Upper mantle seismic anisotropy beneath Antarctica and the Scotia Sea region

cmueller [ at ] awi-bremerhaven.de


Recent investigations on shear wave splitting from recordings ofpermanent and temporary Antarctic seismological stationsgives new ideas for understanding the upper mantle dynamics ofthe Scotia Sea region and the continental margin in the easternWeddell Sea in terms of their tectonic evolution.Analysis of shear wave splitting from teleseismic core- (SKS,SKKS, PKS), and direct S-waves reveals the seismic anisotropyand the strain field of the upper mantle.Similar to the Carribean, anisotropy structures in the AntarcticPeninsula and Scotia Sea regions are assumed to be influencedby mantle flows in easterly directions around the subductingNazca plate.In general, anisotropy polarization directions in the Scotia Seado not contradict this hypothesis with polarizations orientednearly in E-W directions and therefore align with the suggestedmantle flow patterns.Anisotropy strengths decrease from delay times of delta_t = 1.8 s(PMSA, Palmer Station) in the west towards the east with delaytimes of delta_t = 0.3 s beneath HOPE (South Georgia) and CAND(Candlemas, South Sandwich Islands).Nevertheless, a lithospheric and therefore fossil origin cannotbe ruled out. Only the exceptional high delay times at PMSAlikely originate in parts by recent asthenospheric flows aroundthe subduction slab of the former Phoenix Plate beneath thenorth-western margin of the Antarctic Peninsula.The continental margin of western Dronning Maud and Coats Landplays a crucial role in understanding the early processes duringbreak-up of Gondwana.Upper mantle seismic anisotropy with delay times well overdelta_t = 1 s in this region gives new constraints on ancientdeformation processes during break-up and former episodes.A two-layer modelling reveals Archean anisotropy in the upperlayer corresponding well to polarization directions of the SouthAfrican Kaapvaal Craton.Lower layer anisotropy is supposed to been created during earlyGondwana rifting stages.

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Müller, C. (2001): Upper mantle seismic anisotropy beneath Antarctica and the Scotia Sea region , Geophysical Journal International, Vol. 147, pp. 105-122 .

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