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Mantle xenoliths from Late Cretaceous basalt in eastern Shandong Province: New constraint on the timing of lithospheric thinning in eastern China

查看全文 作　　者：YAN Jun, CHEN Jiangfeng, XIE Zhi & ZHOU Taixi School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China 高影响力作者 出　　处：《Chinese Science Bulletin》索引2003年第48卷第19期,共6页高影响力期刊 基　　金：This work was supported by the Chinese Academy of Sciences(Grant No.KZCX2-107). 摘　　要：The age of the alkali basalt from Daxizhuang in Jiaozhou, eastern Shandong, was determined to be 73.5±0.3 Ma by 40Ar-39Ar technique. The basalt gave high eNd(t) values of +7.5 and +7.6, suggesting that the primitive magma was derived from depleted asthenospheric mantle with a formation depth of about 65—95 km. Spinel-lherzolite xenoliths have been discovered in the basalt. The Fo values of olivine from the xenoliths range from 88 to 89. The estimated equilibrium P-T conditions of spinel-lherzolite xenoliths are about 2.0 GPa and 1010—1140℃, suggesting an equilibrium depth of about 65 km. Geochemical characteristics of the Late Mesozoic (125—115 Ma) mantle-derived rocks in Shandong Province suggest an enriched lithospheric mantle along the southern margin of the North China block. However, geochemical characteristics of the Late Cretaceous basalts in Daxizhuang and the equilibrium P-T condition estimated from the xenoliths suggest that the lithosphere at 73 Ma ago was as thick as that of the Cenozoic in the region. Additionally, the xenoliths are rich in basaltic-component, suggesting a derivation from a newly-formed lithosphere. Therefor, lithospheric thinning took place at a time interval between about 120 and 73 Ma along the southern margin of the North China block. 关 键 词：覆盖捕虏岩 白垩纪 玄武岩 山东 东部地区 岩石圈稀释化 ^40Ar-^39Ar技术
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