The Geochemical Characteristics and Geological Significance of Alkaline Complex in Chishan of Shandong Province

Alkaline complex in Chishan is closely related to the origin of rare earth elements (REE) deposits. A systematic study on geochemical characteristics of the complex was conducted to reveal its features of alkaline magma activity, the mineral sources and tectonic settings. Results have shown that the SiO₂ content accounts for 65.08%-69.41%, signifying that the alkaline complex is acidic rock, with total alkaline (K₂O+Na₂O) value of 8.16%-12.92%, and all the samples fell above the alkaline trend line in the TAS chart; As to the composition of trace element, the rock complex enriches in lithophile elements, such as Ba and Sr, but is relatively poor in high field strength elements, such as P, Nb, Ta and Hf; Total values of rare earth elements(ΣREE) are (189.11-2 144.52)×10^-6, where LREE is strongly enriched while HREE is deficient, dominated by a weak negative Eu anomaly. Based on the study and analysis, this paper suggests that the Chishan alkaline complex was formed in extensional tectonic background and was a post-orogenic magmatic product. Belonging to alkaline rock series, its mineral source is deep-seated magma, relating to EMI enriched mantle and being contaminated by crustal materials.