Isotopic study of the Manaslu granite (Himalaya,Nepal): inferences on the age and source of Himalayan leucogranites |
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| Authors: | Catherine Deniel Philippe Vidal Angel Fernandez Patrick Le Fort Jean-Jacques Peucat |
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| Institution: | (1) Département de Géologie et UA 10, CNRS, F-63038 Clermont-Ferrand Cédex, France;(2) Centre de Recherches Pétrographiques et Géochimiques, CNRS, F-54501 Vandoeuvre les Nancy, France;(3) Centre Armoricain d'étude structurale des socles, CNRS, F-35042 Rennes Cédex, France |
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| Abstract: | A detailed isotopic study of the Manaslu leucogranite was carried out. A U-Pb age of 25 Ma and a whole rock Rb-Sr age isochron of 18 Ma were obtained, suggesting that the magmatic activity lasted at least 7 Ma. Initial Sr isotopic ratios are very high (0.740 to 0.760) and initial Nd isotopic ratios are low (
Nd
in
: –13 to –16), and they show the existence of large isotopic variations even at the metre scale. These are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes (e.g. fusion, mixing by convection). These results also support the crustal origin of this leucogranite. The Tibetan slab paragneisses, whose Sr and Nd isotopic ratios are very similar to those of the granite at an age of 20 Ma, are the most probable parental material. Nd model ages for both the leucogranite and the gneisses are in the range 1.5–2 Ga. A model of formation of the Manaslu granite by coalescence of different batches of magma is in agreement with the present data. |
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