Crustal structure of the Filchner-Ronne shelf and Coats Land, Antarctica, from gravity and magnetic data: Implications for the breakup of Gondwana

Understanding the tectonic evolution of the Weddell Sea embayment provides valuable insights on the breakup of Gondwana, Existing geodynamic models fo r this region differ mainly in the nature of the crust beneath the Filchner -Ronne shelf and the movement of the Ellsworth-Whitmore Mountains (EWM) cru stal block. New gravity data presented here constrain the area and timing o f this EWM movement from its prebreakup position to its present-day positio n. The crustal thickness estimates of 29 +/- 5 km and 27 +/- 4 km derived f rom power spectral analysis as well as forward gravity modeling make the ex istence of oceanic crust beneath the Filchner-Ronne shelf unlikely. A new c rustal unit consisting of Precambrian crust has been identified with gravit y and magnetic data and extends similar to 175 km off the coast of Coats La nd. This crustal unit conflicts with the late Mesozoic movement of the EWM in this area. The effective elastic thickness of T-e = 35 +/- 5 km has been estimated from coherence spectra for the Ronne shelf. Together with the cr ustal thickness of 27 km from refraction seismic studies and comparison wit h theoretical models, the thermal age is estimated to be between 165 and 23 0 Ma for the Ronne shelf. This age marks the last significant tectonic even t in this area and is in good agreement with the breakup of Gondwana. It fu rther makes later movements of microplates like the EWM in this region unli kely. Thus a Filchner block consisting of continental crust should be consi dered in any geodynamic model of the early Weddell Sea evolution.