Les filons à micas et tourmalines du Haut Himalaya au Népal central.Témoins des transferts magmatiques entre les migmatites du Haut Himalaya et les granites de type Manaslu.

ln Central Nepal , the High Himalayan dikes, formed both during compressional and extensional tectonic, have 3 main preferred orientations, viz. N120-N150°E, N80-N110°E and N 10-N40°E. Most of them have a leucogranitic type composition. Discrimination of dikes (as well as leucosomes and granites) and identification of source rocks has been made using first K20 and Fe-Mg silicates mineralogy, then trace elements and Sr isotopes. The data imply various amount of fluids during anatexis and along the himalayan range : when water-saturated melting, an high melting ratio is reached and the different source levels (greywackes, schist, gneisses) lead to relatively homogeneous dikes and to Manaslu type granites (biotite predominant on tourmaline, medium K20 content). When low amount of external fluids (Machhapuchare area), less silicate liquids are produced, of diverse compositions, according to the variety of source rocks (biotite and/or tourmaline bearing dikes, very low to hi gh K20 content ). Same fractionnated crystallization of biotite, tourmaline and plagioclase (Fe and Rb increase, Mg, Ba and Sr decrease) occured in the different melts during their ascent. Meanwhile, Ca (plus Ba and Sr) contamination from the calcic levels of the Tibetan Slab lead to precipitation of more calcic plagioclase, modification of the Al/Si ratio of the melts, with at turn recrystallization of less aluminous biotite, enhancing of the muscovite formation and some variations in the tourmaline composition. Empiric estimations of Li20, F et Fe3+/(Fe2+ + Fe3+) contents in himalayan micas and calculated values of Fe3+ /(Fe2+ + Fe3+) and H20 in tourmalines suggest an increase of oxydation conditions from the Formation I to the Manaslu granite. K/Ar and 4OAr/39Ar ages, obtained from several dikes and close host rocks, are used to discuss Tibetan Slab cooling in the light of regional scale hydrothermal perturbations and radiogenic argon excess process.