Conference Agenda

Sedimentary basins in tectonically active settings, such as rift basins, are characterised by complex, dynamic depositional environments, with the interplay between sedimentation and tectonic processes controlling basin architecture and resource distribution. Scaled 3D analogue sandbox experiments with high-resolution digital 3D deformation monitoring, constrained by geological and geophysical data, can realistically simulate upper-crustal brittle deformation on crustal to basin-scale and allow kinematic and mechanical analysis of complex 3D fault systems. First-order syn-kinematic sedimentation can be conceptually applied to the surface of evolving experiments, permitting investigation of its effect on fault localisation, linkage and displacement and resulting tectonic basin subsidence. However, to date, first-order syn-kinematic sedimentation onto analogue models has been done manually; depositing incremental, homogeneous sand layers on top of the evolving experiment surface to simulate tectonic loading. Consequently, current syn-kinematic sedimentation methods are not capable of simulating complex stratal architectures or incorporating depositional controls like eustasy and climate variations. Conversely, numerical stratigraphic-forward modellers are able to produce these more complex stratal geometries, including their controlling parameters, however they currently lack the ability to simulate the complex tectonic subsidence of basins realistically, or in sufficient spatial resolution.

This work presents a new integrated experimental method; applying cellular numerical stratigraphic forward modelling to dynamically scaled analogue sandbox experiments, permitting realistic, incremental deposition of syn-tectonic sediments. Surface topography and displacement components (e.g. subsidence) of the analogue experiment are derived by 3D-Stereo Digital Image Correlation (DIC) and yield scaled inputs for the cellular carbonate stratigraphic forward modelling software (SFM - CarboCAT). These are then run in combination with suitable production parameters (production rate, surface light intensity, extinction coefficient etc.) as a numerical model, to generate a realistic spatial distribution of sediment facies to be incrementally deposited back onto the surface of the evolving sandbox experiment. Deposition of discrete volumes of sand onto the analogue sandbox is achieved using a cellular sieving device which utilises an array of tubes to maintain the spatially heterogeneous material volumes within their corresponding analogue surface locations. This apparatus has been shown to be capable of repeatedly depositing heterogeneous sandpacks with locally controlled volumes and homogeneous mechanical properties.

The novel integrated analogue and numerical workflow is systematically tested in a series of static (depositional ramp) and dynamic (asymmetric half-graben) analogue experiments with varying initial parameters for both the analogue and numerical models. Results demonstrate that model evolution is purely deterministic, producing diverse final architectures solely as a result of initial parameters and ongoing feedback between the analogue tectonic subsidence history and the SFM-derived sediment loading.

Remnant of the Caribbean Large Igneous Plateau (CLIP) are found as thickened zone of oceanic crust in the Caribbean Sea, that formed during strong magmatic activity about 90 Ma. Previous studies have proposed the Galapagos hotspot as the origin of the thermal anomaly responsible for the development of this igneous province.

In this research, we construct a starting 3D lithospheric-scale structural and density model for the Caribbean region, using up-to-date geophysical datasets (i.e.: tomographic data, Moho depths, sedimentary thickness, and bathymetry). Based on the gravity residuals (modelled minus observed EIGEN6C-4 dataset), we reconstruct density heterogeneities both in the crust and the uppermost oceanic mantle (< 50km).

Our results suggest the presence of two positive mantle density anomalies in the Colombian and the Venezuelan basins, interpreted as preserved plume material. Such bodies have never been identified before, but a positive density trend is also observed in the mantle tomography, at least down to 75 km depth.

Using recently published regional plate kinematic models and absolute reference frames, we test the hypothesis of the CLIP origin in the Galapagos Hotspot; however, a misfit of 1000-2000 km between the present hotspot location and the mantle anomalies, reconstructed back to 90 Ma, is observed, as other authors reported in the past.

Therefore, we discuss two possibilities: 1. The Galapagos Hotspot migrated (~1000-2000 km) in the opposite direction than the Caribbean plate, or 2. The CLIP was formed by a different plume, which – if considered fixed - would be nowadays located below the South American continent.

Flanking structures are deflections in linear or planar fabric elements around any cross-cutting element such as a fracture, vein or dyke. They are potentially useful to infer flow kinematics of ductile shear zones. Previous analog and numerical modeling investigations have been limited to situations where the cross-cutting element is either a frictionless free slip surface, or a rigid material. Works with more variable cross-cutting element’s rheology are limited to low finite strains, cross-cutting element’s high aspect ratios and limited cases of cross-cutting element’s initial orientations. In natural cases, the strength, shape and orientation of a cross-cutting element can be highly variable. Flanking structures associated with a cross-cutting dyke or a strong inclusion are common examples. Here, we use our micromechanics Eshelby formalism to simulate flanking structures around a cross-cutting element of varying rheological properties, shape and orientation. Specifically, we regard a cross-cutting element as a 3D Eshelby inhomogeneity embedded in a viscous medium. The numerical exterior Eshelby solutions give the velocity field in the vicinity around the element. The overall macroscale flow field can be assigned and a general plane strain flow ranging from simple to pure shear is used in our investigation. These velocity fields are then used to simulate the deflection of marker elements surrounding the cross-cutting element. We reproduced all observed flanking structure types recognized from natural shear zones. In contrast to the previous models with limited cross-cutting element geometry and rheological properties, our modeling results show that all three types of flanking structures with antithetic (a-type), no- (n-type) and synthetic (s-type) displacement along the cross-cutting element can be formed around any cross-cutting element stronger than the embedding medium. The a-type flanking structure may transition into an s-type depending on cross-cutting element’s viscosity and macroscale finite strain. We have further developed a reverse-dynamic modelling tool that can provide a quantitative estimate of flow vorticity, finite strain and cross-cutting element’s viscosity relative to the embedding medium from an observed natural flanking structure.