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《Earth Science(Journal of China University of Geosciences)》 2009-01
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Water Contents in Peridotite Xenoliths from Subei Basin,Eastern China

LEI Neng-zhong1,2,XIA Qun-ke2,HAO Yan-tao3,LI Pei2,FENG Min21.Department of City Construction and Environmental Science,West Anhui University,Liu'an237012,China2.CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei230026,China3.Department of Geology,University of Ferrara,Ferrara44100,Italy  
Nominally anhydrous minerals,clinopyroxene(Cpx),orthopyroxene(Opx)and olivine(Ol),in peridotite xenoliths hosted by Cenozoic basalts from Panshishan,Lianshan and Fangshan of the Subei basin,eastern China have been investigated by Micro-FTIR for their water contents.All Cpx and Opx grains contain a certain amount of "water" as hydroxyl defect in the crystal structure.Water contents(expressed as H2O wt.)of Cpx and Opx from Panshishan,Lianshan and Fangshan peridotites are 64×10-6-183×10-6,37×10-6-102×10-6,41×10-6-177×10-6 and 16×10-6-61×10-6,13×10-6-45×10-6,21×10-6-74×10-6,respectively.OH peaks can not be detected for almost all olivine grains,indicating that the water content is below the detection limit(~2×10-6)of FTIR.The whole rock water contents calculated according to the water contents of minerals and their volume proportions are 12×10-6-52×10-6,7×10-6-25×10-6 and 13×10-6-44×10-6 for Panshishan,Lianshan and Fangshan respectively.Based on the new results from the Subei basin and the data reported in literatures,the partition coefficient of H2O between Cpx and Opx in the continental lithosphere mantle is estimated to be 2.2±0.4.Peridotite xenoliths from Nüshan,Hannuoba and the Subei basin of the North China block have much lower water contents than those from other localities of the world(South Africa craton,New Mexico,Colorado plateau and basin and Range province of USA,South Mexico,French Central Massif and West Kettle of Canada).This difference is probably induced by the thermal erosion of asthenosphere during Mesozoic-Cenozoic period in the North China block.If this explanation is correct,the present lithosphere mantle in the North China block is mainly the relict after the Mesozoic lithospheric thinning,rather than the new accreted mantle.
【Fund】: 国家自然科学基金(Nos.90714009 40673028 40473007);; 中法先进研究计划(PRAT05-02);; 教育部“新世纪优秀人才支持计划”
【CateGory Index】: P588.145;P575.4
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