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 mafi c rocks are cogenetic and were extracted from a N-MORB like depleted source slightly metasomatized above a subduction zone. Thermobarometry on ultrama fic rocks confirms this geodynamic setting. Considering their position in t he Ladakh-Zanskar area and their geochemical signatures, these ophiolites c ould 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 t he Dras are and the Ladakh Batholith. The model deduced from this study bri ngs new constraints on the thermo-mechanical evolution of the Indian margin . (C) 2000 Academie des sciences / Editions scientifiques et medicales Else vier SAS.