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Crustal Structure of the Northeastern Brazilian Margin Constrained by Seismic Reflection and Potential Field Data and Modeling*

Olav A. Blaich², Filippos Tsikalas¹, and Jan Inge Faleide²

Search and Discovery Article #30060 (2008)

Posted October 25, 2008

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008

¹ENI Norge AS, Stavanger, Norway ([email protected])

²Department of Geosciences, University of Oslo, Oslo, Norway

Abstract

Integration of regional seismic reflection and potential field data along the northeastern Brazilian margin, complemented by crustal-scale gravity modeling, is used 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 variation of potential field anomalies. The study reveals distinct along-margin structural and magmatic changes that are spatially related to a number of conjugate Brazil-West Africa transfer systems, governing the margin segmentation and evolution. 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. Furthermore, the constructed transects, the observed and modeled Moho relief, and the potential field anomalies indicate that the Recôncavo, Tucano, and Jatobá rift system may reflect a polyphase deformation rifting-mode associated with a complex time-dependent thermal structure of the lithosphere. The constructed transects and the available seismic reflection profiles indicate that the northern part of the study area lacks major breakup-related magmatic activity, suggesting a rifted non-volcanic margin affinity. On the other hand, the southern part of the study area is characterized by abrupt crustal thinning and evidence for breakup magmatic activity, suggesting that this region evolved, partially, with a rifted volcanic margin affinity and character. The study clearly shows that integration of potential field and regional deep vertical-incidence and wide-angle seismic data provides a powerful resource for reducing costs and interpretation risks when petroleum exploration advances towards new frontiers.

Selected Figures

¨ Abstract
¨ Figures
¨ Conclusions
¨ References

			Free-air gravity anomalies (Sandwell and Smith, 1997).
			Transect construction—SP-1, SP-2, and SP-3.
			Transect construction—SP-4 and SP-5.
			Forward gravity modeling.
			Conjugate margin setting.

Conclusions

Integration of seismic reflection and potential field data and modeling provides a reliable means of studying the NE Brazilian tectono-magmatic margin evolution, onshore-offshore structural correlations, continent-ocean boundary/transition location and character, and margin segmentation.

· powerful resource for reducing costs and interpretation risks when petroleum exploration advances towards new frontiers.

Prominent conjugate transfer systems appear to be first-order structural elements, governing margin segmentation and evolution.

It seems that the development of the Mesozoic rifting and breakup was strongly influenced by a pattern of structural inheritance from older structural features.

The evolution of the Recôncavo, Tucano, and Jatobá rift system may reflect a polyphase rifting evolution mode (pure-shear initially, and simple-shear at later stages) which is associated with a complex time-dependent thermal structure of the thinning lithosphere.

References

Karner, G.D., and N.W. Driscoll, 1999, Tectonic and stratigraphic development of the West African and eastern Brazilian margins; insights from quantitative basin modeling: in The Oil and Gas Habitats of the South Atlantic; GS (London) Special Publication 153, p. 11-40.

Milani, E.J., and I. Davison, 1988, Basement control and transfer tectonics in the Reconcavo-Tucano-Jatoba Rift, northeast Brazil: Tectonophysics, v. 154/1-2, p. 41-70.

Mohriak, W.U., M.R. Mello, M. Bassetto, I.S. Vieira, and E.A.M. Koutsoukos, 2000, Crustal architecture, sedimentation, and petroleum systems in the Sergipe-Alagoas Basin, northeastern Brazil: in Petroleum Systems of South Atlantic Margins, AAPG Memoir 73, p. 273-300.

Rosendahl, B.R., W.U. Mohriak, M.E. Odegard, J.P. Turner, and W.G. Dickson, 2005, West African and Brazilian conjugate margins; crustal types, architecture, and plate configurations: in Petroleum Systems of Divergent Continental Margin Basins: SEPM/Gulf Coast Section Program and Abstracts Research Conference, v. 25, p. 13-14.

Speziale, S., P. Censi, C.P. Comin, E. Ruberti, and C.B. Gomes, 1997, Oxygen and carbon isotopes in the Barra do Itapirapua and Mato Preto carbonatites (southern Brazil): Mineralogica et Petrographica Acta, v. 40, p. 137-157.

Sandwell, D.T., and W.H.F. Smith, 1997, Marine gravity anomaly from Geosat and ERS 1 satellite altimetry: Journal of Geophysical Research, B, Solid Earth and Planets, v. 102/5, p. 10,039-10,054.

Wannesson, J., J.C. Icart, and J. Ravat, 1991, Structure and evolution of two adjoining segments of the West African margin from deep seismic profiling: in Continental Lithosphere; Deep Seismic Reflections; Geodynamic Series, v. 22, p. 275-289.