"Diapiric architecture controlled by syn- and post-extension prograding sedimentary wedges". ICTJA Student Presentation Award 2016

Why rocks are not always deformed in the same way? How mountain chains are formed? Why rivers are distributed in specific patterns in a mountain region? How the plate tectonics are deformed in a subduction boundary? Some geological processes are difficult to understand when direct observations are limited or almost impossible to obtain. Some million years is quite a long period to waiting for check how a mountain belt is formed. In the same way, it would be amazing to go deep into the planet to check the subduction of a tectonic plate, but it is impossible for the moment. In order to reach a better understanding about the earth dynamics, geologists have been using analogue models since the end of the 19th century to simulate geological processes in a more affordable temporal and dimensional scale. In the present work, we have used analogue modelling techniques in order to study the evolution of diapirs. Diapirs are a type of geological structures formed due to the upward movement of mobile and less dense material (salt or shales) through more brittle rocks. Diapirs can display a large variety of geometries due to different acting parameters. Can sedimentation be one of the major mechanisms controlling the final diapir geometry? The objective of this work is to use analogue models to understand how diapiric structures are influenced by sedimentation. To do so, and according to their physical properties, we used silicone to simulate less dense material constituting diapirs and coloured sand as brittle rocks and sediments. To analyse the impact of sedimentation on the evolution of diapirs, we design a set of analogue models with different sedimentation patterns. From all models we highlight the model with homogeneous sedimentation (Model 1 in Figure 1) and the model with a homogeneous sedimentation phase followed by a prograding sedimentation phase, which implies differential sedimentation along the model device (Model 2 in Figure 1). In areas with high sedimentation, diapirs are well-developed with vertical walls as the one shown in Figure 1. Contrarily, the diapiric structures are less developed and remain in an early diapiric phase in areas with low sedimentation. This would be linked to the loading associated to sediments that would cause a major silicone withdrawal from beneath the sedimentary pile towards diapirs in areas with higher sedimentation. This silicone withdrawal is lower in areas with limited sedimentation. Thus, the comparison among all the models shows that the amount of sedimentation and how and when this sedimentation occurs have a major impact in the final geometry of diapiric structures. Applying the knowledge obtained from our models to real diapiric basins, it is possible to understand better the dynamics of salt-related basins and improve the interpretation of the geological history of diapiric structures worldwide