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 εHf(t) values of +11.2 to +19.6, and the two granodioritic samples exhibit similar εHf(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.
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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