Age, nature, and origin of Ordovician Zhibenshan granite from the Baoshan terrane in the Sanjiang region and its significance for understanding Proto-Tethys evolution

This contribution reports on a better understanding of the Proto-Tethys evolution in the Sanjiang Tethyan region of China. The manuscript presents laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon ages, Sr-Nd-Hf isotope systematics, and whole-rock major and trace element of Ordovician magmatic rocks from the calc-alkaline Zhibenshan granite, which formed along the northern margin of East Gondwana. The U-Pb zircon dating of monzogranite from the Zhibenshan granite yields crystallization ages of 466-457Ma. The monzogranite has Cross-Iddings-Pirsson-Washington normative corundum (3.34%) and is peraluminous with Al2O3/(Na2O+ K2O+CaO) molar ratio of 1.26, similar to S-type granites. All samples are enriched in large ion lithophile elements (LILEs, such as Rb, K, U, and Th) and depleted in high field strength elements (HFSEs, e.g. Nb and Ti). These granites are enriched in light rare earth elements (REEs) and depleted in heavy REEs with strongly negative Eu anomalies (delta Eu=0.19-0.24). The initial Sr-87/Sr-86 ratios range from 0.7118 to 0.7176 and epsilon Nd(t) values from -11.3 to -10.3 with Nd model ages of 2114-2037Ma. Magmatic zircons with early Palaeozoic dates have epsilon Hf(t) values ranging from -13.3 to -1.8 and Hf model ages from 2258 to 1537Ma. These geochemical and isotopic features suggest that the Zhibenshan granite originated from an ancient crustal source. Ordovician granites in the Baoshan terrane represent the southward continuation of the early Palaeozoic granitic belt that extended along the northern margin of East Gondwana, providing important evidence for the evolution of the Proto-Tethyan Ocean.