The internal zone of nephelinesyenite in Liangkou Yajishan

Guangdong Province is composed of amphibolebearing nephelinesyenite

with SiO

2

averaging 60.45%

K

2

O/Na

2

O averaging 0.97

Nb/Ta averaging 22.68

Zr/Hf averaging 39.96，ΣCe/ΣYb averaging 6.32，and δEu(0.30) The external zone

Bi-Am-syenites zone，have average SiO

2

of 60.34%， average K

2

O/Na

2

O of 1.50， average Nb/Ta of 21.23， average Zr/Hf of 43.07，average ΣCe/ΣYb of 7.85，and negative anomaly in Eu（δEu=0.47）. Isotopic studies show that the rock formation time is about 134.6 ± 8.9 Ma (Rb-Sr whole rock isochron method)

with average I

Sr

of 0.706 75， average ε

Nd

(t) of 2.8. Isotope features suggest that the magmatic rocks were derived from the upper mantle. The intrusive rocks formed at a continent-continent post-collisional extension setting

which was significant to the early Cretaceous tectonic evolution of the South China Block.