Tectonic Transition and Extension at the Eastern and Western Ends of the Altyn Tagh Fault: Insights from Triple Junctions

The Altyn Tagh fault (ATF), a significant tectonic boundary on the Tibetan Plateau's northern edge, plays a pivotal role in understanding the plateau's growth through its evolutionary history and tectonic transition mechanisms. The different segments of the ATF have different tectonic settings and evolution histories, and its tectonic transition with Qilian orogenic belt and the Eastern Kunlun fault remain insufficient. The analysis of triple junctions, a critical method in plate tectonics, showcases fault properties and stability from a kinematic perspective, revealing the direction and progression of fault evolution. This paper comprehensively analyzes geological, geomorphological, and seismic data to systematically examine the structural characteristics and activity history of the Subei and Tula triple junctions between segments. Through the stability criteria of triple junctions, we developed evolutionary models for these junctions. Our findings indicate the initiation of the Yemahe-Daxueshan and Qimantagh-Eastern Kunlun faults, the formation of unstable triple junctions, and their transition to stable states, promoting the ATF's "shortcutting". On this basis, a segmented rupture-bidirectional extension model is proposed. These results offer a fresh perspective on the complex tectonic evolution of the North Tibet.