Geochemistry of Cenozoic volcanic rocks from Kirin Province, northeast China

The major volcanic activity in Kirin Province, northeast China occurred in Changpaishan area and lasted from the Miocene to Holocene. The volcanic roc ks include basanite, alkali basalt, tholeiite, trachyte, and rhyolite. Ultr amafic xenoliths and megacrysts occur in the basanite and alkali basalt. Th e compatible (Ni, Cr, Sc, V, Co) and incompatible elements (Rb, Li, Th, Hf, La, Lu, Nb, Zr, Y) vary systematically with 100MgO/(MgO + Sigma FeO) in th e volcanic rocks. Fractional crystallization clearly was important in the m agmatic evolution. The volcanic rocks and their ultramafic xenoliths have c haracteristic Sr and Nd isotopic ratios which fall between DMM and EM-I or EM-II. There are two types of spinel-lherzolite xenoliths in the basalts fr om Kirin Province: (1) an E-type enriched in LREE with (La/Yb)(N) varying f rom 6.6 to 8.15; (2) a D-type depleted in LREE with (La/Yb)(N) varying from 0.2 to 0.7 indicating of mantle heterogeneity in the Kirin region. The E-t ype lherzolites contain higher TiO2, K2O, P2O6, Rb, Sr, Pa, Y, Nb, Ta, Th a nd U than the D-type lherzolites. The former may have resulted from mantle metasomatic processes. The tholeiite, alkali basalt and basanite may have been derived from an iso topically similar mantle source through different degree of partial melting at different P-T conditions. The trachyte may be derived from the basalt t hrough fractional crystallization of plagioclase, olivine, clinopyroxene an d magnetite.