Petrogenesis of Late Carboniferous granitoids in the Chihu area of Eastern Tianshan, Northwest China, and tectonic implications: geochronological, geochemical, and zircon Hf–O isotopic constraints

ABSTRACT

This contribution presents new SIMS zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf–O isotope systematic on an example of Late Carboniferous granodiorite and porphyritic granodiorite intrusions from the Chihu area of Eastern Tianshan, Xinjiang. SIMS zircon U–Pb dating indicates that the Chihu granodiorite and porphyritic granodiorite formed at 320.2 ± 2.4 Ma and 314.5 ± 2.5 Ma, respectively. These rocks are metaluminous to weakly peraluminous with an A/CNK value of 0.92–1.58, as well as low 10000 Ga/Al, Zr + Nb + Y + Ce, and Fe₂O₃^T/MgO values, which suggest an I-type normal island arc magmatic suite. The porphyritic granodiorite has a slightly higher Sr/Y ratio (28–37) and lower Y (6.9–11.7 ppm) and Yb (0.98–1.49 ppm) contents, suggesting mild adakite affinities. In situ Hf–O isotopic analyses using LA-ICP-MS-MC and SIMS indicate that the ε_Hf(t) and δ¹⁸O values of granodiorite zircons vary from +11.5 to +14.9 and 4.80 to 5.85 ‰, respectively, similar to values for porphyritic granodiorite zircons, which vary from +11.9 to +17.2 and 3.78 to 4.71 ‰, respectively. The geochemical and isotopic data imply that the Chihu granodiorite and porphyritic granodiorite share a common origin, most likely derived from partial melts of the subduction-modified mantle. Based on the regional geological history, geochemistry of the Chihu intrusions, and new isotopic studies, we suggest that the Late Carboniferous magma was generated during the period of the northward subduction of the Palaeo-Tianshan ocean plate beneath the Dananhu–Tousuquan island arc.

KEYWORDS:

• Late Carboniferous granitoids
• zircon U–Pb geochronology
• geochemistry
• zircon Hf–O isotopes
• Chihu area
• Eastern Tianshan

Acknowledgements

We are very grateful to the Editor-in-Chief Robert J. Stern, and two anonymous reviewers for constructive comments and assistance in improving the manuscript. We thank Lian-Hui Dong and Jing Feng from the Xinjiang Bureau of Geology and Mineral Exploration for invaluable assistance during the fieldwork. We also appreciate the kind help of Professor Xian-Hua Li from the Institute of Geology and Geophysics, Chinese Academy of Sciences on SIMS zircon U–Pb dating and zircon O isotope analysis. Thanks to Professor Yu-Sheng Zhai from the China University of Geosciences (Beijing) for a helpful scientific review on the original manuscript.

Additional information

Funding

This research was jointly funded by the Fundamental Research Funds for the National Natural Science Foundation of China [41572066], [41030423], the Fundamental Research Funds for the Central Universities of China [2652015019], [2652015032], the Open Research Funds for the State Key Laboratory of Geological Processes and Mineral Resources [GPMR201512], and the Geological Survey Project of China [1212011085471], [1212011220923].