850–790 Ma bimodal volcanic and intrusive rocks in northern Zhejiang, South China: A major episode of continental rift magmatism during the breakup of Rodinia

Abstract

SHRIMP U-Pb zircon ages and geochemical and Nd isotopic data are reported for mid-Neoproterozoic igneous rocks in northern Zhejiang Province, South China. The Shenwu dolerite dykes, the Daolinshan granite-diabase complex, and the Shangshu bimodal (basalt-rhyolite) volcanic rocks were dated at 849 ± 7 Ma, 794 ± 9 Ma and 792 ± 5 Ma, respectively. All the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements, resembling intraplate basaltic rocks in continental rifts. The ∼850 Ma Shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca. 1.1–0.9 Ga Sibao Orogeny, but seem to predate the Neoproterozoic rifting. Our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the Yangtze Block until ca. 800 Ma. The intensive ∼790 Ma bimodal volcanic and plutonic rocks, part of a major phase of mid-Neoproterozoic rifting, are concurrent with the widespread mid-Neoproterozoic intraplate magmatism throughout South China. They are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent Rodinia.