Multi-stage development of the southern Tibet detachment system near Khula Kangri. New data from Gonto La

Field observations from Gonto La (southern Tibet), a pass through the high Himalaya, reveal a continuous, planar, ~l&N-dipping detachment horizon (the Gonto La detachment). The detachment juxtaposes Tethyan dark slates over a footwall of extensive leucogranite of the Khula Kangri pluton, intruded into an injection complex layer regarded as an early Southern Tibet Detachment System (STDS) horizon. The leucogranite emplacement is protracted, and overlaps the STDS development. It is observed to intrude the earlier horizon of the STDS, which is deformed, partially cut by the pluton, and, in the southern part, rotated to a present south dip. Evidence for large scale folding and plutonism is also found east of Khula Kangri at Lhozag-La Kang, where the earlier STDS horizon is inferred. Here it excises the entire Palaeozoic Tethyan sedimentary sequence and is similarly folded. The Gonto La detachment, which cuts the Middle-Upper Miocene Khula Kangri pluton is, in turn, cut by the more steeply N-dipping Dzong Chu fault, demonstrating later N-S extension in this area. We interpret known outliers of Tethyan sequences in Bhutan as klippen, underlain by an early STDS horizon, which provide a more regional illustration of early extension on the STDS. In the Khula Kangri area, early extension was followed by plutonism and local relative uplift, and further N-S extension.