Petrogenesis of early Silurian intrusions in the Sanchakou area of Eastern Tianshan, Northwest China, and tectonic implications: geochronological, geochemical, and Hf isotopic evidence

ABSTRACT

Palaeozoic intrusions in Eastern Tianshan are important for understanding the evolution of the Central Asian Orogenic Belt (CAOB). The Sanchakou intrusions situated in Eastern Tianshan (southern CAOB), are mainly quartz diorite and granodiorite. A comprehensive study of zircon U–Pb ages, zircon trace elements, whole-rock geochemistry, and Lu–Hf isotopes were carried out for the Sanchakou intrusive rocks. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 439.7 ± 2.5 Ma (MSWD = 0.63, n = 21) for the quartz diorite, and 430.9 ± 2.5 Ma (MSWD = 0.21, n = 21) and 425.5 ± 2.7 Ma (MSWD = 0.04; n = 20) for the granodiorites. These data, in combination with other Silurian ages reported for the intrusive suites from Eastern Tianshan, indicate an early Palaeozoic magmatic event in the orogen. In situ zircon Hf isotope data for the Sanchakou quartz diorite shows ε_Hf(t) values of +11.2 to +19.6, and the two granodioritic samples exhibit similar ε_Hf(t) values from +13.0 to +19.5. The Sanchakou plutons show metaluminous to weakly peraluminous, arc-type geochemical and low-K tholeiite affinities, and display trace element patterns characterized by enrichment in K, Ba, Sr, and Sm, and depletion in Nb, Ta, Pb, and Ti. The geochemical and isotopic signatures indicate that the Sanchakou dioritic and granodioritic magmas were sourced from a subducted oceanic slab, and subsequently underwent some interaction with peridotite in the mantle wedge. Combined with the regional geological history, we suggest the Sanchakou intrusions formed due to the northward subduction of the Palaeo-Tianshan Ocean beneath the Dananhu–Tousuquan arc during early Silurian time.

KEYWORDS:

• early Silurian intrusions
• zircon U–Pb geochronology
• geochemistry
• zircon Hf isotope
• Sanchakou 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 Jing Feng of the Xinjiang Bureau of Geology and Mineral Exploration along with Jinzhu San and Shoubo Chen of No. 704 Geological Team of the Xinjiang Nonferrous Geoexploration Bureau, for their great support and assistance in our fieldwork. We also appreciate the kind help of Li Su from the China University of Geosciences (Beijing) on LA-ICP-MS zircon U–Pb dating. We thank Chinese Academician Yusheng Zhai of the China University of Geosciences (Beijing) for a helpful scientific review of an earlier version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

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