Isotopic and trace element studies for Cenozoic volcanic rocks from western China: implication for a crust-like enriched component in the mantle.

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  • Liu Cong-Qiang
    Laboratory for REE Microanalysis, Department of Chemistry, Faculty of Science, The University of Tokyo
  • Shimizu Hiroshi
    Laboratory for REE Microanalysis, Department of Chemistry, Faculty of Science, The University of Tokyo
  • Nakai Shun-ichi
    Laboratory for REE Microanalysis, Department of Chemistry, Faculty of Science, The University of Tokyo
  • Xie Guang-Hong
    The Institute of Geochemistry, Academia Sinica
  • Masuda Akimasa
    Laboratory for REE Microanalysis, Department of Chemistry, Faculty of Science, The University of Tokyo

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Sr, Nd, Ce and O isotopic ratios and trace element abundances were measured for Cenozoic SiO2- and (Na2O + K2O)-rich volcanic rocks from Yutian of Xinjiang, Yumen of Gansu and Tengchong of Yunnan, Western China. All samples investigated, especially the samples from Yutian of Xinjiang, are highly enriched in LREE and other incompatible elements, and are characterized by higher 87Sr/86Sr (0.706-0.709) and lower 143Nd/144Nd (0.5121-0.5126) ratios as compared with MORB and OIB. High 138Ce/142Ce ratios (0.0225767-0.0225810) were also found for the volcanic rocks from Yutian of Xinjiang and Yumen of Gansu provinces. The volcanic rocks from the three areas are concluded to have been derived from LILE (large ion lithophile element)-enriched mantle source regions without significant crustal contamination. Their high δ18O, and low HFSE (high field strength element)/LILE ratio characters imply a crust-like component existing in their mantle source regions, and hence the isotope variations of the volcanic rocks are modeled with mixing between two end members; depleted mantle and crust-like component. The mantle source region below western China, which indicates integration of subduction-related mantle, is disclosed to be clearly different from that below eastern China.

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