Zircon Lu–Hf isotopic constraints on Neoproterozoic subduction-related crustal growth along the western margin of the Yangtze Block, South China

Abstract

Voluminous Neoproterozoic igneous rocks along the western margin of the Yangtze Block, South China, provide an ideal opportunity for examining the nature of the mantle source, petrogenesis of the felsic plutons and processes and timing of crustal growth. The Dadukou, Tongde, Gaojiacun and Shaba mafic plutons, and Datian and Dajianshan adakitic plutons were selected for zircon Lu–Hf isotope analysis. Zircons from the mafic plutons have ɛ Hf( t) values ranging from 1.86 to 11.63, with average ɛ Hf( t) values of the different samples ranging from 4.78 ± 0.42 to 7.60 ± 1.1. Their single-stage model ages range from 0.86 to 1.28 Ga. The two adakitic plutons have ɛ Hf( t) values ranging from 2.26 to 11.68 and single-stage model ages from 0.86 to 1.24 Ga. Our data further confirm that the mafic plutons were extracted from depleted mantle sources, whereas the Datian and Dajianshan adakitic plutons were products of melting of a subducted oceanic slab. The arc-geochemical affinity, relatively high 143Nd/ 144Nd ratios and high zircon ɛ Hf( t) values, as well as the relatively young Hf single-stage model ages of these Neoproterozoic plutons suggest that the continental crustal growth in the region was related to oceanic subduction, rather than upwelling of a mantle plume in a rifting setting. The Neoproterozoic magmatism along the western margin of the Yangtze Block lasted more than 200 My, not show episodic emplacement and contrasting zircon Hf isotopes, suggesting that continental crustal growth in South China was continuously resulted from subduction.