Records of Nanhua island arc activity between the north and south Wuyi terranes in the Cathaysia Block

Abstract

The characteristics and pre-Devonian tectonic evolution between the North and South Wuyi terranes are important for understanding the tectonic framework and aggregation of the micro-terrenes in the Cathaysia Block, as well as the evolution of the South China Block. This paper provides systematic studies on the petrologic features, zircon U–Pb geochronology and geochemical characteristics of the low-grade meta-volcanic and metasedimentary rocks between the North and South Wuyi terranes, and proposes an alternative model for their tectonic evolution. Geochronological data show that the metasedimentary rocks have detrital zircon U–Pb ages ranging from 583 to 3284 Ma with a record of the Nanhua period (764–722 Ma). The meta-volcanic rocks have centralized ages ranging from 720 to 760 Ma and yield weighted average ages of 746–733 Ma. Geochemical studies of the meta-volcanic rocks show similar characteristics to island arc magmatic rocks, with relatively high SiO₂, K₂O and Al₂O₃, low TFeO and MgO contents, and enrichment of Rb, Ba, Th, Pb and Hf elements, and depletion in Ti, Nb, Sr and Ta. These features indicate that the North and South Wuyi terranes may have collided at about 746–733 Ma and eventually pieced together at 583 Ma, with the protoliths of the meta-volcanic rocks and the metasedimentary rocks formed in the same tectonic setting of an island arc during Nanhua island arc magmatism related to the collision. The occurrence of Nanhua island arc activity between the North and South Wuyi terranes suggests that multi-micro-terranes and multi-stage collisions may be major characteristics of the tectonic evolution process in the Cathaysia Block.