New geochemical data for mafic intrusions within the Eocene Nisai Formation along the suture zone between the Indian and Eurasian plates are used to constrain their petrogenesis and assess the local tectonics and mantle dynamics. Petrological and geochemical data indicate that these alkalic intrusions have moderately enriched incompatible trace element compositions similar to ocean island basalt magmatism. Modelling suggests that these intrusions are the result of 1–5% melting of a deep, enriched, predominantly garnet lherzolite, with a small amount of subduction-derived fluids. These melts then underwent fractional crystallization at lithospheric depths of c. 30 km.
Supplementary materials: Detailed information on each analysed sample including field notes and latitude and longitude, replicate analysis of standards, and fractional crystallization modelling are available at http://www.geolsoc.org.uk/SUP18893.