Evoluzione dei fluidi e riattivazione fragile del Main Central Thrust nel Basso Dolpo (catena himalayana, Nepal Occidentale).

The Main Central Thrust Zone (MCT) in Lower Dolpo (Western Nepal) affects both the lower part of the Higher Himalayan Crystallines (HHC) and the upper part of the underlying Lesser Himalayan Sequence (LH) giving rise to a thick zone of penetrative mylonitic deformation. A sudden change in lithology, from the upper migmatitic gneiss and kyanite-bearing gneiss to a lower complex made by garnet-bearing micaschists, white quartzites, amphibolites, paragneisses and phyllites marks the boundary between the HHC and the LH. In the MCT zone an inverted metamorphic field gradient has been confirmed and biotite, garnet, staurolite and kyanite are found progressively upward in the sequence. Shear along the MCT zone and the STDS and erosion in the front of the belt allowed the ductile extrusion of the HHC from depth up to the higher structural levels (HODGES et alii, 1992; GRUIJC et alii, 1996; 2002). This path has been recorded in the MCT zone by a spectacular main ductile fabric with mylonites showing a top to the SW sense of shear, overprinted by later ductile/brittle and brittle shear zones. Overprinting brittle-ductile shear zones point to a top-to-the SW sense of shear too, testifying a later compressive reactivation of the MCT zone after the main ductile phase at upper structural levels.