Macrostructural and microstructural architecture of the Karakoram fault: Relationship between magmatism and strike-slip faulting

A key factor in interpreting the significance of large-scale strike-slip faults in models of continental deformation is an understanding of the temporal relationship between faulting and magmatism. Knowledge of when a strike-slip fault initiated is essential in order to determine its long-term slip rate and its significance in accommodating strain. We review key structural criteria that identify whether magmatism is prekinematic or synkinematic with faulting and apply these criteria to a major Tibet-bounding strike-slip fault. Along the Karakoram fault, in western Tibet, opinion is divided between (1) those advocating that magmatism and shearing were coeval, in which case the youngest U-Pb crystallization age provides a minimum age of shear, and (2) those advocating that magmatism preceded strike-slip shearing, in which case the youngest U-Pb crystallization age provides a maximum age of shear. Fault zone rocks within the central segment of the fault are variably deformed, displaying high- to low-temperature solid-state fabrics. Mylonites indicate subsolidus noncoaxial deformation at temperatures that have not exceeded greenschist - lower amphibolite facies. There is no evidence for submagmatic deformation, and there are no textural or structural indicators that suggest synkinematic magmatism. Consequently, magmatism preceded shearing suggesting that the U-Pb age of proximal leucogranites sets a maximum age for shear. Coupled with a limited offset (