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

• Main Author: Parera Portell, Joan Antoni
• Other Authors: Mancilla Pérez, Flor de Lis, Morales Soto, José, Universidad de Granada. Departamento de Física Teórica y del Cosmos, Universidad de Granada. Instituto Andaluz de Geofísica
• Format: Master Thesis
• Language: English
• Published: 2019
• Subjects: Antarctic; The Antarctic; Antarctic Peninsula; South Shetland Islands; Bransfield Strait; Antarctic Ocean; Deception Island; South Shetland Trench; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10481/57464; https://doi.org/10.30827/Digibug.57464

The Bransfield Strait is a tectonically active region of the Antarctic Ocean comprising the waters located between the South Shetland archipelago and the Antarctic Peninsula. Nowadays the Bransfield region is characterised by the presence of an incipient oceanic spreading ridge possibly driven by ongoing subduction or slab rollback in the South Shetland Trench, to the northwest of the archipelago. A set of twelve seismic stations located in the region provide records of teleseismic earthquakes which allow the study of the deep earth structure, which is thought to be heterogeneous due to the complex tectonics. Here, we use those teleseismic events to obtain P-wave receiver functions in order to infer the structure and spatial variability of the main discontinuities in the crust and upper mantle, including the depth of the Mohorovičić (Moho) discontinuity, the crustal average VP=VS ratio, and the thickness of the Mantle Transition Zone. Results indicate that the structure below the South Shetland Islands is laterally heterogeneous: crustal thickness reaches its minimum in Deception Island (15 km) and grows up to 30-32 km near the southwestern and northeastern ends of the archipelago. In contrast, crustal thickness in the Antarctic Peninsula is similar under all the stations with values between 33-35 km. Average VP=VS ratios display a similar variation than crustal thickness, being more variable in the South Shetland archipelago (1.69-2.19) than in the Antarctic Peninsula (1.68-1.82). A negative correlation between crustal thickness and average VP=VS has also been observed, with high VP=VS clustered around the thinnest crust at the centre of the rift basin, possibly indicating the presence of melts in accordance with the active volcanism in the area. Receiver functions in the South Shetland Islands hint the presence of at least another three seismic interfaces below the Moho, which are interpreted to represent magmatic underplating, a negative gradient-like discontinuity possible related with the mantle wedge, and ...