Analog and Numerical Modeling of Rift‐Rift‐Rift Triple Junctions. Issue 10 (13th October 2022)

• Record Type: Journal Article
• Authors: Maestrelli, D.; Brune, S.; Corti, G.; Keir, D.; Muluneh, A. A.; Sani, F.
• Is Part Of: Tectonics. Volume 41:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-10-13
• Subjects: analog modeling -- numerical modeling -- triple junction -- Rift‐Rift‐Rift junction -- rifting -- Afar; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2022TC007491
• Languages: English
• ISSNs: 0278-7407

Abstract

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. Plain Language Summary: When continents break‐up a rift valley can form and eventually grow to form an ocean. For particular conditions, more than two tectonic plates can be involved in this process. In this case, a "triple junction" is formed that consists of three rift branches. This process shaped the Afar region, where the movement of the Arabian, African, and Somalian plates, which separate at different rates of motion, created the Gulf of Aden, Red Sea, and Ethiopian rifts. The way in which triple junctions work can be difficult to study due to their large extent and several million year‐long activity. Therefore, we performed physical laboratory experiments and numerical experiments on the computer to investigate how triple junction form. We performed models with different rates of motion for the three plates, simulating one or two tectonic stages. The models show that the difference in the rate of motion between the three plates is the main control on the distribution and type of faults forming at triple junctions. Our results suggest that the fault pattern at the Afar triple junction observed nowadays may be explained by two tectonic stages and a lower extension rate occurring between the African and Somalian plates. Key Points: We perform single and two‐stage analog and numerical models of Rift‐Rift‐Rift triple junctions Models show that differential velocity of extension between the plates is key for the geometry of fault patterns at triple junctions Two‐stage models shed light on the geometry and evolution of the Afar triple junction