Mechanical evolution of the wide diamond-shaped Española linkage zone, Rio Grande Rift: insights from structural analysis and analogue modelling

In heterogeneous continental lithosphere, rifts propagate by growth and linkage of discrete segments. Linkage zone geometries reflect this process with different segment overlaps, kinematics, and mechanical properties. Recently, analogue and numerical models compared to natural examples (East African and West European rifts) have allowed significant progresses in understanding the localized transfer zones. Here, we focus instead on wide linkage zones in exceptionally hot crust settings, which is relevant for geothermal exploration.

The Rio Grande Rift is a relatively narrow intra-mountainous system, active since the Miocene, contemporaneous with the Basin and Range extension. Despite substantial extension, rift basins remain at high elevations (>1000 m) with inherited rift shoulders reaching up to ~3700 m. These high elevations and Moho temperatures (800-900°C), indicate significant dynamic support.

To investigate linkage kinematics and strain distribution, we compared analogue models inspired from and structural analysis from DEM-derived fault trajectories and published slip data of the Española basin, a 60-km-wide linkage zone connecting the San Luis and Albuquerque segments. We tested various model rheologies (sand-silicone ratios) and extension velocities to assess their impact on the rift architecture, strain partitioning and fault network.  Our approach aims to constrain the 3D strain field evolution in the linkage zones and highlight the role of crustal rheology and inherited structures on the linkage zone geometry.

The NE-SW trending Española basin comprises early-rift grabens and half-grabens preserved, beneath younger volcano-sedimentary deposits, as ‘embayments’ along the basin margins. Seismic data reveals a two-stage evolution. The early wide rift stage (30-15 Ma) produced distributed shallow basins above low-angle normal faults, consistent with the extension of a thermally weakened crust after the Oligocene magmatism. The late narrow-rift stage (15 Ma-present) showed higher extension rates and high-angle normal faults, with thicker and narrower basins. Española basin is bounded by the NE-SW trending Embudo and Tijeras left-lateral fault systems. Within the linkage zone, fault traces are both concave and convex, indicating a rotational strain component. Late-rift faulting forms multi-scale en-echelon patterns resulting from interaction between the N-S intra-basin faults and the oblique border faults.

Xenolith studies documented Miocene crustal rheological changes: Oligocene crustal melting produced progressive granulitization and mechanical strengthening of the lower crust, which could have caused the localization of deformation during late rifting.

Analogue sand-silicone models with a brittle-ductile transition at 5-10 km depth reproduced the Española basin architecture. The distributed deformation across then multiple N-S to NE-SW sub-basins, matching the observed alternation of narrow half-graben and graben tips forming ‘embayment’. Rotational strain in the linkage zone, produce convex-concave faults similar to those observed in the Española basin. Increasing extension velocity promotes strain localization, particularly along the NE-SW left-lateral fault, replicating the present-day strain pattern.

These results demonstrate that the Española basin formed by rift segment linkage under simple orthogonal extension with increasing strain rate and progressive strengthening of the crust. Segment propagation drove a progressive tip rotation, oblique faulting, and localized strike-slip motion. The models reveal high fault connectivity within the linkage zones, with significant implications for geothermal exploration.