WHAT DRIVES EXHUMATION IN THE HIMALAYA? TECTONIC AND CLIMATIC PROCESSES ON DECADAL TO MILLION-YEAR TIMESCALES

Some of the Earth’s steepest topography and wettest regions occur in the Himalayan orogen and are responsible for some of the highest erosion rates on our planet. The spatial, and partly temporal, correlation between various topographic, climatic, and exhumational (i.e., changes of surface elevation through time, sensu lato) parameters has led researchers in the past two decades to postulate feedback processes between tectonics and surface processes. However, despite recent advances and an increase in thermochronologic and sedimentological datasets, the available information concerning these relationships is still ambiguous and controversies exist when determining the different forcing factors that drive exhumation. As a result, studies along and perpendicular to strike of the Himalaya either argue for tectonic or climatic controls on erosion rates, depending on geographic location, lithologic unit, tectonic setting, or overall climatic parameters. Here, we synthesize and assess these controversies, including recent advances and our new data from the NW Himalaya, to shed light on the reasons for the discrepancies among different studies. Specifically, we highlight the importance of large river systems and climate-controlled aspects of weathering concerning fluvial mass distribution. For example, studies in the vicinity of large-catchment rivers cutting across the orogen find positive feedbacks between tectonics and surface processes, while studies focusing on catchments draining only the Himalayan front suggest a negative correlation. Our analysis emphasizes that the proposed feedback processes between tectonics and surface processes depend on several parameters with individual process thresholds and therefore lead to a complex relationship.