Geochemistry and Sr-Nd-Pb-Hf isotopes of Early Cretaceous basalts from the Great Xinggan Range, NE China: Implications for their origin and mantle source characteristics

Late Mesozoic volcanism is widespread throughout northeastern China, mainly clustering in the Great Xinggan Range, where the major period of volcanic eruption was during the Early Cretaceous. The spatial distribution of volcanic rocksshows a NNE-extending pattern. The lithology of Mesozoic basaltic rocks in the Great Xinggan Range ranges from trachytic basalts, basalts to basaltic andesites. On the basis of lithological associations and spatial relationships, we divide the basalts into four groups, i.e. Tahe, Genhe, Zalute and Xiwu. The Early Cretaceous volcanism in the Great Xinggan Range is characterized by significant large ion lithophile elements (LILE) and light rare earth elements (LREE) enrichment and high field strength elements (HFSE) depletion, with a slightly enriched to depleted Nd-Hf and weakly enriched Sr isotopic compositions (initial (87)Sr/(86)Sr=0.7046-0.7079, epsilon(Nd)(t)=+3.6 to -6.9 and epsilon(Hf)(t) =+8.9 to -4.6). The Pb isotopic compositions are also variable with (206)Pb/(204)Pb, (207)Pb/(204)Pb and (208)Pb/(204)Pb values of 17.791-18.530, 15.477-15.597 and 37.761-38.497, respectively. The Sr-Nd-Pb-Hf isotopic data indicate that the magmatic sources are heterogeneous, showing an enriched to depleted signature of continental lithospheric mantle. The magmatic sources of the Genhe and Zalute groups are characterized by mixing among PM, EM II and DM, whereas the Tahe and Xiwu groups derive from enriched lithospheric mantle that had experienced metasomatism by fluids or melts from subducted Paleo-Asian and Mongol-Okhotsk ocean slabs and possible influence of Precambrian blocks. The Late Mesozoic volcanic rocks in the Great Xinggan Range resemble those of the Cenozoic calc-alkaline magmatism in the Basin and Range Province of the United States. We therefore suggest that the widespread Mesozoic volcanic rocks in the Great Xinggan Range were generated in an extensional tectonic setting. (C) 2008 Elsevier B.V. All rights reserved.