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Modes of extension and oceanization at magma-poor margins: An example from the Brazilian-African margins

Author(s): Marta Perez-Gussinye Dept. Earth.Sciences, Royal Holloway, University of London, Egham,, United Kingdom
Institute of Geosciences/MARUM, University of Bremen, Bremen, Germany
M. Araujo CENPES Research Centre, Petrobras, Rio de Janeiro, Brazil
E. Ros Dept. Earth.Sciences, Royal Holloway, University of London, Egham, United Kingdom
M. Andres-Martinez Dept. Earth.Sciences, Royal Holloway, University of London, Egham, United Kingdom
J. Morgan Dept. Earth.Sciences, Royal Holloway, University of London, Egham, United Kingdom

It is well known that the amount of magmatism and occurrence of serpentinised mantle at rifted margins and oceanic ridges fundamentally depends on spreading rate and mantle potential temperature. Here we show that during continental extension the rheology of the continental lower crust also plays a key factor in determining the onset and amount of melting and serpentinisation. Furthermore, using numerical modeling constrained by multi-channel seismic reflection and wide-angle data from the magma-poor margins of Brazil and Africa, we explore whether it is possible to associate margin architectural styles to types of ocean-continent transitions.

Observed margin architectural styles can be explained by a combination of extensional modes: core-complex, wide and narrow (Buck, 1991), with a fourth mode, sequential faulting, that accounts for conjugate margin asymmetry (Ranero & Perez-Gussinye, 2010, Brune et al., 2014). The prevalence of any of these modes during extension depends on lower crustal rheology, which controls the coupling between crust and mantle deformation, and hence mantle uplift velocity and type of oceanization. For a given extension velocity, a weak lower crust leads to small degree of coupling between crust and mantle, to ultra-wide hyper-extended margins and also to slower mantle uplift, inhibiting melt production and serpentinisation. Hence, ultra-wide hyper-extended margins (North Santos-South Kwanza conjugates, or the Campos-Kwanza conjugates) will tend to present an abrupt transition to thin oceanic and magmatic crust. On the other hand, if lower crust is stronger, mantle uplift velocity and crustal thinning will be fast and effective, leading to the formation of narrow conjugates and a continent-ocean transition that may consist of exhumed and serpentinised mantle, if horizontal extension velocity is slow enough (e.g. as in the Camamu-Gabon margins).


Title:
Modes of extension and oceanization at magma-poor margins: An example from the Brazilian-African margins
Type:
Oral
Origin:
Academia
Day:
2
Session:
1
Daily sequence no.:
04
Lead author last name:
Perez-Gussinye
Lead author first name:
Marta
Affiliation(s):
Dept. Earth.Sciences, Royal Holloway, University of London, Egham,
Country:
United Kingdom
Abstract status:
All ok
UID:
37