Petrogenesis and tectonic implications of Devonian granitoids in the central Beishan orogen, NW China: geochemical and Sr-Nd-Hf isotopic constraints

ABSTRACT

The Devonian granitoids are widespread in the Beishan area of the southern Central Asian Orogenic Belt, which provides key geological records for revealing the middle Palaeozoic evolution of the Paleo-Asian Ocean. This study presents new zircon U–Pb ages, whole-rock major and trace elements, and Sr-Nd-Hf isotopes of four granitic plutons in central Beishan. The Haergen muscovite monzogranites were emplaced in the Early Devonian (401 Ma) and are considered as S-type based on their peraluminous features and high P₂O₅ contents. They show high ⁸⁷Sr/⁸⁶Sr_(i) (0.7097 to 0.7141), low ℇ_Nd(t) (−4.7 to −4.3) and variable ℇ_Hf(t) (0 to 6.9), indicating an ancient crust source. The Balegentai, Haerteerdele, and Miaomiaojing plutons were intruded in the Late Devonian with ages of 381 Ma, 379 Ma, and 361 Ma, respectively. They are I-type granites, as indicated by their metaluminous to weakly peraluminous features and low zircon saturation temperatures. Furthermore, they present depleted ⁸⁷Sr/⁸⁶Sr_(i) (0.7042 to 0.7079), ℇ_Nd(t) (−1.6 to 2.2) and ℇ_Hf(t) (4.0 to 10.6), suggesting that they were derived from the partial melting of juvenile crustal rocks. The Early Devonian granitoids with an age peak of 410 Ma in central Beishan consist of I-S-A type granites with variable Nd-Hf isotopes, implying extensive interactions between juvenile and/or mantle-derived and ancient crust-derived magma. In contrast, the Middle-Late Devonian granitoids with an age peak of 370 Ma consist of I-A type granites with depleted Nd-Hf isotopes, implying the input of more juvenile materials. We conclude that a collisional event between the Mazongshan and Huaniushan units occurred during the Early Devonian. The Middle-Late Devonian magmatism was formed in an extensional setting, and the Huaniushan unit was also influenced by the northwards subduction of the Liuyuan Ocean.

KEYWORDS:

• Devonian
• granitoids
• collision
• beishan
• central asian orogenic belt

Acknowledgments

The authors are grateful to Jian-Guo Yuan, Rui-Bin Liu, Qian Tian, Qiao-Yu Li and Wei-Wei Li for their help with field work. This work was supported by the National Key R&D Program of China (2018YFC0603702); the project of China Geological Survey (DD20190685, DD20221647). Contribution to IGCp#662 (Nos. IGCP662).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2167129

Additional information

Funding

This work was supported by the the project of China Geological Survey [DD20190685, DD20221647]; the National Key Research and Development Program of China [2018YFC0603702].