Structure of the crust and upper mantle beneath the Bransfield Strait (Antarctica) using P receiver functions

Abstract

The Bransfield Strait is a tectonically active back-arc rift basin located between the South Shetland archipelago (SSI) and the Antarctic Peninsula (AP). We use teleseismic P-wave receiver functions from twelve seismic stations in order to improve the current understanding of the crustal and upper mantle structure of the region. We calculate the thickness and average Vp/Vs ratio of the crust, the thickness of the Mantle Transition Zone (MTZ) and their spatial variability along the study area. Our analysis reveals a homogeneous crustal thickness in the AP, averaging 33.5 ± 1.2 km. The VP/VS ratio increases from east to west, with an average of 1.78 ± 0.04 typical of continental crust. In the SSI results are highly heterogeneous. The minimum crustal thickness is observed in Deception Island (~15 km), near the rift axis, while the crust thickens towards the edges of the basin to ~30 km. High crustal VP/VS ratios (>1.95) in the archipelago correlate with a shallow Moho and may be linked to the presence of melts in the crust, in accordance with the active volcanism in the region. We detected an underplating layer and the Moho of the Phoenix slab beneath the SSI. There is evidence of a low velocity zone (LVZ) in the mantle wedge under the SSI and also under the AP, suggesting there is widespread partial melting of the upper mantle. We infer that the Phoenix slab dips steeply, as we observe a thickened MTZ under the AP.