Geochemistry of Cenozoic volcanic rocks and related ultramafic xenoliths from the Jilin and Heilongjiang provinces, northeast China

The late Tertiary to Pleistocene volcanic rocks of the Longgang volcanic group in Jilin province, NE China, consist mainly of alkali basalts and basanites with abundant ultramatic xenoliths. The Jinpohu volcanic rocks located in the Xing'an-Mongolian fold belt of NE China erupted from Paleogene to Holocene time. Rb, Ba, Nb, Zr, Th, Hf and La tend to increase with decreasing magnesium- values in Longgang alkali basalts and basanites which may be related to the degree of partial melting of the mantle source. Judging from the Sr vs. Nd isotopic ratio plots, we suggest that the Longgang and Jinpohu basalts may be derived from partial melting of mantle sources, which may represent two-end member mixing of DMM and EM-1. The Longgang basanites and alkali basalts and Jinpohu basanites generally show a pattern similar to that of oceanic island basalts in spidergrams. The depleted-type Longgang spinel lherzolite xenolith has lower incompatible elements contents than the enriched-type spinel lherzolite; the latter has higher K, Rb, La and Cc contents than those of average continental lithospheric spinel lherzolite indicating that mantle metasomatism might have occurred in the Longgang area of the Jilin province, NE China. (C) 2002 Elsevier Science Ltd. All rights reserved.