Different Formation Modes of the North–South‐Trending Rifts in Southern Tibet: Implications From Ambient Noise Tomography

• Published in: Geophysical research letters 2024-05, Vol.51 (9), p.n/a
• Main Authors: Li, Dandan, Tian, Xiaobo, Liang, Xiaofeng, Nie, Shitan
• Format: Article
• Language: English
• Subjects: Ambient noise; ambient noise tomography; Broadband; Crustal deformation; crustal structure; Deformation; Disruption; Ductile-brittle transition; Evolution; low Vs anomaly; Magma; Miocene; Modes; North‒South‐trending rifts; Plateaus; Rifting; S waves; Seismic arrays; Seismic velocities; Shear wave velocities; Tibetan Plateau; Tomography; Velocity; Wave velocity
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108254

Understanding how the Miocene N–S‐trending rifts on the southern Tibetan Plateau formed is crucial for understanding the evolution of the plateau. Most competing models suggest that all the rifts developed uniformly, but there are differences in magmatism among them. We conducted ambient noise tomography based on a broadband seismic array deployed across the rifts. A mid‐crustal low‐Vs layer extends laterally beneath the Tangra Yum Co Rift and the Pumqu‐Xianza Rift, implying that E‒W stretching of the ductile middle crust segmented the brittle upper crust, causing rifting and subsequent magmatism. In contrast, the Yadong‐Gulu Rift, which experienced prerifting magmatism, is characterized by an isolated low‐Vs anomaly extending subvertically from the surface to the middle crust, indicating that the crust experienced magmatic intrusion and local disruption, which promoted the later formation of a large rift. The results suggest that the various rifts might have distinct formation modes. Plain Language Summary The rifts in the southern Tibetan Plateau are closely related to the growth and evolution of the plateau. These rifts are often considered as a whole in studies on their developmental modes. However, different rifts exhibit variations in terms of the timing of magmatism (before or after rifting). This implies that the developmental modes of different rifts are likely to involve different crustal deformation processes. To further investigate the formation modes of different rifts, we used the ambient noise method to obtain the crustal shear wave velocity structure. The presence of a low‐velocity layer in the mid‐crust indicates a vertical layering of crustal strength, which reveals that the upper crustal segmentation together with ductile deformation of the weak mid‐crust contributed to the formation of some rifts. In contrast, the presence of an isolated low‐velocity anomaly extending to the mid‐crust implies that a disruption of the lateral crustal strength caused the formation of another rift. Our findings will change the traditional understanding of the formation of N–S‐trending rifts and the evolution of the Tibetan Plateau. Key Points The crustal structure beneath the rifts in southern Tibet is revealed by ambient noise tomography Rifts with post‐ or pre‐rifting magmatism lie above a mid‐crustal low‐velocity layer or a subvertical low‐velocity anomaly, respectively The intrinsic differences in crustal structure indicate that the rifts in southern T