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Abstract. Basin inversion is a process that takes place when a sedimentary basin is subjected to compressional stresses and may result in the reactivation of pre-existing faults and/or the localization of deformation along new reverse faults. The Araripe Basin (NE Brazil) is an example of a Cretaceous intracontinental aborted rift with its sedimentary infill found at ca. 1000 m altitude in the present day. Post-rift basin inversion is proposed as the cause of this topographic high, however how inversion mechanisms affected this basin is a matter of debate with two end member scenarios: reactivation of pre-existing normal faults leading to local uplift, or regional tectonic uplift. In this study, we conducted analogue models of basin inversion to test these scenarios. We present two series of crustal-scale brittle-viscous experiments: i) extension followed by compression without sedimentation, with a variation of rifting and inversion directions (orthogonal or 45° oblique) and ii) extension and compression with syn-rift sedimentation, with the same variation in rifting and inversion directions. We used a seed representing a structural weakness that was applied at the base of the brittle layer to localize deformation along the model axis. We found that orthogonal rifting without sedimentation forms through-going border faults, whereas oblique rifting creates initial en-echelon faults that eventually link up creating large border faults. Rift basins with syn-rift sedimentation evolved in a similar fashion, however sedimentary loading increased subsidence. During inversion, most deformation is accommodated along new low angle reverse faults. Within that framework, significant intra-graben fault reactivation occurred in models without sedimentation. By contrast, syn-rift sedimentation caused only minor reactivation of rift faults in oblique inversion since the sediments acted as a buffer during compression; no rift fault reactivation occurred in orthogonal compression situations. Comparing the existing scenarios for inversion in the Araripe Basin with our model results and field data show that these scenarios do not fully explain the natural example. Therefore, we propose an alternative scenario based on our models, involving oblique compression and the development of low angle reverse faults, which better explains inversion in the Araripe Basin.

During continental rifting, extension in the upper parts of the crust is accommodated by brittle faulting. If stretching is distributed evenly throughout the crust (McKenzie, 1978), faulting in the upper crust is balanced by ductile deformation in the lower crust (e.g., Buck, 1991;Kusznir & Karner, 2007). However, at passive margins, subsidence analyzed from geological cross sections differs from expected values when applying the McKenzie uniform stretching model. Such observations led to the development of depth-dependent stretching models (Wernicke, 1985) that account for higher amounts of extension in lower parts of the crust, which permit larger subsidence values. More recent studies of passive margins have suggested ductile crustal flow as an alternative mechanism for removal of lower crustal material. Consequently, mass is not conserved in 2D plane-strain cross sections, which can explain discrepancies between estimated amounts of extension in the upper-and lower crust (P. D. Clift, 2015).Ductile flow in the lower crust should also occur in intracontinental rift settings. Indeed, lower crustal flow is expected in extensional settings where the crustal thickness exceeds 20 km and the upper mantle is strong (McKenzie et al., 2000 and references therein). This phenomenon has been extensively demonstrated in the Basin and Range Province, where flow of the lower crust toward the rift center compensates lateral crustal thickness

<p>Continental rifts typically result from regional horizontal stretching of the lithosphere and in modelling studies, such rifts are typically assumed to be the result of orthogonal or oblique extension. However, in nature often V-shape rift geometries occur indicating an underlying rotational component that results in a divergence velocity gradient along plate boundaries. Consequently, the geometric, kinematic, and dynamic rift evolution in such rotational settings may significantly differ from those of orthogonal or oblique rifts. Here, we present new findings from an analogue modelling study using a crustal-scale model series with a rotational opening component to investigate the effect of such a rift-axis parallel divergence velocity gradient on fault growth and rift propagation towards the rotation axis.</p><p>We use a simplified two-layer system simulating an upper brittle and a lower ductile crust with an imposed initial mechanically weak zone on top of the viscous layer to ensure localized rifting. The experimental monitoring by means of a stereoscopic camera setup and X-Ray computed tomography (XRCT) enables a detailed and quantitative investigation of near-surface rift evolution and internal deformation, respectively. With the combination of 3D surface topography, 3D displacement fields, and XRCT, we gain a comprehensive understanding of deformation evolution in analogue models of rotational rifting. Our modelling results depict a novel characterization of normal fault growth under rotational extension and a rift evolution which is described by (1) rift propagation in two consecutive stages: A first stage showing bidirectional fault growth due to segment linkage with high rift propagation rates, and a second stage during which rift propagation occurs by unidirectional fault growth towards the rotation axis with linearly decreasing growth rates at decreasing distance to the rotation axis, (2) strain partitioning between competing conjugate normal faults with fault activity switching repeatedly from one segment of a normal fault to a segment on the oppositely dipping normal fault, and (3) active faulting migrating from the rift boundary faults inwards to intra-rift normal faults.</p><p>Our quantitative, spatiotemporal fault growth analysis reveals a characteristic segmentation of all deformation features listed above. The conclusion that the gradual decrease of the divergence velocity towards the rotation axis causes segmented deformation propagation is key and can help to understand natural examples of rotational rift settings such as the Taupo Rift Zone in New Zealand.</p>