Main geological features of the Rolwaling-Khumbu Himal between the Khimti Khola and Dudh Khosi valleys (eastern-central Nepal Himalaya).

The main geological features of the Himalayan orogen are described in the region between the Khimti Khola and the Dudh Khosi valleys (eastern-central Nepal). The study is based on geological mapping, structural and petrographic analysis still in progress. In the investigated area, the Greater Himalayan Sequence (GHS) may be divided in two different domains basing on lithological, structural and metamorphic criteria. The lower domain (GHS-L) mainly consists of a metasedimentary sequence recording an increase in metamorphic grade upward, passing from the staurolite zone to the sillimanite zone and, locally, to anatexis. The upper domain (GHS-U, corresponding to the Higher Himalayan Crystallines of much literature) is characterized by high-grade metamorphic rocks, often anatectic, recording a progressive decrease in peak-pressure structurally upward. The tectonic juxtaposition of the high-grade, anatectic rocks of the GHS-U over the low-grade metasedimentary rocks of the Lesser Himalaya Sequence is accommodated by the Main Central Thrust Zone, roughly centred on the GHS-L. This major boundary zone identifies a several km-thick shear zone characterized by a top-to-south ductile shearing, responsible for the pervasive development of mylonitic foliations, mylonites, mesoscopic shear zones and for the tectonic juxtaposition of slices of different lithologies (e.g. phyllonite, augen-gneiss, two-micas paragneiss and micaschist, slate, quartzite, marble and Ca-silicate granofels).