MULTISTAGE 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, similar to 10 degrees N-di pping detachment horizon (the Gonto La detachment). The detachment jux taposes Tethyan dark slates over a footwall of extensive leucogranite of the Khula Kangri pluton, intruded into an injection complex layer r egarded as an early Southern Tibet Detachment System (STDS) horizon. T he leucogranite emplacement is protracted, and overlaps the STDS devel opment. It is observed to intrude the earlier horizon of the STDS, whi ch 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 Pala eozoic Tethyan sedimentary sequence and is similarly folded. The Gonto La detachment, which cuts the Middle-Upper Miocene Khula Kangri pluto n is, in turn, cut by the more steeply N-dipping Dzong Chu fault, demo nstrating later N-S extension in this area. We interpret known outlier s of Tethyan sequences in Bhutan as klippen, underlain by an early STD S horizon, which provide a more regional illustration of early extensi on on the STDS. In the Khula Kangri area, early extension was followed by plutonism and local relative uplift, and further N-S extension.