Exploring the Early History of the South Tibetan Fault System in Bhutan

Arizona State University, Scottsdale AZ

Investigators

Abstract

This research focuses on the South Tibetan fault system, one of the most enigmatic tectonic features of the Himalaya, and one that stirs much controversy in the Tectonics community. The South Tibetan fault system appears to be unique in that its kinematics are those of a low-angle, normal fault system while all other Himalayan fault systems with comparable displacements (many 10s to 100s of kilometers) have the more predictable kinematics of thrust fault systems typically found in mountain belts. The very existence of a feature like the South Tibetan fault system is indicating something fundamental about how the Himalaya, and mountain ranges in general, evolve. The PI and his colleagues work to clarify this message through their research. Unfortunately, in many parts of the Himalaya, the early history of the South Tibetan fault system has been obscured by late-stage deformation. This is not the case in Bhutan, where the PI and others have identified erosional remnants of early faults of the system that have been relatively undisturbed by younger deformation. This proposal describes targeted studies of these remnants. A broad array of techniques will be used to probe the early history of the fault system using these rare exposures. They include geologic mapping and structural analysis; quantitative element-partitioning thermobarometry; 40Ar/39Ar and (U-Th)/He thermochronology; and laser-ablation (U-Th)/Pb geochronology. Because the Himalaya and Tibetan Plateau are still evolving, studies of this natural laboratory provide critical information regarding the role that mountainous regions play in earth system function. For example, we know that the physiography of the Tibetan Plateau defines the weather patterns of the Asian monsoon climate, and this climate is the enabling mechanism for agriculture that feeds roughly 60% of the people on Earth. By detailing the processes that led to the establishment of the modern-day Himalaya and Tibetan Plateau, studies such as the one proposed here inform more effective strategies for the co-evolution of human societies and mountain landscapes.