Study on the Formation Mechanism of Nephelinite- Take Shandong Nephelinites as the Example

Objective‌ Nephelinite is a rare type of strong alkaline volcanic rock mainly found in continental rift environments, oceanic islands, and large igneous provinces. Most of the world's nephelinites are associated with carbonatites and have similar geochemical characteristics to OIBs. Despite numerous studies on the characteristics and formation environments of nephelinite, the genesis of nephelinite and its relationship with carbonatite rock are still controversial, constraining the understanding of nature of mantle source and characteristics of metasomatic agents.

Methods  The petrology, and whole-rock major- and trace elemental analysis was carried out on the nephelinites in Jieshi Mountain and Qixia Dafang Mountain in Shandong Province, and the composition of the primary magma is calculated according to the experimental petrological research results.

Results  The results suggested that the Shandong nephelinite originates from low degree (3%～5%) partial melting of 10%～40% carbonatite + peridotite. In addition, the primary magma has undergone the liquid immiscibility of the carbonate-silicate melt, which can match well with the major and trace elements characteristics and the symbiosis of the nephelinite in Shandong Province.

Conclusion  It's also found that the calculated primitive magma has similar geochemical characteristics to that of typical kimberlite; thus, the author's study might have important implications for the origin of kimberlite magma.