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| Titel |
Structure of the lithosphere-asthenosphere system in the vicinity of the Tristan da Cunha hot spot as seen by surface waves |
| VerfasserIn |
Raffaele Bonadio, Wolfram H. Geissler, Matteo Ravenna, Sergei Lebedev, Nicolas L. Celli, Wilfried Jokat, Marion Jegen, Christoph Sens-Schönfelder, Kiyoshi Baba |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151763
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| Publikation (Nr.) |
 EGU/EGU2017-16520.pdf |
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| Zusammenfassung |
| Tristan da Cunha is a volcanic island located above a hotspot in the South Atlantic. The deep
mantle plume origin of the hotspot volcanism at the island is supported by anomalous
geochemical data (Rohde et al., 2013 [1]) and global seismological evidences (French and
Romanovicz, 2015 [2]). However, until recently, due to lack of local geophysical
data in the South Atlantic and especially around Tristan da Cunha, the existence of
a plume has not yet been confirmed. Therefore, an Ocean Bottom Seismometer
experiment was carried out in 2012 and 2013 in the vicinity of the archipelago, with
the aim of obtaining geophysical data that may help to get some more detailed
insights into the structure of the upper mantle, possibly confirming the existence of a
plume.
In this work we study the shear wave velocity structure of the lithosphere-asthenosphere
system beneath the Island. Rayleigh surface wave phase velocity dispersion curves have been
obtained using a recent powerful implementation of the inter-station cross-correlation method
(Meier et al., 2004 [3]; Soomro et al., 2016 [4]). The measured dispersion curves are used to
invert for the 1D shear wave velocity structure beneath the study area and to obtain phase
velocity tomographic maps.
Our results show a pronounced low shear wave velocity anomaly between 70 and 120 km
depth beneath the area; the lid shows high velocity, suggesting a cold, depleted and
dehydrated shallow lithosphere, while the deeper lithosphere shows a velocity structure
similar to young or rejuvenated Pacific oceanic lithosphere (Laske et al., 2011 [5]; Goes et
al., 2012 [6]). Below the base of the lithosphere, shear wave velocities appear to be low,
suggesting thermal effects and partial melting (as confirmed by petrological data). Decreasing
velocities within the lithosphere south-westward reflect probably a thermal imprint of an
underlying mantle plume.
References
[1] J.K. Rohde, P. van den Bogaard, K. Hoernle, F. Hauff, R. Werner, Evidence for
an age progression along the Tristan-Gough volcanic track from new 40Ar∕ 39Ar
ages on phenocryst phases, Tectonophysics, Volume 604, p. 60-71 (2013).
[2] S. French and B. Romanowicz, Broad plumes rooted at the base of the Earth’s
mantle beneath major hotspots, Nature, 525(7567), 95–99 (2015).
[3] T. Meier, K. Dietrich, B. Stockhert and H. Harjes, One-dimensional models
of shear wave velocity for the eastern Mediterranean obtained from the inversion
of Rayleigh wave phase velocities and tectonic implications, Earth and Planetary
Science Letters, 249(3), 415–424 (2004).
[4] R.A. Soomro, C. Weidle, L. Cristiano, S. Lebedev, T. Meier and PASSEQ
Working Group, Phase velocities of Rayleigh and Love waves in central
and northern Europe from automated, broad-band, interstation measurements,
Geophys. J. Int. (2016) 204, 517–534.
[5] G. Laske, A. Markee, J.A. Orcutt, C.J. Wolfe, J.A. Collins and S.C. Solomon,
R.S. Detrick, D. Bercovici and E.H. Hauri, Asymmetric shallow mantle structure
beneath the Hawaiian Swell–evidence from Rayleigh waves recorded by the
PLUME network, Geophys. J. Int. (2011) 187, 1725–1742.
[6] S. Goes, J. Armitage, N. Harmon, H. Smith and R. Huismans, Low seismic
velocities below mid-ocean ridges: Attenuation versus melt retention, Journal of
geophysical research, Vol. 117, B12403, (2012). |
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