbing system in the uppermost mantle.



Item Type
Conference (Talk)
Authors
Divisions
Primary Division
Programs
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Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
2nd European Mantle Workshop, 25 Aug 2015 - 28 Aug 2015, Wroclaw, Poland.
Eprint ID
39436
Cite as
Geissler, W. , Weit, A. , Jegen, M. , Jokat, W. , Trumbull, R. , Chen, J. , Pandey, S. , Ryberg, T. and Schlömer, A. (2015): Insight into the shallow lithosphere structure and magmatic plumbing system beneath the Tristan da Cunha hot spot from geophysical and petrological studies , 2nd European Mantle Workshop, Wroclaw, Poland, 25 August 2015 - 28 August 2015 .


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