Zircon U-Pb dating for the earliest Neoproterozoic mafic magmatism in the southern margin of the North China Block.

Huge diabase occurs within the Proterozoic strata in the southern margin of the North China Block, geographically in the northern parts of Anhui and Jiangsu provinces, where no strata younger than Neoproterozoic have been found. Zircons from the diabase show three different structures from cathodoluminesecence imaging, but they are all of magmatic origin. SHRIMP U-Pb dating yields a range of ²⁰⁶Pb/238U ages from 2600 to 124 Ma, but two geological events can clearly be identified from both concordant and discordant ages. One gives two weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 976 ± 24 and 1038 ± 26 Ma which are interpreted as timing of diabase crystallization, and the other has a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2523 ± 52 Ma that represents formation time of inherited zircon from the old crust. The dating results indicate that the mafic magmatic event occurred in a transition period from the latest Mesoproterozoic to the earliest Neoproterozoic, consistent with global subduction of Grenvill ocean crust to result in the assembly of supercontinent Rodinia. Therefore, the North China Block needs to be taken into account when reconstructing the position of China continents within the framework of Rodinia supercontinent. [ABSTRACT FROM AUTHOR]