Paleoproterozoic S-type granites in the Lengshui complex, South China: Implications for the tectonic evolution of the Yangtze Block

Abstract

ABSTRACT Paleoproterozoic granitoids provide crucial constraints on the tectonic evolution of the Yangtze Block, South China, and its reconstructed position in the Columbia supercontinent. Here, we report zircon U–Pb age and Hf–isotope data coupled with whole-rock geochemistry for monzogranites from the Lengshui complex (LSC) of the Zhongxiang Terrane in the northern Yangtze Block. Zircon U–Pb dating yields crystallization ages of 2039 ± 36 Ma and 1950 ± 16 Ma for two monzogranite samples, respectively. Both samples show S-type granite affinities. The older S-type granites in the LSC are interpreted to record a subduction-related tectonic setting, whereas the younger ones are related to a syn-collisional setting. This scenario reflects a critical geodynamic transition during the assembly of the Columbia supercontinent at ca. 2.04–1.95 Ga within the Yangtze Block. The two granites have similar zircon Hf isotope ratios with εHf(t) values of −17.11 to −9.69 and TDM2 ages of ca. 3.67–3.22 Ga, suggesting that the monzogranites could have been generated by partial melting of Archaean crustal materials in the Zhongxiang Terrane. Widespread Paleoproterozoic magmatism and metamorphism in the Yangtze Block indicate a change in tectonic regime from ca. 2.15–2.04 Ga subduction to ca. 2.0–1.93 Ga collision followed by ca. 1.87–1.82 Ga post-collisional extension. Based on the similarity of ages and rock types with other blocks in the Columbia supercontinent, our results support that the Yangtze Block may be placed near Laurentia in the Columbia supercontinent.