A PRELIMINARY STUDY ON TRACE ELEMENT GEOCHEMISTRY OF EMEISHAN BASALTS FROM SW CHINA
峨眉山玄武岩微量元素地球化学的初步研究

The Emeishan basalts show a regional variation in trace element abundances which is characterized by the basalts from the Yanyuan-Lijing Depression being lower in incompatible elements but higher in compatible elements compared with those from the Kangdian Uplift and the Dian-Qian Depression. The difference is suggested to be primarily due to different degrees of crystallization experienced by their parental magmas. In addition, the more evolved andesitic basalts and quartz tholeiites are often rich in radiogenic Sr, indicating that to a certain extent crustal contamination was involved in the genesis of these rocks. Compared with the dominant tholeiites the alkaline volcanics from Dongchuan district are less enriched in LREE, probably resulting from earlier melting events in their source. Model calculations using both major and rare carth elements demonstrate that the trachytes from Ertan section could be derived from a basaltic parent via fractional crystallization, in which the optimum separated phases would be similar in composition to the mineralogy of the layered gabbros outcropping in the area investigated.