Review of Iberia-Eurasia plate-boundary basins: Role of sedimentary burial and salt tectonics during rifting and continental breakup
Résumé
We document the role of sedimentary burial and salt tectonics in controlling the deformation style of continental crust during hyperextension. The Iberian-European boundary records a complex history of Cretaceous continental extension, which has led to the development of so-called smooth-slope type basins. Based on the review of the available geological constraints (crustal-balanced cross sections, sedimentary profile evolution, RSCM thermometer, low-temperature thermochronology) and geophysical data (Bouguer anomaly, Moho depth, seismic reflection profiles, and Vp/Vs velocity models) on the Tartas, Arzacq, Cameros, Parentis, Columbrets, Mauléon, Basque-Cantabrian and Internal Metamorphic Zone basins, we shed light on the main characteristics of this type of basin. This synthesis indicates that crustal thinning was influenced by two decoupling horizons: the middle crust and Triassic pre-rift salt, initially located between the basement and pre-rift sedimentary cover. These two horizons remained active throughout basin formation and were responsible for depth-dependent thinning of the crust and syn-rift salt tectonics. We therefore identify several successive deformation phases involving (1) pure shear dominated thinning, (2) simple shear dominated thinning and (3) continental breakup. In the first phase, distributed deformation resulted in the development of a symmetric basin. Field observations indicate that the middle and lower crust were under dominantly ductile conditions at this stage. In the second phase, deformation was localized along a crustal detachment rooted between the crust and the mantle and connecting upwards with Triassic pre-rift salt. During continental breakup, basin shoulders recorded the occurrence of brittle deformation while the hyperextended domain remained under predominantly ductile thinning. The formation of smooth-slope type extensional basins was intrinsically linked to the combined deposition of thick syn-rift and breakup sequences, and regional salt tectonics. They induced significant burial and allowed the continental crust and the pre-rift sequence to deform under high temperature conditions from the rifting to continental breakup stages.
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