Control of rheological stratification on rifting geometry: a symmetric model resolving the upper plate paradox

Publication Type  Journal Article
Year of Publication  2007
Authors  Nagel, T. J.; Buck, W. R.
Journal Title  International Journal of Earth Sciences
Volume  96
Issue  6
Pages  1047-1057
Journal Date  Nov
ISBN Number  1437-3254
Accession Number  ISI:000250302400005
Key Words  continental rifting; s-reflector; detachment fault; parallel-dipping faults; numerical modelling; asymmetric lithospheric extension; ocean-continent transition; prestack depth migration; numerical experiments; tectonic evolution; rifted margin; galicia sp

Numerical experiments reproduce the fundamental architecture of magma-poor rifted margins such as the Iberian or Alpine margins if the lithosphere has a weak mid-crustal channel on top of strong lower crust and a horizontal thermal weakness in the rift center. During model extension, the upper crust undergoes distributed collapse into the rift center where the thermally weakened portion of the model tears. Among the features reproduced by the modeling, we observe: (1) an array of tilted upper-crustal blocks resting directly on exhumed mantle at the distal margin, (2) consistently oceanward-dipping normal faults, (3) a mid-crustal high strain zone at the base of the crustal blocks (S-reflector), (4) new ocean floor up against a low angle normal fault at the tip of the continent, (5) shear zones consistent with continentward-dipping reflectors in the mantle lithosphere, (6) the mismatch frequently observed between stretching values inferred from surface extension and bulk crustal thinning at distal margins (upper plate paradox). Rifting in the experiment is symmetric at a lithospheric scale and the above features develop on both sides of the rift center. We discuss three controversial points in more detail: (1) weak versus strong lower crust, (2) the deformation pattern in the mantle, and (3) the significance of detachment faults during continental breakup. We argue that the transition from wide rifting towards narrow rifting with a pronounced polarity towards the rift center is associated with the advective growth of a thermal perturbation in the mantle lithosphere.


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URL  <Go to ISI>://000250302400005
DOI  DOI 10.1007/s00531-007-0195-x