|
Olav Antonio Blaich, University of Oslo (Norway)
Filippos Tsikalas, University of Oslo, Now at: ENI Norge AS (Norway)
Jan Inge Faleide, University of Oslo (Norway)
Enric León, Concedo ASA (Norway)
Rune Sakariassen, PGS (Norway)
|
|
In one of their pioneer papers, Talwani and Eldholm (1973; Nature, v. 241, p. 325-330) were able to reveal several important features at the boundary between continental and oceanic crust at rifted-sheared continental margins and to develop several concepts of the expression of these margins worldwide. The work was based on integration of seismic reflection, refraction and potential field data from the continental margins off Norway and South Africa and provides, since then, a methodology and conceptual framework for the study of frontier continental margins.
In this study, integration of regional seismic reflection and potential field data, complemented by crustal-scale gravity modelling, are used along the northeastern Brazilian, and the conjugate Argentine-Namibia margins, to reveal and illustrate onshore-offshore crustal structure correlations, the character of the continent-ocean boundary/transition, and the relationship of crustal structure to regional variations of potential field anomalies. Several crustal transects are constructed at the investigated margins. The study reveals distinct along-margin structural and magmatic changes that are spatially related to a number of conjugate South America-West Africa transfer systems, governing the margin segmentation and evolution and clearly implying structural inheritance. Several conceptual tectonic models are invoked to explain the structural evolution of the different margin segments in a conjugate margin context and within the framework of simple-shear, pure-shear and combined-shear deformation modes. In particular, the constructed transects and the available seismic reflection profiles indicate prominent along-margin variations in rift-width, crustal thinning and breakup-related magmatic activity both in between and within individual segments. This may imply that several rift systems reflect a polyphase deformation rifting-mode associated with a complex time-dependent thermal structure of the lithosphere, giving rise to a complex rifted volcanic versus non-volcanic margin affinity and character at individual margin segments. The study clearly shows that integration of potential field and regional deep vertical-incidence and wide-angle seismic data provides a valuable synergy and a powerful resource for reducing costs and interpretation risks when petroleum exploration advances towards new frontiers.
|
