Geochemistry of late Mesozoic lamprophyre dykes from the Taihang Mountains, north China, and implications for the sub-continental lithospheric mantle

Many late Mesozoic lamprophyre dykes occur in the Taihang Mountains (north China). These lamprophyres are rich in large ion lithophile elements (e.g. Rb, Sr, Ba and K) and light REE, and have highly differentiated REE patterns. They show large but regular variations in chemical and Nd-Sr isotopic compositions. All these suggest that the lamprophyres were produced from differentiation of a parental magma, coupled with contamination by lower crust. The parental magma was derived from melting of a long-term enriched sub-continental lithospheric mantle source as is indicated by the highly enriched isotopic signatures of the lamprophyres. Mantle enrichment in the area was probably produced by interaction of volatile-rich melts released from the asthenosphere with the above lithosphere in middle Proterozoic times.