Geochemical research on C-O and Sr-Nd isotopes of mantle-derived rocks from Shandong Province, China  

作　　者：LIU Jianming, ZHANG Hongfu, SUN Jinggui & YE Jie1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 2. School of Earth Science, Jilin University, Changchun 130061, China Correspondence should be addressed to Liu Jianming (email: [e-mail]) 

出　　处：《Science China Earth Sciences》2004年第2期171-180,共10页中国科学（地球科学英文版）

基　　金：This work was financially funded by the Chinese Academy of Sciences (Grant. No. KZCX1-07); the Ministry of Science and Technology of China (Grant No. 1999043210);partly by the National Natural Science Foundation of China (Grant. No. 49873022).

摘　　要：This paper presents systematic studies on the C-O and Sr-Nd isotopic compositions for Cretaceous Badou carbonatites, Fangcheng basalts, and Jiaodong lamprophyres and Paleozoic Mengyin kimberlites in Shandong Province, China. Paleozoic kimberlites have normal and uniform C-O isotopic compositions with δ13C and δ18O in the range of -4.8‰--7.6‰ and +9.9‰-+13.2‰, respectively. However, Cretaceous three different types of mantle-derived rocks have quite different C-O isotopic compositions, indicating that the mantle sources are probably partially contaminated with organic carbon-bearing crustal materials. These Cretaceous rocks show uniform and EMII-like Sr-Nd isotopic compositions and also indicate that the mantle sources were affected by recycled crustal materials. Comparative studies of C-O and Sr-Nd isotopes reveal that the lithospheric mantle beneath the eastern North China Craton had different isotope characteristics in the Paleozoic, the early Cretaceous, and the Tertiary time. This demonstrates that the lithospheric mantle beneath the region underwent at least twice reconstructions since the Paleozoic. Available data imply that the first reconstruction mainly happened during the Triassic-Jurassic time with gradual changes and the second in the Cretaceous with abrupt changes. Results also show that the early Cretaceous (especially at 120-130 Ma) was perhaps the key period leading to the dramatic change of the Mesozoic geodynamics on the eastern North China Craton.This paper presents systematic studies on the C—O and Sr—Nd isotopic compositions for Cretaceous Badou carbonatites, Fangcheng basalts, and Jiaodong lamprophyres and Paleozoic Mengyin kimberlites in Shandong Province, China. Paleozoic kimberlites have normal and uniform C—O isotopic compositions with δ13C and δ18O in the range of ?4.8‰—?7.6‰ and +9.9‰—+13.2‰, respectively. However, Cretaceous three different types of mantlederived rocks have quite different C—O isotopic compositions, indicating that the mantle sources are probably partially contaminated with organic carbon-bearing crustal materials. These Cretaceous rocks show uniform and EMII-like Sr—Nd isotopic compositions and also indicate that the mantle sources were affected by recycled crustal materials. Comparative studies of C—O and Sr—Nd isotopes reveal that the lithospheric mantle beneath the eastern North China Craton had different isotope characteristics in the Paleozoic, the early Cretaceous, and the Tertiary time. This demonstrates that the lithospheric mantle beneath the region underwent at least twice reconstructions since the Paleozoic. Available data imply that the first reconstruction mainly happened during the Triassic-Jurassic time with gradual changes and the second in the Cretaceous with abrupt changes. Results also show that the early Cretaceous (especially at 120-130 Ma) was perhaps the key period leading to the dramatic change of the Mesozoic geodynamics on the eastern North China Craton.

关 键 词：MANTLE-DERIVED rocks  carbonate minerals  C-O isotope  Sr-Nd isotope  LITHOSPHERIC mantle  Shandong. 

分 类 号：P597[天文地球—地球化学]