Geochemical Characteristics and Petrogenesis of the Early Paleozoic Alkali Lamprophyre Complex from Langao County
岚皋早古生代碱质煌斑杂岩地球化学特征及成因探讨

The alkali lamprophyre complex from Langao County, whose chondrite-normalized REE patterns all incline to the right and whose major elements vary regularly, has abundant incompatible elements. Studies on major and trace elements indicate that there existed two parallel fractional crystallization trends during the evolution of primary magma which suffered insignificant contamination of crustal material. The enrichment of LREE and incompatible elements with the change of Zr/Nb, Ce/Y, Dy/Yb, La/Yb and Zr/Sm ratios show that the lamprophyre magma couldn't have been derived from partial melting of spinel-, garnet-lherzolite mantle source or amphibole-bearing spinel or garnet lherzolite mantle source. Sr-Nd-Pb isotope variations indicate that the source of lamprophyre magma was mainly composed of HIMU mantle. The mantle plume not only played an important role in the formation of lamporphyre, but also controlled the metasomatism that occurred in the source of the alkali lamprophyre complex.