Analog and numerical modeling of Rift-Rift-Rift triple junctions

Abstract

Rift-Rift-Rift triple junctions are key features of emergent plate boundary networks during fragmentation of a continent. A key example of such a setting is the Afar triple junction where the African, Arabian and Somalian plates interact. We performed analog and numerical models simulating continental break-up in a Rift-Rift-Rift setting to investigate the resulting structural pattern and evolution. We modified the ratio between plate velocities, and we performed single-stage (with all plates moving at the same time) and two-stage (where one plate first moves alone and then all the plates move simultaneously) models. Additionally, the direction of extension was changed to induce orthogonal extension in one of the three rift branches. Our models suggest that differential extension velocities in the rift branches determine the localization of the structural triple junction, which is located closer to the rift branch experiencing slower extension velocities. Furthermore, imposed velocities affect the deformation resulting in end-member fault patterns. The effect of applying similar velocities in all rift arms is to induce a symmetric fault pattern (generating a Y-shaped geometry). In contrast, a faster plate generates structures trending orthogonal to dominant velocity vectors, while faults associated with the movement of the slower plates remain subordinate (generating a T-shaped pattern). Two-stage models reveal high-angle faults interacting at the triple junction, confirming that differential extension velocities strongly affect fault patterns. These latter models show large-scale similarities with fault patterns observed in the Afar triple junction, providing insights into the factors controlling the structural evolution of this area.

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