A computed tomography approach for understanding 3D deformation patterns in complex folds

Abstract

Analog models are an important tool for understanding complexly folded and faulted geological structures. In this paper, we propose the use of X-ray computed tomography to accurately reconstruct the geometry of analog models using an orthogonal reference system and to completely characterize deformation patterns within the modeled structure in 3D. The rheology and radiological contrast of various different materials have been studied showing that EVA sheets are a good choice to model buckling layers. After considering various possibilities to define the reference system, we opted to screen-print two orthogonal sets of parallel lines on the surfaces using minium (lead tetroxide). The model was then built with gOcad using a series of CT slices that can be closely spaced. This kind of model allows us to reconstruct the volume distribution of strain ellipsoids and can be very accurate and useful to ascertain the orientation of folded lineations in complex structures as well as to characterize the expected deformation on the surfaces. We have built a simple analog model inspired in the Balzes Anticline (located in the External Sierras, Southern Pyrenees) to illustrate the potential of the technique and to analyze the deformation patterns of this complex curved fold that has accommodated significant magnitudes of vertical axis rotation during its formation.