Eocene tearing and fragmentation of Indian lithosphere beneath the Woka rift, southern Tibet

Abstract

When and how the syncontractional N-S−trending rifts formed in the Himalayan-Tibetan Plateau are crucial, yet unsolved issues that could help establish the interplay between geodynamic evolution and uplift of the plateau. Recent geophysical observations indicate that although Indian lithosphere tearing is the most likely trigger for rift formation, the timing of this tearing remains uncertain. To address this issue, we studied the Woka rift, which represents a typical N-S−trending rift in southern Tibet. Our results show that granitoids from the hanging wall and footwall of the Woka rift have significantly different magma crystallization temperatures (770−860 °C versus 650−750 °C) and crustal thickness (∼40 km versus ∼60 km) during the Eocene. These differences were most likely linked to tearing of the Indian lithosphere. The integration of crustal thickness trends and bedrock emplacement depth from the Eocene to the Oligocene suggest that the hanging wall exhumed at a faster rate than the footwall. From this information, it is clear that the Woka rift did not undergo E-W extension during this period. Integrating data from geophysics, thermochronology, mantle-derived, N-S−trending dikes, and adakitic rocks, we propose that Indian lithospheric tearing and fragmentation during the Eocene caused weakening of the Tibetan middle-lower crust rather than directly triggering surface extension of the Woka rift. This study has significant implications for the deep lithospheric processes and surface responses in the Himalayan-Tibetan Plateau.