Geochronology, petrogenesis and tectonic significance of two episodes of Neoproterozoic diabasic magmatism in South China: from orogenesis to intracontinental rifting

ABSTRACT

Neoproterozoic mafic magmatic rocks are widely distributed in the Jiangnan Orogenic Belt. Understanding the petrogenesis and tectonic settings of these mafic rocks has significant implications for the regional tectonic evolution and the assembly and breakup of supercontinent Rodinia. In this research, two Neoproterozoic diabase samples (Baotan and Huaihua) were investigated by zircon and baddeleyite U–Pb dating with the ages of 805 Ma and 788 Ma, respectively. The Baotan samples are depleted in HFSE, enriched in LILE and have enriched Sr–Nd isotope compositions (⁸⁷Sr/⁸⁶Sr_(i) = 0.731620 to 0.745440, ε_Nd(t) = – 3.7 to – 7.6). We suggest that they were derived from an enriched lithospheric mantle in a convergent tectonic setting, which was metasomatized by contemporaneous slab–derived hydrous fluids. On the contrary, the Huaihua diabase samples have trace element patterns similar to oceanic island basalts but little HFSE depletion and slightly enriched Sr–Nd isotopes (⁸⁷Sr/⁸⁶Sr_(i) = 0.703101 to 0.705006, ε_Nd(t) = – 0.1 to – 1.6). We infer that they originated from partial melting of a convective asthenospheric mantle under an extensional environment, which was previously metasomatized by slab–derived melts. In combination with other geological observations, we proposed a geodynamic evolution model for the South China Block from the mid–Neoproterozoic orogenesis to the late Neoproterozoic intracontinental rifting.

Graphical abstract

KEYWORDS:

• Diabase
• Neoproterozoic
• intracontinental rifting
• Jiangnan orogen belt
• South China Block

Highlights

SCB experienced orogenesis to intracontinental rifting in Neoproterozoic

Acknowledgments

We are particularly indebted to Dr Robert J. Stern, Dr Greg Shellnutt and one anonymous reviewer for their constructive comments. This study is supported by Natural Science Foundation of China (No. 41972198), Hong Kong RGC GRF (17306217) and the Cooperation Foundation of Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, CAS (KLMM20180201).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the China Geological Survey [DD20190154]; National Natural Science Foundation of China [No. 41972198]; Hong Kong RGC GRF [17306217]; Cooperation Foundation of Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, CAS [KLMM20180201]; The science and technology innovation Program of Hunan Province [2021RC4055]