Trace Element and Sr–Pb–Nd–Hf Isotope Evidence for Ancient, Fluid-Dominated Enrichment of the Source of Aldan Shield Lamproites

A phase of Mesozoic extension associated with the termination of continental collision at the southern margin of the Aldan Shield produced ultrabasic lamproites in a discontinuous belt 500 km long and ∼150 km wide. The lamproites, locally poorly diamondiferous, were emplaced as dykes, sills and pipes. All Aldan lamproites have primitive chemical characteristics (e.g. MgO up to 22·7 wt %) and are ultrapotassic (