Neoproterozoic basic magmatism in the southeast margin of North China Craton:Evidence from whole-rock geochemistry,U-Pb and Hf isotopic study of zircons from diabase swarms in the Xuzhou-Huaibei area of China  

作　　者：WANG QingHai YANG DeBin XU WenLiang 

机构地区：[1]International Centre for Geoscience Research and Education in Northeast Asia, Jilin University, Changchun 130026, China [2]College of Earth Sciences, Jthn Untverszty, Changchun 130061, China

出　　处：《Science China Earth Sciences》2012年第9期1461-1479,共19页中国科学（地球科学英文版）

基　　金：supported by National Natural Science Foundation of China (Grant Nos. 40772037,90814003)

摘　　要：This paper presents a synthetic U-Pb and Hf isotopic study of zircons and a whole-rock geochemical study on diabase swarms that were emplaced into the Proterozoic formations in the Xuzhou-Huaibei area,the southeast margin of North China Craton.Zircons from the diabase dykes display weak oscillatory zoning in the cathodoluminescence(CL) images and show high Th/U ratios(0.91-6.90),both of which are typical of a magmatic origin.The SHRIMP and Q-ICP-MS U-Pb zircon dating results indicate that the diabase swarms were emplaced at ca.890 Ma.Hf isotopic analysis on these zircons gives Hf(t) values ranging from 2.26 to 14.74 and Hf model age t DM1 and t DM2 ranging from 843 to 1321 Ma and from 808 to 1779 Ma,respectively.Geochemically,the diabase swarms are characterized by a relative enrichment in LREE and LILE(Rb,Ba and La),a comparative enrichment in Cr and Ni,but a slight depletement in HFSE(Th,Nb,Ta,Zr and Hf).They are plotted in the within-plate tholeiite series on the tectonic discrimination diagrams.Taken together,these geochemical and isotopic data suggest that the primary magmas to form the diabase dykes in the Xuzhou-Huaibei area could have been derived from a transitional mantle in the Mesoproterozoic,and were most probably emplaced under a continental margin extensional setting at ca.890 Ma.The results of this study demonstrate that the Neoproterozoic(800-900 Ma)magmatism was not restricted to the Yangtze Block,but also occurred at the southeast margin of the North China Craton.This paper presents a synthetic U-Pb and Hf isotopic study of zircons and a whole-rock geochemical study on diabase swarms that were emplaced into the Proterozoic formations in the Xuzhou-Huaibei area,the southeast margin of North China Craton.Zircons from the diabase dykes display weak oscillatory zoning in the cathodoluminescence（CL） images and show high Th/U ratios（0.91-6.90）,both of which are typical of a magmatic origin.The SHRIMP and Q-ICP-MS U-Pb zircon dating results indicate that the diabase swarms were emplaced at ca.890 Ma.Hf isotopic analysis on these zircons gives Hf（t） values ranging from 2.26 to 14.74 and Hf model age t DM1 and t DM2 ranging from 843 to 1321 Ma and from 808 to 1779 Ma,respectively.Geochemically,the diabase swarms are characterized by a relative enrichment in LREE and LILE（Rb,Ba and La）,a comparative enrichment in Cr and Ni,but a slight depletement in HFSE（Th,Nb,Ta,Zr and Hf）.They are plotted in the within-plate tholeiite series on the tectonic discrimination diagrams.Taken together,these geochemical and isotopic data suggest that the primary magmas to form the diabase dykes in the Xuzhou-Huaibei area could have been derived from a transitional mantle in the Mesoproterozoic,and were most probably emplaced under a continental margin extensional setting at ca.890 Ma.The results of this study demonstrate that the Neoproterozoic（800-900 Ma）magmatism was not restricted to the Yangtze Block,but also occurred at the southeast margin of the North China Craton.

关 键 词：DIABASE geochemistry zircon U-Pb dating Hf isotope NEOPROTEROZOIC Xuzhou-Huaibei area 

分 类 号：P588.121[天文地球—岩石学] P588.14[天文地球—地质学]