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Abstract© 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.
CitationWu G, Lavier LL, Choi E (2015) Modes of continental extension in a crustal wedge. Earth and Planetary Science Letters 421: 89–97. Available: http://dx.doi.org/10.1016/j.epsl.2015.04.005.
SponsorsWe are grateful to Patrice Rey and Loic Labrousse for constructive comments that helped to improve the paper, and Editor Yanick Ricard for helpful assistance. This work was supported in part by the Academic Excellence Alliance program award to Luc L. Lavier from King Abdullah University of Science and Technology (KAUST) Global Collaborative Research under the title "3-D numerical modeling of the tectonic and thermal evolution of continental rifting". This is UTIG contribution 2842.