Evidence of a Tethyan immature arc within the South Ladakh ophiolites (NW Himalaya, India).

The ophiolites of the South Ladakh are evidence of the Neo-Tethys obduction onto the Indian continental margin, during Late Cretaceous times. The mafic rocks are cogenetic and were extracted from a N-MORB like depleted source slightly metasomatized above a subduction zone. Thermobarometry on ultramafic rocks confirms this geodynamic setting. Considering their position in the Ladakh-Zanskar area and their geochemical signatures, these ophiolites could correspond to an immature are rather than a back-are basin. Moreover, they are related to a subduction zone located south of the one related to the Dras are and the Ladakh Batholith. The model deduced from this study brings new constraints on the thermo-mechanical evolution of the Indian margin. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.