Neoproterozoic basic magmatism in the southeast ma

Authors: QingHai Wang DeBin Yang WenLiang Xu

Publish Date: 2012/06/06

Volume: 55, Issue: 9, Pages: 1461-1479

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Abstract

This paper presents a synthetic UPb and Hf isotopic study of zircons and a wholerock geochemical study on diabase swarms that were emplaced into the Proterozoic formations in the XuzhouHuaibei 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 091–690 both of which are typical of a magmatic origin The SHRIMP and QICPMS UPb zircon dating results indicate that the diabase swarms were emplaced at ca 890 Ma Hf isotopic analysis on these zircons gives ɛ Hft values ranging from 226 to 1474 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 withinplate 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 XuzhouHuaibei 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 Mamagmatism was not restricted to the Yangtze Block but also occurred at the southeast margin of the North China Craton

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