The Neoproterozoic continental rift magmatism of the eastern Jiangnan orogen: new evidence from the mafic sheets in northern Zhejiang Province, South China

Abstract

ABSTRACTMassive mafic sheets were recently recognized intruding the Neoproterozoic strata in Fuyang area, eastern Jiangnan orogen. Geochronological, geochemical, and isotopic studies were carried out to understand their mantle source, crust–mantle interaction, and tectonic setting. LA-ICP-MS U-Pb zircon data indicate that the sheets were generated at 808 ± 7 Ma. The mafic sheets consist of two groups: high Ti and low Ti. They are enriched in light rare earth elements (LREE; 3.3–5.3 ppm) and show negligible Eu anomalies (δEu = 0.77–1.12). They also have strong large-ion lithophile element (LILE; Sr, K, Rb, Ba) enrichment, moderately strong high-field-strength element (HFSE) enrichment (except for Nb-Ta depletion), and positive εNd(t) (5.1–9.1). Geochemical and isotopic data indicate that the mafic sheets were generated from a depleted asthenospheric mantle source. The high-Ti mafic sheets have higher HFSE contents and less Nb-Ta depletion than the low Ti series, indicating a lower degree of partial melting and crustal contamination. The mafic sheets grew in a within-plate setting, concurrent with the ~820–750 Ma rifting events in the eastern Jiangnan orogen. They are likely related to the breakup of the Rodinia supercontinent.