STRUCTURAL SEGMENTATION OF THE RIO GRANDE RIFT: INSIGHTS FROM NUMERICAL MODELS

The Rio Grande rift consists of a series of sedimentary basins, linked by accommodation or transfer zones. This structural segmentation of the rift zone is a very fundamental, yet not thoroughly understood characteristic of all continental rifts. It is important to understand the origin and evolution of structural segmentation. In the first place, segmentation plays an important role in the plate-tectonic cycle, as the segmented rift structure is sometimes found to be inherited by seafloor spreading ridges. Secondly, rift segmentation affects hydrocarbon migration, groundwater flow, earthquake distribution, and the location of volcanic activity in rifts; factors of direct influence on human activity.

We present results of a finite element modeling study of rift segmentation. The models are three-dimensional, and consist of a (layered) crustal block. Upon extension the crustal block will deform, and one or multiple rift segments is formed. The models predict deformation within the rift segments as well as deformation and stresses/strain within the accommodation zones. With the models it is possible to predict where faults will be formed and how the crust deforms within and around the segment ends. Our aim is to apply the models to the Española Basin of the Rio Grande rift which is bounded by two structurally very different accommodation/transfer zones.

Preliminary results indicate that rift basins form above inhomogeneities in the lower crust. A set of normal faults develops, dipping toward the inhomogeneity and bordering the basin. The dominant border fault may change polarity between different segments. Deformation is complex within accommodation zones, where the basement is less deep, and shear stresses develop. Models were also developed to study oblique rifting and a rotation in far-field tensional stresses, as occurred in the Rio Grande rift. The results give insight into the 3D evolution of rift segmentation, and, how isolated rift centers interact, evolving into long rift systems.