Geochemical Characteristics of Basic Dikes from Jiling Area in Longshoushan and Its Geological Significance

The mafic dikes from Jiling area in Longshoushan has selected been as the study object, and the magmatic source characteristics and evolutionary processhas been discussed in this paper. SiO₂ content of mafic dikes in Jiling area is 47.09%~51.13%. They are characterized by high aluminum (Al₂O₃=14.56%~15.97%),rich sodium (Na₂O=3.35%~3.69%) and low potassium (K₂O=0.347%~1.23%). The ∑ REE(105.7×10^-6~186.97×10^-6)is relative low with the right type of LREE distribution patterns((La/Yb)_N=4.50~9.63). These mafic dikes have a characteristic of rich Ba, U, Pb, P and Ti and depleted Rb, Th and K, belonging to the tholeiite series. They were formed in extensional intraplateenvironment and experienced fractional crystallization of olivine, clinopyroxene and Ti-Fe oxides.The magma hadn't been contaminated by crustal materials during its ascent process. Its original magma was derived from the melt of the pyrolite which was formed by the mantle metasomatism after the partial melting. Thus, the magma of mafic dikes was derived from transitional mantle source region,with the source of spinel + garnet lherzolite mantle.