Symmetric alternative to asymmetric rifting models

LDEO Publication: 
Publication Type  Journal Article
Year of Publication  2004
Authors  Nagel, T. J.; Buck, W. R.
Journal Title  Geology
Volume  32
Issue  11
Pages  937-940
Journal Date  Nov
ISBN Number  0091-7613
Accession Number  ISI:000225006800003
LDEO Publication Number  6654
Key Words  rifting; continental margin; detachment; numerical model; lower crust; prestack depth migration; galicia spain; fault systems; margin; ocean; west; lithosphere; evolution; atlantic; beneath

We describe the first numerical simulation of continental rifting that reproduces the three major structures observed at magma-poor margins such as the Galicia Margin west of the Iberian Peninsula or the Apulia Margin in the Alps: (1) Distal continental margins consist of fault-bounded blocks separated by oceanward-dipping normal faults. (2) At the tip of the continent, lower crust is scarcely preserved or absent, and upper crust directly overlies exhumed mantle. (3) The base of the rotated crustal blocks is a prominent seismic reflector and represents a high strain zone with a top-to-the-ocean sense of shear. In our model, these structures do not reflect asymmetric rift geometry at a lithospheric scale. Instead, they derive from upper-crustal collapse over a mid-crustal shear zone into the rift center and are present on both sides of the rift axis. The model has a horizontal weak zone in the middle crust on top of strong lower crust and a localized vertical zone of thermal weakness in the rift center. We hypothesize that the development of a thermal perturbation and associated strain localization in the deeper lithosphere may cause the transition from widely distributed faulting and crustal thinning to constricted faulting directed toward a well-defined rift center.


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URL  <Go to ISI>://000225006800003
DOI  Doi 10.1130/G20785.1