Neoproterozoic arc volcanic rocks of the Nanping–Ninghua tectonic belt, South China: Implications for the collision between the North and South Wuyi blocks

Abstract

Numerous volcanic–sedimentary rocks of the Wanquan and Gaiyang groups are found throughout the Nanping–Ninghua tectonic belt, South China. However, detailed studies on the tectonic evolution of the Nanping–Ninghua tectonic belt have been limited by the lack of systematic previous research linking these volcanic–sedimentary rocks. This study presents a systematic petrological, geochronological, and geochemical study of meta‐volcanic rocks from the Louqian Formation in Mingxi County, China. Zircons from these rocks were analysed by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) and yielded a U–Pb weighted mean age of 734.7 ± 3.3 Ma. The SiO2 contents of the meta‐volcanic rocks range from 59.91 to 73.47 wt.%, and they have high Al2O3 and Na2O + K2O contents (13.17–18.80 and 6.73–11.19 wt.%, respectively), and low CaO, MgO, and FeOT contents. All samples are enriched in large‐ion lithophile elements (LILE; e.g., Ba, Rb, and K) and depleted in high‐field‐strength elements (HFSE; e.g., Nb, Ta, Ti, and P). Marked negative Eu anomalies are similar to those in arc igneous rocks. Based on regional geological data and previous studies, we propose that the Nanping–Ninghua tectonic belt formed in an active continental margin environment from 825 to 696 Ma. Island arc magmatism was caused by the oceanic crust subduction, which contributed to the formation of an intermediate–silicic volcanic belt along the Nanping–Ninghua continental margin that was active until 696 Ma. The North and South Wuyi blocks did not assembly to form a unified Wuyi Block before 696 Ma, and there is no unified pre‐Nanhua crystalline basement present in the Cathaysia Block.