关键词: 正长岩, 地球化学, 岩石成因, 庐枞盆地

Abstract:

Majory and trace elements compositions of the syenite in the Luzong basin  show that SiO₂ contents of the syenite are 60.86%-68.85%, with total alkaline (Na₂O+K₂O) values of more than 9.82%, Rittman indexs of more than 3.73 basically, and high K₂O contents, which indicate that the rock  can be assigned to high potassium shoshonite series. In addition, the rock is enriched in large ion lithophile elements, such as Rb, U, Th and Pb, but relatively depleted in high field strength elements, such as Nb, Ti. Total values of rare earth elements (∑REE) are (205.16-496.61)×10^-6, δEu are 0.28-0.78,and they are enriched in LREE.It shows that the magma forming the syenite in the Luzong basin was derived from a deep source, most likely resulting from the partial melting of an alkali basalts along the deep fault, and obviously contaminated by continental crust material.

Key words: syenite, geochemistry, petrogenesis, Luzong basin