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《Geotectonica Et Metallogenia》 2002-04
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GEOCHEMISTRY OF LATE MESOZOIC VOLCANIC ROCKS IN RUCHENG AREA AND ITS IMPLICATION FOR THE SOURCE NATURE

LI Chao wen1, 2, WANG Yue jun1, GUO Feng1, PENG Tou ping1,2 and YU Xiao bin1(1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 2. Postgraduate School of the Chinese Academy of Sciences, Beijing 100039, China)  
The volcanic rocks in Rucheng, southeast of Hunan Province, composed of basalts and andesite dacites, belong to low K calc alkaline series. The two basalt samples from this volcanic sequence yield the K Ar ages of 124.5±2.5Ma and 127.6±1.9 Ma, respectively. These rocks from basalt and andesites dacites have distinct elemental and isotopic compositions. Among them, andesites dacites have high MgO (MgO=3.93%-5.07%) content, and show enrichment in LILE and depletion in Nb Ta Ti P with (La/Yb)N=6.7 7.9, Eu*/Eu=0.74 0.85. The basalts display enrichment in LILE and enrichment in Nb Ta relative to La with (La/Yb)cn=4.0 4.3, Eu*/Eu=1.00 1.16. The high MgO andesite dacites characterized by arc island type trace element patterns while OIB patterns for basalts. Corrected age initial 87Sr/86Sr ratios are that high MgO andesites dacites range from 0.71079 to 0.71118 and εNd(t) from -7.64 to -8.16, whereas basalts show 87Sr/86Sr(t)=0.70812 0.70832 and εNd(t)=0.48 1.03. It is concluded that high MgO andesites dacites are derived from the fractionation of the enriched lithospheric mantle melting and that the basalts are originated from the mixture of enriched lithospheric mantle and asthenospheric mantle in response to intra continental lithospheric extension and thinning.
【Fund】: 院创新项目(KZCX2-102);; 国家973项目(G1999043209);; 国家自然科学基金项目(40002007)资助.
【CateGory Index】: P588.1
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