The Crustal Structure of the Falkland Plateau from Wide-angle Seismic Data

Abstract:

The Falkland Plateau is situated in the South Atlantic Ocean and stretches from the Falkland Islands more than 1500 km eastward to Georgia Basin. The Falkland Plateau Basin is located on the Falkland Plateau between the Falkland Islands in the west and a bathymetric high, the Maurice Ewing Bank, in the east. According to geodynamic models, the Falkland Plateau had a different shape during the Jurassic whereas the Falkland Islands were part of the supercontinent Gondwana.

While the Falkland Islands and Maurice Ewing Bank are proved to be of continental composition, the nature and structure of the crust beneath the Falkland Plateau Basin in between is debatable. The first crustal model derived from sonobuoy data contradicts a recently published 3D-gravity model. To enhance the understanding of Gondwana break-up considering timing, geometry and amount of volcanism, further knowledge about the structure and thickness of the crust is inevitable.

During the ANT-XXIX/5 Polarstern cruise, seismic refraction measurements were conducted using Ocean Bottom Seismometers (OBS) and REF TEK land stations onshore of East Falkland. The OBS were deployed at 78 locations along an approximately 1500 km east-west stretching profile. Based on this data, a P-wave velocity model was calculated using 2D-raytracing techniques.

Beneath the Falkland Plateau Basin the crust exhibits a thickness ranging between 16 km and 22 km and a two-layered velocity structure. The velocity distribution is similar to average oceanic crust with a larger gradient in the upper part and a smaller gradient in the lower part. Lower crustal velocities are up to 7.6 km/s. For Maurice Ewing Bank a different velocity distribution can be observed. The crust is thicker (about 30 km) and velocities do not exceed 7.0 km/s.

Considering crustal thickness and velocity distribution, we interpret the Falkland Plateau with the exception of Maurice Ewing Bank to consist of thickened oceanic crust.